Appendix GDR 00.1 001 C

Appendix GDR 00.1-001-C May 2011

Geotechnical properties for Glacial deposits

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Geotechnical properties for Glacial deposits May 2011 Appendix GDR 00.1-001-C Prepared by Rambøll Arup Joint Venture c/o Rambøll Danmark A/S Hannemanns Allé 53 DK-2300 Copenhagen S Danmark

Phone +45 51611000 Rambøll Arup Joint Venture Danish reg. no: CVR-NR 31749077 Member of FRI This report appendix is based on the geological/geotechnical knowledge, gathered by Femern A/S until May 2011. As the investigations have not been completed, an update of this report appendix is planned for end 2012.

Prepared DJ/CH 2011-05-01

Checked NLSM 2011-05-01

Approved JRF 2011-05-01

Femern A/S Vester Søgade 10 1601 København V Tel.: +45 3341 6300 Fax.: +45 3341 6301 www.fehmarnlink.com CVR no. 28 98 65 64

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Table of contents

1. INTRODUCTION ............................................................................................ 6

2. CLASSIFICATION PROPERTIES ................................................................. 8

2.1 General .............................................................................................................. 8 2.2 Water content and unit weight .......................................................................... 9

2.3 Specific gravity of solids and void ratio ........................................................... 9

2.4 Consistency limits ........................................................................................... 10 2.5 Grain size analyses ......................................................................................... 10 2.6 Content of CaCO3 and organic matter ............................................................ 11

2.7 Conclusions .................................................................................................... 12

3. CPTU .............................................................................................................. 13 3.1 Introduction..................................................................................................... 13 3.2 Cone resistance ............................................................................................... 13 3.3 Conclusions .................................................................................................... 14

4. STRESS AND STRESS HISTORY ............................................................... 16

4.1 General ............................................................................................................ 16 4.2 In-situ vertical effective stress, σ'vo ................................................................ 16 4.3 Pre-consolidation pressure, σ'pc ...................................................................... 16 4.3.1 Introduction..................................................................................................... 16 4.3.2 Principal evaluation of the methods requested ............................................... 16

4.4 Over-consolidation ratio, OCR ....................................................................... 21

4.5 Earth pressure at rest, K0 ................................................................................ 22

4.6 Conclusions .................................................................................................... 22

5. CONSOLIDATION PROPERTIES ............................................................... 24

5.1 General ............................................................................................................ 24 5.2 Laboratory measurements ............................................................................... 24

5.2.1 Constrained oedometer modulus (reloading).................................................. 24

5.2.2 Constrained oedometer modulus (unloading) ................................................. 25

5.2.3 Coefficient of consolidation (loading/unloading) ........................................... 26

5.2.4 Compression ratio (loading) ........................................................................... 27

5.2.5 Creep properties (reloading) ........................................................................... 28

5.2.6 Swelling properties (unloading) ..................................................................... 28

5.2.7 Permeability .................................................................................................... 28 5.3 Large scale testing .......................................................................................... 28 5.4 Conclusions .................................................................................................... 29

6. STATIC SHEAR STRENGTH ...................................................................... 30

6.1 Introduction..................................................................................................... 30 6.2 Undrained shear strength, in-situ stress .......................................................... 30

6.3 Undrained shear strength, SHANSEP ............................................................ 34

6.4 Undrained shear strength, stresses lower than in-situ ..................................... 35

6.5 Effective shear strength, in-situ ...................................................................... 35

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6.6 Anisotropy factors .......................................................................................... 36 6.7 Rate effects ..................................................................................................... 37 6.8 Large scale testing .......................................................................................... 37 6.9 Conclusions .................................................................................................... 37

7. SMALL STRAIN STIFFNESS AND DAMPING ......................................... 39 7.1 Introduction..................................................................................................... 39 7.2 Small strain stiffness ....................................................................................... 39 7.3 Damping ratios................................................................................................ 44 7.4 Conclusions .................................................................................................... 44

8. CYCLIC UNDRAINED SHEAR STRENGTH ............................................. 46 8.1 Introduction..................................................................................................... 46 8.2 Cyclic undrained direct simple shear strength ................................................ 46

8.3 Conclusions .................................................................................................... 47

9. REFERENCES ............................................................................................... 48 LIST OF ENCLOSURES Enclosure C-01: water content against depth for Glacial units

Enclosure C-02: plasticity index against depth for Glacial units

Enclosure C-03a: water content and Atterberg Limits for Upper till

Enclosure C-03b: water content and Atterberg Limits for Glacial Meltwater silt/clay

Enclosure C-03c: water content and Atterberg Limits for Chalk till

Enclosure C-03d: water content and Atterberg Limits for Lower till

Enclosure C-03e: water content and Atterberg Limits for Lowermost till

Enclosure C-04: liquidity index against depth for Glacial deposits

Enclosure C-05: plasticity chart for Glacial deposits

Enclosure C-06: unit weight against depth for Glacial deposits

Enclosure C-07: void ratio against depth for Glacial deposits

Enclosure C-08: clay content against depth for Glacial deposits

Enclosure C-09: activity against depth for Glacial deposits

Enclosure C-10: carbonate content against depth for Glacial deposits

Enclosure C-11: tri-plot of clay mineralogy (smectite content, illite content, kaolinite/chlorite content) for Glacial deposits

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Enclosure C-12: water content against depth for Glacial Meltwater sand unit

Enclosure C-13: unit weight against depth for Glacial Meltwater sand unit

Enclosure C-14: void ratio against depth for Glacial Meltwater sand unit

Enclosure C-15: net cone resistance against depth for Glacial deposits (differentiated between B-boring)

Enclosure C-16: net cone resistance against depth for Upper till

Enclosure C-17: net cone resistance against depth for Glacial Meltwater deposits

Enclosure C-18: net cone resistance against depth for Chalk till

Enclosure C-19: net cone resistance against depth for Lower till

Enclosure C-20: net cone resistance against depth for Lowermost till

Enclosure C-21: net cone resistance against depth for Upper till within all CPTUs adja-cent to A-borings

Enclosure C-22: net cone resistance against depth for Lower, Chalk and Lowermost tills within all CPTUs adjacent to A-borings

Enclosure C-23: effective stress paths for Upper till

Enclosure C-24: effective stress paths for Glacial Meltwater sand unit

Enclosure C-25: effective stress paths for Chalk till

Enclosure C-26: effective stress paths for Lower till

Enclosure C-27: effective stress paths for Lowermost till

Enclosure C-28: Gmax from bender element testing

Enclosure C-29: G0 from vsp logging

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1. INTRODUCTION

The Glacial deposits are comprised of six geological units. These units, listed in the geological sequence typically encountered, are:

• Upper till • Meltwater Silt/Clay • Meltwater Sand • Chalk till • Lower till • Lowermost till The geotechnical properties of the geological strata have been investigated through:

• Classification testing by Fugro of samples from the type A-borings /1/ and /2/. • In situ testing (CPTU) by Fugro in the type B-borings /1/ and /2/. • In situ testing (CPTU) by Fugro in the type C-borings (seabed CPTUs) /3/. • Classification testing by GEO of selected samples extracted from the type A-borings

for advanced laboratory testing /4/. • Advanced geotechnical testing by GEO of selected samples extracted from the type

A-borings /4/. Additionally, the geophysical properties have been investigated through the geophysical borehole logging by Rambøll Arup JV (RA). The results from these tests are summarised in Section 11.5 of the Ground Investigation Report, but are also considered in section 7.2 of the present appendix. Test specimens that were used for strength testing were consolidated in the laboratory prior to testing. Specimens of Lower till were generally consolidated to in-situ stress levels and then sheared. The Upper till specimens were pre-consolidated to a high stress level approaching the estimated pre-consolidation stress before unloading to the in-situ stress and succeeding shearing. The undrained shear strength, as found in-situ, has there-fore been mapped and correlated with the CPTU results. The undrained shear strength testing has been supplemented with testing to identify de-formation properties of the soil during loading and unloading; together with correlation with the CPTU results. During the laboratory testing programme the stress states applied have been defined by RA. The geotechnical background material and data is available within the Femerns Geo Information System /5/. For abbreviations and definitions not defined in this appendix, reference is made to Femerns Geo Nomenclature /6/.

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The geotechnical properties are elaborated in the succeeding sections. The advanced laboratory tests performed on the meltwater deposits are all conducted on one and the same core from borehole 09.A.018. This core was the only core found with sufficient recovery. The grain size curve from this core shows that the soil is classified as silt. This appendix presents the overall derivation of laboratory data and field measurements as established by RA. This overall derivation may deviate from the evaluation of labora-tory results as presented in /4/. In case of conflict between the two different documents, the RA interpretation takes precedence.

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2. CLASSIFICATION PROPERTIES

2.1 General In order to determine the classification properties of the Glacial deposits, a series of geotechnical laboratory classification tests were undertaken on selected soil samples retrieved from the 2009 and 2010 ground investigations. The test results noting the basic classification properties (w, wP, wL, IP, IL, γ) are plotted against depth below seabed/ground level in Enclosures C-01 to C-06. Similarly, the sta-tistical results of these tests are presented below in Table 2-1. Table 2-1: Basic geotechnical classification properties of Glacial deposits

Enclosure C-01 C-03(1) C-03(1) C-02 C-04 C-06 Glacial Unit w wL wP I P I L γγγγ

Upper till Arithmetic mean Standard dev. Number of tests

9.6% 1.6% 467(2)

20.4% 3.5% 123

11.5% 1.6% 123

8.9% 3.0% 123

-0.28 0.23 39

23.0 kN/m3 1.1 kN/m3

421

Meltwater Silt/Clay

Arithmetic mean Standard dev. Number of tests

22.4% 7.8% 40

38.7% 18.0%

12

18.6% 8.6% 12

20.1% 11.0%

12

0.10 0.02

2

20.7 kN/m3 1.3 kN/m3

25

Meltwater Sand


18.4% 5.6% 78

- - -

- - -

- - -

- - -

21.1 kN/m3 1.8 kN/m3

44

Chalk till Arithmetic mean Standard dev. Number of tests

11.9% 4.6% 74

22.3% 2.7% 33

13.7% 1.9% 33

8.6% 2.9% 33

-0.36 0.23 12

22.4 kN/m3 1.2 kN/m3

63

Lower till Arithmetic mean Standard dev. Number of tests

11.5% 3.2% 629

28.1% 9.4% 185

12.3% 2.4% 185

15.8% 7.8% 185

-0.05 0.15 63

22.6 kN/m3 1.0 kN/m3

609

Lowermost till


17.7% 5.9% 264

58.3% 22.7%

94

18.7% 5.0% 94

39.6% 18.9%

94

-0.04 0.15 18

21.4 kN/m3 1.4 kN/m3

200 (1) Enclosure illustrating results of each Glacial unit (2) 30 measurements have been omitted because they were performed on thin sand layers in

the till. Other laboratory classification tests were undertaken to determine the properties of the Glacial deposits. Geotechnical parameters determined from these tests includes; the initial void ratio (e), specific gravity of solids (ds), clay content (Clay T) and calcium carbonate content. The statistical results of these measured properties are presented in Table 2-2; with the test results presented with depth below seabed/ground level in Enclosures C-07 to C-10. It should be noted that the unit Meltwater sand includes thin layers of clay tills and very silty meltwater sands.

