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SADC SecretariatMultinationalBotswana/Zambia

Consultancy Services for the Feasibility and Detailed Designof the Kazungula Bridge, Border Facilities and Corridor

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egis bceom egis jmi Geotechnical Report A3

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Kazungula Bridge Project

Final Design ReportVolume 3 – Appendices

A3Geotechnical Report





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Appendix A3 – Geotechnical Report

Table of Contents

1 Introduction ...............................................................................................1

1.1 GENERAL 1

1.2 APPOINTMENT 2

1.3 Information available 2

2 SITE DESCRIPTION...................................................................................2

2.1 Bridge Layout 2

2.2

Topography 3

3 REGIONAL GEOLOGY ..............................................................................4

3.1 Karoo Igneous Province 4

3.2 Kalahari Group 5

3.3 Recent Alluvial Sediments 5

3.4

FAULT AND SEISMIC RISKS 5

4 CLIMATE ....................................................................................................6

5 FIELDWORK...............................................................................................6

5.1

Rotary Core Boreholes 6

5.2 Standard Penetration Tests 8

5.3 Lefranc Permeability Tests 10

5.4

Lugeon Tests 12

5.5 Trial Pits 13

6 LABORATORY TESTING ........................................................................13

6.1

Soil Samples 13

6.2 Rock Core Samples 16

7 GROUNDWATER LEVELS ......................................................................17





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8 SUMMARY OF THE BOREHOLE LOGS .................................................17

9 BEARING RESISTANCE OF THE FOUNDATION ROCK .......................19

10 CONCLUSIONS........................................................................................21

REFERENCES .................................................................................................22

APPENDIX A: PLANS

APPENDIX B: BOREHOLE LOGS & CORE PHOTOGRAPHS

APPENDIX C: LEFRANC PERMEABILITY TEST SHEETS

APPENDIX D: LUGEON TEST SHEETS

APPENDIX E: LABORATORY TEST RESULTS – SOIL SAMPLES

APPENDIX F: LABORATORY TEST RESULTS – ROCK CORE SAMPLES

APPENDIX G: GROUND WATER LEVEL MONITORING

APPENDIX H: DAILY DRILLING REPORTS





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Table of Figures and Tables

Table A3.1: Coordinates at the centre of pier and abutment positions .........................................3

Table A3.2: Borehole depths .........................................................................................................6

Table A3.3: SPT Test Results .......................................................................................................9

Table A3.4: Lefranc Tests Results...............................................................................................11

Table A3.5: Lugeon Tests Results...............................................................................................12

Table A3.6: Particle Size Distribution and Atterberg Limit Determination Tests .........................14

Table A3.7: Bulk Density and Dry Density from undisturbed samples........................................14

Table A3.8: Moisture Content Analysis undertaken on-site.........................................................15

Table A3.9: Direct Shear Tests....................................................................................................16

Figure A3.10: Groundwater monitoring........................................................................................17

Table A3.11: Bedrock levels obtained from the borehole logs ....................................................18

Table A3.12: Bearing Resistance of the Rock Foundation Materials ..........................................19





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egis bceom egis jmi Geotechnical Report A3 1December 2010

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GEOTECHNICAL REPORT

1 INTRODUCTION

1.1 GENERAL

This factual report presents the results of a geotechnical investigation undertaken for the proposed

construction of a road and rail bridge over the Zambezi River at Kazungula. The proposed bridge

will span between Botswana and Zambia and is located at the confluence of the Chobe andZambezi Rivers.

The objectives of the investigation are as follows:

• Obtain a geotechnical profile of the soil and rock conditions at each borehole location

• Undertake and document the results of in-situ and laboratory tests to determine thegeotechnical properties of the natural materials

• Provide an overview of the regional geological conditions to aid in the interpretation of theinformation provided

The information is required by the bridge designers in order to establish a safe and economical

foundation design for the structure. The information is also required to identify risks and constraints

associated with construction activities.

The investigation was carried out between August and November 2010 and entailed the following:

• Drilling of 10 rotary core boreholes, one at each of the piers and abutments

• Conducting Standard Penetration Tests (SPT’s)

• Conducting Lefranc permeability tests

• Undertaking Lugeon permeability tests

• Recovery of representative disturbed and undisturbed samples for appropriate laboratorytesting

• Monitoring the standing water levels in the boreholes

• Excavation of 4 trial pits using a Tractor-Loader-Backhoe (TLB)

The subsurface conditions described in this report are based on point information obtained at the

respective borehole and trial pit positions. Given the lateral extent of the pier and abutment

footprints, conditions at variance with those described in this report may be encountered during

construction. It is therefore recommended that further, ongoing, geotechnical assessments be

undertaken during construction.





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1.2 APPOINTMENT

To enable Egis Bceom International to effectively design the bridge it was required to appoint a

geotechnical sub-contractor to undertake a geotechnical investigation. The letter of invitation to

tender dated 23 July 2009 and associated documentation were issued to a limited number of

service providers, as shortlisted by SADC.

Both Geomechanics and Terratest were individually invited to submit proposals for the

geotechnical investigation. However, as Geomechanics are specialist geotechnical contractors and

Terratest are specialist geotechnical consultants, the two firms agreed to provide one technical

submission. The proposal was submitted by Geomechanics to include the services of Terratest as

a sub-consultant.

During the course of 2009 and early 2010 various amendments and exclusions to the scope of

works provided in the original tender documents were made by Egis Bceom International. The final

submission including the amended scope of work was submitted by Geomechanics on 18 May

2010.

1.3 INFORMATION AVAILABLE

The following information was provided by Egis Bceom International:

• Coordinates of the ten borehole positions

• Drawing tiled “Kazungula Bridge – Longitudinal Section” dated 01/07/2010, drawingnumber 05 Rev. 0.

