jubilee line - site investigation - · pdf file1 student no. eep50181 1.0 summary this...

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Student no. eep50181

1.0 SUMMARY

This Geotechnical Report relates to a Site Investigation undertaken by Messrs Soil Mechanics

Limited on behalf of London Underground Limited involving Package 4 of the proposed

Jubilee Line Extension in the Bermondsey area of London.

A total of twenty (20 no.) boreholes (14 Cable Percussive, 2 Cable Percussive followed by

rotary drilling, 2 open hole drilled then rotary drilled, 2 Cable Percussive and Self-Boring

Pressuremeter tests) were completed across the site in order to determine the nature and

consistency of the soils beneath the site. This programme of works commenced on the 24th

September, 1990 and ended on the 14th

November, 1990. Drilling depths range from -24.93

mOD (27.60 mbgl) in BH 413P to -49.84 mOD (53.05 mbgl) in BH404T, with the majority

of excavations being completed to a depth of 30.00 to 40.00 mbgl. The soils encountered

include Made Ground, Alluvium and Terrace Gravels (Superficial deposits) overlying solid

geology of the London Clay Formation, Lambeth Group, Thanet Sand Formation and Upper

Chalk Formation. Piezometers were subsequently installed following excavations, and

monitoring completed.

Following this drilling programme laboratory tests were undertaken on selected samples from

a range of stratigraphic units. Properties of these soils are as follows:

Bulk unit

weight

Undrained shear

strength

Effective

Cohesion

Angle of shearing

resistance

Coefficient of

permeability

γ cu c' φ' k

(kN/m³) kN/m² kN/m² (°) (m/s)

MADE GROUND 15 to 19 15 to 70 0 22 to 35 1x10-2

to 1x10-6

ALLUVIUM 16 to 20 25 to 50 0 22 to 29 1x10-4

to 1x10-6

TERRACE GRAVELS 19 to 20 N/A 0 34 5x10-3

to 5x10-6

LONDON CLAY 18 to 20.5 SPT'N' x 4.6 0 to 12 24 to 28 1x10-7

to 1x10-9

BLACKHEATH BEDS 19 to 20 75 to 300 0 20 to 25 1x10-5

to 1x10-7

UPPER SHELLY CLAY 17 to 22 25 to 400 0 to 15 28 to 32 1x10-6

to 1x10-8

UPPER MOTTLED CLAY 19 to 21.5 25 to 400 0 to 15 28 to 32 1x10-6

to 1x10-8

LAMINATED BEDS 20 to 22

100 to 150 (silt)

100 to 300 (clay) 0 to 10

28 (Clays) 28 to 42

(Sands) 1x10-4

to 1x10-7

LOWER SHELLY CLAY 20 to 22

100 to 200 (silt)

200 to 310 (clay) 0 to 15 28 to 32 1x10-6

to 1x10-8

LOWER MOTTLED CLAY 19 to 22

25 to 100 (silt) 100

to 300 (clay) 0 to 15 28 to 32 1x10-6

to 1x10-8

PEBBLE BED 19 to 21.5 N/A 0 37 to 44 1x10-3

to 1x10-6

GLAUCONITIC SAND 20 to 22

10 to 120 (fine

soils) 0 to 10

43 to 44 (granular

soils) 1x10-3

to 1x10-6

THANET BED 20 to 22 N/A 0 40-44 1x10-2

to 1x10-5

BULLHEAD BED 20 to 22 N/A 0 40-44 1x10-2

to 1x10-5

UPPER CHALK 20 to 22 N/A 0 42-44 1x10-1

to 1x10-2

Two phreatic surfaces at approximately -1.00 mOD and -7.00 mOD are identified from

piezometer data, indicating pore pressures within the soils at or about hydrostatic pressures.

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CONTENTS:

1.0 SUMMARY ......................................................................................................................... 1

2.0 INTRODUCTION ............................................................................................................... 4

3.0 SITE DETAILS ................................................................................................................... 4

3.1 TOPOGRAPHY ............................................................................................................... 4

3.2 GEOLOGY ...................................................................................................................... 4

3.2.1 Made Ground ............................................................................................................ 5

3.2.2 Alluvium (includes Peat) .......................................................................................... 5

3.2.3 River Terrace Gravels ............................................................................................... 5

3.2.4 London Clay.............................................................................................................. 5

3.2.5 Blackheath Beds........................................................................................................ 5

3.2.6 Reading Formation – Lambeth Group ...................................................................... 5

3.2.6.1 Upper Mottled Clay ........................................................................................... 5

3.2.6.2 Lower Mottled Clay ........................................................................................... 6

3.2.7 Woolwich Formation – Lambeth Group ................................................................... 6

3.2.7.1 Upper Shelly Clay .............................................................................................. 6

3.2.7.2 Laminated Beds ................................................................................................. 6

3.2.7.3 Lower Shelly Clay ............................................................................................. 6

3.2.8 Upnor Formation – Lambeth Group ......................................................................... 6

3.2.8.1 Pebble Bed ......................................................................................................... 6

3.2.8.2 Glauconitic Sand ................................................................................................ 7

3.2.9 Thanet Sand Formation ............................................................................................. 7

3.2.9.1 Thanet Beds ....................................................................................................... 7

3.2.9.2 Bullhead Bed ...................................................................................................... 7

3.2.10 Upper Chalk Formation .......................................................................................... 7

4.0 GROUND INVESTIGATION............................................................................................. 7

4.1 EXCAVATIONS ............................................................................................................. 8

4.2 IN-SITU TESTING ......................................................................................................... 9

4.3 INSTALLATIONS ........................................................................................................ 10

4.4 SAMPLING ................................................................................................................... 10

4.5 LABORATORY TESTING........................................................................................... 10

4.6 GROUNDWATER MONITORING ............................................................................. 11

5.0 GROUND CONDITIONS ................................................................................................. 11

5.1 STRATIGRAPHY ......................................................................................................... 11

5.2 GROUNDWATER CONDITIONS ............................................................................... 12

5.3 GEOTECHNICAL CHARACTERISATION ............................................................... 12

5.3.1 Made Ground .......................................................................................................... 12

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5.3.2 Alluvium ................................................................................................................. 13

5.3.3 Terrace Gravel ........................................................................................................ 14

5.3.4 London Clay............................................................................................................ 15

5.3.5 Blackheath Beds...................................................................................................... 17

5.3.6 Upper Shelly Clay ................................................................................................... 18

5.3.7 Upper Mottled Clay ................................................................................................ 19

5.3.8 Laminated Beds ...................................................................................................... 21

5.3.9 Lower Shelly Clay .................................................................................................. 22

5.3.10 Lower Mottled Clay .............................................................................................. 24

5.3.11 Pebble Bed ............................................................................................................ 25

5.3.12 Glauconitic Sand ................................................................................................... 27

5.3.13 Thanet Bed ............................................................................................................ 28

5.3.14 Bullhead Bed ......................................................................................................... 29

5.3.15 Upper Chalk .......................................................................................................... 30

6.0 CONCLUSIONS................................................................................................................ 31

7.0 REFERENCES .................................................................................................................. 33

FIGURES:

1. SITE LOCATION PLAN

2. BOREHOLE LOCATION PLAN

3. GEOLOGICAL MAP

4. CROSS SECTION BH401-BH409

5. CROSS SECTION BH409-BH419

6. PORE PRESSURE VS REDUCED LEVEL

7. SPT VS REDUCED LEVEL

8. MOISTURE CONTENT VS REDUCED LEVEL

9. PLASTICITY CHART

10. UNDRAINED SHEAR STRENGTH VS REDUCED LEVEL

11. SULPHATE & pH DATA

APPENDICES:

1. BOREHOLE LOGS

2. LABORATORY TEST RESULTS

3. PIEZOMETER READINGS

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2.0 INTRODUCTION

A Site Investigation was undertaken by Messrs Soil Mechanics Limited in 1990 - carried out

in accordance with the 1987 specifications for Ground Investigation published by the

Department of Transport (Attewell, 1995, p. 39).

These works were completed on behalf of London Underground Limited and involved

Package 4 of the proposed Jubilee Line Extension, comprising of 20 boreholes (18 Cable

Percussive, 2 Rotary) sited in the Bermondsey area of London. Drilling works were

completed on the 16th

November, 1990.

The purpose of the investigation was to determine the ground conditions prior to the proposed

tunnelling in the Bermondsey area.

The following factual and interpretative report describes the works undertaken and presents

copies of the test data obtained.

3.0 SITE DETAILS

3.1 TOPOGRAPHY

The site is represented by the obtained borehole data of Package 4, and follows the proposed

tunnelling route of the extension works southeast of London Bridge Station in Bermondsey,

eastwards towards Canada Water in Rotherhithe.

In view of the proposed tunnelling programme, the site extents (in Easting’s and Northing’s)

are considered to be linear, running from 533343, 179834 (BH401) in the east, to 535222,

179445 (BH417) in the west (Figs. 1 & 2). This generally follows the River Thames at a

distance of approximately 400m from the south bank across the linear run. In plan view, the

tunnel is understood to follow the overland train line southeast of Tower Bridge Station

towards South Bermondsey Station for approximately 600m before curving eastwards and

east-north-eastwards beneath Jamaica Road to the newly proposed Bermondsey Tube Station.

Following on from Bermondsey Tube Station the proposed tunnel route continues eastwards

beneath Southwark Park. The extent of this site area terminates at the corner of Neptune

Street and Moodkee Street on the ‘Canada Estate’.

Across the site the street levels are relatively flat, ranging from 1.9mOD in the western

extent, to 3.6mOD in the east (EDINA, 2010).