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Table 2-2: Additional geotechnical classification properties of Glacial deposits Enclosure C-07 - C-08 C-09 C-10

Glacial Unit e ds Clay T Activity CaCO3

Upper till Arithmetic mean Standard dev. Number of tests

0.27 0.10 117

2.65 0.04

75

14.6% 7.0%

224

0.61 0.27

79

26.0% 8.4%

9

Meltwater Silt/Clay


0.58 0.11

12

2.68 0.04

7

20.9% 11.9%

25

0.92 0.42

9

- - -

Meltwater Sand


0.49 0.17

23

2.64 0.04

16

11.9% 13.0%

51

- - -

30.8% - 1

Chalk till Arithmetic mean Standard dev. Number of tests

0.31 0.04

26

2.68 0.04

17

27.3% 7.6%

36

0.44 0.38

21

57.3% 9.3%

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Lower till Arithmetic mean Standard dev. Number of tests

0.30 0.07 235

2.66 0.04

98

20.2% 7.8%

258

0.75 0.28 123

22.3% 10.1%

29

Lowermost till


0.46 0.21

58

2.66 0.03

35

29.7% 11.4%

136

1.38 0.67

62

21.7% 6.6%

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2.2 Water content and unit weight As shown in Table 2-1, the water content of the Glacial deposits is shown to vary be-tween Glacial units. The results suggest that the water content of the Chalk till and Lower till are generally comparable; with average water contents of 11.9 % and 11.5 %, respec-tively, while the Upper till has a slightly lower water content (9.6 %) Further review of Enclosure C-01 indicates that the water content of these units is generally consistent with depth. Ranges of water content within the Meltwater silt/clay unit, Meltwater sand unit and the Lowermost Glacial units was generally recorded higher than the other Glacial units. This is illustrated in Enclosures C-01 and C-12, and is apparent on review of the average water content values of these units; 22.4 %, 18.4 % and 17.7 %, respectively. The measured unit weights of the Glacial deposits show little variation between Glacial units. The average value of unit weight varies between 20.7 kN/m3 for the Meltwater silt/clay and 23.0 kN/m3 for the Upper till. The unit weight results are plotted with depth for the till units in Enclosure C-06 and for the Meltwater units in Enclosure C-13.

2.3 Specific gravity of solids and void ratio The measured values of specific gravity are shown to be consistent between Glacial units; with the average values of specific gravity varying between 2.64 and 2.68. The initial void ratio of the Glacial deposits is shown to vary between Glacial units. The statistical values of the void ratio values are presented in Table 2-1 and are plotted with depth in Enclosure C-07 for the till units and Enclosure C-14 for the Meltwater units.

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2.4 Consistency limits A total of 447 No Atterberg Limits tests were undertaken on samples of Glacial deposits. The statistical results of these tests are presented in Table 2-1. Review of the plasticity index results in Table 2-1 note a marked difference in the arith-metic mean between Glacial units. For example, the arithmetic mean of the plasticity in-dex for the Upper till is 8.9 %, changing to 20.1 % for the underlying Glacial Meltwater silt/clay, to 8.6 % for the Chalk till, 15.8 % for the Lower till and to 39.6 % for the Low-ermost till. Consequently, on a plot of the plasticity index against depth below top of borehole level is shown in Enclosure C-02, the Glacial units are clearly defined. Given the significant number of Atterberg Limits tests undertaken, the liquid and plastic limits have been plotted with depth for each Glacial unit, and are presented in Enclosures C-03a to C-03e. In-situ water contents are also shown on these enclosures. These plots show that for the Upper till, Chalk till and Lower till, the range of plastic and liquid limits within that particular unit is relatively consistent; with the exception of occasional eleva-ted liquid limit values. Few tests were undertaken on samples of the Meltwater silt/clay; with the results indicating inconsistent ranges of plastic and liquid range. The results of Atterberg Limits tests undertaken on samples of the Lowermost till reveal a significant range between the liquid and plastic limits which appear variable with depth. With the exception of the Meltwater silt/clay, the measured water contents are generally close to, or below, the plastic limit; as illustrated by the liquidity index values shown in Enclosure C-04. However, a number of tests within the Lowermost till and the Lower till recorded water content values in excess of the plastic limit resulting in a positive liquidity index. The Casagrande plasticity chart is shown in Enclosure C-05, with the results of all of the Glacial units shown for comparison. The chart shows that the plasticity of each of the Glacial units is dissimilar and can generally be separated into groupings parallel to the A-line. For instance, the Upper till results are clustered within the CL-ML and CL catego-ries. The Meltwater silt/clay results typically lie between the CL to CM categories; with one result plotting below the A-line within the OH/MH classification. The results of the Chalk till are shown to be clustered in the same area of the chart as the Upper till in the CL-ML and CL regions. The results of the Lower till are varied, although mostly lie in the CL and CM classifications; with a number of results in CH and one in CV region. The plasticity of the Lowermost till is shown to be higher than any of the other units, with the results located within the CM to CV classifications. Six of the 94 Atterberg Limits on samples of the Lowermost till are plotted below the A-line; with three results in the OL/ML region and three results in the OH/MH region.

2.5 Grain size analyses A number of particle size distribution analyses were undertaken on samples of the Glacial deposits. The statistical results of these tests, showing the clay content (Clay T) for each Glacial unit is shown in Table 2-2. The results are presented with depth below top of borehole in Enclosure C-08.

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A plot showing the clay mineralogy, in relation to the composition of kaolinite/chlorite, smectite and illite measured from the X-ray diffraction, is presented in Enclosure C-11. Comparison of the clay content and the plasticity index results for each of the Glacial units provide an indication of the soil classification. When considering the average values (arithmetic mean) of the clay content and plasticity indices, the Glacial units can be clas-sified; as noted in Table 2-3. Table 2-3: Classification of Glacial units based on average clay content and plasticity index

Glacial Unit Average Clay T [%]

Average I p [%] Soil Classification

Upper till 14.6

8.9

Very silty/sandy clay till

Meltwater Silt/Clay 20.9

20.1

Medium plasticity clay

Meltwater Sand 11.9

-

Generally granular

Chalk till 27.3

15.8

Medium plasticity clay till

Lower till 20.2

15.8

Medium plasticity clay till

Lowermost till 29.7

39.6

High plasticity clay till It should be noted that only the average clay content and plasticity indices have been used to determine the soil classifications noted in Table 2-3. Given the variability of the soil, as highlighted in the standard deviation values and review of the enclosures, the geotech-nical properties of the soil within the Glacial units may vary; hence the classification. The statistical results of the activity (Ip/Clay T) of each Glacial unit are presented in Ta-ble 2-2 and are illustrated with depth in Enclosure C-09. Given that the values of activity in the Upper till, Meltwater clay/silt and Chalk till units are typically below 0.75, these units can generally be classified as ‘inactive’ and are not considered to exhibit volume changes with changes in water content. The range of activity in the Lower till is typically between 0.40 and 1.00, suggesting that the unit is inactive to ‘normal’. The range of ac-tivity values within the Lowermost till typically range between 0.90 and 2.00 indicating that the soil classification is both ‘normal’ and ‘active’. Given this, the Lowermost till may be prone to swelling and shrinkage with variations in water content.

2.6 Content of CaCO3 and organic matter The CaCO3 content of the Glacial deposits is shown in Table 2-2 and is illustrated with depth below seabed in Enclosure C-10. Review of this data shows that the Lower and Lowermost tills typically have the lowest CaCO3 content. The highest CaCO3 content was recorded within the Chalk till; with an average content of 57.3 % and a standard deviation of 9.3 %. No organic content or loss on ignition tests was undertaken on samples of the Glacial de-posits.

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2.7 Conclusions Review of the results of the laboratory classification testing, undertaken on samples of Glacial deposits confirm the presence of individual Glacial units. These units are particu-larly well defined on review of the plasticity chart, plasticity index and clay content test results; where the units fall into groupings or are evident through stepped variations of geotechnical parameters. Assessment of the plasticity test results reveals a significant variance of plasticity betwe-en Glacial units. The test results indicate that the Upper and Chalk till are typically of low plasticity, whilst the Meltwater silt/clay and the Lower till are of low to medium plastici-ty. The plastic properties of the Lowermost till are noted to be highly variable, and range from medium to very high plasticity. The plastic and liquid limit results within the Upper till, Chalk till and Lower till are shown to be relatively consistent within each of unit; with the exception of occasional elevated liquid limit results. Few tests were undertaken on samples of the Meltwater silt/clay; with the results indicating irregular ranges of plastic and liquid range. The re-sults of Atterberg Limits tests undertaken on samples of the Lowermost till reveal a sig-nificant range between the liquid and plastic limits which appear variable with depth. With the exception of the Lowermost till, the typical values of activity within the Glacial units are less than 1.25, and thus, the soil can be classified as ‘in-active’ or ‘normal’. However, the range of activity values within the Lowermost till typically range between 0.90 and 2.00 indicating proportions of the unit are ‘active’. Given this, the Lowermost till may be prone to swelling and/or shrinkage with changes in water content.

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3. CPTU

3.1 Introduction A number of down-the-hole CPTUs (B-borings) and seabed CPTUs (C-borings) pene-trated into the Glacial deposits. The results of these CPTUs are presented in /1/ and /2/. For correlation purposes, most CPTUs were undertaken generally within 5m of type A-borings. By doing so, parallels between the known geology within the A-boring and the CPTU profiles could be made. In addition, the results of the laboratory testing from sam-ples recovered from the A-borings were correlated with the CPTU cone penetration data. However, it should be noted that when comparing and correlating geotechnical properties from soil strata encountered in a type A-borings with the CPTU-values in the adjacent type B-boring there is typically 5 m horizontal distance between the two borings. Even within this relatively short distance, variations in the ground conditions and geotechnical properties of the soil occur. The piezocone in the B-borings may react on stones and silt layers that may not be found in corresponding cores from the A-borings at the same depth, and this must also be considered when comparing boring and CPTU data.

3.2 Cone resistance The full set of results from the cone penetration test type B-borings and type C-borings, reported for each borehole, are contained within/1/ and /2/. In total, 19 No CPTUs were undertaken adjacent to A-borings which had samples of Glacial deposits subject to labo-ratory testing. The geology within the CPTU profiles was concluded from the adjacent A-borings and the cone resistance profiles for the each Glacial unit isolated and reviewed. For CPTUs undertaken adjacent to A-borings with samples of Glacial deposits subject to laboratory testing, net cone resistance, qnet, profiles against depth, distinguishing between boreholes, are shown in Enclosure C-15. Plots of net cone resistance against depth for each of the Glacial units are presented in Enclosures C-16 to C-20. It should be noted that the plots do not take into consideration CPTU refusals, and as a result, areas of the Gla-cial deposits may prove to exhibit a higher strength than shown. A plot showing the qnet results with depth for all CPTUs adjacent to A-borings within the Upper till is illustrated in Enclosure C-21. Similarly, a plot showing the qnet results with depth for all CPTUs adjacent to A-borings within the Lower, Chalk and Lowermost tills is illustrated in Enclosure C-22. Review of the cone resistance profiles of the Glacial deposits revealed that the CPTUs had on a number of occasions met refusal. This occurred when the maximum limit of the CPTU equipment was reached (60 MPa), or when excessive and sustained measurements of cone resistance, qc, where recorded and the CPTU operator believed the piezocone to be on hard strata or obstruction. When refusal was met, the piezocone was withdrawn and the use of drilling equipment was employed to drill out the area of the refusal; with a sub-sequent gap within the CPTU data profile.

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Although CPTU tests encountered refusal in most of the Glacial units, it was most preva-lent in the Upper till and Chalk till. Table 3-1 summarises the extent of CPTU refusals within the Upper till in B-borings that were adjacent to the A-borings which had samples subject to laboratory testing. As shown, typically 40 % to 70 % of CPTU pushes under-taken within the Upper till encountered obstructions or soil with a strength greater than the limits of the cone penetration test equipment. Table 3-1: Review of CPTU refusals within Upper till

CPTU No. CPTU Depth [m] No. CPTU Pushes

No. CPTU Refusals

CPTU Push Refusals [%]

09.B.007 2.40 – 12.75 7 5 71 09.B.008 3.90 – 15.86 5 3 60 09.B.013 2.01 – 39.20 24 14 58 09.B.018 0.30 – 11.70 8 3 38 10.B.056 11.20 – 12.88 2 2 0 10.B.057 12.04 – 16.83 4 2 50 10.B.060 12.10 – 19.78 7 4 57 10.B.061 9.10 – 17.04 6 3 50 10.B.064 0.10 – 22.35 16 11 69 10.B.064 27.00 – 32.18 4 3 75 10.B.065 0.80 – 10.59 7 3 43 10.B.065 18.80 – 26.18 5 4 80 As shown in Encl. C-18, an accurate profile of cone resistance could not be determined within the Chalk till as the piezocone repeatedly met refusal. Of the 13 CPTUs under-taken adjacent to borings, which had samples of Glacial deposits subject to laboratory testing, ten met refusal. As a result, a limited number of qnet values were obtained and are not representative of the in-situ strength of the Chalk till.

