APPENDIX 15 · 2019. 7. 15. · appendix 15 geotechnical studies . mbongendhlu geoenvironmental engineers (pty) ltd. reg. no. 2005/008292/07 geotechnical investigations report mngeni

APPENDIX 15

GEOTECHNICAL STUDIES

Mbongendhlu GeoEnvironmental Engineers (Pty) Ltd.

Reg. no. 2005/008292/07

GEOTECHNICAL INVESTIGATIONS REPORT

MNGENI SHAFT

ZULULAND ANTHRACITE COLLIERY REPORT NO: 2019/0004

PREPARED FOR: MARUAPULA ENGINEERS

OFFICE 1B WOODHILL PARK CENTRE

948 ST BERNARD DRIVE

GARSFONTEIN 0042

PREPARED BY: E.T. NCUBE Pr. Sci. Nat DATE: MARCH 2019

Mbongendhlu GeoEnvironmental Engineers (Pty) Ltd. Consulting Engineering Geologists, Geohydrologists and Environmental Scientists

47 Jenner Street, Rayton, 1001

P.O. Box 83, Rayton 1001

Fax: 0866056558, Cell: 0724549247

[email protected]/[email protected]

Contact Person: Edwin Thabile Ncube

Khulani Geoenviro Consultancy

Mbongendhlu GeoEnvironmental Engineers (Pty) Ltd. Reg. No. 2005/008292/07 Page 1

1. INTRODUCTION AND TERMS OF REFERENCE

At the request of Maruapula Engineers, Mbongendhlu GeoEnvironmental Engineers (Pty)

Ltd conducted a Geotechnical Investigation for pollution control dams; stockpile area and

office block for Mngeni Shaft - Zululand Anthracite Colliery in KwaZulu Natal. (Google

Image).

The aim of the investigation was to:

determine the geology and general mechanical properties of the soil and rock horizons

present on the site

make recommendations on the development potential of the site

comment on the excavability and usability of various materials present on site, and

comment on site water regime particularly pertaining to shallow groundwater/seepage

and surface water management.

The investigation was carried out in accordance with the current industry

guidelines listed below.

2. AVAILABLE INFORMATION AND LITERATURE USED

Information from the following literature and guidelines were used in the investigation and

assessment of the site:

1:250 000 Geological Map Series 2830 Dundee and Google Images.

“Guidelines for Urban Engineering Geological Investigations” published by South

African Institute of Engineering Geologists (1997).

“Revised guide to soil profiling for civil engineering purposes in Southern Africa” by

Jennings et al. (1973).

“Soil Survey for Engineering” by Brink A.B.A. et al. (1982).

“Presumed Allowable bearing capacities under static loading” BS 8004 Code of

Practice for Foundations, 1986.


3. APPROACH AND METHODOLOGY

The investigation comprised of liaison; desk study; fieldwork; laboratory tests; data

analysis and reporting.

Liaison involved discussions with the Project Management and Locals.

Desk study concentrated on geology of the area.

Fieldwork comprised of Visual Inspection, In situ Soil Profiling, Testing and

Sampling.

Samples were submitted to Snalab, to analyze for diagnostic mechanical soil

properties.

Soil results were interpreted based on “Soil Survey for Engineering” by Brink et al

(1982).

The report does not reproduce any section of the guidelines and should be used in

conjunction with guidelines listed above and/or any other relevant current

construction industry guidelines.

4. SITE

4.1 Description

The investigated site is in a veld roughly 6km north east of the ZAC Offices. It is

polygonal within an area roughly described by:

A 280 11’ 03.30”S B 280 11’ 04.50”S

310 43’ 22.60”E 310 43’ 27.10”E

C 280 11’ 13.00”S D 280 11’ 15.30”S

310 43’ 25.40”E 310 43’ 22.90”E

E 280 11’ 13.70”S F 280 11’ 05.30”S

310 43’ 16.80”E 310 43’ 16.60”E

Roughly, +8.5 ha (estimated from Google Pro) was covered by the study.