• Brief summary of previous geotechnical investigations was included in the tenderdocumentation

2 SITE DESCRIPTION

The proposed bridge site spans the Zambezi River between Botswana and Zambia. The site is

located in the north east of Botswana, the south of Zambia and immediately adjacent to the eastern

boundary of the Namibian Caprivi.

The site is located at the confluence of the Chobe River and the Zambezi River

A Locality Plan and Site Layout Plan are attached as Figures 1 and 2, in Appendix A.

2.1 BRIDGE LAYOUT

It is proposed to construct a cable stay bridge consisting of eight piers and two abutments. The

proposed bridge will be constructed on a 1000m radius curve in an up-stream (north westerly)

direction.

For the purposes of the design the piers have been designated as “P1” to “P8”, the abutment on

the Botswana side of the river has been designated “A0” and the abutment on the Zambian side of

the river has been designated “A9” (Refer to Figure 2, Appendix A).





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During low flow conditions P2, P3, P4 and P5 are located within the banks of the river and are

referred to as riverside positions in this report. The remaining piers and the two abutments are

located above the river level during low flow conditions and are referred to as landside positions. It

must be noted, however, that some or all of the landside positions may be submerged during

flooding.

The coordinates of the centre of the piers and abutments as well as the ground elevations at each

position are provided in Table A3.1, overleaf. The ground elevations at the riverside positions refer

to the river bed level as measured by the surveyors on 13 October 2010 using a boat-mounted

depth sounder. It should be noted that the river bed level may change due to sediment movement,

particularly during high-flow conditions.

Table A3.1: Coordinates at the centre of pier and abutment positions

A0 P1 P2 P3 P4

X 315800.013 315795.964 315795.653 315808.951 315838.635

Y 8031949.999 8032003.844 8032088.826 8032217.062 8032342.522

Elevation 927.712 928.375 923.000 918.770 920.700

Accessibility at lowwater level

Landside Landside Riverside Riverside Riverside

P5 P6 P7 P8 A9

X 315884.212 315944.925 316019.764 316076.204 316114.852

Y 8032463.121 8032576.854 8032681.832 8032745.367 8032783.075

Elevation 921.470 926.940 925.192 926.971 929.533

Accessibility at lowwater level

Riverside Landside Landside Landside Landside

Notes: i) Elevations of riverside positions accurate to within 100 mm

ii) Horizontal positions of riverside boreholes accurate to within 500 mm

2.2 TOPOGRAPHY

Topographic descriptions of the pier and abutment positions are provided below.

The Zambezi River flows in a south easterly direction at the proposed bridge site. The Chobe River

flows into the Zambezi in a north easterly to easterly direction immediately upstream of the site and

the water masses of the two rivers merge in the vicinity of P3.

Based on aerial photography the width of the Chobe and/or Zambezi flood plains is typically 2 to

5km over the section of river 10km upstream and downstream of the bridge site. The flood plains

are characterised by braided or meandering flow patterns that are either active or paleo-features.

The combined width of the flood plain and river channel in the vicinity of the site is approximately

600 to 700m.

A0 and P1 are located on a reasonably level section of land marginally above the typical yearly

flood level. Both positions appear to be within the high-level flood plain.

P2, P3, P4 and P5 are all located within the river channel. P2 may be classified as being within the

Chobe River, P3 near the confluence and P4 and P5 are within the Zambezi River channel.





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P6 is located on the north eastern side of a peninsula formed by an off-channel of the Zambezi.

Aerial photography indicates that the off-channel is located where a number of paleo-braided

channels within the flood plain re-join the main river.

Local residents indicated that the off-channel may have been dredged in the past to create a

sheltered harbour. This theory is supported by the depth of the channel, which was found to be

5.9m during the bathometric survey.

P7 is located within thick reeds on the northern bank of the off-channel. This area is inundated

seasonally.

The topography at P8 slopes in a gentle easterly direction. The site appears to be located near the

typical yearly flood level.

A9 is topographically higher than the other pier and abutment positions and is located on fairly level

ground above typical flood level. This location will only be inundated under extreme flood

conditions.

3 REGIONAL GEOLOGY

Three broad scale geological units were encountered during the investigation. These are basaltic

bedrock of the Karoo Igneous Province, secondary surface deposits of the Kalahari Group (which

cover much of the bedrock in north eastern Botswana and southern Zambia) and recent alluvial

deposits associated with the Chobe and Zambezi Rivers.

3.1 KAROO IGNEOUS PROVINCE

The bedrock geology of north eastern Botswana consists of basaltic lavas that form part of the

Karoo Igneous Province.

The Karoo Igneous Province is a typical continental flood basalt (CFB) province that covers a very

extensive area of Southern Africa. Flood basalts are extrusive igneous rocks that form during

successive eruptions from a suite of fissures, rather than from prominent volcanic structures. The

eruptions build up to form a sequence of sub-horizontal lava flows that may total hundreds or even

thousands of meters in thickness. Based on studies of similar CFB provinces, some individual lava

flows are estimated to have flowed more than 600km and covered areas greater than 20 000km2,

although the majority of flows are less extensive (Johnson, et.al., 2006).

The Karoo lavas preserved today are only erosional remnants of a far more extensive covering of

lava that once blanketed much of southern Africa. The lava outcrops and sub-outcrops in north

eastern Botswana and southern Zambia are very similar in composition to the outcrops that occur

in the highlands of Lesotho and the Eastern Cape province of South Africa. Both remnants were

emplaced in a largely stable section of a continental plate and differ from the rift-related volcanic

rock sequences such as those encountered in the Thuli Block area in Botswana and the Mwenezi-

Save area in Zimbabwe.