3.3 Conclusions In order to identify the geology within cone penetration test profiles, and to allow compa-risons between laboratory test results with cone resistance profiles, a number of CPTUs were undertaken adjacent to A-borings. Consequently, the following typical ranges of net cone resistance, qnet, have been determined for each of the following Glacial units: • Upper till – typically between 5 MN/m2 and 40 MN/m2 (see following text) • Meltwater silt/clay – typically between 12 MN/m2 and 55 MN/m2 • Meltwater sand – typically between 3 MN/m2 and 40 MN/m2 • Lower till – typically between 2 MN/m2 and 20 MN/m2 • Lowermost till – typically between 2 MN/m2 and 10 MN/m2

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It should be noted that a significant number of CPTUs undertaken within the Upper till met refusal. Review of cone resistance profiles suggest that between 40 % and 70 % of CPTU pushes typically met refusal in the Upper till. Given that the area where the piezo-cone met refusal was drilled out, it is unknown whether these refusals were a result of the piezocone encountering cobbles/boulder obstructions or whether the soil strength exceeds the limit of the test equipment. As a result, the reported Upper limit of the typical range of the Upper till should be adopted with caution. An accurate profile of cone resistance could not be determined within the Chalk till as that the piezocone repeatedly met refusal. As a result, a limited number of net cone resis-tance values were obtained and are not representative of the strata strength.

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4. STRESS AND STRESS HISTORY

4.1 General As an integrated part of understanding the investigated soil, this section describes the background and the results obtained, covering the effective in-situ stress state.

4.2 In-situ vertical effective stress, σ'vo The vertical effective in-situ stress has been established using the effective unit weight of the soil. A hydrostatic pore pressure distribution has been assumed.

4.3 Pre-consolidation pressure, σ'pc

4.3.1 Introduction The pre-consolidation pressure is an important property in order to understand the soil be-haviour. Terzaghi et al. (1996) /7/ identified the pre-consolidation pressure as: “the ef-fective vertical stress at which major changes in the natural soil structure begins to take place.” In order to identify the pre-consolidation pressure, σ'pc, the following types of oedometer testing were carried out on samples of the Glacial deposits:

• Incremental loading (IL). The load is applied stepwise and the specimen is allowed to reach end of primary consolidation (EOP) before the next load step is applied. Pore pressure measurements are not performed.

• Constant rate of strain (CRS). A constant strain rate is used, allowing the measure-ment of pore pressures at the bottom of the specimen to vary.

• Constant rate of pore pressure (CPR). A constant pore pressure ratio is obtained by varying the strain rate.

The methods requested to be used for deriving σ'pc was as follows:

• Becker et al. (1987) /8/ • Casagrande (1936) /9/ • Janbu (1969) /10/ • Akai (1960) /11/

4.3.2 Principal evaluation of the methods requested The pre-consolidation stress values determined from samples of the Glacial deposits in /4/ are presented in Table 4-1. In addition to the values reported in Table 4-1, the Janbu method of analysis was used on a sample recovered from boring 09.A.003 at 13.88m depth. This analysis recorded a σ’pc of 200 kPa. It should also be noted that the Becker analysis results in Table 4-1 report the maximum derived values of σ’pc. However, the minimum σ’pc values were reported for two samples; from borings 10.A.060 at 60.62 m depth and 10.A.610 at 13.79 m depth. These analyses determined σ’pc values of 800 kPa and 750 kPa, respectively.

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It should be noted that the results of the IL tests undertaken to determine the coefficient of earth pressure at rest were not used in the evaluation of pre-consolidation stress given that the stresses were not taken sufficiently high to accurate determine σ’pc.

Table 4-1: Comparison of pre-consolidation values, σ’ pc , derived in /4/.

Boring Depth [m]

Test Type Glacial Unit σ'vo

[kPa] Method and Derived σ’ pc [kPa]

Casagrande Becker Akai 09.A.008 7.85 CRS Upper till 80 2000 1733 - 09.A.008 7.93 IL Upper till 80 400 550 - 09.A.008 7.99 CRS Upper till 80 - 906 - 09.A.008 8.11 CRS Upper till 80 1500 3600 - 09.A.008 10.97 IL Upper till 130 1100 1800 1000 09.A.012 11.21 IL Upper till 135 - - > 4000 09.A.012 11.25 IL Upper till 135 2000 2100 1200 09.A.013 11.21 IL Upper till 140 1200 1500 1200 09.A.013 20.06 IL Upper till 260 - - 1600 09.A.013 30.11 IL Upper till 395 1000 - 2500 09.A.008 19.04 IL Chalk till 235 > 2000 2550 2500 09.A.009 14.98 IL Chalk till 170 - 3500 3500 09.A.003 13.88 CRS Lower till 110 700 1462 - 09.A.003 13.93 IL Lower till 110 1100 1800 3500 09.A.003 13.98 CRS Lower till 110 1600 1686 - 09.A.003 14.16 IL Lower till 110 300 320 - 09.A.003 15.68 IL Lower till 150 700 1500 800 09.A.003 16.74 IL Lower till 160 800 1600 1500 09.A.012 20.59 IL Lower till 260 1400 1550 > 4000 09.A.012 20.71 IL Lower till 260 1100 2000 2000 09.A.012 30.44 IL Lower till 395 1950 1500 > 3000 09.A.012 30.49 IL Lower till 395 1200 1750 1600 09.A.013 41.75 IL Lower till 540 1700 1200 1200 09.A.013 52.11 IL Lower till 690 1100 1150 1200 09.A.605 15.65 IL Lower till 180 1000 1350 - 09.A.605 17.51 IL Lower till 200 1000 950 - 10.A.610 13.79 CPR Lower till 170 800 950 - 10.A.060 60.62 IL Lowermost till 780 1300 950 -

To compare the pre-consolidation pressures in /4/ from each of the methods, and to investigate any possible relationship between σ’pc and Glacial unit, plots of σ’pc versus depth below seabed were completed and are presented in Figure 4-1. With the exception of the Akai method producing several comparatively higher values, the determined σ’pc values using each of the derivation methods were found to be generally similar; with results typically ranging between 300 kPa and 3000 kPa.

18

Figure 4-1: Pre-consolidation pressure against depth, distinguishing between derivation method, left, and Glacial unit, right. Review of the above plots show no consistent relationship between pre-consolidation pressure, Glacial unit and depth. Although the horizons of Glacial units are clearly defined when distinguishing by unit, the σ’pc values are highly variable and cannot be de-fined for individual units. To further investigate the derived σ’pc values, plots of pre-con-solidation pressure against net cone resistance were graphed; shown in Figure 4-2.

Figure 4-2: Pre-consolidation pressure against net cone resistance, distinguishing between derivation method, left, and Glacial unit, right.

19

Review of Figure 4-2 reveals no clear relationship between qnet and σ’pc. The graph di-stinguishing between σ’pc derivation method shows a wide scatter of results when either one of the Casagrande, Becker or Akai methods are used. Evaluation of the graph distin-guishing between Glacial unit shows a division between soil types, however, with distin-guishing parameter being qnet and not the σ’pc/qnet ratio. Given that there are no apparent relationships from the σ’pc values reported in /4/, RA undertook an independent assessment of σ’pc based on the laboratory results provided in /4/. The results of the RA derived σ’pc values are presented in Table 4-2 and presented against depth below seabed in Figure 4-3. Table 4-2: Comparison of σ’ pc values derived by RA

Boring Depth [m]

Test Type Glacial Unit

σ'vo winit σ'pc Method [kPa] [%] [kPa]

09.A.008 7.85 CRS Upper till 80 - 2000 Casagrande 09.A.008 7.93 IL Upper till 80 - 450 Casagrande 09.A.008 7.99 CRS Upper till 80 - - N/P (1) 09.A.008 8.11 CRS Upper till 80 - 1000 Casagrande 09.A.008 10.97 IL Upper till 130 9.7 900 Casagrande 09.A.012 11.21 IL Upper till 135 8.1 - N/P (1) 09.A.012 11.25 IL Upper till 135 8.1 - N/P (1) 09.A.008 18.05 IL Chalk till 220 9.4 - N/P (1) 09.A.008 19.04 IL Chalk till 235 - - N/P(1) 09.A.003 13.88 CRS Lower till 110 - - N/P (1) 09.A.003 13.98 CRS Lower till 110 - 900 Casagrande 09.A.003 14.16 IL Lower till 110 - 320 Casagrande 09.A.009 14.98 IL Lower till 170 9.8 - N/P (1) 09.A.605 15.65 IL Lower till 180 10.9 1000 Casagrande 09.A.003 16.74 IL Lower till 160 9.6 800 Casagrande 09.A.605 17.51 IL Lower till 200 13.5 1000 Casagrande 09.A.012 20.59 IL Lower till 260 6.8 1500 Casagrande 09.A.012 20.71 IL Lower till 260 6.8 - N/P (1) 09.A.012 30.44 IL Lower till 395 10.4 2000 Casagrande 09.A.012 30.49 IL Lower till 395 10.4 1500 Casagrande 09.A.013 41.75 IL Lower till 540 10.2 2000 Casagrande 09.A.013 52.11 IL Lower till 690 10.5 2000 Casagrande 10.A.060 60.62 IL Lowermost till 780 16.9 1300 Casagrande

(1) Very difficult to extract pre-consolidation pressure.

20

Figure 4-3: RA derived σ’ pc values versus depth The plot of pre-consolidation pressure against depth, Figure 4-3, shows no apparent trend in the results with depth for the Upper till. However, it is apparent that the σ’pc of the Lo-wer till increases with increasing depth. In order to examine this relationship further, the derived values of σ’pc were correlated with the adjacent CPTU net cone resistance values. The results of these correlations are illustrated in Figure 4-4.

Figure 4-4: RA derived σ’ pc values versus qnet As shown on review of Figure 4-4, there is no apparent correlation between σ’pc and qnet for the Upper till. However, it is illustrated that, with regards to the Lower till, an esti-mate of the pre-consolidation pressure may be found using the correlation: σ’pc = 0.3⋅qnet. This correlation may be used for all the clay till formations provided that the net cone re-sistance does not exceed 8000 kPa. For qnet > 8000 kPa, use qnet = 8000 kPa.

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500

De

pth

[m

]Pre-consolidation Pressure, σ' pc [kPa]

Upper Till Lower Till Lowermost Till

σ' pc = 0.3qnet

0

2000

4000

6000

8000

10000

12000

14000

0 500 1000 1500 2000 2500

qn

et[k

Pa

]

Pre-consolidation Pressure, σ' pc [kPa]


21

4.4 Over-consolidation ratio, OCR As previously discussed within Section 4.3.2 of this report, given the high strength of the Glacial units, it has proved difficult to accurately define values of pre-consolidation pres-sure. As a result, RA have re-interpreted the laboratory test results in /4/ and concluded alternative pre-consolidation pressures; as defined in Table 4-2. As the over consolidation ratio, OCR, is defined as the ratio between the pre-consolida-tion pressure and the in-situ stress (σ’pc/σ’ vo), meaningful OCR values cannot be deter-mined without reliable values of σ’pc. Given that the RA derived σ’pc values are conside-red to be more appropriate, these shall be used to assess the OCR of the Glacial units. Consequently, plots of σ’ vo against σ’pc for Upper till and Lower and Lowermost tills are presented in Figure 4-5 and Figure 4-6, respectively.

Figure 4-5: Pre-consolidation pressure against in-situ stress for Upper till

Figure 4-6: Pre-consolidation pressure against in-situ stress for Lower and Lowermost till As shown from the above plots, the OCR for the Upper till is shown to be highly variable; with values ranging between 5.0 and 25.0. The OCR for the Lower till is shown to typically vary between 2.5 and 13.0.

22

To examine the relationship of OCR with depth, a plot of log(OCR) against depth below seabed/ground level for every derived value of pre-consolidation pressure, distinguishing between individual Glacial units, is shown in Figure 4-7.

Figure 4-7: Over consolidation ratio against depth below seabed As shown from the above plot, with the exception of the Upper till, the value of OCR is shown to typically reduce with increasing depth. The OCR for the Lower till appears to decrease linearly with depth on a log plot, with an OCR of approximately 8.0 at 12 m depth decreasing to 2.9 at 52 m depth. The scatter of OCR values within the Upper till is likely to be associated with the difficulty of establishing reliable σ’pc values for this unit.