The site is currently being used as grazing land mainly for goats – and during the

time of the investigations the area was vegetated /pristine. Plate 1 shows

parts of the site.


The climate of the area is ‘sub humid dry’ with intermittent rainfall in summer.

Surface drainage is through sheet flow into dongas that cut through the western

side of the site. The dongas feed into Black Mfolozi River which is within a

kilometer radius from the site.

Plate 1: Parts of the site (ZAC, March 2019)

4.2 Geology

The site is in an area overlain by medium to coarse grained sandstone, grey

micaceous shale and coal of the Vryheid Formation that belongs to Ecca Group of

the Karoo Sequence. Also occurring in the area are dolerite intrusions of the

Jurassic (1:250 000 Geological Map Series 2830 Dundee).

On site, transported material of alluvial and hillwash origin overly residual/

weathered sandstone/shale material.


5. GEOTECHNIAL INVESTIGATIONS

5.1 Liaison

The following information was collected during this exercise:

A new shaft is to be opened on site.

Two pollution control dams, a stockpile area and a single storey office block

will be built on site.

Mfolozi River rarely runs dry.

Clayey material overlies thick porous sandstone (Consultant Mine Geologist).

5.2 Desk Study

The study concentrated on the geology as no previous geotechnical reports of the

area were obtained.

5.3 Fieldwork

Fieldwork comprised of Visual Inspection, In situ Soil Testing, Profiling and

Sampling for laboratory analysis.

5.3.1 Visual Inspection

The area was thoroughly inspected and the following observations were

made:

The site is currently used as grazing area.

There is a village within 1km radius from the site.

They are dongas that expose sandstone/shale below transported

clayey cover soil.

There are some ant holes on site.

There is also hillwash material in parts of the site.

Plate 2 is a collection of photos randomly picked showing different

sceneries that affect the geotechnical aspects of the area.


Plate 2: Randomly picked photos showing different surface scenic (ZAC, March 2019).

5.3.2 In Situ Soil Profiling, Testing and Sampling

Fourteen test pits, dug by a TLB, were used to test, profile and sample the

soil. The position and the physical properties of the pits are shown in

Google Image and Table 2 respectively. Their locality was mostly dictated

by accessibility. Care was taken not to destroy vegetation and donga

banks. Minimal vegetation clearance in thick bush was done along an

existing path used by locals. On the main, testpits were dug on open and

easily accessible places.

The testpits were dug as deep as possible up to refusal/considerable

resistance. The profiles were recorded using 6 descriptors, viz.: moisture

condition, colour, consistency, structure, soil texture and origin (i.e.

MCCSSO for short) according to the guidelines of Jennings et al. (1973).


Photos of profiles were taken and are included in the text or clipped on

detailed soil profile sheets in Appendix.

Seven disturbed samples - taken on different dates - were submitted to

Snalab for compaction and foundation indicator analysis. No undisturbed

samples were taken as the bulk of the site was generally fissured.

Table 1: Physical properties of Testpits

TESTPIT

I.D.

POSITION

Latitude Longitude

DEPTH OF

PIT(m)

SAMPLING

DEPTH

(+ m) Pit 1

Pit 2

Pit 3

Pit 4

Pit 5

Pit 6

Pit 7

Pit 8

Pit 9

Pit 10

Pit 11

Pit 12

Pit 13

Pit 15

Pos 1

Pos 2

280 11’ 04.00”

280 11’ 04.80”

280 11’ 05.90”

280 11’ 07.70”

280 11’ 09.70”

280 11’ 10.30”

280 11’ 12.20”

280 11’ 12.80”

280 11’ 13.90”

280 11’ 14.70”

280 11’ 10.50”

280 11’ 09.80”

280 11’ 08.40”

280 11’ 08.30”