3.2 GEOLOGY

The site is considered to be located on a number of solid and drift deposits at or near ground

level (Fig. 3) identified in BGS solid and drift 1:50,000 maps (256 - North London; 270 -

South London). For simplicity, the geological units which are likely to be encountered at

depth across the site, from superficial to solid geological units are described below in order of

youngest to oldest.

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3.2.1 Made Ground

Often very variable in thickness, these deposits are representative of the urbanisation and

industrial development (Burland et al. 2001, p62). This stratum can be considered as highly

variable in nature, consisting of a mix of concrete, rubble, brick and refuse intermingled with

gravel and sands frequently within a matrix of silt or clay.

3.2.2 Alluvium (includes Peat)

This stratum is localised around the River Thames, generally resting unconformably upon

River Terrace Gravels (Ellison, 2004). The Alluvium consists predominantly of silty clay and

clayey silt, with locally developed beds of fine-to coarse-grained sand. Interbedded peat is

known to occur eastwards of Southwark and Westminster, with the most extensive deposits

extending west to the Rotherhithe tunnel (Ellison, 2004).

3.2.3 River Terrace Gravels

These deposits consist of variable proportions of sand and gravel, having been deposited in a

braided river system approximately 5km wide across the River Thames floodplain (Ellison,

2004). The appended geological map (Fig. 3) suggests that deposits in this region of London

are representative of the Taplow Gravel Formation, resting unconformably upon the solid

geology of the area.

3.2.4 London Clay

The London Clay Formation is predominantly argillaceous in its upper part, with the majority

of the formation comprising overconsolidated heavily bioturbated, fissured bluish-grey

slightly calcareous, silty to very silty clay (Ellison, 2004) often containing pyrite and

carbonate concretions (claystone) of ferroan calcite (Huggett, 1994 in Ellison, 2004). This

upper part is often oxidised and weathered to a brown colouration, whilst the basal unit is

notably sandier and siltier than the upper horizons (Burland et al, 2001).

3.2.5 Blackheath Beds

Underlying the London Clay, this stratum is generally less than 1m thick (Burland et al,

2001), and generally comprises of sands, gravels and pebble beds (Hight et al. 2004; Ellison,

2004).

3.2.6 Reading Formation – Lambeth Group

3.2.6.1 Upper Mottled Clay

Identified principally within cores in central and eastern London, this stratum consists

predominantly of mottled clay, silty clay and silts with colours including pale brown, pale

grey-blue, dark brown, pale green, red-brown and crimson, based upon the oxidation state of

the constituents (Ellison, 2004). At the base of this unit laminated sand and/or silt with minor

burrowing and local ripple laminations are evident (Hight et al, 2004).

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3.2.6.2 Lower Mottled Clay

Although similar to the Upper Mottled Clay, this lower horizon also includes purple to the list

of potential colourations (Ellison, 2004). Furthermore, it is also noted to contain carbonate

nodules up to 0.5m in diameter, particularly in the top parts – in east London these appear to

have coalesced to form a limestone up to 1.6m thick (Hight et al, 2004). Minor amounts of

irregularly cemented calcareous clayey sands are recorded in east London, becoming

increasingly dominant further eastwards (Hight et al, 2004).

3.2.7 Woolwich Formation – Lambeth Group

3.2.7.1 Upper Shelly Clay

Distributed mainly in south London between Westminster and Bermondsey (Ellison et al,

2004; Height et al, 2004), this strata is generally a maximum thickness of 3m, comprising

grey shelly clay thinly interbedded with grey-brown silt and fine sand (Height et al, 2004).

Locally, there is a weakly cemented shell bed up to 0.43m thick, whilst between Bermondsey

and Lewisham a continuous grey limestone bed (the Paludina Limestone) can be identified,

with a thickness of 0.1-1.83m (Ellison, 2004).

3.2.7.2 Laminated Beds

Generally resting conformably on the Lower Shelly Clay, this stratum generally comprises of

thinly interbedded and laminated fine- to medium-grained sands, silts and clays with

scattered shells (Ellison, 2004). Localised bodies of sand of thicknesses up to 4m – probable

buried channels – are known to occur particularly around the Lambeth and Bermondsey

areas, and typically comprise of pale olive to pale brown medium-grained well sorted sands

(Hight et at, 2004).

3.2.7.3 Lower Shelly Clay

Generally thickening from central London towards the south-east, this rests disconformably

on the Lower Mottled Clay of the Reading Formation, whilst the top of the unit is generally

sharp or transitional with the Laminated Beds or the Upper Mottled Clay (Ellison, 2004). The

predominant lithology is that of dark grey to black clay, with abundant shell fragments (Hight

et al, 2004). Some beds are almost entirely formed of weakly cemented shells, whilst less

often brownish grey clay beds, slightly cemented with siderite (Ellison, 2004) are identifiable

through this highly variable stratum. An oyster-rich bed can occur locally near the base

(Hight et al, 2004).

3.2.8 Upnor Formation – Lambeth Group

3.2.8.1 Pebble Bed

This unit can only be identifiable as a separate substratum from the lower Glauconitic Sand

unit in the London area (Ellison, 1991 in Hight et al, 2004).In this area this strata is up to 3m

thick, generally comprising of well-rounded flint pebbles, generally less than 30mm in

diameter, but have been identified as large as 200mm (Hight et al, 2004; Ellison, 2004).

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3.2.8.2 Glauconitic Sand

Dominated by fine- to medium-grained sand and clayey sands with variable amounts of

glauconite grains of fine to medium sands – grey to greenish grey when fresh, weathering to

pale grey-brown and yellow brown (Hight et al, 2004). Localised carbonate concretions have

developed either as hard irregular masses or powdery patches up to 0.5m in diameter (Ellison,

2004). Sporadic beds of well-rounded flint pebbles (Hight et al, 2004) occur throughout this

unit, as do clay dominated units of up to 0.3m thickness (Ellison, 2004).

It is important to note that the relationship between the Lambeth Group Formations is most

complex in London’s central and south-east extents, (Ellison, 2004), with interbedding

between the Reading and Woolwich Formations common, and the Upnor Formation less so.

3.2.9 Thanet Sand Formation

3.2.9.1 Thanet Beds

Consisting of a generally coarsening-upwards sequence of fine-grained heavily bioturbated

grey sands (Ellison, 2004), these beds reach a maximum thickness of approximately 30m

within the London Basin (Royse et al, 2008). The lower beds are noticeably clayey and silty,

whilst bioturbation structures are identifiable by wisps of dark grey clay and silty clay

(Ellison, 2004).

3.2.9.2 Bullhead Bed

Marking the bottom of the Thanet Sand Formation, this bed is considered to be a basal

conglomerate, consisting of sporadic rounded black flint pebbles (Royse et al, 2008) set

within a dark greenish grey, clayey fine- to coarse-grained sandy matrix with glauconite

pellets (Ellison, 2004).

3.2.10 Upper Chalk Formation

Essentially a very fine-grained white Limestone, this formation consists predominantly of

coccoliths composed almost entirely of calcium carbonate in the form of low magnesian

calcite, with sporadic to occasional flint bands (Ellison, 2004). In the London area the lower

parts of this formation is mapped as the Lewes Chalk, or the Lewes Nodular Chalk, which is

best defined as a hard to very hard nodular Chalk with interbedded soft to hard gritty Chalks

and regular flint bands (Bristow et al, 1997).

4.0 GROUND INVESTIGATION

The following works were undertaken in order to assess the soils and subsoils beneath the

proposed Package 4 Jubilee Line extension. These works were undertaken by Messrs Soil

Mechanics Ltd, commencing on the 24th

September, 1990, and ending on the 17th

December,

1990.

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4.1 EXCAVATIONS

A total of twenty (20 no.) boreholes were completed across the site in order to determine the

nature and consistency of the soils beneath the site. This programme of works commenced on

the 24th

September, 1990 and ended on the 14th

November, 1990. Drilling depths range from -

24.93 mOD (27.60 mbgl) in BH 413P to -49.84 mOD (53.05 mbgl) in BH404T, with the

majority of excavations being completed to a depth of 30.00 to 40.00 mbgl. Chiselling of

harder strata horizons was undertaken where necessary. Hand-dug starter pits were completed

at all locations to a depth of between 0.60 mbgl (metres below ground level) and 1.20 mbgl in

order to check for utilities before drilling was commenced.

Fourteen (14 no.) of these boreholes were completed using Cable Percussive techniques in

shell diameters of between 150mm and 250mm depending on the number of reductions

required per borehole (depth and geology dependant).

A further two (2 no.) boreholes were initially excavated using open hole drilling (404T,

407T) using a tricone rock bit, followed by Rotary drilling to the base of the boreholes.

Similarly, two (2 no.) boreholes (410T and 415T) were commenced using Cable Percussive

methods, followed by Rotary drilling methods to the base of the boreholes. In all four

boreholes Rotary drilling employed polymer mud flush and SK6L wireline 100mm coring

equipment.

The remaining two (2no.) boreholes (403P and 413P) were drilled using Cable Percussive

equipment with the inclusion, at times, of Self-Boring Pressuremeter (SBP) tests), used

primarily to drill and test the London Clay Formation and Upper Mottled Clays and, where

applicable, the Thanet Sand Formation.

A more in-depth summary of each borehole is outlined in Table 1 below.

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Table 1 – Borehole data including location, start and finish dates, depths and inspection pit information.

4.2 IN-SITU TESTING

A number of tests were undertaken within the boreholes during excavation. These included

the following:

Standard Penetration Tests (SPT), with Split spoon testing completed within clay and silt

horizons and Cone Penetration Testing (CPT) were completed within sand and gravel

horizons during Cable Percussive excavation. Both methods are essentially the same,

although split spoon testing allows a sample to be retrieved, whilst CPT methods involve a

solid cone penetrating the strata, and therefore no sample in obtained. These tests involve an

initial number of seating blows to a depth of 150mm from the test start datum, with the

number of blows required to drive the split spoon or cone a further 300mm counted, giving

an N-value.

