FOUNDATION SYSTEM FOR THE PRELIMINARY TREATMENT FACILITIES

7/27/2019 FOUNDATION SYSTEM FOR THE PRELIMINARY TREATMENT FACILITIES

http://slidepdf.com/reader/full/foundation-system-for-the-preliminary-treatment-facilities 1/38

Consortium Themeliodomi S.A. – Passavant-Roediger Anlagenbau GmbH

for the Contract A of the Constanta sewerage and wastewater treatment rehabilitation project

CONSTANTA NORTH WWTP

FOUNDATION SYSTEM FOR THE

PRELIMINARY TREATMENT FACILITIES

CONTRACTOR

Themeliodomi S.A.Dr. Ing. K. Xanthopoulos

DESIGN COLLABORATOR

Prof. Dr. Ing. V. Ianuli

TECHNICAL AUDITOR LAW Nr.10

Prof. – Ing. V. G. Breaban

FOUNDATION SYSTEM FOR THEPRELIMINARY TREATMENT FACILITIES

00 08 04 04 First edition GEOGNOSI S.A.

Rev. Date Description Edit. Appr . Page: 1 of 38 No: 2923-CA-13-112923-FM-CA-01.DOT / p1






C O N T E N T S

1. INTRODUCTION................................................................................................3

1.1 Scope of the work ............................................................................................. 3

1.2 Structural data ...................................................................................................3

1.3 Geological, seismological and geotechnical data ............................................. 3

2. SUBSURFACE GROUND CONDITIONS - SOIL STRATIGRAPHY..................4

3. GEOTECHNICAL ANALYSIS........................................................................... 6

3.1 Shallow foundations without improvement........................................................ 6

3.1.1 Bearing capacity - Allowable pressure................................................... 6

3.1.2 Settlements estimation......................................................................... 14

3.2 Shallow foundation with soil improvement (stonecolumns).............................. 18

3.2.1 Soil improvement - Stonecolumns....................................................... 18

3.2.2 Soil improvement design.......................................................................23

3.2.3 Bearing capacity - Allowable pressure................................................. 26

3.2.4 Settlements estimation..........................................................................31

4. CONCLUSIONS.............................................................................................. 34

182811587.doc / Page 2 of 38






1. INTRODUCTION

1.1 Scope of the work

The purpose of this work is to present the proposed foundation system concerning the

preliminary treatment facilities of the Constanta “Sewerage and Wastewater treatment rehabilitation

project”.

1.2 Structural data

The preliminary treatment facilities could be divided into three distinct areas according the

dimensions, the loads and the foundation level of each structure.

The first one is in the inlet pumping station – coarse screen, a structure with a very low

foundation level and medium working loads. The second one is the fine screening station with thestorm – water tank founded on the free surface having medium working loads and finally the grit and

grease removal chamber, with medium loads also. The last one will be founded on an embankment.

1.3 Geological, seismological and geotechnical data

All the necessary geological seismological and geotechnical data, concerning the area of the

Constanta “Sewerage and Wastewater treatment rehabilitation” area, were presented in the

“GEOTECHNICAL INVESTIGATION AND GEOSTATICAL COMPUTATIONS” report, prepared by

GEOGNOSI S.A., during March 2003.

182811587.doc / Page 3 of 38






2. SUBSURFACE GROUND CONDITIONS - SOIL STRATIGRAPHY

According to the afore mentioned report, five distinguished soil layers were recorded, at the

area under consideration which are the following :

Layer “FILL” : This landfill layer with concrete blocks, bricks, woods and glass has an average

thickness of about 1,0m (CH).

Layer “S” : Layer “S” is a grey, loose to medium, sand-silty sand, poorly graded with a depth

range between 5,0m to 8,0m (SP, SM).

Layer “C” : Layer “C” is a grey, soft to firm clay with low plasticity and a variable percentage of

sand. It’s thickness varies between 2,0m to 8,0m (CL).

Layer “C1” : This layer is a brown firm to stiff clay to sandy clay, with low plasticity and

calcareous concretions. In places sublayers of dense sand were found. It’s

thickness varies between 4,0m to 10,0m (CL, CH).

Layer “D” : This layer consists of boulders of white to yellowish weathered limestone with stiff

to very stiff low plasticity marly clay. Also, in places was found very dense clayey

sand of low plasticity.

For the design analysis, a typical design section was established. In figure 1 the typical design

section for the preliminary treatment facilities area, is being presented.

182811587.doc / Page 4 of 38






Figure 1. Typical design section of the preliminary treatment facilities

Altitude (m) Ground level Altitude (m)

+2.75 0.00

FILL: Concrete blocks, bricks, woods and glass (CH)

W=22,2 e≅0,678

γ≅19,4 φ’=25

γd≅16,0 Εs=3

+1.00 1.75

S : Grey, loose to medium, sand - silty sand, poorly graded (SP, SM)

G.W.L. 0.75 ΝSPT≅21 W=25,0 e≅0,560 φ’=32 G.W.L. 2.00

γ=21,4

γd=16,8 Εs=15

-4.50 7.25

C : Grey, soft to firm clay low plasticity, variable percentage of sand (CL)

ΝSPT≅10 W=26,8 e≅0,805 φ’=14 Cc=0,211

WL=35,3 γ=19,4 c’=20 Cr =0,022

WP=16,1 γd=15,1 Cu=30 Cv=3,3⋅10-3

PI=19,2 IC=0,4 Eu=20 Εs=10

-6.50 9.25

C1: Brown, firm to stiff clay to sandy clay, low plasticity, calcareous concretions(CL CH)