4.5 Earth pressure at rest, K0 Four incremental loading oedometer tests for the determination of K0 were undertaken (IL,K 0); with three tests undertaken on Lower till and one on Chalk till. The results of these tests are presented in /4/. The IL,K0 results reported values of K0 varying between 0.43 and 1.25 for the Lower till with varying ratios of OCR (σ’max/σ’unloading). Similarly, K0 values between 0.44 and 5.10 were reported for the Chalk till. The results of the IL,K0 tests, showing OCR against the corresponding calculated values of K0, are plotted within /4/ and equations that fit the up-per and lower bound test results from both Upper and Chalk till have been derived. These equations are as follows:

• Upper bound value: K0 ≈ 0.42 OCR0.40 • Lower bound value: K0 ≈ 0.42 OCR0.28

4.6 Conclusions In order to identify the stress history, a number of oedometer tests were carried out on samples of the Glacial till deposits.

0

10

20

30

40

50

60

70

1 10 100

De

pth

[m

]

OCR


23

It has been attempted to correlate the net cone resistance and the estimated pre-consolida-tion pressure for the Glacial till units. Two main challenges are: • The soil is generally very hard implying that a distinct break down of the structure is

not easy to identify. A possible explanation for this is that trimming the oedometer specimens in stiff soils will always imply an irregular perimeter. Once loading is on-going, the specimen will gradually try to establish contact with the oedometer ring and the higher load the better the contact. In this way the breakdown of the soil is “shaded”.

• The net cone resistance carries a large scatter with jumps, reflecting stones and varia-bility within the soil formation.

In light of this, no correlation between pre-consolidation and net cone resistance can be established for the Upper till. However, with regards to the Lower till, an estimate of the pre-consolidation pressure may be found using the correlation: σ’pc = 0.3⋅qnet. This corre-lation may be used for all the clay till formations provided that the net cone resistance does not exceed 8000 kPa. As reliable values of pre-consolidation pressure are necessary to establish the over-conso-lidation ratio of the soils, it was difficult to establish meaningful OCRs for the Upper Glacial till; given the issues previously discussed. However, using the RA derived σ’pc values, OCRs were found to range between 5.0 and 25.0 for the Upper till and between 2.5 and 13.0 for the Lower till. To establish a coefficient of earth pressure, incremental loading oedometer tests with measurements of horizontal stress have been used. Equations to fit the upper and lower bound test results for both the Upper and the Chalk till are provided in /4/. For the upper bound results, K0 is approximately 0.42 OCR0.40 and for the lower bound results, K0 is approximately 0.42 OCR0.28.

24

5. CONSOLIDATION PROPERTIES

5.1 General A total of 38 No. incremental loading oedometer tests were performed on samples of Glacial units; comprising of 8 No. tests on samples of Upper till, 5 No. tests on samples of Chalk till, 20 No. tests on samples of Lower till and 5 No. tests on samples of Lower-most till. These tests were undertaken to determine the following geotechnical parame-ters:

• The constrained oedometer secant modulus, Eoed,sec • The coefficient of consolidation, ck • The compression ratio, Q • The rate of secondary consolidation, Cαε • The rate of secondary swell, Csw

For detailed laboratory procedures and test results for each of the above parameters, see /12/ and /4/, respectively.

5.2 Laboratory measurements

5.2.1 Constrained oedometer modulus (reloading) Incremental loading oedometer testing has been carried out on samples of the Glacial deposits in order to determine reloading values of secant oedometric modulus, Eoed,sec. The measured secant values of the constrained oedometer modulus are noted in /4/. A plot of derived values of secant oedometric modulus for samples where the pressure after unloading is comparable to the in-situ effective stress is presented with depth in Figure 5-1. For each of the tests shown, the applied vertical stress does not exceed the in-situ stress plus 500 kPa.

Figure 5-1: Oedometric secant modulus against depth below seabed

0

10

20

30

40

50

60

70

0 200 400 600 800 1000 1200 1400

De

pth

[m

]

Eoed,sec [MPa]

Upper Till Chalk Till Lower Till Lowermost Till

25

It is apparent from Figure 5-1 that the individual Glacial units can be distinguished from oedometer secant modulus; which is also shown to increase with depth for each Glacial unit. Given that the Eoed,sec values vary with increased depth, a summary noting the mini-mum derived values of Eoed,sec for each Glacial unit, with a stress increase not exceeding 500 kPa from the in-situ stress, is presented in Table 5-1.

Table 5-1: Oedometer modulus during reloading from in-situ stress

Glacial Unit Stress Increment,

∆σ∆σ∆σ∆σ [kPa] Secant Oedometric

Modulus, Eoed,sec [MPa] Upper till 200 600 Chalk till 200 1114 Lower till 80 83 Lowermost till 200 31

A series of trend lines to predict lower bound values of Eoed,sec for each of the till units has been determined in /4/. These trend lines predict Eoed,sec values based on the plasticity index of the soil, provided that the stress after unloading is between 120 kPa and 500 kPa. A summary of the formula and adjusted parameters used to predict these trend lines is pre-sented in Table 5-2. A discussion and detailed account of these trend lines is contained in /4/. Table 5-2: Trend lines for lower bound values of oedometric secant modulus where Eoed,sec = A + (B×σ’ unl) and 120 kPa < σ’ unl < 500 kPa Glacial Unit I p [%] A [kPa] B Upper till < 10 200 × 103 1000 Chalk till - 200 × 103 500

Lower till

< 10 40 × 103 750 10 – 14 20 × 103 750 14 – 18 0 750

> 18 0 500 Lowermost till - 0 250

5.2.2 Constrained oedometer modulus (unloading) During unloading, it is anticipated that the soil will expand and the constrained modulus will decrease. Therefore, a single incremental unloading test was undertaken on a sample of Lower till, from boring 10.A.054 at a depth of 13.54 m, to determine a value of secant unloading modulus, Eoed,sec. The results of this test, together with the method used for de-riving Eoed,sec, is contained within /4/. Besides being undertaken to determine a value of Eoed,sec, for the Lower till, the unloading incremental loading test was carried out to investigate the relationship between unloading and reloading values of secant constrained modulus. To enable this comparison to be made, an incremental loading test was undertaken on a sample of Lower till, obtained from the same borehole and at a similar depth, to the unloaded tested sample. The result of this comparison is illustrated in Figure 5-2, with the stress increments plotted against the derived values of Eoed,sec. On this figure ∆σ represents the absolute value of the stress change from the initial in-situ stress, σ’ v0.

26

Figure 5-2: Oedometric secant modulus against stress increments The relationship between unloading and reloading constrained oedometer modulus was further investigated by comparing the ratio of Eoed,sec between the two tests. Where the applied stress increments were different between tests, Eoed,sec values were interpolated from the Figure 5-2. The result of this comparison is noted in Table 5-3 and shows that the ratio between the derived values of Eoed,sec. decreases with increasing stress increments. Table 5-3: Comparison of oedometer modulus during unloading and reloading

∆∆∆∆σσσσ’ v/σσσσ’ vo Unloading Eoed,sec

[MPa] Reloading Eoed,sec

[MPa] Unloading Eoed,sec /Reloading Eoed,sec

0.40 58 1198 1/20 0.50 (43) (1080) 1/25 0.60 (29) (938) 1/33 0.70 16 (782) 1/50 0.80 14 (627) 1/45

Values interpreted of Eoed,sec shown in brackets

5.2.3 Coefficient of consolidation (loading/unloading) The laboratory coefficient of consolidation, ck, has been determined from CRS and IL testing for a number of Upper and Lower till samples. The full results of these tests are contained within /4/. In summary, the tests concluded ck values ranging between 2×10-7 and 2×10-5 m2/sec for the Upper till and between 1×10-7 and 1×10-5 m2/sec for the Lower till. These laboratory determined values are very low and it is probable that field measure-ments will show significantly higher values.

0

200

400

600

800

1000

1200

1400

0,0 0,2 0,4 0,6 0,8 1,0 1,2

Eo

ed

,se

c[M

Pa

]

∆σ/σ'vo

Unloading Reloading

27

5.2.4 Compression ratio (loading) The compression ratio, Q, has been derived either from the stress-strain measurements at the end of consolidation stage within the incremental loading oedometer tests or from the stress-strain values in the CRS tests. Details on the method to derive Q from the stress-strain measurements are provided within /4/. The results of the incremental loading oedometer tests are contained within /4/. A sum-mary of statistical values for the compression ratio of each Glacial unit is presented in Table 5-4. Table 5-4: Compression ratios for Glacial units Statistic Upper till Chalk till Lower till Lowermos t till Arithmetic mean [%] 3.8 - 5.1 - Standard deviation [%] 1.4 - 1.3 - No. Tests 10 2 18 2

To evaluate Q values with depth and Glacial unit, a plot of Q against depth below seabed is presented in Figure 5-4. This shows that the Q value of each unit is highly variable; with values in the Upper till ranging between 1.9 and 6.0 % and between 3.1 and 7.1 % in the Lower till.

Figure 5-4: Compression ratio against depth below seabed The relationship of Q with measured values of plasticity index, Ip, has been investigated in /4/ for each Glacial unit and has concluded Q values between various ranges of Ip. Analysis in /4/ concluded that for Glacial till with an Ip less than 9 % the corresponding Q value was between 2 and 4 %, and, with an Ip between 10 and 16 % the Q value was be-tween 4 and 7 %. Similarly, samples of Glacial till with an Ip of approximately 38 % were found to have a Q value in excess of 8 %.

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7 8 9 10

De

pth

[m

]

Q [%]

Upper Till Chalk Till Lower Till Lowermost Till

28

5.2.5 Creep properties (reloading) A number of incremental loading oedometer tests have been carried out on samples of the Upper, Chalk, Lower and Lowermost till units, with the aim of deriving the rate of secon-dary consolidation, Cαε. The results of these tests are presented in /4/; together with plots of normalised effective stress relative to the vertical in-situ stress (σ’/σ’ vo) against the rate of secondary consolidation for different Glacial units and loading and reloading results . Review of the plots shows no distinction between Glacial units. However, a division is shown between the loading and reloading data; where maximum Cαε along the initial loading curve was determined to be 0.26 % per log cycle of time and the maximum Cαε along the reloading curve was found to be 0.09 % per log cycle of time. In both the load-ing and reloading testing, the rate of secondary consolidation was found to increase with increasing effective stress.

5.2.6 Swelling properties (unloading) On review of the incremental loading oedometer tests carried out on samples of the Gla-cial deposits, /4/ indicates that Glacial deposits with an Ip less than 20 % have no swell potential.

5.2.7 Permeability Although no laboratory tests have been undertaken to specifically determine the coeffici-ent of permeability, k (hydraulic conductivity), this has been determined from CRS and IL testing; based on the coefficient of consolidation, ck. Review of these results provided in /4/ has concluded the values of k, presented in Table 5-5, at the vertical effective in-situ stress level, σ'vo, at reloading. Table 5-5: Coefficient of permeability of Glacial units at σ’ vo at re-loading Glacial Unit No. of

results Range

[10–12 m/sec] Arithmetic mean

[10–12 m/sec] Standard dev. [10–12 m/sec]

Upper till 5 3.4 – 47.9 18.5 19.3 Chalk till 3 2.0 – 22.3 9.3 11.3 Lower till 7 5.6 – 55.4 18.3 18.6 Lowermost till 2 2.2 – 4.1 3.1 1.3 In light of the results from the CRS and IL tests, the reported k values corresponding to vertical in-situ stress level at reloading, as noted in Table 5-5, would deem each of the Glacial units as ‘low permeability’. The low permeability values result of the low values of coefficient of consolidation reported in 5.2.3, and field measurements may show sig-nificantly higher values.