Down-hole falling head permeability tests were undertaken during the drilling operations

within a number of the boreholes (403, 404T, 409, 411 413P, 414, 416, 417, 418, 419).

BH Drilling Method Eastings Northings

Hand

Dug Pit

Depth

(mBGL)

Start Finish

Depth

(m) Date

Reduced

Level

(mOD)

Date

Reduced

Level

(mOD)

401 Cable Percussive 533344 179834 1.2 24/09/1990 2.96 29/09/1990 -36.74 39.70



403P Cable Percussive/SBP 533551 179737 1.2 01/10/1990 3.52 21/10/1990 -34.48 38.00

404T Open Hole/Rotary 533638 179605 1.1 24/09/1990 3.21 03/10/1990 -49.84 53.05



407T Open Hole/Rotary 534043 179407 1.2 08/10/1990 3.26 19/10/1990 -47.11 50.37



410T

Cable

Percussive/Rotary 533406 179414 0.6 17/10/1990 2.79 30/10/1990 -40.71 43.50



413P Cable Percussive/SBP 534525 179429 1 30/10/1990 2.67 14/11/1990 -24.93 27.60


415T

Cable

Percussive/Rotary 534905 179439 0.8 06/10/1990 2.5 18/10/1990 -38.30 40.80


417 Cable Percussive 515222 179446 1 19/10/1990 1.95 31/10/1990 -33.05 35.00


419 Cable Percussive 534985 179460 1 16/10/1990 2.52 21/10/1990 -27.48 30.00

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Self-boring Pressuremeter (SBP) tests were conducted within boreholes 403P and 413P.

These tests enable a variety of total and effective stresses to be determined in-situ for clays

and silts, including undrained shear strength (cu) and pore water pressures (Clarke, 1990). In

sands, this test method can determine the angle of shearing resistance, angle of dilation, and

the secant and tangential shear modulus (Hughes et al, 1977).

4.3 INSTALLATIONS

The majority of the boreholes excavated during this investigation were installed with one

piezometer and sand filter in order to enable groundwater measurements and fluctuations

across the line of section. Exceptions to this include six (6 no.) boreholes (402, 403, 407T,

410T, 415T and 416) which were dual-installed with an upper and lower piezometer, and

BH403P, which was not installed. Following installation or completion all boreholes were

backfilled with bentonite.

4.4 SAMPLING

In excess of 1200 samples have been collected for testing and characterisation. These

involved different sampling methodology involving the following:

• Undisturbed Samples within clayey and silty horizons – Obtained predominantly

using 100mm diameter driven tubes. Some samples obtained using pushed piston

methods.

• Small disturbed samples – Obtained from SPT tests in clayey and silty horizons, or

taken at intervals determined by the drilling methodology.

• Bulk disturbed samples – Obtained following CPT testing on sand and gravel

horizons.

• Core samples – extracted from rotary cored boreholes (404T, 407T, 410T and 415T)

• Water samples – Extracted from a number of boreholes on occasions where

groundwater levels were noted.

4.5 LABORATORY TESTING

A number of tests were conducted on a selection of the samples extracted from the borehole

programme in order to give a good and detailed spread of the site data. Laboratory testing

was undertaken by Messrs Soil Mechanics Ltd, with the following tests undertaken:

• Index Properties testing on clayey and silty samples in order to identify the Liquid and

Plastic Limits of the samples, their Plasticity Index, and the natural moisture contents.

• Undrained triaxial tests were undertaken on undisturbed clay and silt samples in order

to calculate the undrained shear strength (cu) values of a selection of samples. Where

deemed appropriate, the laboratory cut three (3no.) 38mm diameter undisturbed

samples from the original 100mm diameter samples in order to subject the soil to

different cell pressures.

• Soil and water sulphate tests, including pH testing, were undertaken on a number of

water, undisturbed and disturbed samples.

11


The results of all the laboratory tests are located in Figures 7 to 11.

4.6 GROUNDWATER MONITORING

Monitoring of all the installed piezometers was undertaken in the period of the 4th

October

1990 to the 17th

December 1990. All installations were monitored for the depth of the

groundwater on several occasions over this period with the exception of BH403.

The results from groundwater monitoring have been plotted on the cross-sections (Figures 4

& 5), with pore pressures calculated and plotted in Figure 6.

5.0 GROUND CONDITIONS

5.1 STRATIGRAPHY

Stratigraphic logging of the boreholes revealed the following soil succession underlying the

site:

FORMATION STRATA REDUCED LEVEL (mOD) THICKNESS (m)

TOP BOTTOM MIN MAX

N/A MADE GROUND 3.52 -1.71 0.30 5.00

ALLUVIUM ALLUVIUM 2.21 -2.19 0.50 3.60

PEAT -0.49 -0.99 0.50 0.50

RIVER THAMES TERRACE GRAVEL TERRACE GRAVEL 0.96 -7.95 2.70 6.90

LONDON CLAY FORMATION LONDON CLAY (WEATHERED) -4.21(-3.96) -35.84 (-7.29) 0.30 (0.50) 28.55 (0.55)

HARWICH FORMATION BLACKHEATH BEDS -4.28 -32.15 0.20 0.70

UPPER WOOLWICH FORMATION UPPER SHELLY CLAY -4.8 -36.54 0.55 2.50

UPPER READING FORMATION UPPER MOTTLED CLAY -4.18 -36.74 1.60 7.65

LOWER WOOLWICH FORMATION LAMINATED BEDS -5.78 -32 1.10 2.98

LOWER SHELLY CLAY -8.68 -32.98 0.33 4.57

LOWER READING FORMATION LOWER MOTTLED CLAY -9.78 -34.8 0.25 1.75

UPNOR FORMATION PEBBLE BED -10.28 -32.44 0.57 3.10

GLAUCONITIC SAND -13.38 -37.94 2.00 6.80

THANET SAND FORMATION THANET BEDS -19 -49.84 10.50 12.50

BULLHEAD BED -31.4 -38.51 0.26 0.60

UPPER CHALK FORMATION UPPER CHALK -31.4 -47.11 (NP) 2.65 (NP) 8.6 (NP)

Table 2 – Stratigraphic data identifying the order of the soils from shallowest to deepest for package 4 of the

Jubilee Line. Note – NP means that the base of the strata was not proven.

Cross-sections through the site are located in Figures 4 and 5, with lines of sections shown in

Figure 2.

Both Table 2 and the Figures 4 and 5 indicate that the Woolwich and Reading Formations are

interbedded beneath the site area. There also appears to be a north-northwest dip of the solid

geological succession from consideration of boreholes 401 to 408, where the cross-section is

12


from northwest to southeast. This is less evident in the remaining boreholes because the

corresponding cross-section is orientated west to east.

5.2 GROUNDWATER CONDITIONS

Groundwater levels monitored and measured within the piezometers were observed to form

two distinct phreatic surfaces present (Figure 6). An upper surface at approximately -1.00

mOD is identified, whilst a second, lower phreatic surface at approximately -7.00 mOD is

also observed.

This upper surface is considered to correspond with the permeable Terrace Gravels overlying

the relatively impermeable London Clay Formation in the northwest and west of the section

(BH 401 to BH 408), and continues in the eastern section of the site with the Terrace Gravels

overlying the less permeable beds of the Upper Shelly Clay and Upper Mottled Clay (BH

410T to BH419).

The lower groundwater surface is considered to relate to the pore pressures within the

Lambeth Group and the Thanet Sands.

The water levels measured within the piezometers plot about the hydrostatic lines drawn

through -1.00 mOD and -7.00 mOD, and it is therefore considered that pore pressures within

the strata at both shallow and deep levels closely match hydrostatic pore pressures, taking

into consideration minor fluctuations between boreholes – for example, BH 401 indicated

groundwater at 0 mbgl. Furthermore, it is not considered that there is any under-drainage of

soils beneath the site. It should be noted that piezometers which has been installed within clay

horizons may take weeks, month or longer for groundwater conditions to stabilise after the

drilling programme. The monitoring round extends for no more than three months after initial

installations, and it is therefore recommended that further monitoring be undertaken to

identify any recent changes to the groundwater conditions. The findings may or may not

indicate the pore pressures to plot closer to the hydrostatic lines at -1.00 mOD and -7.00

mOD, or may indicate that the phreatic surfaces have moved.

5.3 GEOTECHNICAL CHARACTERISATION

Whilst down-hole permeability tests and SBP tests were undertaken during the drilling

programme, this information has not been made available for this report. Therefore, these will

not be discussed in the following sections.

5.3.1 Made Ground

Encountered at ground level within all excavations, this stratum was very of very variable

thickness across the site, ranging from 0.30m (BH 416) to 5.00m (BH402). This comprised of

topsoil (0.10 to 0.20m thick), tarmac (0.05 to 0.15m), or concrete (0.05 to 0.40m), or a

combination of these, overlying soft to firm brown grey green and black silty sandy Clay with

abundant fine to coarse angular to rounded brick, concrete, ash, tile mortar, flint coal and

chalk gravels and rare cobbles of tile, chalk, concrete and timber. Although contamination

13


testing is beyond the remit of this report, it should be noted that Made Ground within BH 403

was described as ‘oily’, whilst being described as having a ‘pungent’ odour in BH414.

Chiselling was required within six boreholes (Figures 4 and 5), whilst SPT ‘N’ values for this

stratum vary from 3 to 24, in line with the variability of the soils. Only one index properties

test was completed, with a result indicating the following:

LL (%) PL (%) PI (%) w (%)

42 30 12 33

This indicates that the tested soil plots below the A-line and is therefore a silt of intermediate

plasticity (Figure 9).