ΝSPT>26 W=23,9 e≅0,750 φ’=18 Cc=0,185

WL=45,8 γ=19,5 c’=32 Cr =0,027

WP=17,6 γd=15,9 Cu=60 Cv=1,3⋅10-3

PI=28,1 IC=0,8 Eu=35 Εs=10

-10.50 13.25

D : Boulders of white to yellowish weathered limestone with stiff to very stiff lowplasticity marly clay, in places very dense clayey sand of low plasticity

ΝSPT≥50 W=19,8 e≅0,790

WL=33,7 γ=19,5WP=15,1 γd=16,4 Cu=150PI=18,6 IC=0,8 Εs=100

<-22.00 >24.75

AbbreviationsG.W.L.: Ground watertable level (m)NSPT : Standard penetration test (blows/30cm)WL : Liquid l imit (%)WP : Plastic limit (%)PI : Plasticity indexW : Natural water content (%)IC : Consistency index = (WL-W)/(WL-WP)γ : Bulk density (kN/m3)γd : Dry density (kN/m3)e : Void ratioCu : Undrained cohesion (kN/m2)φ' : Friction angle (effective value) - UU Triaxial compression test (Deg)c' : Friction cohesion (effective value) - UU Triaxial compression test (kN/m2)

182811587.doc / Page 5 of 38






φ : Angle of friction - UU Triaxial compression test (Deg)c : Cohesion - UU Triaxial compression test (kN/m2)Cc : Compressibility indexCv : Consolidation coefficient (cm2/s)

Es : Compressibility modulus (MN/m2)Εu : Compressibility modulus in unloading conditions (MN/m2)

182811587.doc / Page 6 of 38






3. GEOTECHNICAL ANALYSIS

3.1 Shallow foundations without improvement

3.1.1 Bearing capacity - Allowable pressure

A raft foundation was considered for the structures of the preliminary treatment facilities.

Bearing design resistance, σd, is estimated in accordance with Eurocode 7 - case C standards and

specifications. Each distinct structure of the preliminary treatment facilities presents differences as

far as concerns the foundation level, the working loads and the dimensions. The following table 1

presents the characteristic values of each distinct structure of the preliminary treatment facilities.

Tablel 1. Characteristic values concerning the structures of the preliminary treatment facilities

Dimensions

Object number

in drawing 24

Foundation

altitude (m)Length (m) Width (m) L/B

Working load

(kN/m2)

Inlet pumping

station - coarse

screen

1 -2.70 17.35 15.30 1.13 90

Fine screening

station - storm

water tank

2+13 +2.60 44.15 28.10 1.57 93*

Grit and grease

removal

chamber

3 +3.85 37.25 28.10 1.33 108*

∗ The working loads includes also the loads from the necessary embankments, creating the foundation level

for these structures.

Bearing design resistance, σd, is calculated, using the typical soil profile of figure 1 (see

paragraph 2). Furthermore, due to the material texture of the first layer shown in the typical design

section (FILL), is considered to be replaced by a (sand gravel) layer up to an altitude at +2.0m and

thus creating the necessary working level. This replacement layer (SG) is considered to cover the

preliminary treatment facilities area, except area of the inlet pumping station – coarse screen.

182811587.doc / Page 7 of 38






Two cases are examined concerning the design bearing resistance σd :

- Assuming undrained subsoil conditions with value of friction φ≅28° for layer S. Methodology

and results for static loading conditions are shown in figures 2a, 2b and 2c respectively for

each structure. Bearing design resistance (allowable pressure against soil failure) under

undrained static conditions is calculated greater than σd≥1.000kPa, for only vertical loading,

while smaller values of σd must be considered when horizontal loads are acting upon

simultaneously (see figure 2a, 2b and 2c).

- Assuming drained conditions with value of friction φ’=32° for layer S. Methodology and results

of σd are presented in figures 3a to 3c respectively for each structure. Based on figures 2 and3, it is proved that the corresponding resulting value of σd under drained conditions is higher

than the value of σd under undrained conditions, assuming that only vertical loading is applied.

Once again, lower values of σd must be considered when horizontal loads are acting upon

simultaneously, as figures 3a to 3c indicates.

In the following table 2, the results from the bearing capacity analysis are being presented,

concerning each structure of the preliminary treatment facilities.

Tablel 2. Bearing capacity concerning the preliminary treatment facilities structures

Bearing capacity (kN/m2)Undrained conditions Drained conditions

Value Figure Value Figure

Inlet pumping station - coarse screen 1.527 2a 1.687 3a

Fine screening station - stormwater tank 1.087 2b 1.227 3b

Grit and grease removal chamber 1.040 2c 1.175 3c

As far as the method of design is concerned with respect to bearing capacity, the pressure on

soil due to factorized load combinations according to Eurocodes 2 and 3 should be calculated. The

calculated applied soil pressure should include the self weight of the foundation as well as the self

weight of the backfilling material. Moreover, the eccentricities and the reduction of soil bearing

resistance due to horizontal loading at foundation level should be also taken into account, although

these loadings are expected to be not significant.