In terms of their mineral composition the basaltic rocks of the Karoo Igneous Province consist

predominantly of plagioclase feldspar, augite (a type of clinopyroxene) and olivine. The rocks are,





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however, tholeiitic (silica oversaturated) and many rocks are characterised by the presence of

orthopyroxene (low-Ca pyroxene). Interstitial patches of alkali feldspar and quartz may be present

in coarser grained rocks.

Extrusive rocks are typically glassy or extremely fine-grained due the rapid rate of cooling of the

magma. However, the basalts of the central area Karoo Igneous Province (i.e. those in the

Kazungula area) generally exhibit a fine grained texture similar to that of dolerite. This is attributed

to the thickness of the individual lava flows, which may be several tens of meters, and therefore

cool at a sufficiently slow rate to allow for mineral crystallization.

The Karoo Igneous Province formed approximately 183 million years ago over a short period of

geological time. As such the rock units show a lack of well developed weathering horizons or

significant interbedded sedimentary units within the lava sequence.

The Karoo Igneous Province is part of a larger Gondwana-wide belt of magmatism and is related to

the break-up of the super continent.

Basaltic bedrock of the Karoo Igneous Province was encountered in all ten boreholes.

3.2 KALAHARI GROUP

The Kalahari Group is the most extensive body of terrestrial sediments in Southern Africa and

covers most parts of central and northern Botswana, parts of eastern Zambia and occurs in other

southern African countries. The deposits formed in inland basins created during the break-up of

Gondwanaland and subsequent tectonic uplifts.

The older units generally have a fluvial origin and consist of gravels interlayered with calcareous

clays. Aeolian deposits, informally termed Kalahari sand, form the upper unit of the Kalahari Group

and cover most of the underlying sediments.

Pedocretes in the form of calcrete (calcium carbonate cementing agent) and silcrete (silica

cementing agent) typically occur at the base of the aeolian sands. Calcrete may be in the form of

sandy limestone or calcareous sand or gravel. Silcretisation of the sandy limestone is known to

occur in many locations (Johnson, et.al., 2006).

Kalahari Group deposits were encountered above the bedrock at BH A0, BH P1 and BH A9.

3.3 RECENT ALLUVIAL SEDIMENTS

Alluvial sediments deposited by the Chobe and Zambezi rivers were distinguished from the

Kalahari Group sediments by a lack of pedogenic alteration or signs of consolidation. The

sediments typically consisted of fine to medium grained sand.

3.4 FAULT AND SEISMIC RISKS

The geological map provided in Appendix A does not indicate the presence of any major faults in

close proximity to the proposed bridge site. No evidence of faulting was encountered in the

boreholes. However, the bridge must be designed to tolerate seismic movements in accordance

with the seismic risk profile of the area.





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4 CLIMATE

The climatic regime plays a fundamental role in rock weathering and the development of a soil

profile. The climate in Botswana is generally semi-arid to arid in the extreme south west. The

Kazungula area receives more rainfall than the rest of the country and has an average annualrainfall of approximately 650mm (Republic of Botswana, Roads Department, 2000).

Weinert (1964), through his work on basic igneous rocks in Southern Africa, demonstrated that

mechanical disintegration is the predominant mode of rock weathering in areas where his climatic

“N-value” is greater than 5, while chemical decomposition predominates where the N-value is less

than 5. Weinert’s climatic N-value for the Kazungula area is approximately 2. This implies that

chemical decomposition is the dominant mode of rock weathering.

The N-value is calculated from climatic data as follows:

N = 12.Ej / Pa Where: Ej = evaporation during January

Pa = annual precipitation

5 FIELDWORK

The fieldwork was undertaken from August to November 2010 during the dry winter season.

The positions of the boreholes are shown on the Site Plan, Figure 2 in Appendix A.

5.1 ROTARY CORE BOREHOLES

Ten vertical rotary core boreholes were drilled to depths of between 12.01m and 22.40m below

ground level. The holes were advanced to achieve 12m of penetration into the bedrock.

Six landside boreholes and four riverside boreholes were drilled during the investigation, one at the

centre of each proposed pier and abutment location. The elevations and final depths of the

boreholes are summarised in Table A3.2.

Table A3.2: Borehole depths

Borehole Elevation (masl)Final depth below

ground level

Elevation at final depth

(masl)

A0 927.712 17.50m 910.21

P1 928.375 17.05m 911.32

P2 923.000 12.01m 910.99

P3 918.770 12.01m 906.76

P4 920.700 14.02m 906.68

P5 921.470 17.88m 903.59

P6 926.940 22.40m 904.54

P7 925.192 18.10m 907.09

P8 926.971 16.70m 910.27

A9 929.533 16.00m 913.53





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The four riverside boreholes were drilled from a jack-up floating barge. The barge had four

hydraulically operated legs that enabled the barge to be founded on the riverbed and raised up

during drilling.

The locations of the boreholes were determined by a land surveyor. The surveyor oversaw the

positioning of the floating barge at each riverside borehole and was responsible for ensuring that

the borehole position was within the 0.50m tolerance specified by the client.

5.1.1 DRILLING METHOD

The boreholes were drilled using the T6-146 drilling system. This rotary core drilling method

produces a core diameter of 123mm and a hole diameter of 146mm. This fairly large diameter

drilling method was required in order to maximise core recovery in the weathered and fractured

bedrock. A temporary casing with an outer diameter of 168.3mm was installed to a depth where

stable formations were encountered in order to prevent collapse of the borehole during drilling and

to allow for the drilling of the riverside boreholes.

The T6-146 system uses a double tube corebarrel with a solid inner tube. In order to extract the

core from the inner tube it is often necessary to hold the core barrel in a near vertical position and

to strike the barrel with a hammer in order to dislodge the core, which then falls out of the

corebarrel. This manner of extraction can affect the integrity of the core (as discussed further in

Section 6.1.2).

