harbour report

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KENCH SURVEYS LIMITED

GEOTECHNICAL INVESTIGATION REPORT

ON THE

HARBOUR SITE

FOR

JOLOMI ENGINEERING SERVICES LIMITED

AT MUSHESHE FISH YARD,

OFF ENERHEN ROAD,

WARRI

Client: Consultants:Jolomi Engineering Services Limited, Kench Surveys LimitedWarri, Warri.Delta State Delta State

August 2010

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CONTENT

NOTATIONS iii

EXECUTIVE SUMMARY iv

1.0 INTRODUCTION 1

2.0 SCOPE OF WORK 1

3.0 SITE DESCRIPTION AND GEOLOGY 2

4.0 FIELD WORK 3

5.0 LABORATORY TESTS 5

6.0 SOIL STRATIGRAPHY 6

7.0 ENGINEERING PROPERTIES OF THE SOILS 7

8.0 DISCUSSIONS 9

9.0 BEARING CAPACITY CALCULATIONS Shallow Foundation 10

10.0 BEARING CAPACITY CALCULATIONS Pile Foundation 12

11.0 DESIGN LENGTH OF SHEET PILE 16

12.0 RECOMMENDATION 18

13.0 CONCLUSIONS 19

14.0 LIMITATIONS 20

References 21

APPENDICES

APPENDIX A: Site Plan

APPENDIX B: Borehole Logs

APPENDIX C: Index Summary

APPENDIX D: Atterberg Limits

APPENDIX E: Triaxial Shear Strength

APPENDIX F: Direct Shear Strength

APPENDIX G: Consolidation Results

APPENDIX H:Particle Size Distriution

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NOTATIONS

B width of raft foundation

b half the width of raft foundation in the calculation of settlementvalues

BS British Standard

c - undrained cohesion of the soil

Cv - coefficients of consolidation

f - unit skin friction

H - Thickness of strata under consideration = 2B

I - Influence factor from Bousinesqs chart

K - coefficient of lateral earth pressure

mv - coefficient of volume compressibility

Nq - bearing capacity factor

Po - effective overburden pressure of the soil at the point, kPa

q - unit end bearing capacity for driven piles

Qall - allowable bearing capacity for raft foundation for a safety factor of 3

Qs - safe bearing capacity for a limiting maximum settlement of 50mm for raftfoundation

Qu - ultimate bearing capacity for raft foundation

Sc - consolidation settlement

Si - immediate settlement

St - Total settlement = Immediate settlement + consolidation settlement

= Si + Sc

Soed - One dimensional consolidation calculated from laboratory oedometer test

Su - undrained shear strength of the cohesive soil

v - vertical stress, at the point under consideration, beneath the corner of arectangular foundation

4x v - vertical stress, at the point under consideration, beneath the centre of arectangular foundation

SPT - Standard Penetration Test

- pile bearing capacity factor = 0.5-0.50 for < 1.0 & 0.5-0.25 for >

1.0 - unit weight of soil

- ratio of undrained shear strength to overburden pressure = Su/Po

- friction angle between the soil and pile wall

- Applied pressure at point under consideration

- angle of friction taking as zero for undrained condition of the soil

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EXECUTIVE SUMMARY

Kench Surveys Limited was commissioned by Jolomi Engineering Surveys Limited to

carry out a geotechnical investigation at the site for its proposed administrative office,warehouse, jetty, harbour and slipway at its property site in Musheshe Fish yard, off

Enerhen road, Effurun near Warri in Delta State. The investigation is to obtain soil

parameters for the foundation design of the proposed facilities at the site. The scope

of the investigation, which was, carried out on August 22 and 23, 2010 includes the

exploration of two (2) number boreholes using the cable percussive drilling method.

All explorations were to a maximum depth of 20m below the existing ground level.

The stratigraphy reveals a stratum of loose to dense sand on the entire site overlaid

by a 4.5m thick layer of soft to firm clay at the approach of the site and a 4.0m thick

layer of clayey peat towards the waterfront.