182811587.doc / Page 8 of 38






182811587.doc / Page 9 of 38






182811587.doc / Page 10 of 38






182811587.doc / Page 11 of 38






182811587.doc / Page 12 of 38






182811587.doc / Page 13 of 38






182811587.doc / Page 14 of 38






3.1.2 Settlements estimation

In this case, approximate parametric settlement analyses for the three areas of the preliminary

treatment facilities is carried out, assuming foundation levels for each structure, loads, and

dimensions according to the table 1.

For the purpose of settlement analyses, the typical soil profile of figure 1 was used, assuming

that the level of -35,0m corresponds to an incompressible layer. The settlement calculations of the

foundations are performed using the Boussinesq stress distribution. Furthermore, the assumption of

a rigid base was considered and one mean value of settlement was obtained. Results of the

parametric settlement analyses are presented in figures 4a, 4b and 4c.

The results from these calculations are being presented in table 3 for the anticipated working

loads.

Table 3. Results of settlements for the preliminary treatment facilities.

No StructureApplied load

(kN/m2)Settlements (cm) Figure

1 Inlet Pumping station - coarse screen 90 2.48* 4a

2 Fine screening station - storm water tank 93 7.86 4b

3 Grit and grease removal chamber 108 8.83 4c

* Conservatively was considered that the ground water table level reaches the excavation level.

Based on these results, the settlements for the preliminary treatment facilities are pretty high,

except the inlet pumping station - coarse screen structure. Thus a soil reinforcement method should

be utilized.

The average value of the modulus of subgrade reaction K for the inlet pumping station - coarse

screen structure was estimated as follows :

K= 4.500-5.500kN/m3

(L/B=1.13 and B=15,0m)The aforementioned K values correspond to static conditions. For earthquake, K values should be

taken at least two times higher than these for static conditions.

182811587.doc / Page 15 of 38






182811587.doc / Page 16 of 38






ΠΡΟΣΕΓΓΙΣΤΙΚΟΣ ΠΑΡΑΜΕΤΡΙΚΟΣ ΥΠΟΛΟΓΙΣΜΟΣ ΚΑΘΙΖΗΣΗΣ ΘΕΜΕΛΙΟΥ ΣΕ ΥΠΟΓΕΙΟ

PARAMETRIC ANALYSIS OF SETTLEMENT OF FOOTINGS IN BASEMENT

ΕΡΓΟ - PROJECT: Σχήμα: 4a

L/B = 1,13 Δυσκαμψία - Rigidity = 2

Bmin (m) = 14,00 k = 1

Bmax (m )= 16,00 Θέση-Position = 4

D (m) = 4,70 W (m) = 4,70

γ (kN/m3) = 19,4

γD (kN/m2)= 91,18

νωση uD (kN/m2)= 0

zε(m)= +2,0 Izi= Boussinesq

Στρώση zb(m) zi (m) Hi (m) Es (MPa)Es(oc )

(MPa)Β(m)= 14,0 14,5 15,0 15,5 16,0

1 -4,5 -3,6 1,80 15,0 30,0 0,968 0,971 0,973 0,975 0,9772 -6,5 -5,5 2,00 10,0 20,0 0,715 0,727 0,738 0,749 0,760

3 -10,5 -8,5 4,00 10,0 20,0 0,477 0,487 0,497 0,507 0,517

4 -35,0 -22,8 24,50 100,0 100,0 0,166 0,173 0,181 0,188 0,195

Καθίζηση / Settlement S (cm)

F.S=σεδρ /uD σεδρ (kPa) σεδρ-uD Β(m)= 14,0 14,5 15,0 15,5 16,0

70 70 1,86 1,90 1,93 1,97 2,00

80 80 2,12 2,17 2,21 2,25 2,29

90 90 2,39 2,44 2,48 2,53 2,57

100 100 2,85 2,91 2,96 3,02 3,07

110 110 3,34 3,41 3,47 3,53 3,59

0,00

1,00

2,00

3,00

4,00

5,00

6,00

Τάση έδρασης σεδρ (kPa)

Κ α θ ί ζ η σ η / S e t t l e m e n t S ( c m )

B= 16,0 m

B= 15,5 m

B= 15,0 m

B= 14,5 m

B= 14,0 m

1=Εύκαμπτο - Flexible

2=Δύσκαμπτο - Rigid

1=Κέντρο - Center

2=Γωνία - Corner

3=Μέσο πλευράς L - Middle of

Long side

4=Μέσος ορος - Average

zb-1

D, γ

B

L

zi

zε

zb

σεδ

E

CONSTANTA SEWERAGE AND WASTEWATER TREATMENTREHABILITATION PROJECT - Preliminary treatment -

without improvement - A area

D E

)(*)1( IH=S

D E

)(

E

)( IH=

i

i

ii

i

s

zi

1=i

ss

zi

1=i

γ σ γ ι α γ σ

γ σ γ ι α γ σ γ

ε δρ

εδ ρ

ε δρ

ε δρ

≤−−−−

>

−−+

−

∑

∑−

o c

D Dn

D D

o c

Dn

u Dk u

u Dk uu Dk S

ΥΥw

182811587.doc / Page 17 of 38






ΕΡΓΟ - PROJECT: Figure 4b


Bmin (m) = 27,00

Bmax (m) = 30,00 Θέση-Position = 4

D (m) = 0,00

γ (kN/m3) = 19,4

zε(m)= +2,0 Δσ/q - Boussinesq

Layer zb(m) zi (m) Hi (m) Es (MPa) Β(m)= 27,00 27,50 28,00 28,50 29,00 29,50 30,00