Two sulphate and pH tests were also completed indicating a pH of 7.5 to 8.0, a soil sulphate

content of 0.05 % and a water sulphate content of 0.09 g/l. It cannot be recommended that

such a variable stratum be characterised using limited data. However, these results suggest

that DS-1 grade concrete may be employed at this level.

Further research suggests that the following soil properties may be considered for Made

Ground (After Burland et al, 2001):

Bulk unit weight γ (kN/m³) 15 to 19

Undrained shear strength cu kN/m² 15 to 70

Effective Cohesion c' kN/m² 0

Angle of shearing resistance φ' (°) 22 to 35

Coefficient of permeability k (m/s) 1x10-2 to 1x10-6

5.3.2 Alluvium

Encountered in all but six boreholes (402, 403P, 407T, 408, 414 and 419) situated beneath

the Made Ground, this stratum is of variable thickness across the site, ranging from 0.50m

(BH401) to 3.60m (BH405). This can be described generally as a soft to firm yellow orange

brown and green slightly sandy (fine to medium) occasionally very sandy silty to very silty

CLAY with occasional fine to coarse angular to sub-rounded flint gravel with rare rootlets.

Some beds are also observed to be predominantly sandy, comprised of loose to medium

dense greyish yellow orange and brown clayey and silty SAND with occasional fine to

medium angular to sub-rounded flint gravel and occasional pockets (<20mm) of brown very

clayey silt. One instance of Peat was identified within a bed of Alluvium in BH405 at -0.49

mOD, 0.50m thick. This was describes as firm black SILT with abundant fragments of

organic material (decaying wood), within the borehole log.

SPT ‘N’ values vary between 3 and 23, highlighting a similar variability to that of Made

Ground. Based upon this a design line of N=8 is proposed for the Alluvium, taking into

consideration the sand and gravel fractions of this stratum. This relates to a drained friction

14


angle of 29° (Peck et al, 1974). Three index tests were completed on the Alluvium, with the

findings as follows:

LL (%) PL (%) PI (%) w (%)

24 to 58 15 to 28 9 to 31 10 to 24

This outlines the variability of this stratum, with clays plotting as clays with low to high

plasticity, and the silt fraction plotting within the intermediate plasticity in Figure 9. Two of

the three moisture contents plot to the left (less than) the plastic limit. This would suggest that

these soils are often in a semi-solid state. One bulk density test on the clay fraction of this

Alluvium was carried out, with a result of 2.01 Mg/m³.

Two pH and sulphate tests were completed, identifying a pH range of 7.1 to 7.8, a soil

sulphate of 0.05% and a water sulphate concentration of 0.12g/l. These results both plot

within the DS-1 class concrete range (Figure 11).

Further research suggests that the following properties can be considered for Alluvium at this

site:






All data in the above table refers to Burland et al (2001) with the exception of the coefficient

of permeability, which relates the observed soils to BS 8004: 1986 (in Craig, 2004).

5.3.3 Terrace Gravel

Encountered in all excavations, this stratum was identified immediately beneath the Alluvium

– if Alluvium was encountered – otherwise located beneath Made Ground. Thicknesses of

this stratum range between 2.70m (BH411) and 6.90m (407T), and is generally described as a

medium dense to dense orange brown very sandy medium to coarse sub-angular to sub-

rounded flint GRAVEL with occasional flint cobbles and pockets of brown silty clay.

Chiselling was required at the base of the Terrace Gravels in BH409 (6.90-7.70mbgl for 2

hours). SPT ‘N’ values range from 4 to 79, with the majority of values plotting between 11

and 47. Based on this data a design line of N=23 is proposed for the Terrace Gravels, which

indicates a drained friction angle of 34° (Peck et al, 1974).

Owing to the sandy and gravelly nature of this stratum, plasticity index, triaxial and moisture

content tests were not undertaken, as it is considered that these soils are non-plastic.

However, 15 water soluble sulphate and pH tests were carried out on water samples obtained

within the Terrace Gravels. The results of these indicate a pH range of 7 to 9.7, and a water

15


soluble sulphate level of 0.08 to 0.31 g/l. These results plot within the boundaries of DS-1

class.

Further research indicates the following table of soil properties for the Terrace Gravels (after

Burland et al, 2001, with the exception of φ’, which is calculated from Peck et al, 1974):


Undrained shear strength cu kN/m² N/A


Angle of shearing resistance φ' (°) 34


5.3.4 London Clay

Observed in twelve of the twenty boreholes (401-408, 410T, 412 and 413P) beneath the

Terrace Gravels, this stratum is of a variable thickness owing to the inferred dip of the

geological strata to the north-northwest, and was, therefore, not identified east of BH413P.

Thicknesses of the London Clay range from 29.65m (BH401 – combination of weathered and

unweathered strata) to 0.30m (BH410T), with the top of the formation noticeably weathered

in BH401 (0.55m thick) and BH412 (0.50m)

This stratum is described generally as a stiff to very stiff thinly laminated very closely to

closely fissured dark grey and grey-brown CLAY occasionally bioturbated with occasional

pockets and partings (<2mm) of light brown grey silty fine sand and rare strong claystone

gravels and cobbles, pyrite nodules and shell fragments. Fissures are randomly orientated

clean planar to undulose smooth and occasionally polished.

The upper weathered section was similar to the above description, with the exception of

being brown in colour.

The base of this stratum is noticeably siltier with a proportion of sand, and can be described

as stiff to very stiff thinly laminated very closely to closely fissured very silty slightly sandy

CLAY occasionally bioturbated with occasional pockets (<20mm) and discontinuous partings

(<10mm) of light brown grey silty fine to medium sand and occasional pyrite and lignite

nodules. Fissures are randomly orientated clean planar to undulose smooth to rough.

The presence of some polished fissure surfaces suggests that these could be representative of

shear surfaces. Chiselling was required in BH401 (16.50mbgl to 17.10mbgl for 1 ¼ hours;

22.50mbgl to 23.40mbgl for 1 ½ hours), corresponding with irregular claystone layers within

the London Clay.

Sixty-four (64 no.) SPT tests were conducted throughout the London Clay sequence, with ‘N’

values varying from 12 to 99 (extrapolated values to 1500).

16


Plasticity Index testing was completed on thirty (30 no.) samples, with the results as follows:

LL (%) PL (%) PI (%) w (%)

50 to 86 19 to 43 21 to 58 8 to 35

The vast majority (75%) of the samples plot within the very high plasticity clay section of the

Plasticity Chart (Fig. 9), with approximately 20% plotting in the high plasticity clays. One

sample (BH401 at 33.20mbgl) plots as a silt of intermediate to high plasticity, and another

(BH403 at 21.20mbgl) plots as a silt of very high plasticity. Both of these samples are from

the London Clay’s basal beds, and therefore match the borehole records. For London Clay

with a Plasticity Index (PI) of 21% to 58% Stroud and Butler (1975) report case histories

where cu/N (kN/m²) ranges between 4.3 and 4.8. A design line based upon cu/N =4.6 (kN/m²)

provides a relatively good fit to the data, and it is therefore recommended that this be used in

the design.

The natural moisture contents plot (Fig. 8) suggests that the majority of the samples have

moisture contents at or less than the plastic limit, indicating that the London Clay is likely in

a plastic to semi-solid state.

Bulk density tests on the London clay show a range of values from 1.90 to 2.10 Mg/m³.

Triaxial tests were conducted on twenty-eight (28no.) samples, with undrained shear strength

(cu) values ranging from 66 kN/m² to 394 kN/m². These results show a relatively good

correlation (Fig. 10) with the design line of 4.6N identified from SPT testing (Fig. 7),

although samples at depths greater than -25.00 mOD appear to be under quantified compared

to the design line.

Ten (10 no.) pH and sulphate tests were completed, identifying a pH range of 6.9 to 8.6, a

soil sulphate content between 0.02% and 0.45% and a water sulphate concentration of 0.05g/l

to 0.92g/l. The results of these tests suggest that DS-2 grade concrete should be used within

this stratum. The presence of pyrite within the London Clay would also suggest that localised

areas with significantly lower pH values than have been identified in the tests are likely to be

present.

Further research indicates the following table of soil properties for the London Clay:

Bulk unit weight γ (kN/m³) 18 to 20.5

Undrained shear strength cu kN/m² SPT ‘N’ x 4.6

Effective Cohesion c' kN/m² 0-12

Angle of shearing resistance φ' (°) 24-28


All data based upon information from Buriton et al (2001) with the exception of cu which has

been calculated using Stroud and Butler (1975), and the permeability (k) which has been

calculated from Craig (2004), considering that fissuring of the London Clay will significantly

influence the soils permeability.

17


5.3.5 Blackheath Beds

Identified within the majority of the excavations underlying the London Clay or, in its

absence, the Terrace Gravels, this stratum is of a fairly constant thickness, with depths of

between 0.20m (BH413P) and 0.70m (BH411). It was not identified within BH401 due to the

base of the London Clay not being reached, and in BH410T a void was located where this

unit would have been expected (Figure 5). Elsewhere, this unit was not identified because the

geological succession is considered to dip gently to the north-northwest, based on cross-

sectional data.

This stratum can be described as a stiff to very stiff grey brown black slightly sandy very silty

CLAY with occasional to abundant medium to coarse sub-rounded to rounded flint gravels

and rare flint cobbles and rare to occasional shell fragments with rare to occasional pockets

(<40mm) of green grey glauconitic silty sand.