From analysis, using the average shear strength value of 23kPa for a soft to firm

clay, the allowable bearing capacity for a rectangular footing founded at a depth of

1.0m below the ground level is observed to be between 45 and 65kPa, for a breadth-

length (B/L) aspect ratio between 0.1 and 1.0.

Individual pad footings founded at a minimum depth of 1.0m below the existing

ground level is recommended to support the administrative building. The warehouse

should be founded also on raft foundations founded at the same depth. The jetty

should be supported on driven concrete piles to check corrosion while the harbour

should be heldin by steel sheet piles. and harbour building. Settlements from the

pile foundations are not expected to exceed 50mm. However, pile load test should

be carried out on all piles driven to confirm their working loads.

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1.0 INTRODUCTION

Jolomi Engineering Services Limited is proposing the construction of administrative

building and a warehouse on their site at the Mosheshe Fish Yard, off Enerhen road,

Effurun, near Warri in Delta State. At the water front, the construction of a jetty and

an harbour are being proposed also. Kench Surveys Limited was contracted by

Jolomi Engineering Services Limited to carry out a geotechnical investigation on the

site for these facilities. The investigation is to obtain soil parameters for the

foundation design of the proposed facilities at this site. The scope of the

investigation, which was, carried out on August 22 and 23, 2010 includes the

exploration of two (2) number boreholes using the cable percussive drilling method.

All boreholes explorations were to a maximum depth of 20m below the existing

ground level.

2.0 SCOPE OF WORK

The detailed work scope for the investigation is as presented below:

(i) Carry out two (2) number soil boring at the designated locations to a

maximum depth of 20m below the existing ground level.

(ii) Perform Standard Penetration Test on cohesionless material encountered in

the borehole.

(iii) Perform standard laboratory tests on soil samples obtained from (i) above

and determine relevant soil properties.

(iv) Submit of a detailed report including:

(a) An assessment of the sub-soil conditions for the proposed project and

suggested soil improvement where necessary.

(b) Engineering properties of the soils encountered and their effects on the

project.

(c) Assessment of the suitability of the soil and recommendation of

appropriate foundation type and design parameters.

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3.0 SITE DESCRIPTION AND GEOLOGY

The project site is situated within the Musheshe Fish yard off Enerhen road in

Enerhen Community of Delta State Part of the site towards the water front is

occasionally flooded by virtue of the fact that the entire area was a Swamp forest in

Delta State. Delta State is one of the nine states of the Niger Delta region of Nigeria.

The local geology of the location is composed of sediments which are characteristic

of several depositional environments as the River Niger empties her load into the

Atlantic ocean. The tidal swamp forest covers a substantial area of the delta

coastline, with the exception of the zone adjacent to the river plains, where they are

overlain by recent deposits of river mouth sediments. The growth of plants on the

surfaces of this sediment aided the slowing down of the Niger River flow which

encouraged further plant growth. Slowly these sediment deposits had displaced

portions of the river water to give way to what we now have as the Enerhen

community, on which this site lies.

At the time of this investigation, the entire project site was bare and empty.

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4.0 FIELD WORK

The investigation comprised mainly drilling two (2) geotechnical boreholes.

Appendix A shows the location of the test points. The field work for the investigation

was carried out between August 22 and 23, 2010.

The boreholes were advanced using a cable percussion boring rig.

4.1 Boring

The boreholes were drilled by the shell and auger cable percussive method, using a

manual drilling rig. The manual drilling rig is fitted with a free fall auger. The auger is

lifted to a height of about 1.0m above ground level. At this height it is allowed to free-

fall under gravity to advance the boring. As the auger falls it cuts through the soil

such that the cut soil material is retained inside it by means of a non-return flap valve

(commonly called the clark) at its lower end. The auger is then brought to the

surface where the soil retained in it is emptied out and samples taken. To prevent

collapse of the borehole wall, the hole is lined with 100mm diameter steel casings

(commonly called shells).