1 +1,0 +1,5 1,00 50,0 0,999 0,999 0,999 0,999 0,999 0,999 0,999

2 -4,5 -1,3 6,50 15,0 0,897 0,901 0,904 0,908 0,911 0,914 0,9173 -6,5 -5,5 2,00 10,0 0,654 0,660 0,667 0,672 0,678 0,684 0,690

4 -10,5 -8,5 4,00 10,0 0,544 0,550 0,556 0,561 0,567 0,572 0,578

5 -35,0 -22,8 24,50 100,0 0,306 0,311 0,315 0,320 0,324 0,329 0,333


σεδρ (kPa) q=σεδρ-γD Β(m)= 27,00 27,50 28,00 28,50 29,00 29,50 30,00

80 80 6,66 6,71 6,76 6,81 6,85 6,90 6,9487 87 7,20 7,25 7,31 7,36 7,41 7,46 7,51

93 93 7,74 7,80 7,86 7,91 7,97 8,02 8,07

100 100 8,28 8,34 8,41 8,47 8,52 8,58 8,64

106 106 8,82 8,89 8,95 9,02 9,08 9,14 9,20

ΠΡΟΣΕΓΓΙΣΤΙΚΟΣ ΠΑΡΑΜΕΤΡΙΚΟΣ ΥΠΟΛΟΓΙΣΜΟΣ ΚΑΘΙΖΗΣΗΣ ΘΕΜΕΛΙΟΥ

PARAMETRIC ANALYSIS OF SETTLEMENT OF FOOTINGS

GEOGNOSI S.A. Geotechnical Engineering Consultants

P.O. Box 60480, 570 01, Thermi, Thessaloniki, Greece, Tel. +30.2310. 469169, Fax. +30.2310.469161, E-mail: [email protected]

6,0

7,0

8,0

9,0

10,0

70 80 90 100 110

Κ α θ ί ζ η σ η / S e t t l e m e

n t S ( c m )

B= 27,0 m

B= 27,5 m

B= 28,0 m

B= 28,5 m

B= 29,0 m

B= 29,5 m

B= 30,0 m





3=Μέσο πλευράς L - Middle of Long side


S q H E

q

s

= ∑∆ σ

CONSTANTA SEWERAGE AND WASTEWATER TREATMENT

REHABILITATION PROJECT - Preliminary treatment -

without improvement - B area

zb-1

D, γ

B

L

zi

zε

zb

σεδ

Ηι

Esi

182811587.doc / Page 18 of 38






ΕΡΓΟ - PROJECT: Figure 4c


Bmin (m) = 27,00


D (m) = 0,00

γ (kN/m3) = 19,4



1 +1,0 +1,5 1,00 50,0 0,999 0,999 0,999 0,999 0,999 0,999 0,999

2 -4,5 -1,3 6,50 15,0 0,885 0,889 0,893 0,897 0,900 0,904 0,9073 -6,5 -5,5 2,00 10,0 0,628 0,634 0,640 0,646 0,652 0,658 0,664

4 -10,5 -8,5 4,00 10,0 0,519 0,525 0,530 0,536 0,541 0,546 0,552

5 -35,0 -22,8 24,50 100,0 0,288 0,293 0,297 0,302 0,306 0,310 0,315



80 80 6,46 6,51 6,56 6,61 6,66 6,70 6,7589 89 7,20 7,26 7,32 7,37 7,42 7,48 7,53

99 99 7,95 8,01 8,08 8,14 8,19 8,25 8,31

108 108 8,70 8,77 8,83 8,90 8,96 9,03 9,09

117 117 9,44 9,52 9,59 9,66 9,73 9,80 9,87





6,0

6,5

7,0

7,5

8,0

8,5

9,0

9,5

10,0

10,5

70 80 90 100 110 120


n t S ( c m )

B= 27,0 m

B= 27,5 m

B= 28,0 m

B= 28,5 m

B= 29,0 m

B= 29,5 m

B= 30,0 m







S q H E

q

s

= ∑∆ σ


REHABILITATION PROJECT - Preliminary treatment -without improvement - C area

zb-1

D, γ

B

L

zi

zε

zb

σεδ

Ηι

Esi

182811587.doc / Page 19 of 38






3.2 Shallow foundation with soil improvement (stonecolumns)

The bearing capacity of the S layer can easily undertake the loads of the preliminary treatment

facilities, but the settlements due to working loads gave values of settlements which are high enough

for these structures (except the inlet pumping station – coarse screen structure). In order to overco-

me the settlements problem, a soil improvement method (stonecolumns) is recommended and

presented herein.

3.2.1 Soil improvement - Stonecolumns

Stonecolumns constitute a soil improvement system by which vertical columns of compacted

gravel are installed in a soil. Stonecolumns serve a foundation in four ways:

1. The gravel column is much stiffer than the surrounding soil. Vertical stresses in the columns

are between 2 to 5 fold higher than in the surrounding soil. Thereby the total settlements are

reduced.

2. Differential settlements in a ground treated by stonecolumns can be assumed to be only in the

order of 15% to 20% of total settlements as compared to 50% to 100% for untreated soil. This

stems from the fact that columns are installed with a diameter varying over depth depending on

the soil strength and thus homogenizing the stiffness properties of the soil / column matrix.

3. The gravel column serves as a vertical drain and thus reduces excess pore pressures caused

by rapid loading or earthquake, allowing for a faster loading or making soil liquefaction less

likely.