280 11’ 08.40”

280 11’ 08.30”

310 43’ 23.50”

310 43’ 22.00”

310 43’ 21.10”

310 43’ 19.50”

310 43’ 20.60”

310 43’ 19.50”

310 43’ 18.20”

310 43’ 21.40”

310 43’ 23.20”

310 43’ 22.10”

310 43’ 22.00”

310 43’ 23.10”

310 43’ 24.40”

310 43’ 21.50”

310 43’ 24.40”

310 43’ 21.50”

1.20

1.00

0.90

0.70

0.60

1.10

0.60

0.70

0.50

0.60

0.80

0.80

1.10

0.30

0.40

0.30

0.40

0.40

0.30

0.60

Table 2: In situ consistency test results

SAMPLE I.D. MOISTURE CONTENT AND CONSISTENCY

Pit 1

Pit 2

Pit 3

Pit 4

Pit 5

Pit 6

Pit 7

Pit 8

Dry – stiff

Dry – stiff

Dry - stiff

Dry – stiff

Dry – stiff

Dry - stiff

Dry – stiff

Dry – stiff


Pit 9

Pit 10

Pit 11

Pit 12

Pit 13

Pit 14

Dry - stiff

Dry – stiff

Dry – stiff

Dry - stiff

Dry – stiff

Dry – stiff

From the in situ profiling and testing, the following observations were

made:

The site is covered by clayey alluvium overlying weathered

shale/sandstone.

The profile has more or less uniform texture across the site.

Consistency was generally stiff becoming stiffer/denser with depth.

Clayey material is dominantly greyish brown with visible ground cracks in

some places.

Shale/sandstone is well exposed along donga beds.

No groundwater seepage was encountered in all testpits.

Plates 3 are randomly picked photos showing textural uniformity across the site.


Plate 4: Uniform texture across the site (ZAC, March 2019)

5.4 Laboratory Test Results

Laboratory results are summarized in Tables 3. Detailed Test Results Sheets are

presented as Appendix.

Table 3 Summary of the Laboratory Indicator Test – Disturbed Samples

SAMPLE I.D.

FINES

%

PI LS PE AASTHO Classification

Pos 1 (Layer 1)

Pos 2 (Layer 2)

Pit 1 Layer 1

Pit 4

Pit 9

Pit 10

Pit 15

43

46

31

31

37

40

29

10

14

14

8

10

16

8

4.8

7.0

6.9

3.9

5.4

7.7

4.3

Low

Low

Low

Low

Low

Low

Low

A-4(1)

A-6(2)

A-2-6(1)

A-2-4(0)

A-4(0)

A-6(2)

A-2-4(0)

PI– Plasticity Index, LS–Linear Shrinkage, PE Potential Expansion,

Table 4 Compaction Tests

SAMPLE I.D. OMC

(%)

MMD

(kg/m3)

CBR

(100% Rel Comp)

Pos 1

Pos 2

4.8

6.3

2055

2034

9.7

12.3 MDD – Maximum Dry Density, OMC – Optimum Moisture Content, CBR – California Bearing Ratio

From the lab test results, the following deductions could be made:

The site is generally covered by clayey sand with varying proportions of silt.

The Plasticity Index ranges from +8 to +16.

The material can be compacted to a high density at low optimum moisture

content.

The soils range from excellent to poor subgrade material according to PRA

ratings in Brink 1982 {A-2-6(4) and A-6(2)}.


6. SITE ASSESSMENT

The site is in an area covered by clayey soils believed to be predominantly of alluvial origin.

These are underlain by shale/sandstone and coal. Clayey material suffers volumetric

changes when subject to moisture variation. The extent of volume change/expansion

depends on clay type, proportions of coarser material and layer thickness.