Chiselling of this stratum was required within four boreholes (BH402 – 35.40mbgl to

35.60mbgl for approximately 1 ½ hours; BH403 – 25.20mbgl to 25.80mbgl for

approximately 1 hour; BH403P – 26.10mbgl to 26.50mbgl for 1 hour; BH405 – 20.70mbgl to

21.40mbgl for 3 hours). A SBP test within BH403P at 31.25mbgl was noted to have burst at

2200kPa within this strata.

Two SPT ‘N’tests were undertaken, with values of 39 and 214 (extrapolated). It is not

considered that enough data has been obtained in order to give a design value of any accuracy

for this stratum. Owing to the clayey nature of this unit, three index tests were completed,

with the results as follows:

LL (%) PL (%) PI (%) w (%)

63 to 72 25 to 27 38 to 45 22 to 25

Two of these results plot as clays with a high to very high plasticity (Figure 9), whilst one

sample (BH412 at 8.15mbgl) is regarded as non-plastic. One of the samples (BH402 at

34.00mbgl) plots to the left of its plastic limit, suggesting that some parts of this stratum are

in a semi-solid state. Seven bulk density tests were completed, with results varying from 1.93

to 2.01 Mg/m³. Furthermore, two samples were selected for triaxial testing, with cu results

varying from 111 (-4.48 mOD) to 235 kN/m² (-5.61 mOD).

Only one pH and soil sulphate test was conducted within this strata, with values of 6.3 and

0.31 % respectively, which plots within the DS-2 class.

18


Based upon the engineering description of the Blackheath Beds beneath the site area the

following table outlines the design properties of this stratum:






All data has been estimated using tables and data made available by Waltham, (2002) with

the exception of permeability, which has been estimated using tables in Craig (2004).

5.3.6 Upper Shelly Clay

Observed within thirteen (13 no.) of the boreholes (BH401-403, BH404-413P) beneath the

Blackheath Beds or, where this is not present, Terrace Gravels, this stratum is of a reasonably

constant thickness, ranging from 0.55m (BH412) to 2.50m (BH408), and is cut out of the line

of section due to the gently dipping nature of the geology, with the exception of BH403P,

where it is not within the sequence. This is considered to be due to the interbedded nature of

the Woolwich and Reading Beds of the Lambeth Group.

This material comprises of very stiff locally thinly laminated closely fissured dark grey and

grey-green very silty CLAY with abundant shells, occasional pockets and partings of grey-

green sandy (fine) silt and occasional sub-rounded flint gravels, with thin (<90mm)

impersistent strong to very strong grey shelly Limestone, recovered as fine to coarse sub-

angular gravel. Fissures are random to sub-vertical clean and planar.

Chiselling was required in three boreholes – BH402 through the Blackheath Beds through to

the Upper Mottled Clay (35.40mbgl to 36.50m for 7 hours); BH403 through the Blackheath

Beds to the Upper Mottled Clay (25.20mbgl to 26.70mbgl for 3 hours); BH405 (22.10mbgl to

within the Upper Mottled Clay at 25.20mbgl for 5 ½ hours). These episodes of chiselling are

considered to correlate with the Limestone and flint gravel bands identified within the

boreholes

Twelve (12 no.) SPT tests were carried out on the Upper Shelly Clay, with ‘N’ values varying

from 32 to 273 (extrapolated).

Plasticity Index tests were completed on five samples with the results as follows:

LL (%) PL (%) PI (%) w (%)

29 to 62 14 to 26 14 to 36 17 to 30

These samples plot predominantly as clays of low to intermediate plasticity, with the

exception of BH407T (13.34mbgl) which corresponds to a clay of high plasticity, with a

significantly higher liquid limit than other samples of this stratum. The natural moisture

contents plot (Fig. 8) suggests that the majority of the samples have moisture contents at or

19


less than the plastic limit, indicating that the Upper Shelly Clay is likely in a plastic to semi-

solid state.

For a PI of 14% to 36% Stroud and Butler report cu/N (kN/m2) case histories of between 4.3

and 6. However, their chart indicates that Woolwich and Reading Clays plot significantly

lower than their best fit line, at between 3 and 3.5. A design line based upon cu/N =3 (kN/m²)

provides a relatively good fit for the data.

Bulk density tests on the Upper Shelly Clay show a range of values from 1.71Mg/m3 to

2.18Mg/m3. Triaxial tests were competed on four samples, with an Undrained Shear Strength

(cu) varying from 26 kN/m2 up to 132 kN/m

2. From consideration of the triaxial plot (Fig. 10)

and the borehole data, the lower cu value is considered to be due to the sample (-8.09 mOD in

BH408) being composed predominantly of Silt, compared to the other samples being of clay.

One pH and soil sulphate test were completed by the laboratory, with results of 6.3 and

0.03% respectively. These plot within the DS-1 grade boundaries (Fig. 11).

Further research indicates the following table of soil properties for the Upper Shelly Clay:






Effective cohesion, angle of shearing resistance and coefficient of permeability based upon

information from Buriton et al (2001).

5.3.7 Upper Mottled Clay

Identified within all boreholes with the exception of BH402 which terminated above the

presumed stratum, this is situated beneath the Upper Shelly Clay or, where this is not present,

the Terrace Gravels or the Blackheath Beds (BH403P). This stratum is of variable thickness

across the site, identified at between 1.60m (BH419) and 7.65m (BH403).

This stratum is considered to be variable in its stratigraphy, comprising predominantly of stiff

to very stiff extremely closely fissured green grey blue red brown mottled CLAY

occasionally very silty and sandy with rare to occasional angular to sub-rounded flint gravel

and occasional pockets of light brown silty sand. Fissures are random to sub-vertical planar

smooth and occasionally polished with rare slickenlines. Rare moderately strong to strong

limestone bands and occasional beds of very dense brown blue green and grey silty fine to

medium SAND are also present.

The presence of slickenlines and polished surfaces on some fissures suggests that some may

represent relict shear surfaces.

Chiselling was required in five of the boreholes on more than one occasion. This information

is identified within Figures 4 and 5 and the borehole logs. Episodes of chiselling are

20


considered to be representative of sections where the Upper Mottled Clay could be described

as hard.

Forty-nine (49 no.) SPT tests were undertaken on the Upper Mottled Clay, with ‘N’ values

varying from 15 to 333 (extrapolated).

Plasticity Index tests were completed on twenty-four (24 no.) samples with the results as

follows:

LL (%) PL (%) PI (%) w (%)

20 to 80 11 to 31 9 to 50 11 to 35

These samples plot from low plasticity clays through to very high plasticity clays

predominantly centred around the high to very high plasticity clay sections. Two samples –

BH411 at 14.30mbgl and BH405 at 25.50mbgl – plot within the intermediate and high

plasticity silts, respectively. The results indicate the variability of this stratum. The natural

moisture contents plot indicates that all samples have moisture contents that plot at or higher

than their liquid limits; clays and silts within this stratum can therefore be considered as

plastic.




provides the best fit for the Upper Mottled Clays clay fractions.

Bulk density tests on the Upper Mottled Clay show a range of values from 1.88Mg/m3 to

2.15Mg/m3. Triaxial tests were completed on twenty-two (22 no.) samples, with Undrained

Shear Strength (cu) varying from 22 kN/m2 up to 277 kN/m

2. From consideration of the

triaxial plot (Fig. 10) and the borehole data, the lower cu value is considered to be due a

number of the tested samples having polished fissures. In these instances it may have been

the residual strength of these samples which was being measured. Whilst the design line fits

the less fissured Clays, it is not considered to represent a good fit of the data for the strata

with polished fissures.

Nine pH tests were completed, varying from 6.4 to 8.4. Five soil sulphate tests and six water

sulphate tests were also completed, with values varying from 0.01% to 0.42% and 0.06 g/l to

0.46 g/l respectively. These values suggest that DS-2 grade concrete be used within this

strata, if necessary.

Further research indicates the following table of soil properties for the Upper Mottled Clay:

21


Bulk unit weight γ (kN/m³) 19 to 21.5





Effective cohesion, angle of shearing resistance, coefficient of permeability and the upper

level of undrained shear strength are based upon information from Buriton et al (2001).

5.3.8 Laminated Beds

Observed within all boreholes with the exception of BH401 and BH402, where drilling ended

before the stratum was reaches, the Laminated Beds are located beneath the Upper Mottled

Clay in all instances, with thicknesses varying from 1.10m (BH405) to 2.98m (BH418).

The Laminated Beds can be generally described as a very stiff thinly to thickly laminated

grey occasionally brown silty to very silty CLAY with occasional partings (<6mm) of brown

silt and sand and rare carbonaceous pockets, interlaminated with very dense thinly to thickly

laminated grey silty fine to medium SAND with occasional bands of grey very silty sandy

clay, and very stiff thinly laminated grey very clayey sandy SILT with rare shell fragments.

Despite its very stiff and very dense attributes chiselling was only required once during the

drilling programme, in BH409 (15.50mbgl to 15.80mbgl for 1 ½ hours). This is presumed to

be due to the very stiff nature of the very silty Clay in this instance. A void was noticed

within BH404T from -28.29 mOD to -29.30 mOD, which may relate to groundwater flow

within the Laminated Beds.

Nineteen (19 no.) SPT tests were completed within this stratum; with ‘N’ value results

ranging from 25 to 300 (extrapolated), with the majority ranging between 25 and 82. The four

values greater than this were observed within very dense Sand (188, 210 and 300) and very

stiff silt (110).

Plasticity Index tests were completed on fifteen (15 no.) samples with the results as follows:

LL (%) PL (%) PI (%) w (%)

27 to 85 14 to 35 5 to 62 20 to 35

These samples plot from low plasticity clays through to very high plasticity clays

predominantly centred around the intermediate to high plasticity clay sections. One sample

(407T at 16.73mbgl) plots as a low plasticity silt, with the sample itself described as a very

sandy silt. The stratigraphic variability of the Laminated Beds is evident in these results. The

majority of these samples’ natural moisture contents plot within or on the plasticity limit,

which suggests that this stratum is in a plastic state.