5.3 Large scale testing Not applicable.

29

5.4 Conclusions A number of incremental loading oedometer tests have been undertaken on samples of the Glacial units in order to determine the constrained secant oedometer modulus, Eoed,sec, the coefficient of consolidation, ck, the compression ratio, Q, the rate of secondary con-solidation Cαε (or εs) and the rate of secondary swell, Csw. It is apparent that the derived values of Eoed,sec are markedly different between Glacial units and have been shown to increase with depth. The minimum derived values of Eoed,sec, with a stress increase not exceeding 500 kPa from the in-situ stress, has been shown to be 600 MPa for Upper till, 1114 MPa for Chalk till, 83 MPa for Lower till and 31 MPa for Lowermost till. It should be noted that /4/ has devised a series of trend lines to predict lower bound values of Eoed,sec for each Glacial units. These trend lines predict Eoed,sec values based on the plasticity index of the soil, provided that the unloading stress is between 120 kPa and 500 kPa. The laboratory coefficient of consolidation, ck, range between 2×10-7 and 2×10-5 m2/sec for the Upper till and between 1×10-7 and 1×10-5 m2/sec for the Lower till. These are very low values and field measurements may show significantly higher values. The Q values of each Glacial unit were found to be highly variable; with values in the Upper till ranging between 1.9 and 6.0 % and between 3.1 and 7.1 % in the Lower till. However, analysis in /4/ has established an approximate relationship between Q and plas-tic index, Ip. For Glacial till with an Ip less than 9 % the Q value was between 2 and 4 %, and, with an Ip between 10 and 16 % the Q value was between 4 and 7 %. Similarly, samples of Glacial till with an Ip of approximately 38 % were found to have a Q value in excess of 8 %. Review of the creep properties noted a maximum value of Cαε along the initial loading curve of 0.26 % per log cycle of time and a maximum value of Cαε along the reloading curve of 0.09 % per log cycle of time. In both the loading and reloading testing, the rate of secondary consolidation was found to increase with increasing effective stress. Ref /4/ indicates that Glacial deposits with an Ip less than 20 % have no swell potential. The coefficient of permeability, k (hydraulic conductivity), has determined from CRS and IL testing at the corresponding vertical effective in-situ stress level, σ'vo, at reloading. These tests have concluded average k values ranging from 3.4 to 47.9×10-12 m/sec for the Upper till, 2.0 to 22.3×10-12 m/sec for the Chalk till, 5.6 to 55.4×10-12 m/sec for the Lower till and 2.2 to 4.1×10-12 m/sec for the Lowermost till. Such values would indicate that these Glacial units have very low permeability.

30

6. STATIC SHEAR STRENGTH

6.1 Introduction In order to obtain information to allow the derivation of geotechnical strength parameters for the Glacial deposits, a total of 27 No. triaxial tests (consisting of 21 No. undrained compression and 6 No. undrained extension) and 5 No. direct simple shear tests were un-dertaken on selected samples. A detailed account of the laboratory procedures and test re-sults is discussed in /12/ and /4/ respectively. A number of laboratory tests (17 No. CAUc, 6 No. CAUe and 4 No. DSSst) were under-taken on samples of Glacial deposits that were recovered from borings drilled within 5 m of CPTUs. As a result, the geological logs of the boring can be compared to the CPTU profile and a correlation between the laboratory test results and the CPTU profile made. By comparing this data, a direct assessment of the strength properties in the Glacial till deposits can be derived.

6.2 Undrained shear strength, in-situ stress The undrained shear strength from triaxial and direct simple shear tests, with consolida-tion stresses corresponding to the in-situ stress of the samples, is presented in Table 6-1. Lower till triaxial specimens were consolidated to the estimated in-situ stress levels and then sheared, but Upper till specimens were pre-consolidated to a high stress level ap-proaching the estimated pre-consolidation stress before unloading to the in-situ stress. All DSS specimens were initially consolidated to a vertical stress level approaching the estimated pre-consolidation stress before unloading to the in-situ stress It should be noted that in the undrained triaxial compression tests on specimens of Chalk till negative pore water pressures developed during the test. The negative pore water pressures increased as the axial stress increased resulting in the apparent undrained shear strength of the sample increasing with increasing applied stress. When there is no peak in the deviator stress due to pore water pressure becoming progressively more negative as the axial stress is increased ‘undrained shear strengths’ reported in /4/ is based on the de-viator stress at 10% axial strain. Table 6-1: Triaxial and direct simple shear test results

Boring Depth [m]

Test Type Glacial Unit σ’ vo

[kN/m 2] cu

C

[kN/m 2] cu

E

[kN/m 2] cu

DSS [kN/m 2]

09.A.007 6.11 CAUc Upper till 68 807 - - 09.A.008 11.10 CAUc Upper till 130 820 - - 09.A.012 11.30 CAUc Upper till 135 924 - - 09.A.013 11.48 CAUc Upper till 140 1224 - - 09.A.013 11.58 CAUe Upper till 140 - 418 - 09.A.009 15.35 CAUc Chalk till 170 1204 - - 09.A.009 18.17 CAUc Chalk till 220 1788 - - 10.A.054 15.62 DSSst Lower till 155 - - 208 10.A.054 15.67 CAUc Lower till 155 186 - - 09.A.003 15.74 CAUc Lower till 150 411 -

31

Boring Depth [m]

Test Type Glacial Unit σ’ vo

[kN/m 2] cu

C

[kN/m 2] cu

E

[kN/m 2] cu

DSS [kN/m 2]

10.A.054 15.77 CAUe Lower till 155 - 131 - 09.A.605 15.82 CAUc Lower till 180 328 - - 09.A.605 15.90 CAUc Lower till 180 326 - - 09.A.003 15.96 CAUe Lower till 150 - 208 - 09.A.003 16.54 CAUc Lower till 160 365 - 09.A.003 16.63 CAUe Lower till 160 - 359 - 09.A.003 16.82 CAUe Lower till 160 - 151 - 09.A.605 17.32 DSSst Lower till 200 - - 285 09.A.605 17.47 DSSst Lower till 200 - - 203 09.A.605 17.65 CAUc Lower till 200 339 - - 10.A.054 20.38 CAUc Lower till 210 677 - - 10.A.057 21.59 DSSst Lower till 215 - - 404 09.A.013 42.01 CAUc Lower till 540 347 - - 09.A.605 29.42 CAUc Lowermost till 360 295 - - 09.A.605 29.52 CAUe Lowermost till 360 - 188 - 09.A.605 29.61 DSSst Lowermost till 360 - - 387

A graph of the laboratory determined undrained shear strength results (excluding results for Chalk till) against depth below seabed from triaxial compression testing is presented in Figure 6-1. This graph notes the units that comprise the Glacial deposits and highlights the range of measured values of cu

C.

Figure 6-1: Undrained shear strength, cu

C against depth By comparing the borehole logs and laboratory strength test results with the adjacent CPTU profiles, values of net cone resistance (qnet) corresponding to the sample depths can be derived. Table 6-2 highlights the undrained shear strength test results from the laboratory testing, together with interpreted cone resistance. The calculated cone factor (Nkt= qnet/cu) is also presented.

0

5

10

15

20

25

30

35

40

45

0 250 500 750 1000 1250 1500

De

pth

[m

]

cuc [kN/m2]


32

Table 6-2: Triaxial CAUc shear strength results correlated with CPTU data

Boring Depth [m] Glacial Unit σ’ vo

[kN/m 2] cu

C

[kN/m 2] qnet

[kN/m 2] Nkt

(qnet/cuC)

09.A.007 6.11 Upper till 68 807 7490 9.28 09.A.008 11.10 Upper till 130 820 8335 10.16 09.A.013 11.48 Upper till 140 1224 14000 11.44 10.A.054 15.67 Lower till 155 186 3175 17.07 09.A.605 15.82 Lower till 180 328 3385 10.32 09.A.605 15.90 Lower till 180 326 3385 10.38 09.A.605 17.65 Lower till 200 339 3010 8.88 10.A.054 20.38 Lower till 210 677 5842 8.63 09.A.013 42.01 Lower till 540 347 5705 16.44 09.A.605 29.42 Lowermost till 360 295 4510 15.29

Given that most of the correlations between the laboratory strength testing and the CPTU data is from samples of Upper and Lower till, plots of the net cone resistance against the undrained shear strength, cu

C, for these units are illustrated in Figure 6-2 and Figure 6-3.

Figure 6-2: Undrained shear strength against net cone resistance for the Upper till

0

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4000

6000

8000

10000

12000

14000

16000

0 250 500 750 1000 1250 1500 1750 2000

qn

et[k

N/

m2]

cuc [kN/m2]

33

Figure 6-3: Undrained shear strength against net cone resistance for the Lower till A plot of the cone factor Nkt against depth, distinguishing between Glacial unit is pre-sented in Figure 6-4.

Figure 6-4: qnet/cu

C (Nkt factor) against depth As demonstrated within Figure 6-4, the calculated cone factor for each Glacial unit is va-riable, with no consistent trend observed with depth In light of the variability of Nkt factors within Glacial units, published literature suggests that the geometric mean value of the Nkt value may provide an informed estimate of the cone factor to be used in design /13/. Statistical analysis of the Nkt values for each unit is provided in Table 6-3.

0

2000

4000

6000

8000

10000

0 200 400 600 800 1000

qn

et[M

N/

m2]

cuc [kN/m2]

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

De

pth

[m

]

qnet/cuC


34

Table 6-3: Cone factor statistics for Glacial units Unit Statistic Nkt

[qnet/cuC]

Unit Statistic Nkt [qnet/cu

C]

Upper till Arithmetic mean Geometric mean Standard dev. Number of tests

10.3 10.3 1.1 3

Chalk till Arithmetic mean Geometric mean Standard dev. Number of tests

- - - 2

Lower till Arithmetic mean Geometric mean Standard dev. Number of tests

12.0 11.5 3.8 6

Lowermost till

Arithmetic mean Geometric mean Standard dev. Number of tests

- - - 1

Although there are a limited number of correlated tests the Nkt values for the Upper and Lower Glacial tills are generally in agreement with published literature /14/.

6.3 Undrained shear strength, SHANSEP The SHANSEP procedure provides a method of estimating the undrained shear strength of an over-consolidated clay from the pre-consolidation stress and the in situ vertical effective stress. Past experience for Danish till /14/ is that the undrained triaxial compressive strength (cu

C) of intact clay till can be estimated using the relationship: cu

C = 0.42 σꞌv0 (σꞌpc/σꞌv0)0.85

Using σꞌpc determined from the relationship σꞌpc = 0.3 qnet proposed in Section 4.3.2 and the estimated in-situ vertical effective stress σꞌv0, Figure 6-6 shows cu

C/σꞌv0 for the Upper till, Lower till and Chalk till plotted against OCR for test results in Table 6-1 which have corresponding CPTU data.

Figure 6-6: cu

C/σꞌv0 versus OCR (assuming σꞌpc = 0.3 qnet)

0,00

2,00

4,00

6,00

8,00

10,00

12,00

14,00

0,0 5,0 10,0 15,0 20,0 25,0 30,0 35,0 40,0

c u/σσ σσ

' v0

OCR = 0.3qnet/σσσσ 'v0

Upper Till

Lower Till

Chalk Till

Shansep relationship

35

The SHANSEP relationship previously proposed for Danish till is also shown on Figure 6-6 for comparative purposes. It can be seen that cu

C values for the Upper till and the Chalk till are higher than predicted by the SHANSEP relationship but the results for the Lower till lie above and below the SHANSEP line. No obvious explanation can be provi-ded why some of the Lower till results lie below the SHANSEP line, but the test results that give the lower cu

C/σꞌv0 values are those that give the higher Nkt values shown on Fi-gure 6-4. This suggests that the measured cu

C strength is low in comparison to the qnet value used to derive the OCR value.

6.4 Undrained shear strength, stresses lower than in-situ Not applicable. No strength testing has been undertaken on samples of the Glacial depos-its where the applied stresses are less than that in-situ.

6.5 Effective shear strength, in-situ Effective shear strength parameters have been determined from undrained triaxial com-pression and extension tests with pore water pressure measurements and from drained triaxial compression tests. All triaxial tests are on test specimens with a height to diame-ter ratio of 1:1. The advanced laboratory testing for the Glacial deposits comprised; 10 no. anisotropica-lly consolidated drained compression tests (CADc), 12 No. anisotropically consolidated undrained compression tests (CAUc), and 3 No. anisotropically consolidated undrained extension (CAUe) tests. The specimens were consolidated to the estimated in-situ stress levels before the actual loading programme is applied. Specimens of Lower till were generally consolidated to in-situ stress levels and then sheared but Upper till specimens were pre-consolidated to a high stress level approaching the estimated pre-consolidation stress before unloading to the in-situ stress and succeeding shearing. Effective stress paths from undrained tests and peak stress ratios from drained tests are shown in Enclosures C-23 to C-27. Effective shear strength parameters have been derived by drawing best fit failure lines to the stress path envelopes. These are shown on Enclosures C-23 to C-27. The inferred effective shear strength parameters for the Glacial units are listed in Table 6.4. A number of the stress paths from undrained tests have been excluded due to no back pressure being applied or problems with the back pressure (12 No. tests) or wrong test procedure (one extension test). The cyclic tests are also omitted. Undrained tests where the pore water pressure has clearly reached a limit governed by the back pressure are only included for the stress path below the limit because the effective stress includes the pore pressure value. Also where exceptionally high effective friction angles are indicated by stress paths from extension the friction angle in extension has been limited to the com-panion effective friction angle in compression.

