GROUND IMPROVEMENT

SITE INVESTIGATON

November 2009

Lankelma ltd Cold Harbour Barn Cold Harbour Lane Iden, East Sussex

TN31 7UT U.K.

T: +44 (0)1797 280050 E: info@lankelma.com

www.lankelma.com

Gardline Lankelma - Abu Dhabi simon.mallen@gardline.com

T: +971 (0)566 014916

2

Contents

1. Introduction 3

2. Role of the CPT 3

3. Compliance testing 4

4. Settlement of deep compaction fills 5

5. CPT plant 6

Appendix A

Soil behaviour charts

Appendix B

Influence of compressibility on normally consolidated, uncemented, unaged predominantly quartz sands

Appendix C

Plant capabilities

Appendix D

Soil parameters

Appendix E

Case studies

3

1. Introduction

In general terms ground improvement may be considered to be “when the

engineer forces the soil to adapt to the project requirements by altering its natural

state, rather than changing the engineering design in response to the natural

limitations of the soil”.

An overview of ground improvement techniques includes:

Densification – vibro and dynamic compaction; blasting and compaction

gravity.

Consolidation – pre-loading; vertical drains; electro-osmosis and vacuum

consolidation.

Reinforcement – soil nailing; piles; stone columns and fibre reinforcement.

Weight Reduction – wood; fly-ash; slag; tyres and geofoam.

Chemical Treatment – soil mixing; lime columns and jet/fracture grouting.

Thermal Stabilisation – ground freezing; vitrification

Biotechnical Stabilisation – brush matting; bush layering

Geosynthetics – geotextiles; geogrids and geomeshes.

A number of these techniques readily lend themselves to investigation and

compliance testing with the CPT.

2. Role of the CPT

For non-cohesive sands and silty sands requiring densification by the techniques outlined above, the CPT has been found to be one of the best methods to monitor and document the effect of densification due to the continuous and repeatable nature of the CPT process and data (see figure 1).

For shallow compaction the CPT can also be useful in checking the variability of a fill compacted in layers, or in checking whether unsatisfactory material has been left below a fill.

Figure 1

● before compaction

o after compaction

qc (MPa)

0

1

2

3

4

5

6

7

8

9

Depth

(m

)

4

In the improvement of cohesive soils by means of surcharge, with or without

vertical drains, the primary task is the monitoring of the rate of dissipation of

generated excess pore water pressures, as well as the assessment of general

variations of hydraulic conductivity of the soil. For these activities a cone

penetrometer with an additional pressure transducer (piezocone) is required.

A selection of guidelines to the zone of soil behaviour where vibrocompaction

techniques are most applicable are given on the CPT soil behaviour charts

presented in appendix A.

3. Compliance Testing

The required effect of any deep compaction technique can be set directly in terms

of measured cone resistance, or in terms of “equivalent relative density”.

Other analytical approaches that utilise the CPT platform for compliance testing of

deep compaction projects include the full displacement push pressuremeter and

the seismic cone.

The shear wave velocity obtained from the seismic cone, like the pressuremeter,

can be directly related to the small strain shear modulus (Go), and is therefore a

direct measure of the soil stiffness. Hence, a compaction specification of

compliance criterion could also include a minimum normalized shear wave

velocity, or the pressuremeter limit pressure.

A further advantage in earthquake prone geographic regions, is that the shear

wave velocity can be used as an additional measure of liquefaction potential,

especially in silty sands.

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4. Settlement of Deep Compaction Fills

The settlement analysis is fundamental to the design of most compaction applications. The analysis requires a knowledge of the soil compressibility, that is, the soil modulus and preconsolidation stress. Since the Factor of Safety against bearing capacity failure is usually high for foundations on coarse grained soil, the designer is interested in a modulus, E25, for an average applied stress limited to a value equal to about 25% of the estimated ultimate bearing resistance. The modulus can be obtained directly from the seismic cone shear wave velocity, or the full displacement push pressuremeter, or indirectly from the average cone tip resistance as follows:

E25 = α qt where E25 = secant modulus for a stress equal to about 25% of the ultimate stress. α = an empirical coefficient qt = cone resistance

A simple approach promoted by the Canadian Foundation Engineering Manual (CFEM 1992) states that the ratio between E25 and qt is a function of both soil type and compactness and is presented on Table 1. Table 1.

α = E25 / qt from static cone penetration tests.

The above values of E25 apply to a settlement analysis that can be

assumed to behave as linearly elastic media.

Soil Type α = E25 / qt

silt and sand 1.5

compact sand 2.0

dense sand 3.0

sand and gravel 4.0

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5. CPT Plant

A variety of CPT units are available for deep compaction verification and

compliance testing purposes. Plant type selection should assess whether

wheeled or track mounted units are appropriate for the surface traffic conditions.