4. The high friction angle of the gravel increases the composite shear strength of the column / soil

matrix and thus allows for a higher cyclic stress before liquefaction is triggered.

Accordingly the site conditions, a variety of vibro methods is used in order to achieve the best

results (wet top feed, dry bottom feed). In sites where high ground water conditions exist the wet top

feed method is used.

182811587.doc / Page 20 of 38






Stonecolumns have been used to improve a wide range of soils, from very soft clays and peat.

The stonecolumns are suitable for a wide range of soils as indicated on the attached grain size curve

(figure 5).

Figure 5. Relationship between particle size and available vibro techniques

182811587.doc / Page 21 of 38






Figure 6. Installation process of the stonecolumns

182811587.doc / Page 22 of 38






Stonecolumn construction

The installation process of the stonecolumn includes three stages (figure 6) which are the

following:

1. Penetration

Assisted by jetting water, the oscillating vibrator penetrates to the designed depth under its

own weight. Thereafter the water jets are adjusted in such a way that an annular space

remains open around the vibrator and its extension tube.

2. Replacement

Once at depth coarse grained backfill material is now filled into the hole down to the toe of the

vibrator. By moving the vibrator in small steps up and down and by the horizontal forces of the

machine itself, the supplied stones are pressed into the existing soil.

3. Finishing

With stones being added as required this process is repeated up to ground level, leaving on

completion a well compacted, tightly interlocked stonecolumn surrounded by soil of enhanced

density.

The stone shall consist of hard, durable, screened or washed, free from organic or other

deleterious material. The gradation of the stone shall be measured by ASTM D422 and shall con-

form to the following requirements :

- d5>0,1mm

- d30>40mm

- d100<160mm

(where d5, d30 and d100 is the maximum grain diameter corresponding to 5%, 30% and 100% of the

soil material respectivelly).

To permit estimating the in-situ diameter of the stonecolumn after construction the maximum

and minimum density of the stone following ASTM Method C29 before stonecolumn construction

begins, should be determined.

182811587.doc / Page 23 of 38






Important construction aspects

1. Inspection records should be carefully analyzed for differences in times from one column to the

next to both construct the hole and the stonecolumn. Any significant differences may indicate

(1) A change in construction technique, (2) a change in soil properties, or (3) collapse of the

hole.

2. During construction in soft ground, the probe should be left in the hole at all times and large

quantities of water used to help insure (1), stability of the hole (2), a clean stonecolumn due to

the removal of fines and organics. More water is required during jetting of the hole, with the

quantities of water decreasing as the column comes up.

3. The initial construction of a strong base at the bottom of the stonecolumn is important to insure

proper performance. Therefore, additional penetrations of the probe are desirable together with

extra care in construction during compaction of the first several increments of stonecolumn

backfill. When stone is first dumped down the hole some of it will probably penetrate into the

soil surrounding the hole near the surface. Therefore, the diameter of the column at the base

will not be as large as calculations indicate.

4. If organics such as peat are encountered caution should be exercised to flush this material out

of the hole; extra flushings are necessary to assure proper removal of the peat. These extraflushings may enlarge the diameter of the hole in the peat and increase the stone take in this

area. The stonecolumn should be built as rapidly as possible in peat, silts and sensitive soils.

5. Stone may “hang up” in the hole before it gets to the bottom. To prevent this and to clean out

any soil which may have been knocked loose, the probe should be lifted and dropped (stroked)

2 to 3 m several times after the stone has been added.

6. When the power consumed by the vibrator motor reaches the specified value, this primarily

means that good contact exists between the probe and the stone. Reaching the specified

power consumption alone is therefore not a complete guarantee construction is satisfactory

and a high density has been achieved; it does not eliminate the need for carefully watching the

entire construction sequence. Power consumption as defined by ammeter reading is, however

a useful field control that can de continuously monitored.

7. As an important supplement to the ammeter reading, carefully watch the amount of repe-

netration of the probe after stone has been added to the hole the first repenetration should

182811587.doc / Page 24 of 38






extend through the newly placed stone with less penetration occurring on successive

repenetrations.

8. The presence of any obstructions shall be reported, and described in the daily documentation

reports. When obstructions prevent the advancement of the vibratory probe over an area of

multiple columns, one of the following must be done according the in-situ conditions:

a. Adjust the location or spacing of the treatment grid.

b. Place additional treatment points to bridge the obstruction.

c. Pre-auger through the obstruction.

d. Remove the obstruction and backfill the hole and then commence stonecolumn

construction at planned locations.

Quality control

In order to inspect the stonecolumns installation, a quality control program should be carried

out. This program should include the following items prior, during and afterwards the installation :

• Stonecolumn location and characteristics. The center of the stonecolumn should be within

25cm of the plan location. The stonecolumn number, the data and time of the installation, the

time required to form the hole, the stonecolumn length and bottom tip elevation should be

recorded.

• Resistance level as measured by amp meter (Vibrator draws more current indense soils) over

time and depth.

• Quality of the stonecolumn material (the source of the backfill material as well as it’s

characteristics).

• Quantity of the stone added (theoretical column diameter and length of the stonecolumn).

• Stonecolumn acceptance tests. The probe is considered to be calibrated since a huge amount

of work (concerning stonecolumns installation) has been executed in the area. Furthermore, a

number of 4 tests Standard Penetration Tests (ASTM D-1586) should be performed to prove

the quality of the stonecolumns (stone column numbers 54, 60, 304 and 310 could be tested)

giving a minimum number of blows, recorded inside the column, 30.