The boreholes were advanced through unconsolidated soils by “wash boring” using the T6-146

drilling system described above. Given the unconsolidated and non-cohesive nature of the soils,

samples could not be captured in the core barrel. An indication of the soil profile was, however,

obtained from the “wash samples” comprising material returned to surface in the drilling fluid.

The drilling was undertaken with the aid of a commercial drilling fluid additive sold under the brand

name “Ezeemix” produced by SAMCHEM. Ezeemix is a biodegradable polymer that increases the

viscosity of the drilling fluid.

5.1.2 CORE LOGGING

The soils and rock cores obtained during the drilling were profiled by one of Terratest’s Engineering

Geologists in accordance with accepted South African standards. Soils were described in

accordance with the method of Jennings et al., (1973).

Rock core was logged in accordance with the methods contained in the publication “A guide to

core logging for rock engineering” published by the Core Logging Committee of the South African

Section of The Association of Engineering Geologists. A summary of both publications is included

in Appendix I. It must be noted that the terminology used for the core logging differs from standard

European terminology.

In addition to the primary description of the rock mass, the borehole logs include parameters for

“percentage core recovery”, “Rock Quality Designation” (RQD) and “Fracture Frequency”.





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“Percentage core recovery” is the measured core recovery per drill run expressed as a percentage.

The core recovery was measured after the core had been extracted from the core barrel and

reassembled in the core box. Given the highly fractured nature of the core it was not always

possible to fully reassemble the separated core fragments and as such the measured recovery

sometimes exceeded the length of the drill run. In this case the recorded core recovery wasreported as 100%.

The RQD provided in the borehole logs was recorded per meter. The RQD is defined as the total

length of individual core sticks greater than 100mm expressed as a percentage of 1.00m. The RQD

was measured along the central axis of the core.

For the purposes of this investigation the RQD values provided are described in terms of “handled

RQD”. A review of the borehole logs indicates that many of the joints and fractures in the rock

mass are cemented with calcite or other precipitated mineral infilling. The strength of the

recemented joints was highly variable, ranging from very weakly recemented to strongly

recemented. As mentioned in Section 6.1.1 removal of the core from the core barrel had the

potential to affect the integrity of the core. In some cases the core could be removed easily with

little disturbance, while in other cases force was needed and the core was recovered in a fractured

condition. In order to reduce the variable affect of core extraction on the RQD values, the integrity

of the re-cemented joints were tested by hand. Only where the joints could not be fractured by

hand was the core described as being solid for the purposes of measuring the RQD.

Fracture frequency is obtained by counting the number of natural fractures that occur per meter

length of core. The fracture frequency provided in the borehole logs was recorded per meter.

Where the fracture frequency exceeded 20 fractures per meter “>20” was recorded on the borehole

logs. Only numbers 0 to 20 and >20 were therefore recorded. The fracture frequency was

measured after the core had been handled to assess the integrity of the recemented joints.

5.2 STANDARD PENETRATION TESTS

Standard Penetration Tests (SPT’s) were undertaken in the boreholes at 1.00m intervals until

refusal of the SPT probe was obtained. The SPT apparatus consisted of an automated 63.5kg

hammer falling a distance of 760mm onto a string of rods attached to a standard split spoon

sampler (Raymond Spoon).

The number of blows per six increments of 75mm is recorded. The upper 150mm (i.e. the first two

blow counts) are considered “disturbed material” and are discarded. The sum of the blow counts for

the remaining 300mm is recorded as the SPT N-value.

Refusal was recorded when the blow count exceeded 25 blows per 75mm, which corresponds to

an SPT N-value in excess of 100.

The SPT probe could be advanced under the weight of the rods alone in some of the very soft or

very loose materials encountered on site. An SPT N-value of 0 was recorded when this occurred.

The SPT N-values are summarised in Table A3.3. The SPT N-values are also included in the

borehole logs (Appendix B) and the field results are included in the Daily Drilling Reports

(Appendix H).





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Table A3.3: SPT Test Results

Borehole Ref. Start Depth End Depth SPT N-value Material type

1.00 1.45 7 Sand

2.00 2.45 9 Sand

3.00 3.45 21 Gravel & cobbles

4.00 4.45 35 Gravel & cobbles

A0

5.00 5.00 >100 Silcrete

1.00 1.45 10 Sand

2.00 2.45 6 Sand

3.00 3.45 21 SandP1

4.00 4.45 7 Sand

P2 0.00 0.16 >100 Weathered basalt

P3 0.00 0.05 >100 Weathered basalt

0.00 0.45 6 Sand

1.00 1.45 3 SandP4

2.00 2.20 >100 Weathered basalt

0.00 0.45 26 Sand

1.00 1.45 10 Sand

2.00 2.2 1 Sand

3.00 3.45 13 Sand

4.00 4.45 25 Sand

P5

5.00 5.2 1 Sand

1.00 1.45 8 Sand

2.00 2.45 1 Sand

3.00 3.45 18 Sand

4.00 4.45 28 Sand

5.00 5.45 35 Sand

7.00 7.45 17 Sand

8.00 8.45 13 Sand

9.00 9.45 39 Sand

P6

10.00 10.17 >100 Weathered Basalt

0.00 0.45 0 Sand

1.00 1.45 0 Sand

2.00 2.2 1 Sand

3.00 3.45 10 Sand

4.00 4.45 6 Sand

P7


1.00 1.45 17 Gravel

2.00 2.45 21 Gravel

3.00 3.45 54 Sand & GravelP8


1.00 1.45 25 Gravel

2.00 2.45 41 Gravel

3.00 3.45 44 Gravel

4.00 4.45 16 Gravel

A9

5.00 5.45 38 Gravel





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5.3 LEFRANC PERMEABILITY TESTS

Lefranc permeability tests were undertaken at six locations within the un-consolidated soils

encountered in the boreholes. The Lefranc test is an in-situ ground investigation method used to

evaluate the local hydraulic characteristics of a soil. The tests were undertaken in accordance with

the French Standard NF P 94-132 of October 2000.