22


lower than their best fit line, at between 3 and 3.5. A design line based upon cu/N =3.5

(kN/m²) provides a reasonable fit for the clay fractions of the Laminated Beds.

Bulk density tests on the Laminated Beds show values varying from 2.00Mg/m3 to

2.20Mg/m3. Triaxial tests were completed on eleven samples, with Undrained Shear Strength

(cu) varying from 102 kN/m2 to 314 kN/m


and the borehole data, the lower cu value is considered to be due a number of the tested

samples containing significant amounts of silt, or comprising predominantly of silt. Whilst

the design line is considered to fit around the clay data, it is not considered to represent a

good fit of the data for other soil types within the Laminated Beds.

Considering the SPT data for the sand horizons of the Laminated Beds in relation to Peck et

al (1974) a drained angle of shearing resistance for the sands within the Laminated Beds is

considered to be of 38°to 42°.

Six pH tests were completed, with results varying from 6.2 to 8.6. Five soil sulphate tests and

four water sulphate tests were also completed, with values varying from 0.01% to 0.51% and

0.30 g/l to 0.63 g/l respectively. These values suggest that DS-2 grade concrete be used

within this stratum, although one sample plotted narrowly inside the DS-3 class for soil

sulphate content.

Further research indicates the following table of soil properties for the Upper Mottled Clay:


Undrained shear strength cu kN/m² 100 to 150 (silt) 100

to 300 (clay)


Angle of shearing resistance φ' (°) 28 (Clays) 38 to 42

(Sands)


Effective cohesion, angle of shearing resistance of clays and the coefficient of permeability

are based upon information from Buriton et al (2001).

5.3.9 Lower Shelly Clay

Identified within all boreholes with the exception of BH401 and BH402 which terminated

above the presumed stratum, the Lower Shelly Clay is located beneath the Laminated Beds.

This stratum is of a variable thickness across the site, ranging from 0.33m (BH404T) to

4.57m (BH407T).

This stratum is considered generally comprise of very stiff extremely to very closely fissured

thinly to thickly laminated dark grey mottled green yellow brown and purple very silty

CLAY locally calcareous cemented with occasional to abundant shell fragments and

occasional partings (<6mm) and pockets (13mm) of light grey silt and fine sand and rare fine

to medium sub-angular to sub-rounded flint gravel. Fissures are predominantly horizontal to

sub-horizontal planar to undulating smooth and slightly polished.

23


The presence of polished surfaces on fissures may suggest relict shear surfaces, whilst locally

cemented may suggest the presence of thin Limestone bands within this stratigraphic

sequence.

Chiselling was required in nine of the boreholes. This information can be viewed within

Figures 4 and 5 and the borehole logs. Episodes of chiselling are considered to be

representative of sections where the Lower Shelly Clay could be described as very stiff to

hard.

Twenty-two (22 no.) SPT tests were undertaken on the Lower Shelly Clay, with ‘N’ values

varying from 22 to 750 (extrapolated), but predominantly ranging between 22 and 76. Five

tests showed values greater than this, and were all situated within very stiff, possibly hard,

clays.

Plasticity Index tests were completed on nineteen (19 no.) samples with the results as

follows:

LL (%) PL (%) PI (%) w (%)

37 to 71 18 to 28 19 to 45 18 to 36

These samples plot from intermediate to very high plasticity clays (Figure 9), with the

majority of samples plotting in the intermediate to high plasticity range. One sample (BH417

at 13.30mbgl) plotted as a high plasticity silt, with the borehole log describing the sample as a

clay with lenses of silt and sand. The natural moisture contents of the majority of these

samples plot at or below the plastic limit of the sample, indicating that the soils are in a

plastic to semi-solid state in-situ.


and 5.3. However, their chart indicates that Woolwich and Reading Clays plot significantly

lower than their best fit line, at between 3 and 3.5. A design line based upon cu/N =3.5

(kN/m²) provides the best fit for clay fractions of the Lower Shelly Clay.

Bulk density tests on the Lower Shelly Clay show a range of values from 2.01Mg/m3 to

2.23Mg/m3. Triaxial tests were completed on seven samples, with Undrained Shear Strength



and the borehole data, the lower cu value is considered to be based upon the very silty nature

of the clay sample (BH414 at -13.61 mOD), with the remaining clay samples plotting at and

above 200 kN/m2. Whilst the design line plots the best-fit line of the tested samples, it is

important to note that the samples rarely plot near to the design line. This is likely due to the

variable nature of the predominantly clay-rich strata in combination with sands, silts and

fissures.

Four pH tests were completed with results varying from 6.6 to 9.9. Three soil sulphate tests

and two water sulphate tests were also completed, with values varying from 0.06% to 0.41%

24


and 0.17 g/l to 0.51 g/l respectively. These values suggest that DS-2 grade concrete be used

within this strata, if necessary (Fig. 11).

The following table of soil properties for the Lower Shelly Clay is considered prudent for

future designs:


Undrained shear strength cu kN/m² 100-200 (silt)

200-310 (clay)




Effective cohesion, angle of shearing resistance and coefficient of permeability are based

upon information from Buriton et al (2001).

5.3.10 Lower Mottled Clay

Identified within all boreholes with the exception of BH401 and BH402 which terminated

above the presumed stratum, the Lower Mottled Clay underlies the Lower Shelly Clay. This

stratum is of a variable thickness across the site, ranging from 0.25m (BH417) to 1.75m

(BH404T).

The Lower Mottled Clay generally comprises of very stiff extremely to closely fissured

yellow brown grey purple blue and green mottled CLAY occasionally very silty and rarely

interbedded with SILT, with occasional fine to medium gravels of very weak limestone and

moderately strong siltstone and rare to occasional pockets (<5mm) of light brown silty fine

sand. Fissures are vertical to sub-vertical and random, planar smooth and occasionally

polished and striated.

The presence of polished and striated surfaces on some fissures may suggest relict shear

surfaces.

Chiselling was required in ten of the boreholes. This information can be viewed within


representative of sections where the Lower Mottled Clay could be described as very stiff to

hard. Two voids were identified within BH407T (-19.11 to -20.08 mOD and -20.56 to -21.11

mOD) either side of a pure Silt bed. It is inferred from this that flow within this portion of the

Lower Mottled Clay may occur, although this was not seen within any other excavations.

Twelve (12 no.) SPT tests were completed within the Lower Mottled Clay, with ’N’ values

varying from 44 to 500 (extrapolated). Eleven of the twelve samples have values ranging

from 44 to 250, with the higher values (inclusive of the 500 result) are all described as being

in very stiff clay.

25


PI tests were completed on eight samples with the results as follows:

LL (%) PL (%) PI (%) w (%)

33 to 70 17 to 29 14 to 44 13 to 29

These samples plot from low to high plasticity clays (Figure 9), with the majority of samples

plotting in high plasticity range. The natural moisture contents of the majority of the samples

plot to the left of the plasticity limit in Figure 8, suggesting that the most part of the Lower

Mottled Clay is in a semi-solid state in-situ.


and 6.2. However, their chart indicates that Woolwich and Reading Clays plot significantly


is considered to provide the best fit for clay fractions of the Lower Mottled Clay.

Bulk density tests on the Lower Mottled Clay show a range of values from 1.89Mg/m3 to

2.21Mg/m3. Triaxial tests were completed on three samples, with Undrained Shear Strength



and the borehole data, the lower cu value is considered is considered to be linked to the soil

being described as a silt (BH417 at -12.85 mOD). A design line of N3.5 therefore appears to

accurately depict the clay horizons of the Lower Mottled Clay. However, only two results

were plotted on this line, and more tests and plots of the results would be required to prove

this.

One pH test was conducted on samples of this stratum, with a result of 7.3. Similarly, one

water sulphate test was completed with a result of 0.27 g/l. This falls within the DS-1

sulphate class, but it is recommended that further tests be completed on alternative samples to

confirm this class for the Lower Mottled Clay.

The following table of soil properties for the Lower Mottled Clay is considered prudent for

future designs:


Undrained shear strength cu kN/m² 25-100 (silt)

100-300 (clay)




Effective cohesion, angle of shearing resistance and coefficient of permeability are based

upon information from Buriton et al (2001).

5.3.11 Pebble Bed

Identified within boreholes 404T to 419, the Pebble Bed was observed underlying the Lower

Mottled Clay, with the exception of BH403, where it was thinned out of the sequence; this

stratum is of a variable thickness of 0.57m (BH404T) to 3.10m (BH419).

26


The pebble bed is best described as a very dense yellow-brown mottled blue green purple red

and grey clayey slightly sandy fine to coarse sub-angular to rounded GRAVEL with horizons

of grey very stiff silty sandy CLAY and rare to occasional pockets of blue-green glauconitic

silty fine sand.

Chiselling was required in twelve of the boreholes. This information can be viewed within


representative of sections where the Pebble Beds are very dense.

Forty-seven (47 no.) SPT tests were completed within the Pebble Bed, with ’N’ values

varying from 36 to 690 (extrapolated) with one test measuring zero penetration after 50

blows. The majority of values range from 108 to 375; From this data a design line of N=195

should be used for design purposes within the Pebble Bed. Considering data from Peck et al

(1974) this corresponds to a drained angle of shearing resistance of approximately 44º, with a

lower bound of 37º.