182811587.doc / Page 25 of 38






3.2.2 Soil improvement design

The construction of the preliminary treatment facilities (except the inlet pumping station -coarse screen structure), produce a significant amount of settlements. So, the design criteria for

these structures was to minimize the settlements. In order to achieve this objective, a system of soil

improvement, composed by stonecolumns, was drawn.

More specifically the soil improvement as well as the construction phases for the area of the

preliminary treatment facilities consist from the following stages (drawing 26).

Stages : (1) Removing the superficial layer FILL (up to an altitude of +1.0m)

(2) Creating a working level with sand gravel material up to an altidute of +2.0m

(3) Soil improvement with the stonecolumns.

(4) Raising the free ground surface from level +2,0m to the appropriate altitude of each

structure, in order to construct the foundations.

As far as concerns the stonecolumns installation the recommended pattern is the following:

1 Technology used : Vibroreplacement

2 Minimum diameter : D=0,90m

3 Average length : L = 12.00 – 13.50m

4 Installation grid : Triangular

5 Spacing : a = 2.50m

The materials used to raise the ground level in order to construct the foundation of the

preliminary treatment facilities (except the inlet pumping station - coarse screen structure) consists of

sand gravel material (A1a, A1b, A1c) having a compaction degree ≥95% according to AASHO T-

180D.

According to the aforementioned soil improvement, the mechanical properties of the soils are

changing, the new ones are calculated and being presented in figure 7 for each soil layer that the

stonecolumn penetrates.

Taking into account the improved soil properties, the typical design section is changing. The new one

is given in figure 8.

182811587.doc / Page 26 of 38






FIGURE: 7

PROJECT :

Layer φ's(Deg) c's (Kpa) Cu (Kpa) E (Mpa) Cc Cr Layer : (Layers that are being penetrated by the stonecolumns)

S 32,0 0 15,00 φ's : (Friction angle of soil)

C 14,0 20 c's : (Cohesion of soil)

C 30 10,00 0,211 0,022 Cu : (Undrained shear strength)

C1 18,0 32 E : (Soil compressibility modulus)

C1 60 10,00 0,185 0,027

dw (m) = 0,9 φcol= 40 dw : Stonecolumns diameter

d (m) = 2,5 d : Dimension of the grid

αp : Soil replacement percentage

αp = 0,118 αp =πd2

w/(2 d2) (Triangular grid)

Ac(m2)= 0,63617 αp =πd

2w/(4d

2) (Rectangular grid)

A (m2)= 5,41 Ac : Area of the stonecolumn surface

Ac/A = 11,75% A : Foundation influence area. Assumed Α=Αc/αp

n = 11,81 According Schulze(1978) φ'col : Friction angle of the stonecolumn material.

n = 6,38 According Priebe (1976) φ'cor : Equivalent friction angle (Soil + Stonecolumn)

c'cor : Equivalent cohesion (Soil + Stonecolumn)

Improvement Relations of the Mechanical Characteristics Cucor : Equivalent undrained cohesion (Soil + Stonecolumn)

Effective Characteristics Ecor : Equivalent compressibility modulus (Soil + Stonecolumn)

Εp : Stonecolumn compressibility modulus

n=σ΄1p/σ΄1s=Ep/E

c'cor =(1-αp)cs

Undrained conditions

φ's=0

According Schulze(1978)

Cucor =(1-αp)Cu Where:

Mechanical Characteristics of Compression Dext=(4A/π)0.5

Ecor =E(1-αp)+Epαp Ac=(π/4)d2

w

where Εp=nE Rcol=(1/2)dw

According Priebe (1976)

Layer φ'col(Deg) c'cor (Kpa) Cucor (Kpa) Ecor (Mpa) Cc cor Cr cor

S 37,1 0 34,05

C 31,4 18C 27,2 26 22,70 0,093 0,010 where :

C1 32,6 28

C1 27,2 53 22,70 0,081 0,012 ν' Poisson ratio (usually ν'=1/3=0.33)

ν' : 0,33 β : 1,63

Valid n=1+(β-1)/α p

Layer φ'col(Deg) c'cor (Kpa) Cucor (Kpa) Ecor (Mpa) Cc cor Cr cor

S 35,9 0 24,48

C 27,5 18

C 21,1 26 16,32 0,129 0,013

C1 29,3 28

C1 21,1 53 16,32 0,113 0,017

RESULTS

Equivalent Mechanical Soil Characteristics According to Priebe

(1976)

Equivalent Mechanical Soil Characteristics According to Shulze

(1978)

Stonecolumns characteristics

DATA

Calculation of n

σ΄1p and σ΄1s the effective vertical stresses to the stonecolumn and to

the soil respectively.