4.1.1 Collecting Undisturbed Samples

Undisturbed samples were taken at approximately 1.0m intervals of depths in clays

and silts. This is done by driving thin-walled tube into the soil, using a U4 bomber to

its full length of 0.45m or otherwise penetration refusal. The tube is then pulled to the

surface, removed from the sampling hammer, labelled and waxed top and bottom to

prevent loss of natural moisture from the soil.

4.1.2 Collecting Disturbed Sample

Representative disturbed samples were taken at regular intervals of 1.0m depth, and

also when a change in soil type was observed. The samples were used for a detailed

and systematic description of the soil in each stratum in terms of its visual properties

and for laboratory analysis. The borehole log obtained is presented in Appendix B. A

large number of disturbed samples were taken for examination and laboratory

analysis.

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4.2 Groundwater Conditions

Field measurements of ground water showed that the ground water was observed at

a depth of 4.50m below the existing ground surface, at the time of the field work.

5.0 LABORATORY TESTS

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Detailed laboratory investigations are being carried out on representative samples

obtained from the borehole for the classification tests and other tests. All tests are

being carried out in accordance with BS1377:1990 Methods of test for soil for civil

engineering purposes. Brief comments on the tests are given below:

Classification

Atterberg consistency limit tests were carried out on the cohesive samples. The

results show that the samples are low to medium plasticity silty clay. The particle size

distributions of a number of representative samples of the cohesionless soils were

determined by sieve analysis. The results disclosed that the samples are

predominantly, fine to medium dense sand with occasional gravels as shown in

Appendix D.

Undrained Shear Strength

This type of test is usually performed on undisturbed samples of cohesive soils. Depending

on the consistency of the cohesive material, the test specimen is prepared by trimming the

sample or by pushing a mould into the sample. A latex membrane with thickness of

approximately 0.2mm is placed around the specimen. A lateral confining pressure of

600kPa to 1000 kPa is maintained during axial compression loading of the specimen.

Consolidation and drainage of pore water during testing is not allowed.

The test is deformation controlled (strain rate of 60%/h), single stage, and stopped when

an axial strain of 15% is achieved.

The deviator stress is calculated from the measured load assuming that the specimen

deforms as a right cylinder.

The presentation of test results includes a plot of a Mohr circle. The undrained shear

strength, Cu, is taken as the point of intercession of a common tangent to the semi-circles

and the ordinate of the chart.

6.0 SOIL SRATIGRAPHY

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The soil stratigraphy encountered on the project site as observed from the explored

boreholes are as presented in Appendix B - borehole logs. The stratigraphy reveals

a stratum of loose to dense sand overlain by a 4.0m thick layer of soft to firm clay

around borehole 1 and a 4.0m thick layer of clayey peat around borehole 2. The

sand stratum is observed, in the entire site, to the maximum 20.0m depth of the

investigation.

The soil profile is as presented below.

Table 1:The profile is as presented in table 1 below.

Stratum No. DescriptionAverage depth

(m)

1

CLAY, soft to firm, dark reddish

brown (in borehole 1)

PEAT, clayey, very soft, blackish grey

(in borehole 2)

0 - 4.0

2SAND, loose to dense, occasionally

clayey, light grey to whitish grey4.0 - 20

7.0 ENGINEERING PROPERTIES OF THE SOIL

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The engineering properties of the formation encountered during the investigation are

as summarised below.

7.1 THE SOFT TO FIRM CLAY

This surface soft to firm clay is characterized by moderate compressibility and,moderate moisture content. This clay stratum is encountered from the ground level

to a depth of 4.0m below the existing ground level.

The variation in the engineering properties is as presented below:

Min Max Mean

Moisture content (%) 47 47 47

Bulk unit weight (kN/m3) 19.20 21.60 20.40

Dry unit weight (kN/m3) 13.06 14.69 13.88

Liquid limit (%) 49 53 51

Plastic limit (%) 20 24 22

Plasticity index (%) 29 29 29

Liquidity index 0.80 0.94 0.87

Consistency index 0.20 0.06 0.13

Undrained strength (kPa) 23 23 23

7.2 THE CLAYEY PEAT

This surface, very soft clayey peat observed close to the water front is characterized

by very high compressibility and moderate moisture content. This peat is fibrous and

possesses no engineering property of significance. That it is fibrous confirms the fact

that the settlement cannot be predicted. Under any imposed stress, the organic

fibres will continually decompose and reduce in volume. This reduction in volume will

give rise to large unpredicted settlements. It is recommended that about 2.0m thick

of this material be removed and replaced with clean river sand. This will reduce the

overall settlement that would have resulted from the entire mass.