Laboratory results show a generally low activity – Plasticity Index (PI) ranging from 8 to

16. This can be attributed to high sand content and lean silt. However, this does not rule

out occurrences of pockets with higher PI - suggesting concerns for swelling and

shrinkage problems. This is also demonstrated by shrinkage cracks/shatter in some parts

of the site.

The typical permeability value of clayey sand is +5.50 x 10-9m/s. On site, this figure may

be affected by fissures, roots, ant cavities, exploration holes and sand proportions. No one

figure can describe the whole area. The pH is slightly acidic – at 6.49 and electrical

conductivity at 0.171S/m. This adds to the corrosive nature of fine material.

The typical presumed bearing capacity for stiff clayey soils ranges between 150 to

300kPa. However, when softened by water, it losses its strength to a bearing capacity of

less than 75kPa. Laboratory CBR at 100% relative compaction is 9.7% - indicative of

relatively low strength, though producing high maximum dry density.

The shale/sandstone underlying clayey material has proportions of clay, silt and sand that

suggest a potential problem of settlement and/or collapse.

Settlement might be caused by:

compaction due to the rearrangement of particles responding to new load

closure of voids where there is open texture

Collapse occurs due to sudden weakening of the ‘gluing effects’ of fine material when

saturated with water. This is typical of relatively loose profiles that show stability/pseudo

strength during excavation as shown by the sidewalls of all test pits. However, the high


content of fine material and shallow shale/sandstone to some degree, mitigate sever collapse.

The varying depths to refusal across the site and the occurrence of hillwash indicate

consistency variation both laterally and vertically. It is therefore logical that some structures

will straddle hard and soft ground resulting in differential settlement.

The occurrence of anthills presents a potential problem of collapse when resultant

underground cavities yield to load. The position and sizes of anthills that are on site might

not be representative of the underground cavities as they might have been destroyed and

eroded overtime. Also, where hard ground is shallow the cavities might not be confined to

where the holes manifest on the ground but could be spread laterally underground. This

exacerbates the collapse potential.

Permeability of shale and sandstone are in the region of 1.00 x 10-13 3.00 x 10-10m/s

respectively. The figures can be affected by bedding fissures/joints, roots, ant cavities and

exploration holes. No solid figure can be a representative of the whole area.

The typical presumed allowable presumed bearing capacity for loose sand to strong shale

ranges between <100 to 2000kPa. Shale generally losses integrity when soaked in water for

long periods. Laboratory CBR at 100% relative compaction is 12.3% - indicative of

relatively low strength.

The site is within a kilometer radius from a semi to perennial Black Mfolozi River.

Topography gentle slopes southwards towards the river. Clayey material has poor

percolation, leading to run off and erosion as testified by the numerous dongas on the

western side of the site. The soil on the eastern side is protected by vegetation.

No slope instability is foreseen.

Though no groundwater seepage was encountered, soil discolouration is evidence of past or

seasonal groundwater inundation. Clay and shallow shale inhibit water from percolating

downwards and might result in perched ground- and surface water during prolonged periods

of heavy rain. Clayey soils are slippery during rainy seasons. With seasonal moisture


changes, corrosiviness is anticipated – due to high percentage of fine and slightly acidic

material.

The site is within a coal mining region - hence seismic activities are highly anticipated.

Excavation will need an excavator as the TLB struggled on stiff soil and hard country rock.

As construction material, the soil in generally classifies as excellent to poor subgrade, {A-

2-4(0) and A-6(2)} – according to the PRA ratings in Brink et al. (1982).

7. CONCLUSION

On the basis of the information presented above, the profile is generally considered as not

good founding material at its natural state. Heaving, Settlement and/or Collapse problems

are anticipated across the site. It is, however, believed that the site is suitable for the

proposed development if subjected to stringent and appropriate precautionary measures. The

precautionary measures should at all cost minimize negative effects on the prevailing

ecosystem. The site should be regarded as very sensitive with respect to ground- and surface

water pollution – as it is within a kilometer radius from a river that passes through many

villages, game reserve and farms downstream.