The Lefranc test method involves creating a cavity of known dimensions at the base of the

borehole within the subsoil to be tested. The cavity is bounded by the borehole bottom and part of

the sidewall and is connected to the surface of the soil by a tube. The test is undertaken by

producing a change in the hydraulic head inside the cavity, either by sampling water at a constant

flow rate throughout the test or by changing the hydraulic head at the start of the test before any

measurement is carried out.

For the purposes of this investigation the cavity was created using casing and a gravel filter

material. The procedure used was as follows:

• The casing was advanced to the base of the test level (base of borehole)

• Any soil within the casing was removed to surface by lowering the drill string and flushingwith clean water

• Filter material (gravel) was inserted into the casing to accumulate at the bottom of theborehole within the casing

• The casing was raised to a height equal to the length of the cavity

The test setup at each borehole position is illustrated diagrammatically in the Lefranc Test Sheets

included in Appendix C. The water levels were measured using a dip meter from within a temporary

piezometer installed within the casing.

The Lefranc tests (with exception of the test at BH A0) were undertaken according to the constant

flow rate test method by adding water to the borehole at a constant rate to increase the head in the

cavity. The test at BH A0 was carried out using the variable head test method by injecting water at

the start of the test to increase the head in the cavity.

At BH P5 and BH P6 two tests were undertaken on the same section of borehole using different

flow rates.

The locations, depths, type of the Lefranc tests preformed and estimated permeability coefficients

calculated from the test results are summarised in Table A3.4. The method of obtaining the

permeability coefficients and the shape factors used for the determination is provided below the

table.





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Table A3.4: Lefranc Tests Results

BoreholeDepth of test

(m)Test Method Soil type

Permeability coefficient(k)

A0 3.15 – 4.00Variable head (increased

head)

Clayey sand (alluvium) 3.1 x 10-7

m/s**

P1 3.30 – 5.50Constant flow rate(increased head)

Sand / silcrete / basalt 3.7 x 10-5

m/s *

P5Test A

5.3 x 10-4

m/s *

P5Test A

4.95 – 5.80Constant flow rate(increased head)

Sand (alluvium)

3.5 x 10-4

m/s *

P6Test B

2.6 x 10-4

m/s *

P6Test C

5.30 – 7.00Constant flow rate(increased head)

Sand (alluvium)

2.6 x 10-4

m/s *

P8 2.60 – 3.45Constant flow rate(increased head)

Sand (alluvium) /residual basalt

>1.10-6

m/s

A9 3.15 – 4.00

Constant flow rate

(increased head)

Silcrete gravel & silty

sand >1.10

-6

m/s

Notes * Calculated from equation k = Q/(F.H)

k - permeability coefficient (m/s)

Q – effective inflow (m3 /s)

H – Hydraulic head at equilibrium

F – shape factor calculated according to prEN ISO 22282-1

Annex B Equation 7

** Calculated from equation B.3 published in prEN ISO 22282-2

The test results and information required for further interpreting the Lefranc tests are contained in

the Lefranc Test Sheets included in Appendix C.

The tests undertaken at P5 and P6 indicate that the sandy alluvial soils have permeability

coefficients of between 2.6 x 10-4 m/s and 3.5 x 10-4 m/s (the latter value is taken from the results

of P5 Test B).

The tests undertaken at P8 and A9 indicate that the infiltration rates over the test sections were

low. The test water levels could not reach equilibrium within the available head provided by the

casing. Given that the Lefranc tests are undertaken over a relatively short period of time, the tests

are best suited to soils with a permeability coefficient greater that approximately 10-6 m/s.

Obtaining accurate permeability coefficients for soils of lower permeability may be unreliable. The

permeability coefficients for the tests undertaken at P8 and P9 are therefore indicated as >1.10-6

m/s.

Given the presence of clean, coarse grained alluvial sand observed at BH P8 (2.5-3.30m)

considerably higher permeability values should be used for estimating groundwater seepage rates

for construction purposes at this pier position.





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5.4 LUGEON TESTS

Fourteen Lugeon tests (packer tests) were undertaken within the basalt bedrock. Lugeon testing is

undertaken to assess the hydrological properties of various horizons within a borehole.

The tests were undertaken using a single packer apparatus. The test section is therefore defined

as the length of borehole between the lower end of the inflatable packer and the base of the

borehole during the test. The tests involved five consecutive water pump-in tests, each of ten

minutes duration, at the following pressures:

Stage 1: Low pressure (pressure “a”)

Stage 2: Medium pressure (pressure “b”)

Stage 3: Peak pressure (pressure “c”)

Stage 4: Medium pressure (pressure “b”)

Stage 5: Low pressure (pressure “a”)

The volume of water entering the test section was recorded at two minute intervals during each test

stage using a flow meter.

The test setup at each borehole position is illustrated diagrammatically in the Lugeon Test Sheets

included in Appendix D.

The locations, depths, water loss per stage and “Lugeon Value” of the Lugeon tests preformed are

included in Table A3.5.