Head Office: P.O. Box 60480, 570 01, Thermi, Thessaloniki, Tel. +30.2310. 469169, Fax. +30.2310.469161, E-mail: [email protected]

SUBSOIL MECHANICAL CHARACTERISTICS IMPROVEMENT DUE TO

STONECOLUMNS INSTALLATION

Mechanical characteristics of soil

3

)/(21

)/1)(21(

21

1)/,(

2

2

A΄

A΄

΄ ΄

΄ A΄ f

c

c

c

Α+−Α−−

−−

−=Αν

ν

ν ν

ν ν

)/ln()2

'

4(tan

)/ln(21

2col ext

col ext

R D

R Dn

col φ π −

+=

)1(1

tantan)1('tan

−+

+−=

n

΄ n΄

p

col p s p

cor

α

φ α φ α φ

)1(1

tan'tan

−+=

n

΄ n

p

col p

cor

α

φ α φ

Constanta Sewerage and Wastewater Treatment Rehabilitation Project - Preliminary

treatment

−

Α−

Α+

Α

Α+= 1

)/,()2

'

4(tan

)/,(2/11

2 A΄ f

A΄ f

c

col

cc

ν φ π

ν β

182811587.doc / Page 27 of 38






Figure 8. Typical design section (improved soil)

Altitude (m) Ground level Altitude (m)

+2.00 0.00

SG: Sand gravel material

γ≅21,5 φ’>35 Εs=50

+1.00 1.00

S : Grey, loose to medium, sand - silty sand, poorly graded (SP, SM)

G.W.L. 0.75 ΝSPT≅21 W=25,0 e≅0,560 φ’=37,1 G.W.L. 2.00

γ=21,4γd=16,8 Εs=34,05

-4.50 6.50

C : Grey, soft to firm clay low plasticity, variable percentage of sand (CL)

ΝSPT≅10 W=26,8 e≅0,805 φ’=31,4 Cc=0,093

WL=35,3 γ=19,4 c’=18 Cr =0,010

WP=16,1 γd=15,1 Cu=26 Cv=3,3⋅10-3

PI=19,2 IC=0,4 Eu=20 Εs=22,7

-6.50 8.50

C1: Brown, firm to stiff clay to sandy clay, low plasticity, calcareous concretions(CL CH)

ΝSPT>26 W=23,9 e≅0,750 φ’=29,3 Cc=0,081

WL=45,8 γ=19,5 c’=28 Cr =0,012

WP=17,6 γd=15,9 Cu=53 Cv=1,3⋅10-3

PI=28,1 IC=0,8 Eu=35 Εs=22,7 S.B.L

-10.50 12.50

D : Boulders of white to yellowish weathered limestone with stiff to very stiff lowplasticity marly clay, in places very dense clayey sand of low plasticity

ΝSPT≥50 W=19,8 e≅0,790

WL=33,7 γ=19,5WP=15,1 γd=16,4 Cu=150PI=18,6 IC=0,8 Εs=100

<-22.00 >24.00

AbbreviationsG.W.L.: Ground watertable level (m)S.B.L. : Stonecolumns base level (m)NSPT : Standard penetration test (blows/30cm)WL : Liquid l imit (%)

WP : Plastic limit (%)PI : Plasticity indexW : Natural water content (%)IC : Consistency index = (WL-W)/(WL-WP)γ : Bulk density (kN/m3)γd : Dry density (kN/m3)e : Void ratioCu : Undrained cohesion (kN/m2)φ' : Friction angle (effective value) - UU Triaxial compression test (Deg)c' : Friction cohesion (effective value) - UU Triaxial compression test (kN/m2)φ : Angle of friction - UU Triaxial compression test (Deg)c : Cohesion - UU Triaxial compression test (kN/m2)Cc : Compressibility index

182811587.doc / Page 28 of 38






Cv : Consolidation coefficient (cm2/s)Es : Compressibility modulus (MN/m2)Εu : Compressibility modulus in unloading conditions (MN/m2)

182811587.doc / Page 29 of 38






3.2.3 Bearing capacity - Allowable pressure

The bearing design resistance, σd, is estimated in accordance with Eurocode 7 - case C

standards and specifications, the same way as in paragraph 3.1.1.

Two cases were examined concerning the bearing design resistance σd for the structures of

the fine screening station - storm water tank and the grit and grease removal chamber:

- Assuming undrained subsoil conditions with value of friction φ≅32,5° for layer S. Methodology

and results for static loading conditions are shown in figure 9a and 9b respectively for each

structure. Bearing design resistance (allowable pressure against soil failure) under undrained

static conditions is calculated greater than σd>2.000 MPa, for only vertical loading, while small-

er values of σd must be considered when horizontal loads are acting upon simultaneously (see

figures 9a and 9b).

- Assuming drained conditions with value of friction φ’=37,1° for layer S. Methodology and re-

sults of σd are presented in figures 10a and 10b respectively for each structure. Based on figu-

res 9 and 10 it is proved that the corresponding resulting value of σd under drained conditions is

higher than the value of σd under undrained conditions, assuming that only vertical loading is

applied. Once again, lower values of σd must be considered when horizontal loads are acting

upon simultaneously as figures 10a and 10b indicates.

As far as the method of design is concerned with respect to bearing capacity, the pressure on

soil due to factored load combinations according to Eurocodes 2 and 3 should be calculated. The

calculated applied soil pressure should include the self weight of the foundation as well as the self

weight of the backfilling material. Moreover, the eccentricities and the reduction of soil bearing

resistance due to horizontal loading at foundation level should be also taken into account, although

these loadings are expected to be not significant.

182811587.doc / Page 30 of 38






182811587.doc / Page 31 of 38






182811587.doc / Page 32 of 38






182811587.doc / Page 33 of 38






182811587.doc / Page 34 of 38






3.2.4 Settlements estimation

In this case, approximate parametric settlement analyses for the two areas of the preliminary

treatment facilities is carried out, assuming foundation levels for each structure, loads, and

dimensions according to the table 1.