The variation in the engineering properties is as presented below:

Min Max Mean

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Moisture content (%) 89 94 92

Bulk unit weight (kN/m3) 19.22 21.46 20.34

Dry unit weight (kN/m3) 9.91 11.35 10.63

Liquid limit (%) 116 130 123

Plastic limit (%) 48 130 89

Plasticity index (%) 82 83 82

Liquidity index 0.50 0.74 0.62

Consistency index 0.50 0.26 0.38

Undrained strength (kPa) 8 8 8

7.3 LOOSE to DENSE SAND

The fine to coarse silty sand encountered immediately beneath the firm to stiff clay is

of medium dense to very dense sand. This sand formation presents an SPT N value

between 9 and 41. From the SPT values it is observed that the sand formation

increases in density with depth. This formation of sand is competent to support high

bearing pressures without excessive settlement.

The variation of the geotechnical parameters is as presented below:

Min Max Ave

Effective Particle Size, d10 (mm) 0.08 0.14 0.11

Mean Particle Size, d30 (mm) 0.09 0.27 0.17

Particle Size, d60 (mm) 0.16 0.60 0.30

Coefficient of Uniformity, Cu = d60/ d10 2.00 4.29 2.83

Coefficient of Curvature, Cc = d302/d10.d60 0.71 0.91 0.80

Angle of Frictional Resistance, 29 40 35

8.0 DISCUSSIONS

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The investigation was carried out with the aim of obtaining geotechnical parameters

for the administrative building, warehouse, jetty and harbour belonging to Jolomi

Engineering Services Limited on her property at the Musheshe Fish yard, Enerhen

near Warri. The 4m thick near surface soft to firm clay soil encountered toward the

entrance to the site is of moderate compressibility but the peat towards the water

front is of very high compressibility. This peat is characterized by very low shear

strength and high moisture content. This peat is fibrous and possesses no

engineering property of significance. The fibrous nature confirms the fact that the

settlement cannot be predicted. Under any imposed stress, the organic material will

decompose and reduce the entire volume of the mass. This reduction in volume will

give rise to large unpredicted settlements. As a result, it has to be removed to as

deep as 2.0m, and replaced with clean river sand, for the construction of the slipway.

This will minimize the overall settlement that would have resulted from the entire

mass.

The administrative building and the warehouse can be supported on raft foundations

directly on the formation. Settlements from these rafts should create no problems.

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9.0 BEARING CAPACITY CALCULATIONS Shallow Foundation(Administrative Building and Warehouse)

The ultimate bearing capacity, Qu, for shallow rectangular foundations on cohesive

soils, using consistency values of a soft to firm clay is given below as:

Qu = .Df. + 0.67c[1+0.3(B/L)]Nc

where = unit weight of soil at depth

Df = depth of foundation

c = shear strength of the soil

B = Foundation width

L = Foundation Length

Nc = Bearing Capacity factor

Below are bearing capacity charts for ultimate bearing capacity versus foundation

aspect ratios at various depth of foundation

Table 2: Values of Ultimate Bearing Capacity, kPa, for various foundation depth

Df B/L Ratio

(m) 0.1 0.2 0.5 1.0

0.5 111 114 123 138

1.0 120 123 132 147

1.5 129 131 140 155

2.0 137 140 149 164

Table 3: Values of Allowable Bearing Capacity, kPa, for various foundation depth

Df B/L Ratio

(m) 0.1 0.2 0.5 1.0

0.5 37 38 41 46

1.0 40 41 44 49

1.5 43 44 47 52

2.0 46 47 50 55

Below are the charts for both the ultimate and allowable bearing capacities

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Fig. 1: Ultimate Bearing Capacity Chart for foundations at different Breadth/Length ratios

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Fig. 2: Allowable Bearing Capacity Chart for foundations at different Breadth/Lengthratios

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9.1 SETTLEMENT Shallow Foundation

Total settlements for the allowable bearing capacity are within the limits of maximum

allowable settlement. Settlement of this formation under the administrative buildingwill not exceed the maximum allowable settlement were a raft on individual pad

foundation is used.