Table A3.5: Lugeon Tests Results

Water loss (total litres / stage)Borehole

Depth of test(m) Stage 1 Stage 2 Stage 3 Stage 4 Stage 5

ReportedLugeonValue*

A0 6.00 – 8.19 7.4 16.2 34.8 17.2 3.5 7

A0 11.00 – 13.50 4.9 3.3 5.0 3.1 1.8 1

P1 8.00 – 11.00 0.1 0.2 0.5 0.1 0.0 0

P1 14.00 – 17.50 223.6 266.0 230.6 93.4 73.6 16

P2 2.33 – 3.93 0.0 14.9 69.2 57.3 36.1 0

P3 2.85 – 5.15 101.4 149.3 187.1 122.5 80.9 102

P3 8.01 – 12.01 59.6 92.5 149.9 93.1 59.3 13

P4 3.93 – 5.93 146.0 182.5 226.3 174.5 139.6 126

P5 8.11 – 11.11 150.7 207.2 217.4 149.5 91.3 121

P5 11.61 – 15.61 3.65 8.53 15.40 7.45 0.20 2

P6 11.50 – 13.46 136.4 203.5 251.9 155.6 82.9 60

P6 13.50 – 15.50 22.5 102.9 152.8 106.6 52.1 25

P8 5.00 – 7.00 0.3 3.1 15.2 0.0 0.0 2

A9 7.00 – 10.00 0.0 0.05 0.05 0.0 0.0 0

Notes * i) Reported Lugeon Value obtained according to the method of Houlsby, 1976

ii) Lugeon value = water taken in test (l/m/min) x [10 (bars) / test pressure (bars)]

The Lugeon test results and information required for further interpreting the tests are contained in

the Lugeon Test Sheets included in Appendix D.





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5.5 TRIAL PITS

Four trial pits were excavated by means of a tractor-loader-backhoe (TLB) adjacent to the landside

boreholes A0, P1, P8 and A9. The trial pits were excavated in order to recover soil samples for

laboratory testing. The trial pits enabled undisturbed block samples to be obtained for direct shear

box testing. A further advantage is that the soils are recovered at their natural in-situ moisture

content.

6 LABORATORY TESTING

Laboratory testing was undertaken on soil and rock samples recovered from the trial pits and

boreholes.

6.1 SOIL SAMPLES

The following laboratory tests were carried out on disturbed and/or undisturbed soil samples

recovered from the boreholes and trial pits:

• Grading Analyses and Hydrometer tests

• Atterberg Limit and Linear Shrinkage Determinations

• Direct shear testing

• Bulk density and dry density testing

• Moisture content testing

The following recovery methods were utilised to obtain the soil samples:

• Wash bore samples from the boreholes

• Split spoon samples from the SPT tests

• Disturbed bulk samples from the trial pits

• Undisturbed block samples from the trial pits

Moisture content testing was undertaken on site using an AND MX-50 moisture analyser. The

remaining testing was undertaken in South Africa by Civilab Civil Engineering Testing Laboratories.

Civilab is a South African National Accreditation System (SANAS) accredited testing laboratory

(Certification No. T0062).

Direct shear testing (shear box testing) was undertaken on both undisturbed block samples and on

disturbed samples remoulded to a specified dry density in the laboratory. All samples were

consolidated and saturated prior to shearing. Three load increments were utilised at normal stress

increments of 50, 100 and 200kPa. The tests were either undertaken at a shear rate of 1.2

mm/minute (undrained test) or 0.12 mm/minute (drained test).

The results of the laboratory testing are provided in Appendix E and are summarised in Tables

A3.6 to A3.9.



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Table A3.6: Particle Size Distribution and Atterberg Limit Determination Tests

PNo

Depth(m)

Sampling method Description

Clay S

TP A0 2.00 – 3.10Disturbed sample

from trial pitSlightly clayey slightly silty sand (alluvium) 5 1

TP P1 3.00 – 3.30Disturbed sample

from trial pitSlightly silty sand (alluvium) 2


from trial pitSlightly silty sand (alluvium) 3

BH P1 3.45 – 4.00Wash samplefrom borehole

Slightly silty sand (alluvium) 1

BH P6 3.00 – 7.00 Wash samplefrom borehole Slightly silty sand (alluvium) 2


from trial pitSlightly clayey, slightly gravelly, silty sand

(calcified residual basalt)6 2

TP A9 2.50 – 2.80Disturbed sample

from trial pitGravelly silty sand (silcrete in a calcareous silty

sand matrix)5 3

LL- Liquid Limit LS - Linear Shrinkage PI - Plasticity Index NP –

Table A3.7: Bulk Density and Dry Density from undisturbed samples

Trial Pit NumberDepth

(m)

Moisture Content(%)

In-situ bulk de

(kg/m

3

)A0 3.00 18.7 2037

P8 3.00 20.8 2023





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Table A3.8: Moisture Content Analysis undertaken on-site

No Depth (m) Sampling methodMoisture

Content % Soil type

1.00-1.45 Split spoon sample 14.4 Sand (Colluvium)

2.00-2.45 Split spoon sample 13.1 Silty sand (alluvium)

3.00-3.45 Split spoon sample 13.5 Clayey sandy gravel (alluvium)BH A0

4.00-4.45 Split spoon sample 11.8 Clayey sandy gravel (alluvium)

TP A0 3.00Disturbed sample

from trial pit14.8

Slightly clayey slightly silty sand(alluvium)

1.00-1.45 Split spoon sample 19.9 Gravelly silty sand (colluvium)

2.00-2.45 Split spoon sample 14.4 Gravelly clayey sand (alluvium)

3.00-3.45 Split spoon sample 11.3 Sand (alluvium)BH P1

4.00-4.45 Split spoon sample 18.3 Gravelly silty sand (alluvium)

TP P1 3.00-3.30Disturbed sample

from trial pit12.1 Slightly silty sand (alluvium)

1.00-1.45 Split spoon sample 13.7 Sand (alluvium)






BH P6


2.00* Split spoon sample 78.1 Organic silt (alluvium)2.40* Split spoon sample 19.8 Silty sand (alluvium)

3.0-3.45 Split spoon sample 15.9 Sand (alluvium)BH P7


1.00-1.45 Split spoon sample 17.3 Silt (Colluvium / alluvium)

2.00-2.45 Split spoon sample 18.5 Sand & gravel (alluvium)