For the purpose of settlement analyses, the typical soil profile of figure 8 was used, assuming

that the level of -35,0m corresponds to an incompressible layer. The settlement calculations of the

foundations are performed using the Boussinesq stress distribution. Furthermore, the assumption of

a rigid base was considered and one mean value of settlement was obtained. Results of the

parametric settlement analyses are presented in figures 11a and 11b.

The results from these calculations are being presented in table 4 for the anticipated working

loads.

Table 4. Results of settlements for the preliminary treatment facilities.

No StructureApplied load

(kN/m2)Settlements (cm) Figure

1 Fine screening station - storm water tank 93 3.97 11a

2 Grit and grease removal chamber 108 4.45 11b

Based on these results, the settlements for the preliminary treatment facilities are satisfactory

and acceptable.

The average value of the modulus of subgrade reaction K for these structures was estimated

as follows :

K= 2.000-3.000kN/m3

The aforementioned K values correspond to static conditions. For earthquake, K values should be

taken at least two times higher than these for static conditions.

182811587.doc / Page 35 of 38






ΕΡΓΟ - PROJECT: Figure 11a


Bmin (m) = 27,00


D (m) = 0,00

γ (kN/m3) = 19,4



1 +1,0 +1,5 1,00 50,0 0,999 0,999 0,999 0,999 0,999 0,999 0,999

2 -4,5 -1,3 6,50 34,1 0,897 0,901 0,904 0,908 0,911 0,914 0,9173 -6,5 -5,5 2,00 22,7 0,654 0,660 0,667 0,672 0,678 0,684 0,690

4 -10,5 -8,5 4,00 22,7 0,544 0,550 0,556 0,561 0,567 0,572 0,578

5 -35,0 -22,8 24,50 100,0 0,306 0,311 0,315 0,320 0,324 0,329 0,333



80 80 3,36 3,39 3,41 3,44 3,46 3,49 3,5187 87 3,63 3,66 3,69 3,72 3,75 3,77 3,80

93 93 3,90 3,94 3,97 4,00 4,03 4,06 4,08

100 100 4,18 4,21 4,24 4,28 4,31 4,34 4,37

106 106 4,45 4,49 4,52 4,56 4,59 4,62 4,66





3,0

4,0

5,0

70 80 90 100 110


n t S ( c m )

B= 27,0 m

B= 27,5 m

B= 28,0 m

B= 28,5 m

B= 29,0 m

B= 29,5 m

B= 30,0 m







S q H E

q

s

= ∑∆ σ


REHABILITATION PROJECT - Preliminary treatment -

with improvement - B area

zb-1

D, γ

B

L

zi

zε

zb

σεδ

Ηι

Esi

182811587.doc / Page 36 of 38






ΕΡΓΟ - PROJECT: Figure 11b


Bmin (m) = 27,00


D (m) = 0,00

γ (kN/m3) = 19,4



1 +1,0 +1,5 1,00 50,0 0,999 0,999 0,999 0,999 0,999 0,999 0,999

2 -4,5 -1,3 6,50 34,1 0,885 0,889 0,893 0,897 0,900 0,904 0,9073 -6,5 -5,5 2,00 22,7 0,628 0,634 0,640 0,646 0,652 0,658 0,664

4 -8,0 -7,3 1,50 22,7 0,559 0,564 0,570 0,576 0,582 0,587 0,593

5 -10,5 -9,3 2,50 22,7 0,498 0,504 0,509 0,514 0,520 0,525 0,530

6 -35,0 -22,8 24,50 100,0 0,288 0,293 0,297 0,302 0,306 0,310 0,315

1,5 Καθίζηση / Settlement S (cm)


80 80 3,25 3,28 3,31 3,33 3,36 3,38 3,4189 89 3,63 3,66 3,69 3,72 3,75 3,78 3,80

99 99 4,01 4,04 4,07 4,10 4,14 4,17 4,20

108 108 4,38 4,42 4,45 4,49 4,52 4,56 4,59

117 117 4,76 4,80 4,84 4,88 4,91 4,95 4,99





2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

70 80 90 100 110 120


n t S ( c m )

B= 27,0 m

B= 27,5 m

B= 28,0 m

B= 28,5 m

B= 29,0 m

B= 29,5 m

B= 30,0 m







S q H E

q

s

= ∑∆ σ


REHABILITATION PROJECT - Preliminary treatment -with improvement - C area

zb-1

D, γ

B

L

zi

zε

zb

σεδ

Ηι

Esi

182811587.doc / Page 37 of 38






4. CONCLUSIONS

This report presents the recommended foundation system for the preliminary treatment

facilities. Although the bearing capacity of the subsoil reveals high values the anticipated settleme-

nts are higher than the defined ones for this kind of structures (except the inlet pumping station

coarse screen structure). In order to construct the foundations of the inlet pumping station - coarse

screen structure a solution of a sheet pile wall could be utilized due to the geotechnical conditions

and the level of the ground water.

The solution to the problem of high settlements was given by improving the mechanical

characteristics of the subsoil utilizing the vibroreplacement (stonecolumns) method.

The configuration of the stonecolumns was, a triangular grid with spacing a=2.50m of columns

made by appropriate gravel material, having a minimum diameter of D=0,90m and length varying

from L=12.00 to 13.50m.

This soil improvement method results reduction of the settlements for the structures into

acceptable limits, faster rates concerning the construction matters, as well as a stable and secure

solution for the foundation of the preliminary treatment facilities.

Documents

FOUNDATION SYSTEM FOR THE PRELIMINARY TREATMENT FACILITIES