PI tests were completed on three fine-grained samples with the results as follows:

LL (%) PL (%) PI (%) w (%)

25 to 51 13 to 22 12 to 32 10 to 22

Two of these samples plot as low plasticity clays, with the third plotting within the high

plasticity clay section of the graph (Fig. 9). Natural moisture contents of two of the three

samples are equal to the plasticity limit, with one plotting at a lower value than its plasticity

level. This suggests that in-situ clay soils of the Pebble Bed are in a plastic or semi-solid

state.



lower than their best fit line, at between 3 and 3.5. A design line has not been recommended

for the clay fractions of the Pebble bed owing to the variability of the strata and the dominant

gravel beds and the lack of data for properties of the clay fractions.

Neither bulk density tests nor undrained triaxial tests were undertaken on the Pebble Bed.

Three pH tests were completed within the Pebble Bed samples, with values ranging from 7.3

to 9.0. One soil sulphate test was completed with a value of 0.01%, whilst two water sulphate

tests were completed, with values ranging from 0.06 g/l to 0.23 g/l. These results are within

the boundaries of the DS-1 class for sulphate.

The following table of soil properties for the Pebble Bed is considered prudent for future

designs:

27







Bulk unit weight, effective cohesion, angle of shearing resistance and coefficient of

permeability are based upon information from Buriton et al (2001).

5.3.12 Glauconitic Sand

Identified within all boreholes with the exception of boreholes 401, 402 and 403P which were

not bored to a deep enough level to observe this stratum, the Glauconitic Sands varies in

thickness (proven) across the site, from 2.00m (BH406) to 6.80m (BH412).

The Glauconitic Sand is a highly variable unit comprised of very dense grey-green and blue-

green occasionally mottled clayey and silty fine to medium SAND with rare to occasional

fine to medium rounded to sub-rounded flint gravel occasional to abundant pockets (<20mm)

grey and blue silty clay and rare nodules (30-50mm) of weak grey highly weathered

Limestone, interbedded with very stiff dark green grey and blue silty to very silty sandy

CLAY with occasional fine to medium flint gravels and rare to occasional partings of brown

very silty clay.

Chiselling was required in six of the boreholes. This information can be viewed within


representative of sections where the Glauconitic Sands are very dense and/or where bands of

weak Limestone are located.

Eighty-nine (89 no.) SPT tests were undertaken within the Glauconitic Sand, with ‘N’ values

varying from 30 to 750 (extrapolated). The majority of values range between 60 and 250,

with a recommended design line for the granular horizons of the Glauconitic Sand of N=120.

Considering data from Peck et al (1974) an undrained angle of friction in the order of 43-44º

is recommended for design purposes.

PI tests were completed on twelve samples with the results as follows:

LL (%) PL (%) PI (%) w (%)

29 to 41 16 to 23 6 to 23 15 to 33

These samples plot as low to intermediate plasticity clays, with two samples plotting as low

plasticity silts (Figure 9). The natural moisture contents of the majority of the samples plot

close to and within the plastic limit of the sample, suggesting that the majority of the fine-

grained part of the Glauconitic Sand is in a plastic state, although approximately 25% of the

tested samples plotted as semi-solid.

28


For a PI of 6% to 23% Stroud and Butler report cu/N (kN/m2) case histories of between 5 and

7. However, their chart indicates that Woolwich and Reading Clays plot significantly lower

than their best fit line, at between 3 and 3.5. Triaxial tests were completed on five samples,

with Undrained Shear Strength (cu) varying from 13 kN/m2 to 118 kN/m

2. From

consideration of the triaxial plot (Fig. 10) and the borehole data, the lower cu values (13, 45

kN/m2) are described as very sandy clays, whilst the upper values are sandy clays. This

highlights the bearing of silts and sands on the undrained triaxial test. In response to this, a

design line of cu/N=0.75 is considered to provide a best fit for the sandy clays within the

Glauconitic Sand identified during this investigation.

Bulk density tests on the Glauconitic Sand show a range of values from 2.00Mg/m3 to

2.18Mg/m3.

Two pH tests were completed on Glauconitic Sand samples, with results ranging from 6.3 to

8.7. Two soil sulphate tests were also undertaken, with results ranging from 0.01% and

0.33%, with the latter result correlating with a DS-2 class.

The following table of soil properties for the Glauconitic Sand is considered prudent for

future designs:


Undrained shear strength cu kN/m² 10-120 (fine

soils)


Angle of shearing resistance φ' (°) 43-44 (granular

soils)


Effective cohesion and coefficient of permeability are based upon information from Buriton

et al (2001).

5.3.13 Thanet Bed

Proved within boreholes 404T-419 (other boreholes not drilled to a deep enough level) the

Thanet Beds are observed underlying the Glauconitic Sand in all instances, with a variable

thickness of between 10.50m (BH411 - proved) and 12.50m (BH417 – not proved).

The Thanet Bed is comprised of very dense grey grey-brown and grey-green glauconitic fine

to medium SAND with rare fine sub-rounded flint gravels, becoming slightly silty to silty

with occasional pockets (<30mm) of grey clay with depth.

Chiselling was not required within the Thanet Bed during the drilling programme.

One hundred and one (101 no.) SPT tests were completed within the Thanet Bed, with ‘N’

values varying from 94 to 1000 (all data required extrapolating from raw data) with two tests

incurring zero penetration. The majority of values range from 94 to 300, with a recommended

design line of N=175. Considering data from Peck et al (1974) an undrained angle of friction

29


of 44º is recommended for design purposes. However, Buriton et al (2001) recommend that

40º be used for this strata.

Two PI tests were completed on Thanet Bed samples with the results as follows:

LL (%) PL (%) PI (%) w (%)

26 to 31 14 to 15 11 to 17 14 to 15

These samples plot as low plasticity clays, with their natural moisture contents both plotting

at the same percentage as their plastic limits. This suggests that in-situ clay horizons within

the Glauconitic Sand are in a plastic state, albeit at the plastic limit.

Owing to the sandy nature of the Thanet Bed not triaxial testing was undertaken. It is not

considered relevant to propose a design line for the Thanet Bed based upon clay data as it is

considered that the unit will behave in a granular manner.

Bulk density tests were not conducted on the Thanet Bed.

Two pH tests were completed on the Thanet Bed samples, with results ranging from 8.2 to

8.4. Two soil sulphate tests were also undertaken, with the results varying from 0.04% to

0.15%. These plot within the boundaries of the DS-1 class for concrete.

The following table of soil properties for the Thanet Bed is considered prudent for future

designs:






Bulk unit weight is based upon information from Buriton et al (2001), whilst the coefficient

of permeability is based upon BS 8004:1986 (in Craig, 2004).

5.3.14 Bullhead Bed

Identified beneath the Thanet Bed within six boreholes (407T, 410T, 411, 414, 415T and

418) the Bullhead Bed is of a relatively constant thickness of between 0.26m (BH418) and

0.60m (415T).

This unit comprises of very dense dark grey and black fine to medium SAND with abundant

fine to coarse angular to rounded flint gravels and cobbles, occasionally clayey to very clayey

(very stiff) and silty to very silty. In summary, this unit can be considered as a conglomerate.

Chiselling was required throughout the Bullhead Bed in BH414 (37.00mbgl to 37.30mbgl for

1 hour) because here the unit was comprised almost entirely of flint cobbles within a clay

matrix.

30


Two SPT tests were completed within the Bullhead Bed, with ‘N’ values varying from 138 to

300, with both values being extrapolated from the raw data. Owing to these results it is

recommended that the design line of N=175 for the Thanet Bed is also suitable for the

Bullhead Bed.

No other tests were conducted on the Bullhead Bed. It is recommended that for design

purposes this unit follows the recommendations in the Thanet Bed.

5.3.15 Upper Chalk

Located beneath the Bullhead Bed of the Thanet Sand Formation, the Upper Chalk was

identified within six of the twenty boreholes (407T, 410T, 411, 415T and 418). The base of

this stratum was not proven, whilst the maximum thickness of the unit (unproven) was 8.60m

within BH407T.

The excavated Upper Chalk is best described as a weak to moderately weak white CHALK

with occasional rinded flint cobbles with very closely to medium spaced fractures often

infilled between 2mm and 9mm with light brown comminuted Chalk. This Chalk is described

as a Grade of between II and IV. However under new CIRIA documentation (Spink, 2002)

this is better defined as a chalk of between C4 and A3, but predominantly of C3 to C4.

Chiselling was required in BH411 (37.80mbgl to 38.20mbgl for 2 hours), presumed to be due

to flint cobbles.

Eight SPT tests were undertaken within the Upper Chalk, with ‘N’ values varying from 61 to

260 (extrapolated), with seven of the tests recording blows (N/300mm) of 61 to 85. The

recommended design line for the Upper Chalk in this instance is N=75. At this N-value Peck

et al (1974) suggest that an angle of shearing resistance in the order of 42º to 44º is

achievable.

No other tests were conducted on the Upper Chalk.

The following table of soil properties for the Thanet Bed is considered prudent for future

designs:






Bulk unit weight and effective cohesion is based upon information from Buriton et al (2001),

whilst the coefficient of permeability is based upon BS 8004:1986 (in Craig, 2004).

31


6.0 CONCLUSIONS

General geological conditions beneath the site suggest that solid geological strata are gently

dipping to the north-northwest.

An upper phreatic surface at approximately -1.00 mOD is identified, whilst a second, lower

phreatic surface at approximately -7.00 mOD is also observed. The upper surface is

considered representative of the intersection between the Terrace Gravels and London Clay,

whilst the lower level is representative of pore pressures within the Lambeth Group and

underlying strata.

Engineering Descriptions:

Made Ground - soft to firm brown grey green and black silty sandy Clay with abundant fine

to coarse angular to rounded brick, concrete, ash, tile mortar, flint coal and chalk gravels and

rare cobbles of tile, chalk, concrete and timber.