3.00-3.45 Split spoon sample 10.0 Gravel (alluvium)BH P8

4.00-4.45 Split spoon sample 13.2 Clayey sand (residual basalt)

TP P8 3.00-3.20Disturbed sample

from trial pit24.3

Slightly clayey, slightly gravelly,silty sand (calcified residual basalt)

TP A9 2.50 Disturbed samplefrom trial pit 9.1 Gravelly silty sand (silcrete in acalcareous silty sand matrix)

BH A9 4.0-4.45 Split spoon sample 16.2Gravelly silty sand (silcrete in a

calcareous silty sand matrix)

* Approximate depth

Notes: i) Testing undertaken using an AND MX-50 moisture analyser

ii) Sample size approximately 5g per test

iii) Minimum of 5 tests undertaken per sample

iv) Samples preserved in sealed plastic sleeves prior to testing





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Table A3.9: Direct Shear Tests

NoDepth

(m)

Sample Type(Dry Density kg/m

3

specified forrecompaction)

Test type

Angle of Internal

Friction

(Peak Strength)Degrees

Cohesion

(Peak Strength)

kPa

TP A0 3.00 Undisturbed Drained 15.3 34.1

TP P1 3.00 – 3.30Remoulded(1600kg/m3)

Drained 40.4* 0*

BH P1 3.45 – 4.00Remoulded(1770kg/m3)

Undrained 20.6 68.1


Undrained 21.4 35.9


Undrained 23.5 37.9


Drained 24.0 60.6


Drained 38.0 4.0

* Best fit line results in negative cohesion. See test results sheet.

Notes: Undrained tests undertaken at a shearing rate of 1.2 mm/minute

Drained tests undertaken at a shearing rate of 0.12 mm/minute

Sample saturated prior to testing

Specified normal stress: 50, 100, 200kPa

The full direct shear test results are included in Appendix E.

6.2 ROCK CORE SAMPLES

The following laboratory testing was undertaken on rock core samples recovered from the

boreholes:

• Uniaxial Compressive Strength (UCS) tests with digital photography of the core at failure

• Measurement of apparent specific weight

• Measurement of absolute specific weight

•

Point load testing

The testing was undertaken in South Africa by ROCKLAB Rock Mechanics Laboratory. ROCKLAB

is a South African National Accreditation System (SANAS) accredited testing laboratory.

The rock encountered in the boreholes was typically very closely to closely jointed and fractured,

particularly at shallow depth. Obtaining sufficient lengths of intact core in order to undertake the

UCS testing was problematic and the samples were recovered selectively based on the availability

of intact core sticks of sufficient length for the tests.





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The presence of recemented joints and micro-fractures within the intact core sticks was

problematic during sample preparation and a number of samples were fractured in the laboratory

during preparation and could not be tested. Failure of a large proportion of the UCS tests took

place along existing planes of weakness within the rock. Interpretation of the UCS test results

should take into account the highly jointed and fractured nature of the rock being tested.

The full test reports for the UCS and point load tests are included in Appendix F.

7 GROUNDWATER LEVELS

Standpipe piezometers were installed in the landside boreholes in order to allow for monitoring of

the groundwater levels. The water levels recorded during the period that Geomechanics were

mobilised on site are contained in Appendix G and are illustrated in Figure A3.10.

Figure A3.10: Groundwater monitoring

8 SUMMARY OF THE BOREHOLE LOGS

A summary of borehole logs indicating the depth at which bedrock was encountered is provided in

Table A3.11. The full borehole logs are attached in Appendix B.

Basaltic bedrock was encountered in all ten of the boreholes. The rock was described as

amygdaloidal basalt in BH P7 between 5.25 and 12.55m.





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With the exception of BH P8 and A9, residual basalt soils (which are derived from the complete in-

situ weathering of the rock) were not encountered and weathered basalt rock was found to occur

directly beneath the overlying unconsolidated deposits.

The majority of the rock was found to be very closely jointed and fractured. However some of the

joints were recemented. Very closely to closely spaced sub-horizontal jointing and fracturing was

prominent in all of the boreholes. Medium to widely spaced sub-vertical to vertical joint sets were

also encountered over a large proportion of the core. Widely spaced joints dipping between

approximately 30 to 70 degrees were also observed.

The presence of noticeable open or partly open joints was observed in many of the riverside

boreholes.

Although the basaltic rock showed a general decrease in weathering with increasing depth,

irregular weathering was observed in many of the boreholes. Narrow bands (25mm or less) of

completely weathered rock or residual basalt soil were encountered within more competent rock.

These features appear to be associated with joints and have been recorded in the borehole logs.

Evidence of fault plains or zones of shearing were not observed in the borehole cores. Weakly

developed slickensides were, however, noted on two sub-vertical joints in borehole P7 between

15.40m and 18.10m. The weakly developed nature of these features indicates that the amount of

movement was limited.

Table A3.11: Bedrock levels obtained from the borehole logs

A0 P1 P2 P3 P4

Elevationat ground level 927.712 928.375 923.000 918.770 920.700

Bedrock level (meters)(Below ground level)

5.70 4.75 0.09 0.00 2.00

Elevation ofbedrock level

922.01 923.63 922.91 918.77 918.70

P5 P6 P7 P8 A9

Elevationat ground level

921.470 926.940 925.192 926.971 929.533

Bedrock level (meters)

(Below ground level) 5.95 9.60 5.25 4.18 5.50

Elevation ofbedrock level

915.52 917.34 919.94 922.79 924.03

Notes: i) Bedrock level refers to the level at which rock in any form was first encountered

in the borehole

ii) Bedrock level does not necessarily represent “competent rock”

iii) Bedrock level does not indicate or imply any foundation level and should not be

interpreted as such





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9 BEARING RESISTANCE OF THE FOUNDATION ROCK

The allowable bearing pressure on weak or fractured rocks depends on the compressibility andstrength of the rock mass and on the permissible settlement beneath the structure. The

compressibility of a rock mass is related to the uniaxial compressive strength of the intact rock, the

lithology and the nature, frequency and orientation of discontinuities (BS 0884 1986).