36

Table 6-4: Estimates of effective shear strength properties Compression Extension Glacial Unit φ’ [ °°°°] c’ [kPa] No. tests φ’ [ °°°°] c’ [kPa] No. tests Upper till 33.4 54 5 ‒ ‒ ‒ Meltwater Sand 37.6 44 3 ‒ ‒ ‒ Chalk till 36.2 99 5 ‒ ‒ ‒ Lower till 36.2 0 8 36.2 0 2 Lowermost till 31.3 0 1 31.3 0 1

6.6 Anisotropy factors In order to examine the potential anisotropic influences within the Glacial deposits, the undrained shear strength in compression, cu

C, in extension, cuE and in direct simple shear,

cuDSS, of laboratory tests of samples that were recovered within 0.25 m of one another

within borings, were compared. The findings of this review are presented in Table 6-5 and Table 6-6.

Table 6-5: Comparison of undrained shear strength results for Glacial deposits

Boring Unit Depth [m] Sample Range [m]

cuC

[kN/m 2] cu

E [kN/m 2]

cuDSS

[kN/m 2] 09.A.013 Upper till 11.48 – 11.58 0.10 1224 418 - 10.A.054 Lower till 15.62 – 15-77 0.15 186 131 208 09.A.605 Lower till 15.47 – 15.71 0.24 519 - 123 09.A.605 Lower till 17.32 – 17.56 0.24 407 - 285 09.A.605 Lower till 17.47 – 17-56 0.09 407 - 203 09.A.605 Lowermost 29.48 – 11-58 0.19 295 188 387

Table 6-6: Comparison of undrained shear strength ratios for Glacial deposits Boring Unit Depth [m] cu

C/cuE cu

C/ cuDSS cu

E /cuDSS

09.A.013 Upper till 11.48 – 11.58 2.93 - - 10.A.054 Lower till 15.62 – 15-77 1.42 0.89 0.63 09.A.605 Lower till 15.47 – 15.71 - 4.22 - 09.A.605 Lower till 17.32 – 17.56 - 1.43 - 09.A.605 Lower till 17.47 – 17-56 - 2.00 - 09.A.605 Lowermost 29.48 – 11-58 1.57 0.76 0.49 As shown in Table 6-6, there is a large variation in the ratios between the measured val-ues of undrained shear strength. It is also noted that there is a limited amount of data to compare for each Glacial unit, making it difficult to distinguish any trends. In order to visually ascertain any potential relationship between values of undrained shear strength, a plot of undrained shear strength in compression against undrained shear strength in ex-tension and direct simple shear for the Lower till is shown in Figure 6-7.

37

Figure 6-7: Comparison of undrained shear strength results within the Lower till Because of the limited number of data points, and the large variability in the ratios be-tween measured values of undrained shear strength, there are no obvious trends within the data. As a result, it is not possible to predict anisotropic factors for individual Glacial units but it is clear that the tills demonstrate anisotropic behaviour.

6.7 Rate effects Not applicable.

6.8 Large scale testing Not applicable.

6.9 Conclusions A number of laboratory tests were undertaken on samples of Glacial deposits that were recovered from borings drilled within 5 m of CPTUs. As a result, the geological logs of the boring can be compared to the CPTU profile and a correlation between the laboratory strength testing results and the qnet values made. Despite a high variability in the cone factors calculated for the Glacial units, it is propo-sed that an Nkt value of 10.0 is adopted when predicting cu on basis of qnet for the Upper and Chalk tills. For Lower and Lowermost tills, a value of 11.5 is adopted.

0

50

100

150

200

250

300

0 100 200 300 400 500 600

Tri

ax

ial

ex

ten

sio

n (

c uE )

an

d D

ire

ct S

imp

le

Sh

ea

r (c

uD

SS)

stre

ng

th [

kP

a]

Triaxial Compression (cuC) Strength [kPa]

Lower Till

CuDSS

CuE

38

Danish experience notes that the undrained shear strength of clay till can be related to pre-consolidation pressure and in situ vertical effective stress using the SHANSEP proce-dure. The Upper till and Chalk till have higher undrained shear strengths than the tills to which the SHANSEP procedure has previously been applied. It has been found that when used with the previous correlation factors, together with pre-consolidation pressures de-rived from CPT qnet values testing, the SHANSEP procedure underestimates the undrain-ed shear strength of the Upper till but does not provide consistently reliable estimates of undrained shear strength for the Lower till. Given the limited number of compression, extension and direct simple shear measure-ments of undrained shear strength at close proximity to one another, and the large va-riability in the ratios between those values obtained, it is not possible to predict aniso-tropic factors for individual Glacial units but indeed the tills behave anisotropic.

39

7. SMALL STRAIN STIFFNESS AND DAMPING

7.1 Introduction Small strain testing of the Glacial units proved difficult to implement due to the inherent high strength and stiffness of these materials. Many of the till specimens were too stiff for resonant column testing and installing bender elements within these test specimens also proved to be difficult to achieve. As a consequence, limited testing has been carried out to obtain small strain stiffness data for the Glacial deposits and to determine how soil stiff-ness and damping vary with strain. Testing has been limited to specimens of Lower till and Chalk till; no small strain testing has been undertaken for the Upper till, Lowermost till and Meltwater deposits. Testing consisted of one resonant column test on a specimen of Lower till, 3 no. cyclic triaxial tests on Chalk till specimens and 6 no. cyclic triaxial tests on specimens of Lower till. Details of the test carried out are given in Table 7-1. Table 7-1: Tests carried out to derive small strain stiffness data

Boring Core No. Specimen Depth [m]

Test Type Unit

σ’ vo [kPa]

Bender Element

09.A.009 09-101807 12.36 CAUcy Chalk till 150 09.A.009 09-101807 12.53 CAUcy Chalk till 150 09.A.009 09-101807 12.70 CAUcy Chalk till 150 Yes 10.A.057 10-105950 19.03 CAUcy Lower till 180 10.A.057 10-105952 19.81 CAUcy Lower till 180 10.A.057 10-105952 19.98 CAUcy Lower till 180 10.A.061 10-106176 22.88 CAUcy Lower till 250 10.A.061 10-106186 23.83 CAUcy Lower till 250 Yes 10.A.061 10-106186 23.99 CAUcy Lower till 250 09.A.013 09-100241 55.05 RC Lower till 725 Yes

7.2 Small strain stiffness The small strain shear modulus has been determined in the laboratory using bender ele-ments and by resonant column testing. Bender elements were used in two cyclic triaxial test specimens (CAUcy) and in the test specimen used for resonant column (RC) testing. Upper bound values of small strain shear modulus (Gmax) determined using bender ele-ments reported in /4/ are summarised in Table 7-2, together with Gmax determined from resonant column testing. Estimated values of in-situ vertical effective stress (σꞌvo) and final vertical consolidation stress (σꞌv) are also provided in Table 7-2. Gmax values vary between 200 MPa and 500 MPa with Gmax increasing with depth. However, with such a small data set it is difficult to draw any conclusions about which parameters have the most effect on the measured values of Gmax.

40

Table 7-2: Gmax measurements in Chalk till and Lower till from bender elements and resonant column testing

Boring Depth [m]

Test type Unit

σ’ vo [kPa]

σ’ v [kPa] σ’ v /σ’ vo

Gmax,bender [MPa]

Gmax,RC [MPa]

09.A.009 12.70 CAUcy Chalk

till 150 146 1.0 204 -

10.A.061 23.83 CAUcy Lower

till 250 598 2.4 288 -

09.A.013 55.05 RC Lower

till 725 400 0.6 398 401 725 600 0.8 490 497

Vertical Seismic Profiling (vsp) has been carried out in a number of onshore boreholes to determine seismic P-wave and S-wave velocities. The small strain shear modulus (G0) has been determined from S-wave velocities and is reported in /16/ at 1 m depth intervals over the logged depth. The small strain shear modulus for all field and laboratory tests (G0 and Gmax) within the Glacial deposits are plotted versus depth on Figure 7-1. The boreholes from which the specimens used for bender element and resonant column test-ing were recovered are not the same as those in which vsp logging has been carried out. Nevertheless, within the same formation unit there is agreement between Gmax values obtained from laboratory testing and G0 obtained from vsp logging. G0 values vary between approximately 200 MPa and 600 MPa. The lower values apply to the Lowermost till and Lower till at depths less than about 15m, while the higher values were measured in Upper till at depths less than about 15 m. Below 20 m depth the derived G0 values generally converge to values generally between 300 and 400 MPa.

41

Figure 7-1: Gmax and G0 values for the Glacial deposits determined using bender elements

and downhole vsp logging Table 7-3 shows Gmax/qnet obtained using bender element and resonant column Gmax values for the Lower till and qnet (the net cone resistance) from the adjacent CPTU at the corresponding depth. The data shows the Lower till at 24 m depth has a Gmax/qnet ratio of 17 but at 55 m depth the Gmax/qnet ratio in the Lower till varies between 80 and 100. The-re is insufficient data to draw any general conclusions from these results.

Table 7-3: Gmax/qnet ratios using bender element and resonant column Gmax data for Glacial deposits

Boring Depth [m]

Test type Unit

Gbender [MPa]

GRC [MPa]

qnet [MPa]

Gmax,bender

/qnet [MPa]

Gmax,RC

/qnet [MPa]

09.A.009 12.70 CAUcy Chalk

till 204 No CPT

10.A.061 23.83 CAUcy Lower

till 288 16.70 17

09.A.013 55.05 RC Lower

till 398 401 4.97 80 81 490 497 4.97 99 100

0

10

20

30

40

50

60

0 200 400 600 800 1000 1200

De

pth

(m

)G0 and Gmax (MPa)

Lowermost Till

Meltwater Sand

Lower Till

Upper Till

Lower Till RC

Lower Till BE

Chalk Till BE

42

Figure 7-2 shows G0/qnet profiles from boreholes where CPTU testing and vsp logging was carried out in adjacent boreholes. The G0/qnet profiles show little difference between the Glacial units to about 20 m depth but below this depth the range of Gmax/qnet ratio is similar to that determined from the bender element and resonant column testing.

Figure 7-2: G0/qnet and Gmax/qnet ratios for Glacial units Enclosure C-28 summarises Gmax from bender element testing by borehole, depth and formation and Enclosure C-29 summarises the vsp logging average G0 values for each formation logged by borehole. Average Gmax/qnet and G0/qnet values are also tabulated. The variation of shear modulus with shear strain has been investigated by resonant co-lumn and cyclic triaxial testing. Results of these tests are provided in /4/ Sections 7 and 9 as plots of shear modulus (G) against cyclic shear strain (γ). Normalised versions of the data provided in /4/ are shown on Figures 7-3 and 7-4 where values of G/Gmax are shown versus cyclic shear strain. For the cyclic triaxial tests the Gmax value used for normalisa-tion is that obtained from bender element results for the relevant specimen and for the resonant column testing Gmax is taken as the measured value of G at the smallest shear strain.

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140 160 180

De

pth

(m

)

G0/qnet and Gmax/qnet

Lowermost Till

Meltwater Sand

Lower Till

Upper Till

Lower Till RC

Lower Till BE

43

Bender element testing was only carried on two CAUcy test specimens. Figure 7-3 inclu-des the results for these two tests together with the results from the resonant column test on Lower till. The three points shown for each test are values after 2, 10 and 50 cycles of loading.

Figure 7-3: G/Gmax versus cyclic shear strain from Resonant column and cyclic triaxial tests

with bender element measurement of Gmax Assuming that Gmax measured on one specimen is valid for other specimens from the same core, or an adjacent core, Figure 7-4 shows normalised plots based on three CAUcy tests in the Lower till and 3 tests in the Chalk till. This figure indicates that the degrada-tion curve for Chalk till lies below the corresponding curve for Lower till. Additional testing will be required to verify the degradation properties if cyclic loading is important.