10.0 BEARING CAPACITY CALCULATIONS Pile Foundation(Jetty and Harbour)

The ultimate bearing capacity, Qu, of driven piles is determined by the equation

below:

Qu = q.Ab + f.As

where q = unit end bearing capacity = kPa

f = unit skin friction = kPa

Ab = gross base area of pile tip, m2

As = side surface area of pile, m2

10.1 End Bearing & Skin Friction in Cohesive Soils

For piles in cohesive soils,

The unit end bearing, q = 9. Su 9.1.1

The unit skin friction, f = .Su 9.1.2

Where, Su = undrained shear strength of the soil, kPa

10.2 End Bearing & Skin Friction in Cohesionless Soils

For piles in cohesionless soils,

The unit skin friction, f = K Po tan 9.2.1

The unit end bearing, q = po Nq 9.2.2

Where,

K = coefficient of lateral earth pressure

= friction angle between the soil and pile wall

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= 0.75 x (angle of frictional resistance)

Nq = bearing capacity factor

po = effective overburden pressure of the soil at the point, kPa

Chart of Ultimate Pile Capacity for Concrete Piles

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Fig. 3 Chart of Ultimate pile capacity for straight shaft steel pipe pile

Using a safety factor of 3 on the ultimate pile capacity, the chart for the allowable pile

capacity is as presented in figure 4 below.

Chart of Allowable Pile Capacity for Concrete Piles

Fig. 4 Chart of Allowable pile capacity for straight shaft steel pipe pile

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Table 4:Allowable Pile Capacity, kN for concrete pile at various depth (m)

Pile depth (m) 300mm diameter

pile

400mm diameter

pile

500mm diameter

pile

10 55 80 108

15 176 257 349

20 389 558 746

11.0 DESIGN LENGTH OF SHEET PILE

In cohesionless soil, C is zero.

The active and passive lateral earth pressure of soil can be written as

Ka=tan2(45- /2) is the active lateral earth pressure coefficient

Kp= tan2(45+ /2) is the passive lateral earth pressure coefficient, and

is internal friction angle.

is unit weight of soil, h is the height difference between the existing ground level

and the river-bed.

The lateral forces Pa is calculated as

Pa=Ka h2/2

Below the bottom of excavation, the sheet pile is subjected to active pressure on the

earth side and passive pressure on the side of the river-bed.

Where Kp is passive earth pressure coefficient. When the sheet pile rotates away

from the earth side, there are active pressure on the earth side and passive pressureon the river bed side.

Calculating embed depth D

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Once D is determined, the minimum embedded depth of entire sheet pile is equal to

h+D. Usually a factor of safety between 1.2 and 1.4 is applied to D, and the length of

sheet pile L is equal to h+D*FS. FS is factor of safety from 1.2 to 1.4.

Example 1: Design cantilever sheet pile in cohesionless soil.

Given:

Depth of existing ground level to river bed, h = 6 m

Take depth of sheet pile below the river bed as D

Therefore (h + D) = depth between existing ground level and bottom of sheet pile

Unit weight of soil, = 19.8 9.81 = 9.99 say 10.0 kN/m3

Average Internal friction angle, = 30 degree

Requirement: Design length of a cantilever sheet pile

Solution:

Design length of sheet pile:

Calculate lateral earth pressure coefficients:

Ka = tan2 (45- /2) = 0.333

Kp = tan2 (45+ /2) = 3

The lateral earth pressure at bottom of excavation is

pa =0.5Ka (h+D)2 = 0.5*0.333*10.0*(6 + D)2 = 1.665(6 + D)2

pp =0.5KpD2 = 0.5*3.0*10.0* D2 = 15.0D2

Taking moment of these forces about the base of the wall, we have

Mo = pa * (h+D)/3 - pp * D/3 = 0

1.665(6 + D)2 *(h+D)/3 - 15.0D2 *( D/3) = 0

0.555(6 + D)3 - 5 D3 = 0

Solving for the depth D by trial and error, we have

D = 5.55m , say 6.0m

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Checking

pa = 1.665(6 + D)2 = 1.665*122 = 239 kN

pp = 15 * 62 = 540 kN

pa * (h+D)/3 = 239 * 4 = 956 kNm

pp * D/3 = 1080 kNm

Length of sheet pile = h + D = 6 + 6 = 12m

Using a safety factor of 1.4 for D

Total length of sheet pile 6 + 1.4 * 6 = 14.4m

Use pile length of 15m from the existing ground level.

12.0 RECOMMENDATIONS

Considering the imposed load from the administrative building, which is not expected

to be more than a one-storey high, and the moderate compressibility of the soft to

firm clay, it is recommended that the administrative building and the warehouse be

founded on raft foundations. Driven concrete piles are preferred for the jetty area to

check the problem of corrosion to steel pipe piles. Analysis has been carried out for

300mm, 400mm and 500mm diameter concrete piles in this report. Other sizes can

be provided upon request.

The minimum embedded depth for the sheet piles is 15.0m below the existing ground

level, that is about 9.0m below the river bed. Sheet piles are commonly of steel

which are susceptible to corrosion hence, adequate cathodic protection should be put

in place to minimize corrosion of the sheet piles.

13.0 CONCLUSION

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Kench Surveys Limited was requested by Jolomi Engineering Surveys Limited to

carry out a geotechnical investigation on a six storey building along Airport Road,

Warri in Delta State. The investigation was by means of two (2) number boreholes to

a maximum depth of 20m.

Field and laboratory investigations revealed a surface soft to firm clay spanning to a

depth of 4.0m below the existing ground level. Beneath the clay, the formation

presents a stratum of loose to dense to the final 20.0m depth of investigation.

Determination of ultimate bearing capacity using the average cohesion of a soft to

firm clay of 23kPa gave an ultimate bearing capacity of 120kPa for a rectangular

footing founded at a depth of 1.0m below the ground level. Using a safety factor of 3,

the allowable bearing capacity for this soil at this depth is observed to be about

40kPa.

Considering the moderate compressibility of the surface soft to firm clay, the

administrative building and the warehouse can be founded on a raft, but the jetty can

only be founded on piles. The sheet piles should be taken to a minimum depth of

15.0m below the existing ground level that is about 9.0m below the river bed. Driven

concrete piles are preferred for the jetty area to check the problem of corrosion to

steel pipe piles.

Settlement of the piles is not expected to be more than 25mm where the maximum

imposed load on the group is taken as half the total number of single piles in the

group multiplied by the allowable bearing capacity. However, pile load tests should

be carried out on all piles installed to confirm their work load.

14.0 LIMITATIONS

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This investigation is carried out in accordance with accepted geotechnical

engineering practice. The recommendations and conclusions reached in the report

are based on the data obtained from soil boring, and the laboratory analysis. It is not

anticipated that the soil conditions will vary significantly from those described.

However, should the soil conditions during actual construction vary, it would be

necessary to evaluate the engineering significance of such variations which could

result in further investigations and supplemental recommendations.

Suv. Chris Ojukoko

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References

1. Bowles, J. E, (1997); Foundation Analysis and Design, McGraw-Hill Companies

Inc.; 5th edition

2. Gopal, R. & Rao, A.S.R, (1991); Basic and Applied Soil Mechanics, pages 474

-545; New Age International Publishers; 2nd edition.

3. Murthy, V. N. S, (2007); Textbook of Soil Mechanics and Foundation

Engineering, page 630; CBS Publishers; 1st edition.

4. Tomlinson, M. J. (1994); Pile Design and Construction Practice; E & F N Spon; 4th

edition,

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