The assumed bearing resistance of the weathered and fractured rock encountered within the

boreholes has been estimated using method contained in the British Standard BS 0884 1986,

which is included in Eurocode 7 EN 1997-I:2004.

The assumption is provided for square pad foundations bearing on rock for settlements not

exceeding 0.5% of the foundation width.

For the purposes of estimating the bearing resistances the presence of open joints within the rock

mass has been assumed.

The assumed bearing resistance of the rock is provided in Table A3.12.

Table A3.12: Bearing Resistance of the Rock Foundation Materials

Borehole Depth Range Estimated Bearing Resistence*

5.70-8.69 1200 kPa

8.69-13.50 1600 kPa

13.50-15.20 2000 kPa

A0

15.20-17.50 2000 kPa

4.75-6.00 400 kPa

6.00-9.42 1500 kPa

9.42-9.65 1000 kPa

9.65-11.50 1500 kPa

11.50-11.84 1000 kPa

11.84-13.39 2500 kPa

13.39-15.24 2000 kPa

15.24-16.22 2000 kPa

P1

16.22-17.05 2500 kPa

To be continued





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0.30-1.00 400 kPa

1.00-2.60 2000 kPa

2.60-3.06 1000 kPa

3.06-5.10 2000 kPa

5.10-6.56 3000 kPa

6.56-7.80 2500 kPa

P2

7.80-12.01 4000 kPa

0-1.50 500 kPa

1.50-2.50 3500 kPa

2.50-3.35 3000 kPa3.35-5.15 3500 kPa

P3

5.15-12.01 4000 kPa

0-3.31 1200 kPa

3.31-4.80 2500 kPa

4.80-5.30 3000 kPa

5.30-7.30 3000 kPa

P4

7.30-14.20 5000 kPa

5.70-5.95 100 kPa

5.95-6.40 1000 kPa

6.40-9.20 3500 kPa

9.20-11.90 3000 kPa

P5

11.90-14.60 3500 kPa

9.60-11.00 300 kPa

11.33-13.25 400 kPa

13.25-20.90 3500 kPa

P6

20.90-22.40 4500 kPa

5.25-5.40 500 kPa

5.40-6.25 800 kPa

6.25-8.45 1500 kPa

8.45-12.55 3500 kPa

12.55-15.40 2500 kPa

15.40-15.60 1500 kPa

15.60-16.00 1200 kPa

P7

16.00-18.10 2500 kPa

To be continued





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4.18-4.35 400 kPa

4.35-7.00 500 kPa

7.00-8.80 800 kPa

8.80-12.70 1500 kPa

P8

12.70-16.70 3000 kPa

5.50-7.30 400 kPa

7.30-10.40 1400 kPa

10.40-12.60 2500 kPa

12.60-13.90 3000 kPa

A9

13.90-16.00 3500 kPa

* Notes: i) Estimated using the British Standard BS 0884 1986

ii) Estimate is provided for square pad foundations bearing on rock for settlements

not exceeding 0.5% of the foundation width

iii) Not corrected for depth factors

iv) Not corrected for foundations placed below ground water level

10 CONCLUSIONS

This factual report presents the results of a geotechnical investigation undertaken for the proposed

construction of a road and rail bridge over the Zambezi River at Kazungula.

The investigation indicates that the site is underlain by basaltic bedrock of the Karoo Igneous

Province. Weathered and fractured bedrock was encountered at depths of between 0 and 9.60m

below existing ground level which corresponds to between 915.5 and 924.0m above sea level. The

bedrock is overlain by younger sedimentary rock units of varying thickness.

The borehole logs and borehole photographs are included in Annexure B of this report.

The results of various in-situ and laboratory tests are summarised herein and the full results are

attached.

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REFERENCES

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 Institution of Civil

Engineers, Vol. 15.

Core Logging Committee of the South African Section of the Association of Engineering Geologists

(1976). A Guide to Core Logging for Rock Engineering. Proceedings of the Symposium on

Exploration for Rock Engineering, Johannesburg.

Johnson, C.R., Anhaeusser, C.R. and Thomas, R.J. (2006). The Geology of South Africa. Council

for Geoscience.

Weinert, H. H. (1964) Basic igneous rocks in road construction. Research Report 218, CSIR,

Pretoria.

Table of Appendices

APPENDIX A: PLANS

APPENDIX B: BOREHOLE LOGS & CORE PHOTOGRAPHS

APPENDIX C: LEFRANC PERMEABILITY TEST SHEETS

APPENDIX D: LUGEON TEST SHEETS

APPENDIX E: LABORATORY TEST RESULTS – SOIL SAMPLES

APPENDIX F: LABORATORY TEST RESULTS – ROCK CORE SAMPLES

APPENDIX G: GROUND WATER LEVEL MONITORING

APPENDIX H: DAILY DRILLING REPORTS





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APPENDIX A

PLANS





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APPENDIX B

BOREHOLE LOGS

CORE PHOTOGRAPHS





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APPENDIX C

LEFRANC PERMEABILITY TEST SHEETS





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APPENDIX D

LUGEON TEST SHEETS





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APPENDIX E

LABORATORY TEST RESULTS

SOIL SAMPLES





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APPENDIX F

LABORATORY TEST RESULTS

ROCK CORE SAMPLES





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APPENDIX G

GROUND WATER LEVEL MONITORING





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APPENDIX H

DAILY DRILLING REPORTS

appendix a3_rev 1.pdf

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