Figure 7-4: G/Gmax versus cyclic shear strain from Resonant column and cyclic triaxial tests

using nearest bender element measurement of Gmax

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0,0001 0,001 0,01 0,1 1 10

G/

Gm

ax

Cyclic Shear strain (%)

Lower Till RC

Lower till CAUcy

Chalk till CAUcy

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0,0001 0,001 0,01 0,1 1 10

G/

Gm

ax


Lower Till RC

Lower Till CAUcy

Chalk Till CAUcy

44

7.3 Damping ratios Damping ratios obtained from resonant column and cyclic triaxial testing are provided in Sections 7 and 9 of /4/. The damping measurements are shown plotted against shear strain on Figure 7-5. The damping ratios determined from the CAUcy tests are high and do not show the ex-pected trend of increasing damping ratio with increasing cyclic shear strain and do not appear to be consistent with the low ratios determined from the resonant column testing. No explanation has been found for this unexpected behaviour and these test results should be treated with caution.

Figure 7-5: Damping ratios versus shear strain for Chalk till and Lower till

7.4 Conclusions Small strain testing of the Glacial units proved difficult to achieve due of the inherent high strength and stiffness of these materials. Because of these constraints a limited amount of laboratory testing has been completed to provide small strain stiffness data for the Glacial deposits and to define how soil stiffness and damping vary with strain. Test-ing has been limited to specimens of Lower till and Chalk till; no small strain testing has been undertaken for the Upper till, Lowermost till and Meltwater deposits. The laboratory testing is complemented by small strain stiffness values derived from downhole logging using Vertical Seismic Profiling within boreholes through the Glacial deposits. The test results indicate that small strain stiffness (G0) derived from vsp logging varies between approximately 200 MPa and 600 MPa. The lower values apply to the Lower-most till and Lower till at depths less than about 15 m, while the higher values were mea-sured in Upper till at depths less than about 15 m. Below 20 m depth the G0 values gene-rally converge to values generally between 300 and 400 MPa.

0

5

10

15

20

25

30

35

0,0001 0,001 0,01 0,1 1 10

Da

mp

ing

Ra

tio

(%

)


Lower Till RC

Lower Till CAUcy

Chalk Till CAUcy

45

Laboratory testing and downhole logging results indicate Gmax/qnet and G0/qnet ratios in the range 20 to 100 with no distinct variation between the Glacial units. Due to the size of the data set firm conclusions on how stiffness and damping vary with shear strain have not been determined. Normalised plots of G/Gmax follow the expected ‘S’ shape profile when stiffness degradation profile is plotted against the log of cyclic shear strain, but the damping ratio values derived from cyclic triaxial tests appear to be high and do not show the expected trend of increasing damping ratio with increasing cy-clic shear strain.

46

8. CYCLIC UNDRAINED SHEAR STRENGTH

8.1 Introduction The undrained cyclic shear strength is defined as the sum of the average shear stress, τa and the cyclic shear stress, τcy as addressed in /15/. These stress components will depend on the in-situ stress state of the soil, the type of structure applied and the load scenario driving the design, e.g. size of load, direction of load, variation of load with time and the equivalent number of load cycles to be applied.

8.2 Cyclic undrained direct simple shear strength In order to determine the number of cycles to fail the Lower till with a combination of average and cyclic shear stresses, six cyclic undrained direct shear tests as constant volu-me were undertaken on samples recovered from 10.A.057. The results of these tests are presented in Table 8-1. Details of the test procedures for undertaking the cyclic undrained direct simple shear strength tests are found in /2/. The full results of these tests are con-tained in /4/. Table 8-1: Results of cyclic undrained direct simple shear strength tests on Lower till

Boring Depth [m]

σ’ vo

[kPa] τcy

[kPa] τa

[kPa] No. cycles to failure τcy/cu

DSS τa/cuDSS

10.A.057 19.19 180 197.8 80 28 0.49 0.20 10.A.057 19.23 180 - 0 - - 0.00 10.A.057 19.36 180 117.2 235 1 0.29 0.58 10.A.057 21.64 215 175.7 6 141 0.43 0.01 10.A.057 21.75 215 259.7 0 19 0.64 0.00 10.A.057 21.79 215 317.6 0 5 0.79 0.00

The result of a static undrained direct simple shear test, undertaken on a sample from 10.A.057 at 21.59 m, was used to provide a value of cu

DSS which could then be used to determine the ratios of cyclic shear stress against static undrained shear stress and aver-age shear stress against static shear strength. Figure 8-1 shows these ratios plotted against one another at failure conditions; which is defined as the number of cycles required to reach 15 % shear strain.

47

Figure 8-1: Ratio of average shear stress against cyclic shear stress, relative to static undrained shear strength, for the Lower till The blue dashed line represents the envelope of combinations of average and cyclic shear stress ratios that lead to failure in 10 cycles of loading. If N exceeds 10 in the design, the undrained cyclic shear strength will be lower and conversely if N < 10. The N=10 envelope shown on Figure 8-1 is consistent with the results of previous cyclic testing on clay till reported in /17/.

8.3 Conclusions To determine the number of cycles required to fail the Lower till with a combination of average and cyclic shear stresses, i.e. reach 15 % shear strain, six cyclic undrained direct shear tests as constant volume were undertaken. Simplified diagrams have been used to assess the undrained cyclic shear strength. Such methods have indicated that when failure is reached in 10 cycles (N = 10) the undrained cyclic shear strength equals between approximately 70 % and 100% of the undrained static shear strength dependant on the ratio of the cyclic shear stress to the static undrained DSS strength..

N=1

N=5

N=19

N=28

N=141

0,00

0,20

0,40

0,60

0,80

1,00

0,00 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00

τc

y/c u

DSS

[-]

τa/cuDSS [-]

N=10

48

9. REFERENCES

/1/ GDR 17.0-001, Boring Campaign 2009, January 2011, prepared by Fugro. /2/ GDR 17.0-003, Boring Campaign 2010, January 2011, prepared by Fugro. /3/ GDR 17.0-002, Seabed CPT Campaign 2009, May 2010, prepared by Fugro. /4/ GDR 18.0-004, Advanced Laboratory Testing, Glacial Deposits, March 2011,

prepared by GEO. /5/ Femern A/S. Geo Information System /6/ Femern A/S. Geo Nomenclature /7/ Terzaghi el al (1996) /8/ Becker, D.E., Crooks, J.H.A., Been, K. and Jefferies, M.G. (1987), Work as a

criterion for determining in situ and yield stresses in clay, Canadian Geotechnical Journal, Volume 24, p. 549

/9/ Casagrande, A. (1936), The determination of the pre-consolidation load and its practical significance, Proceedings of the First International Conference on Soil Mechanics and Foundation Engineering, Volume 3, Discussion D-34, p. 60, Boston, June 22 to 26, 1936

/10/ Janbu, N. (1969). The resistance concept applied to deformation of soils. Proceedings of the 7th International Conference on Soil Mechanics and Foundation Engineering, Volume 1, p. 191, Mexico City, August 1969

/11/ Akai, K. (1960). Die Strukturellen Eigenschaften von Schluff, Mitteilungen Heft 22, Die Technische Hochschule, Aachen

/12/ GDR 18.0-002, Advanced Laboratory Testing, Laboratory Procedures, March 2011, prepared by GEO.

/13/ Mortensen, J.K., Hansen, G., Sørensen, B., 1991: Correlation of CPT and Field Vane Tests for Clay tills. Danish Geotechnical Society, Bulletin No. 7.

/14/ Sørensen, C.S, Steenfelt, J.S., Mortensen, J.K.: Foundations of the East Bridge for the Storebælt Link. Danish Geotechnical Society, Bulletin No. 11. Vol. 5. 1995.

/15/ Andersen, K.H., A. Kleven and D. Heien. Cyclic Soil Data for Design of Gravity Structures. NGI Publication 175, Oslo, 1988.

/16/ GDR 04.0-002, Geophysical Borehole Logging, December 2010, prepared by Rambøll Arup JV

/17/ Kleven, A. And Andersen, K.H. Cyclic laboratory tests on Storebælt Clay till. Proceedings of the 1st Seminar on Design of Exposed Bridge Piers, Copenhagen, 22 January 1991.

Encl. C-01

Fehmarnbelt Fixed Link

Classification data

Water content

Glacial units

2011-05-01

09.A.00109.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.00909.A.01009.A.01109.A.01209.A.01309.A.014

10.A.059A10.A.059B10.A.06010.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.60710.A.61010.A.610A10.A.610B

09.A.01509.A.015A09.A.01609.A.01709.A.01809.A.01909.A.60109.A.60209.A.602A09.A.60309.A.603B09.A.60409.A.605

09.A.60609.A.60709.A.70109.A.70209.A.70309.A.704

10.A.05410.A.05510.A.05610.A.05710.A.05810.A.059

0 20 40 60

Water content [%]

80

60

40

20

0

Depth

[m]

Upper tillMeltwater silt/clayChalk tillLower tillLowermost till

Encl. C-02


Classification data

Plasticity index

Glacial units

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.01009.A.01109.A.01209.A.013

10.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.61010.A.610A10.A.610B

09.A.01409.A.01509.A.01609.A.01709.A.01809.A.01909.A.60109.A.60509.A.606

09.A.70109.A.70209.A.703

10.A.05410.A.05710.A.05810.A.05910.A.059B10.A.060

0 20 40 60 80 100

Plasticity index [%]

80

60

40

20

0

Depth

[m]

Upper tillMeltwater silt/clayMeltwater sandChalk tillLower tillLowermost till

Encl. C-03a


Classification data

Water content and Atterberg limits

Glacial upper till units

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.01009.A.01109.A.012

10.A.05910.A.059A10.A.06010.A.06110.A.06310.A.06410.A.06510.A.07110.A.607

09.A.01309.A.01409.A.01509.A.01609.A.01709.A.01809.A.01909.A.602

09.A.70109.A.70209.A.70309.A.704

10.A.05510.A.05610.A.05710.A.058

0 20 40 60 80 100

Water content [%]

80

60

40

20

0

Depth

[m]

Upper till

l lwP wL

Water content

Encl. C-03b


Classification data


Glacial meltwater silt/clay units

2011-05-01

09.A.00509.A.60209.A.70309.A.704

10.A.06010.A.06510.A.071

0 20 40 60 80 100

Water content [%]

80

60

40

20

0

Depth

[m]

Meltwater silt/clay

l lwP wL

Water content

Encl. C-03c


Classification data


Glacial chalk till units

2011-05-01

09.A.00809.A.00909.A.01509.A.01609.A.704

10.A.05410.A.05710.A.059B

0 20 40 60 80 100

Water content [%]

80

60

40

20

0

Depth

[m]

Chalk till

l lwP wL

Water content

Encl. C-03d


Classification data


Glacial lower till units

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.01009.A.01109.A.01209.A.013

10.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.61010.A.610A10.A.610B

09.A.01409.A.01509.A.01609.A.01709.A.01809.A.01909.A.60109.A.60509.A.606

09.A.70109.A.70209.A.703

10.A.05410.A.05710.A.05810.A.05910.A.059B10.A.060

0 20 40 60 80 100

Water content [%]

80

60

40

20

0

Depth

[m]

Lower till

l lwP wL

Water content

Encl. C-03e


Classification data


Glacial lowermost till units

2011-05-01

09.A.00409.A.01509.A.01609.A.60109.A.60209.A.602A09.A.60309.A.603B09.A.60409.A.605

09.A.60609.A.60709.A.704

10.A.05610.A.059B10.A.06010.A.06110.A.06210.A.610A

0 20 40 60 80 100

Water content [%]

80

60

40

20

0

Depth

[m]

Lowermost till

l lwP wL

Water content

Encl. C-04


Classification data

Liquidity index

Glacial units

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.00909.A.01009.A.01109.A.01209.A.013

10.A.05910.A.059B10.A.06010.A.06110.A.06310.A.06410.A.06510.A.07110.A.60710.A.61010.A.610A

09.A.01409.A.01509.A.01609.A.01709.A.01809.A.01909.A.60109.A.60209.A.602A09.A.603

09.A.60509.A.60609.A.70209.A.70309.A.704

10.A.05410.A.05510.A.05610.A.057

-1 -0.5 0 0.5 1 1.5

Liquidity index [-]