Even though the potential expansiveness of the sand clay layer is expressed as low in the

laboratory test results, precautionary measures must accommodate a safety factor. The

thickness of the layer is on average around 1m. Such material is also known to be susceptible

to long-term settlement. Exploration logs can be used to get precise thickness and depth to

groundwater, therefore H2/S2 should be the minimum design on clayey layer.

The integrity of underlying shale and sandstone can be affected by differential weathering,

loose loamy beds and ant activities. These can trigger some differential settlement,

settlement and/or collapse of structures. C1/S2 should be the minimum design on

shale/sandstone; unless proven otherwise during foundation excavation. The main donga


can be sealed to curb erosion and divert clean water away from contamination sources.

Haulage routes, driveways, walkways and parking should be designed and engineered in a

way that totally quells potential slipperiness and minimizes contamination of water

resources.

It should be emphasized that the evaluation is based on interpolation of information

between testpits that are unevenly distributed, it is therefore possible that variations from

the described conditions might occur; also taking into account that footprint investigations

couldn’t be conducted on all structures.

It is however believed that the information presented exhausts the bulk of the problem and

the site can be engineered - within the confines of legislation - to suite the proposed

development.

8. GROUND PREPARATION AND CONSTRUCTION RECOMMENDATIONS

Planning should highly consider preserving the prevailing ecosystem.

A 1:100 year flood line should be determined and a buffer zone added to protect the

river/valley.

Where vegetation is cleared, all roots and humus must be removed from site.

To minimize erosion; the main donga within the site can be concrete sealed and used

as storm water conduit/tunnel.

Silt traps must also be placed strategically along the tunnel.

Infrastructure:

Though there are many solutions, a raft foundation is highly recommended for office

block (SANS10400H:2012).

All surface water must be directed away from the structure and stringent precautionary

measures on wet services must be applied as stipulated in guidelines.

Remove up to half a meter depth of clay along ‘haulage tracks’, drive ins, walkways

and packing.

Refill with G5 to G7 material and pave according to anticipated loads.


Pollution control dams and stockpile:

Remove all clay up to shale/sandstone across the site. (This will reduce ground activity

and add to storage capacity.)

Engineer some of the clayey material for use as core/seal to curb permeability and

improve attenuation capacity below and around the dams and the stockpile.

Thorough compaction of replacement or blended material - coupled with shallow

shale/sandstone- should provide adequate bearing capacity.

An impermeable reinforced concrete seal for dams and stockpile is highly

recommended due to high sensitivity of the site.

On the occurrence of conditions that totally vary from those described above, a

geotechnical competent person should be consulted for a qualified opinion.

Mbongendhlu GeoEnvironmental Engineers cannot be held liable for any damages to any

structure should the recommendations contained herein be not properly executed.

EDWIN THABILE NCUBE Pr. Sci. Nat ENGINEERING GEOLOGIST


REFERENCES

Brink A.B., Partridge T.C. and Williams A.A.B. (1982), Soil Survey for Engineering, Caledon

Press, Oxford.

Bryne G., Everett J.P. and Schwartz K. (1995), A Guide to Practical Geotechnical Engineering

in Southern Africa, Franki, Johannesburg.

Jennings J.E., Brink A.B.A. and Williams A.A.B. (1973) Revised guide to soil profiling for civil

engineering purposes in Southern Africa, Transactions of the South African Institute of Civil

Engineers, Vol. 15, No 1.

South African Institute of Engineering Geologists (1997), Guidelines for Urban Engineering

Geological Investigations.

BS 8004 Code of Practice for Foundations (1986) “Presumed Allowable bearing capacities under

static loading”

Documents

APPENDIX 15 · 2019. 7. 15. · appendix 15 geotechnical studies . mbongendhlu geoenvironmental engineers (pty) ltd. reg. no. 2005/008292/07 geotechnical investigations report mngeni