Alluvium - soft to firm yellow orange brown and green slightly sandy (fine to medium)

occasionally very sandy silty to very silty CLAY with occasional fine to coarse angular to

sub-rounded flint gravel with rare rootlets. Some beds are also observed to be predominantly

sandy, comprised of loose to medium dense greyish yellow orange and brown clayey and

silty SAND with occasional fine to medium angular to sub-rounded flint gravel and

occasional pockets (<20mm) of brown very clayey silt.

Terrace Gravels - medium dense to dense orange brown very sandy medium to coarse sub-

angular to sub-rounded flint GRAVEL with occasional flint cobbles and pockets of brown

silty clay.

London Clay - stiff to very stiff thinly laminated very closely to closely fissured dark grey

and grey-brown CLAY occasionally bioturbated with occasional pockets and partings

(<2mm) of light brown grey silty fine sand and rare strong claystone gravels and cobbles,

pyrite nodules and shell fragments. Fissures are randomly orientated clean planar to undulose

smooth and occasionally polished.

Blackheath Beds - stiff to very stiff grey brown black slightly sandy very silty CLAY with

occasional to abundant medium to coarse sub-rounded to rounded flint gravels and rare flint

cobbles and rare to occasional shell fragments with rare to occasional pockets (<40mm) of

green grey glauconitic silty sand.

Upper Shelly Clay - very stiff locally thinly laminated closely fissured dark grey and grey-

green very silty CLAY with abundant shells, occasional pockets and partings of grey-green

sandy (fine) silt and occasional sub-rounded flint gravels, with thin (<90mm) impersistent

strong to very strong grey shelly Limestone, recovered as fine to coarse sub-angular gravel.

Fissures are random to sub-vertical clean and planar.

Upper Mottled Clay - stiff to very stiff extremely closely fissured green grey blue red brown

mottled CLAY occasionally very silty and sandy with rare to occasional angular to sub-

32


rounded flint gravel and occasional pockets of light brown silty sand. Fissures are random to

sub-vertical planar smooth and occasionally polished with rare slickenlines. Rare moderately

strong to strong limestone bands and occasional beds of very dense brown blue green and

grey silty fine to medium SAND are also present.

Laminated Beds - very stiff thinly to thickly laminated grey occasionally brown silty to very

silty CLAY with occasional partings (<6mm) of brown silt and sand and rare carbonaceous

pockets, interlaminated with very dense thinly to thickly laminated grey silty fine to medium

SAND with occasional bands of grey very silty sandy clay, and very stiff thinly laminated

grey very clayey sandy SILT with rare shell fragments.

Lower Shelly Clay - very stiff extremely to very closely fissured thinly to thickly laminated

dark grey mottled green yellow brown and purple very silty CLAY locally calcareous

cemented with occasional to abundant shell fragments and occasional partings (<6mm) and

pockets (13mm) of light grey silt and fine sand and rare fine to medium sub-angular to sub-

rounded flint gravel. Fissures are predominantly horizontal to sub-horizontal planar to

undulating smooth and slightly polished.

Lower Mottled Clay - very stiff extremely to closely fissured yellow brown grey purple blue

and green mottled CLAY occasionally very silty and rarely interbedded with SILT, with

occasional fine to medium gravels of very weak limestone and moderately strong siltstone

and rare to occasional pockets (<5mm) of light brown silty fine sand. Fissures are vertical to

sub-vertical and random, planar smooth and occasionally polished and striated.

Pebble Bed - very dense yellow-brown mottled blue green purple red and grey clayey slightly

sandy fine to coarse sub-angular to rounded GRAVEL with horizons of grey very stiff silty

sandy CLAY and rare to occasional pockets of blue-green glauconitic silty fine sand.

Glauconitic Sand - very dense grey-green and blue-green occasionally mottled clayey and

silty fine to medium SAND with rare to occasional fine to medium rounded to sub-rounded

flint gravel occasional to abundant pockets (<20mm) grey and blue silty clay and rare nodules

(30-50mm) of weak grey highly weathered Limestone, interbedded with very stiff dark green

grey and blue silty to very silty sandy CLAY with occasional fine to medium flint gravels and

rare to occasional partings of brown very silty clay.

Thanet Beds - very dense grey grey-brown and grey-green glauconitic fine to medium SAND

with rare fine sub-rounded flint gravels, becoming slightly silty to silty with occasional

pockets (<30mm) of grey clay with depth.

Bullhead Beds - very dense dark grey and black fine to medium SAND with abundant fine to

coarse angular to rounded flint gravels and cobbles, occasionally clayey to very clayey (very

stiff) and silty to very silty.

Upper Chalk - weak to moderately weak white CHALK with occasional rinded flint cobbles

with very closely to medium spaced fractures often infilled between 2mm and 9mm with light

brown comminuted Chalk.

33


Summary of the key properties of the Geological Strata:

Bulk unit

weight

Undrained shear

strength

Effective

Cohesion

Angle of shearing

resistance

Coefficient of

permeability

γ cu c' φ' k

(kN/m³) kN/m² kN/m² (°) (m/s)

MADE GROUND 15 to 19 15 to 70 0 22 to 35 1x10-2

to 1x10-6

ALLUVIUM 16 to 20 25 to 50 0 22 to 29 1x10-4

to 1x10-6

TERRACE GRAVELS 19 to 20 N/A 0 34 5x10-3

to 5x10-6

LONDON CLAY 18 to 20.5 SPT'N' x 4.6 0 to 12 24 to 28 1x10-7

to 1x10-9

BLACKHEATH BEDS 19 to 20 75 to 300 0 20 to 25 1x10-5

to 1x10-7

UPPER SHELLY CLAY 17 to 22 25 to 400 0 to 15 28 to 32 1x10-6

to 1x10-8

UPPER MOTTLED CLAY 19 to 21.5 25 to 400 0 to 15 28 to 32 1x10-6

to 1x10-8

LAMINATED BEDS 20 to 22

100 to 150 (silt)

100 to 300 (clay) 0 to 10

28 (Clays) 28 to 42

(Sands) 1x10-4

to 1x10-7

LOWER SHELLY CLAY 20 to 22

100 to 200 (silt)

200 to 310 (clay) 0 to 15 28 to 32 1x10-6

to 1x10-8

LOWER MOTTLED CLAY 19 to 22

25 to 100 (silt) 100

to 300 (clay) 0 to 15 28 to 32 1x10-6

to 1x10-8

PEBBLE BED 19 to 21.5 N/A 0 37 to 44 1x10-3

to 1x10-6

GLAUCONITIC SAND 20 to 22

10 to 120 (fine

soils) 0 to 10

43 to 44 (granular

soils) 1x10-3

to 1x10-6

THANET BED 20 to 22 N/A 0 40-44 1x10-2

to 1x10-5

BULLHEAD BED 20 to 22 N/A 0 40-44 1x10-2

to 1x10-5

UPPER CHALK 20 to 22 N/A 0 42-44 1x10-1

to 1x10-2

The majority of the fine-grained samples from all strata plot at the edge of the plasticity limit

or beyond this within the semi-solid state. This results in the vast majority of fine grained

samples being stiff to very stiff.

7.0 REFERENCES

Attewell, P. (1995). Tunnelling contracts and site investigation. London: Taylor & Francis.

Burland, J. B., Standing, J.R., Jardine, F.M. (2001). Volume 1: Projects and methods.

Buliding response to tunnelling. Case studies from construction of the Jubilee Line

Extension, London. Thomas Telford Publishing.

Bristow, R., Mortimore, R., Wood, C. (1997) Lithostratigraphy for mapping the Chalk of

southern England. Proceedings of the geologists' Association. Vol 108, pp 293-315.

Clarke, B.G. (1990) Session 2: Pressuremeter Testing in Soils. Consolidation characteristics

of clays from self-boring pressuremeter tests. Geological Society, London, Engineering

Geology Special Publications; 1990; vol. 6, pp 33-37.

Craig, R.F. (2004) Craig's Soil Mechanics 7th

Edition. Spon Press, Abingdon, Oxfordshire.

34


EDINA (2010). Carto, Land-Form Register, Ordnance Survey,

http://digimap.edina.ac.uk/carto3/index.jsp?useJS=true accessed on 14th

February, 2010.

Ellison, R.A. (2004). Geology of London. Special Memoir for 1:50 000 Geological sheets

256 (North London), 257 (Romford), 270 (South London) and 271 (Dartford) (England and

Wales). British Geological Survey, Keyworth, Nottingham.

Hight, D.W., Ellison, R.A., Page, D.P. (2004) Engineering in the Lambeth Group. CIRIA,

London.

Hughes, J.M.O., Wroth, C.P., Windle, D. (1977) Pressuremeter tests in sands. Geotechnique

Vol. 27 Issue 4, pp 455-477.

Peck, R.B., Hanson, W.E., Thorburn, T.H. (1974) Foundation Engineering, 2nd

Edition. John

Wiley and Sons, New York.

Royse, K.R., Rutter, H.K., Entwisle, D.C. (2008) Property attribution of 3D geological

models in the Thames Gateway, London: new ways of visualising geoscientific information.

Bulletin of Engineering Geology and the Environment, Vol. 68 pp 1-16.

Spink, T.W. (2002) The CIRIA Chalk description and classification scheme. Quarterly

Journal of Engineering Geology and Hydrogeology Vol. 35 Iss. 4 p 363-369.

Stroud, M.A., Butler, F.G. (1975) The Standard Penetration Test and the Engineering

Properties of Glacial Materials. Proceedings of the symposium on Engineering Properties of

glacial materials, Midlands, U.K.

Waltham, T.(2002) Foundations of Engineering Geology 2nd

Edition. Spon Press, Abingdon,

Oxfordshire.

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