80

60

40

20

0

Depth

belowsurfaceofchalk[m

]


0 100 200 300

Liquid Limit [%]

0

40

80

120

PlasticityIndex[%]

CL CM CH CV

OH/MH

OL/MLML

CL - ML

Encl. C-05


Classification data

Plasticity chart

Glacial units

2011-05-01


Encl. C-06


Classification data

Unit weight

Glacial units

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.00909.A.01009.A.01109.A.01209.A.01309.A.014

10.A.059A10.A.059B10.A.06010.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.60710.A.61010.A.610A

09.A.01509.A.01609.A.01709.A.01809.A.01909.A.60109.A.60209.A.602A09.A.60309.A.603B09.A.60409.A.605

09.A.60609.A.70109.A.70209.A.70309.A.704

10.A.05410.A.05510.A.05610.A.05710.A.05810.A.059

10 15 20 25 30 35

Unit weight [kN/m3]

80

60

40

20

0

Depth

[m]


Encl. C-07


Classification data

Void ratio

Glacial units

2011-05-01

09.A.00309.A.00409.A.00609.A.00709.A.00809.A.00909.A.01209.A.01309.A.01509.A.01809.A.605

10.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.61010.A.610A

10.A.05410.A.05510.A.05610.A.05710.A.05810.A.05910.A.059A10.A.059B10.A.060

0 0.4 0.8 1.2 1.6

Void ratio [-]

80

60

40

20

0

Depth

[m]


Encl. C-08


Classification data

Clay content

Glacial unit

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.00909.A.01009.A.01109.A.01209.A.01309.A.014

10.A.05810.A.05910.A.059B10.A.06010.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.60710.A.61010.A.610A

09.A.01509.A.015A09.A.01609.A.01709.A.01809.A.01909.A.60109.A.60209.A.602A09.A.60309.A.603B09.A.604

09.A.60509.A.60609.A.60709.A.70109.A.70209.A.70309.A.704

10.A.05410.A.05510.A.05610.A.057

0 20 40 60 80 100

Clay content [%]

80

60

40

20

0

Depth

[m]


Encl. C-09


Classification data

Activity

Glacial unit

2011-05-01

09.A.00309.A.00409.A.00509.A.00609.A.00709.A.00809.A.00909.A.01009.A.01109.A.01209.A.01309.A.014

10.A.05910.A.059B10.A.06010.A.06110.A.06210.A.06310.A.06410.A.06510.A.07110.A.60710.A.61010.A.610A

09.A.01509.A.01609.A.01709.A.01809.A.01909.A.60109.A.60209.A.602A09.A.60309.A.603B09.A.60409.A.605

09.A.60609.A.60709.A.70109.A.70209.A.70309.A.704

10.A.05410.A.05510.A.05610.A.05710.A.058

0 1 2 3 4

Activity [-]

80

60

40

20

0

Depth

[m]


Encl. C-10


Classification data

Carbonate content

Glacial units

2011-05-01

09.A.00309.A.00709.A.00809.A.00909.A.01009.A.01209.A.01309.A.01409.A.605

10.A.05410.A.05610.A.05710.A.05910.A.059B10.A.06010.A.06110.A.06410.A.06510.A.610

0 20 40 60

Carbonate content [%]

80

60

40

20

0

Depth

[m]


100 80 60 40 20 0

Kaolinite/Chlorite

0

20

40

60

80

100

Illite

0

20

40

60

80

100Smectite - - Upper till

( ) Meltwater silt/clay( ) Chalk till- - Lower till( ) Lowermost till

Encl. C-11


Classification data

Clay mineralogy

Glacial units

2011-05-01

Encl. C-12


Classification data

Water content

Glacial meltwater sand unit

2011-05-01

09.A.00509.A.00709.A.01309.A.01409.A.01509.A.01809.A.01909.A.60109.A.60609.A.701

10.A.05610.A.05910.A.059B10.A.06110.A.06310.A.06410.A.06510.A.607

0 20 40 60

Water content [%]

80

60

40

20

0

Depth

[m]

Encl. C-13


Classification data

Saturated unit weight


2011-05-01

09.A.00709.A.01309.A.01809.A.60209.A.60609.A.701

10.A.05610.A.05910.A.059B10.A.06110.A.06310.A.06410.A.065

10 15 20 25 30 35

Saturated unit weight [kN/m3]

80

60

40

20

0

Depth

[m]

Encl. C-14


Classification data

Void ratio


2011-05-01

09.A.00709.A.01810.A.05910.A.059B10.A.06110.A.06310.A.06410.A.065

0 0.4 0.8 1.2 1.6

Void ratio [-]

80

60

40

20

0

Depth

[m]

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

0 5 10 15 20 25 30 35 40 45 50 55 60

De

pth

[m

]Net Cone Resistance [MN/m2]

09.B.003 09.B.007 09.B.008 09.B.013

09.B.018 09.B.605A 10.B.054 10.B.056

10.B.057 10.B.060 10.B.061 10.B.064

10.B.065

Encl. C-15Feharmbelt Fixed Link

Net cone resistanceGlacial units2011-05-01

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45 50 55 60

De

pth

[m

]Net Cone Resistance[MN/m2]

09.B.003 09.B.007 09.B.008 09.B.013

09.B.018 10.B.056 10.B.057 10.B.060

10.B.061 10.B.065 10.B.064


Net cone resistanceUpper Till

2011-05-01

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 5 10 15 20 25 30 35 40 45 50 55 60

De

pth

[m


09.B.007 09.B.013 09.B.018 10.B.056

10.B.061 10.B.065 10.B.064


Net cone resistanceGlacial Meltwater Deposits

2011-05-01

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45 50 55 60

De

pth

[m


09.B.008 10.B.054 10.B.057A


Net cone resistanceChalk Till

2011-05-01

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

0 5 10 15 20 25 30 35 40 45 50 55 60

De

pth

[m


09.B.003 09.B.007 09.B.008 09.B.013

09.B.018 09.B.605A 10.B.054 10.B.057A

10.B.057 10.B.060 10.B.061 10.B.065

10.B.064


Net cone resistanceLower Till

2011-05-01

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 5 10 15 20 25 30 35 40 45 50 55 60

De

pth

[m


09.B.605A 10.B.056 10.B.060 10.B.061


Net cone resistanceLowermost Till

2011-05-01

Encl. C-21


Net cone resistance

Glacial upper till

2011-05-01

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60

Dep

th [

m]

Net cone resistance, qnet [MPa]

10.B.055

10.B.056

10.B.057

10.B.058

10.B.059

10.B.060

10.B.061

10.B.062

10.B.063

10.B.064

10.B.065

10.B.071

09.B.003

09.B.004

09.B.006

09.B.007

09.B.008

09.B.010

09.B.013

09.B.015

09.B.017

09.B.018

09.B.019A

09.B.602B

09.B.602C

09.B.602D

09.B.602E

09.B.701A

09.B.702A

Encl. C-22


Net cone resistance

Glacial lowermost, lower and chalk till

2011-05-01

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60D

epth

[m

]

Net cone resistance, qnet [MPa]

10.B.054

10.B.055

10.B.056

10.B.057

10.B.059

10.B.059B

10.B.059C

10.B.060

10.B.061

10.B.062

10.B.063

10.B.064

10.B.065

10.B.071

10.B.610

09.B.003

09.B.004

09.B.006

09.B.007

09.B.008

09.B.010

09.B.013

09.B.015

09.B.017

09.B.018

09.B.019A

09.B.601C

09.B.601D

09.B.602B

09.B.602C

09.B.602D

09.B.602E

09.B.602F

09.B.603A

09.B.603B

09.B.603C

09.B.603DE

09.B.604A

09.B.605A

09.B.606G

09.B.607A

09.B.607B

09.B.607C

09.B.701A

09.B.702A

0 500 1000 1500 2000 2500

Average effective stress [kPa]

0

500

1000

1500

Effectiveshearstress[kPa]

Encl. C-23


Laboratory data

Effective stress paths

Glacial upper till unit

2011-05-01

Drained tests:09.A.007_CADc_09-100734_14_2109.A.007_CADc_09-100734_27_3409.A.012_CADc_09-100567_27_34

Undrained tests:09.A.007_CAUc_09-100734_01_0809.A.008_CAUc_09-100418_20_27

--- Shear compressional failure line:' 33.4º

c' 54 kPa

0 400 800 1200 1600 2000 2400


0

250

500

750

1000

1250

1500

1750


Encl. C-24


Laboratory data



2011-05-01

Drained tests:09.A.018_CADc_09-100040_41_4809.A.018_CADc_09-100040_52_59

Undrained tests:09.A.018_CAUc_09-1000420_62_69


c' 44 kPa

0 1000 2000 3000 4000


0

500

1000

1500

2000

2500


Encl. C-25


Laboratory data


Glacial chalk till unit

2011-05-01

Drained tests:09.A.009_CADc_09-101802_12_1909.A.009_CADc_09-101802_22_29

Undrained tests:09.A.008_CAUc_09-100452_22_2909.A.008_CAUc_09-100452_32_3909.A.009_CAUc_09-101802_02_09

--- Shear failure line:' 36.2º

c' 99 kPa

0 400 800 1200 1600 2000


-500

0

500

1000


Encl. C-26


Laboratory data


Glacial lower till unit

2011-05-01

Drained tests:09.A.013_CADc_09-100272_31_3810.A.054_CADc_10-105406_07_1410.A.054_CADc_10-105406_17_24

Undrained tests:09.A.003_CAUe_09-101868_32_3909.A.013_CAUc_09-100272_41_4810.A.054_CAUc_10-105426_07_1410.A.054_CAUe_10-105426_17_2410.A.054_CAUc_10-105399_03_1010.A.057_CAUc_10-105950_42_49

••• 10.A.061_CAUc_10-106162_34_41


c' 0 kPa--- Shear extensional failure line:

' 36.2º

c' 0 kPa

0 200 400 600 800 1000


-500

-250

0

250

500


Encl. C-27


Laboratory data


Glacial lowermost till unit

2011-05-01

Undrained tests:09.A.605A_CAUc_09-102005_02_0909.A.605_CAUe_09-102005_12_19


c' 0 kPa--- Shear extensional failure line:

' 31.3º

c' 0 kPa

Data on Gmax determined from bender element testing

11,3

32,4

38,8

16,1

16,3

09.A.003 46,02

09.A.009 12,70 204

20,71

20,85

55,05 398

55,05 490

10.A.052 43,59

10.A.054 30,17

10.A.055 46,07

10.A.056 40,77

39,11

39,27

10.A.061 23,83 288

10.A.610 34,06

11,3

32,4

38,8

Depth [m] Upper Till

Lower

Till Chalk Till

Lowermost

Till

Chalk Till

Lowermost

Till

09.A.001

09.A.002

09.A.010

09.A.013

10.A.058

Gmax from bender element [MPa]

Gmax/qnet using G from bender element

Meltwater sand Meltwater clay

Meltwater sand Meltwater clay

09.A.001

Depth [m] Upper Till

Lower

Till

16,1

16,3

09.A.003 46,02

09.A.009 12,70 No CPT data

20,71

20,85

55,05 80 (81)[1]

55,05 99 (100)[1]

10.A.052 43,59

10.A.054 30,17

10.A.055 46,07

10.A.056 40,77

39,11

39,27

10.A.061 23,83 17

10.A.610 34,06

[1]

resonant column testing

Numbers in brackets are values of Gmax determined from

10.A.058

09.A.002

09.A.010

09.A.013

Data on G0 determined from vsp logging

196 197 149

70

193

305

108

277

343

217 462

436

599 502 315

380

393 403

Lower

Upper Till

Meltwater

sand

Meltwater

clay

Lowermost

Till

Lower

Till

G0 from vsp logging [MPa]

G0/qnet from vsp logging

Meltwater Meltwater Lowermost

09.A.605

09.A.606

09.A.701

09.A.703

09.A.602

09.A.603

09.A.604

42 20 38

17

12

73

109

46

58

16 74

60

38 47 40

68

Note:

Lower

Till

Values reported are average values for each

continuous section of the relevant Glacial unit

09.A.602

09.A.603

09.A.604

Upper Till

Meltwater

sand

Meltwater

clay

Lowermost

Till

09.A.605

09.A.606

09.A.701

09.A.703No CPT data

Documents

Appendix GDR 00.1 001 C