Appendix A

Guideline for soils suitable for vibrocompaction techniques

Soil classification for deep compaction based on the Eslami-Fellenius chart

Soil classification for deep compaction based on CPT data

Appendix B

Influence of compressibility on normally consolidated, uncemented, unaged

predominantly quartz sands (after Jamiolkowski et al 1985)

Appendix C

All Lankelma CPT units can deploy the following devices:

Cone penetration testing

Friction cone - cone tip and friction sleeve resistance

Piezocone - cone tip and friction sleeve resistances and porewater pressure

Seismic cone - as the piezocone, but with the measurement of shear wave velocity and hence the small strain shear modulus, Gmax

Soil moisture probe - as the piezocone, but with the additional in-situ water content, temperature and soil conductivity measurement

Environmental probes - a variety of probes are available including fuel fluorescence detection, resistivity, conductivity and temperature

Shear vane equipment - Lankelma can deploy a Geonor penetration shear vane for the assessment of in-situ undrained shear strength

Push full displacement pressuremeter - to assess in-situ soil stiffness

Sampling

Soil sampling - fixed piston MOSTAP samples, thin wall Shelby tubes, push windowless samples

Geotechnical instrumentation

Instruments include - conventional standpipes and standpipe piezometers, vibrating wire piezometers, gas monitoring wells, inclinometers

See our website www.lankelma.com for further details.

Appendix D

Soil parameters and ground types

The applicability and usefulness of in-situ tests

Applicability:

A = high; B = moderate; C = low; - = none

* ф = will depend on soil type

Soil parameter definitions:

u = in-situ static pore pressure

ф’ = effective internal friction angle

su = undrained shear strength

mv = coefficient of compressibility

cv = coefficient of consolidation

k = coefficient of permeability

G0 = shear modulus at small strains

σh = horizontal stress

OCR = overconsolidation ratio

CPT cone penetration testing:

120 – 150m per day

Continuous profile

Soil characterised in-situ

Instantaneous results

Minimal soil disturbance

High quality, repeatable results

Electronic – fast, flexible data transfer

Gro

un

d t

ype

Pea

t

B

A

A

A

A

A

B

Cla

y

B

A

A

A

A

A

A

Silt

B

A

A

A

A

A

-

San

d

A

A

A

A

A

A

-

Gra

vel

B

C

C

- - B

-

Soft

rock

C

C

C

C

C

C

-

Har

d

rock

- - - - - - -

Soil

Par

amet

ers

OC

R

C

C

B

B

B

C

B/C

σh

- C

B/C

B/C

B

- -

Go

C

C

B

B

A

C

-

k - - - B

B

- -

c v

- - - A/B

A/B

- -

mv

- C

C

B

B

- -

S u

C

C

B

B

A/B

C

-

*ф’

C

C

C

B

B

C

A

u

- - - A

A

- -

Pro

file

B

A/B

A

A

A

B

C

Soil

typ

e

C

B

B

A

A

A

B

Pen

etro

met

er

Dyn

amic

Mec

han

ical

Elec

tric

(C

PT)

Pie

zoco

ne

(CP

TU)

Seis

mic

(SC

PT/

SCP

TU)

Stan

dar

d p

en

etra

tio

n t

est

(SP

T)

Van

e t

esti

ng

Appendix E

Two case studies

1. Ground Improvement at Great Yarmouth, UK

The outer harbour, Great Yarmouth, is currently under construction – a project

undertaken by a Van Oord/Bam Nuttall joint venture. With a view to expanding Great

Yarmouth’s port operational capabilities, the outer harbour will service a whole range of

ships including freight ferries and container ships.

1,600,000m3 of dredged sand

The project involves the dredging of 1,600,000m3 of sand from in and around the harbour

to allow the reclamation of around 17 hectares of land.

Currently, dredging and placement of the sand has been completed by Van Oord in the

surrounding areas of the harbour. This material has been hydraulically pumped into areas

surrounding the quay walls to depths of over 12m. Levelling of the reclaimed land started

in late May 2009.

Pre and post compaction

Lankelma’s role in this project is to test the level of pre and post compaction of the placed

material. This will provide the client with an indication of what further works may be

required to minimize settlements to structures that are constructed on the site. The CPT

has proved to be an ideal technique for collecting this form of information. It readily

provides verification and specification compliance of the placed sand, and allows the

rapid identification of any weak zones within the fill that may require further compaction.

Track truck excellence

Testing was carried out by our combination track truck vehicle – UK15. This rig excelled

in this instance; wheeled operations allowed quick mobilization and rapid movements

around staging areas, whilst track deployment of the unit was necessary for traversing the

reclaimed land due to the loose surface sand. The use of both trafficking modes meant

for rapid and safe testing.

2. Ground Improvement at a port in the UAE

Gardline Lankelma carried out CPTs at one of the new major ports that are being

developed in the Gulf region. The port is based in the UAE, with newly reclaimed land

stretching 4km out from the shore

Testing 24/7

Operations were soon increased to 24/7 operations to cope with the high volume of

testing that was needed, and to keep up with the dredging activities. Piezocone tests

were carried out pre and post vibrocompaction, and also to test the strength of the gravel

columns. 7,518m of tests were completed.

Dynamic compaction circa 1629