Ground Conditons of the Bermondsey Area of London: a Geotechnical Report for Package 4 of the Jubilee Line Extension

GROUND CONDITONS OF THE BERMONDSEY AREA OF LONDON: A GEOTECHNICAL REPORT FOR PACKAGE 4 OF THE JUBILEE LINE EXTENSION

Student No: 701890

NOVEMBER 21, 2016 UNIVERSITY OF PORTSMOUTH

Contents

1.0 INTRODUCTION ...... 1

2.0 THE SITE ...... 1

2.1 Topography ...... 1

2.2 Geology ...... 2

2.2.1 Stratigraphy ...... 2

2.2.2 Groundwater ...... 3

2.2.3 Made Ground ...... 3

2.2.4 Alluvium ...... 3

2.2.5 Kempton Park Gravel Member ...... 3

2.2.6 Thames Group ...... 4

2.2.7 Lambeth Group ...... 4

2.2.8 Thanet Sand Formation ...... 5

2.2.9. Upper Chalk Formation ...... 5

2.3 Potential Ground Hazards ...... 5

2.3.1 Groundwater levels ...... 5

2.3.2 Seepage and Chemical Damage...... 6

2.3.3 Subsidence ...... 6

3.0 GROUND INVESTIGATION ...... 6

3.1 General ...... 6

3.2 Boreholes ...... 6

3.3 In Situ Testing ...... 7

3.4 Installations...... 7

3.5 Sampling ...... 7

3.6 Laboratory Testing ...... 8

3.7 Groundwater Monitoring ...... 8

4.0 GROUND CONDITIONS ...... 9

4.1 Stratigraphy ...... 9

4.2 Groundwater Conditions ...... 10

4.3. Results of the Laboratory and In Situ Testing...... 10

4.4 Geotechnical Characterisation ...... 10

4.4.1 Made Ground ...... 11

4.4.2 Alluvium ...... 11

4.4.3 Kempton Park Gravel Member ...... 12

4.4.4 London Clay ...... 13

4.4.5 Blackheath Beds ...... 14

4.4.6 Upper Shelly Clay ...... 14

4.4.7 Upper Mottled Clay ...... 15

4.4.8 Laminated Beds ...... 16

4.4.9 Lower Shelly Clay ...... 17

4.4.10 Lower Mottled Clay ...... 18

4.3.11 Pebble Bed ...... 18

4.4.12 Glauconitic Sands ...... 19

4.4.13 Thanet Bed ...... 20

4.4.14 Bullhead Bed ...... 21

4.4.15 Upper Chalk ...... 21

5.0 CONCLUSION ...... 22

6.0 REFERENCES ...... 23

APPENDIX 1 – Engineering Descriptions ...... 33

List of Figures

1 Site Location Map ...... 24

2 Borehole Location Map ...... 25

3 Geological Map ...... 26

4 Geological Cross Section ...... 27

5 Standard Penetration Test vs Level ...... 28

6 Plasticity Index Chart ...... 29

7 Moisture Content vs Level ...... 30

8 Undrained Shear Strength vs Level ...... 31

9 pH vs Level ...... 32

List of Tables

1 A summary of the geological strata of the London Basin ...... 2

2 A summary of the groundwater piezometer data ...... 8

3 A summary of the soil succession beneath the site ...... 9

4 Summary of geotechnical properties for Made Ground ...... 11

5 Index test summary for Made Ground ...... 11

6 Summary of geotechnical properties for Alluvium ...... 11

7 Index test summary for Alluvium ...... 12

8 Summary of geotechnical properties for Kempton Park Gravel ...... 12

9 Summary of geotechnical properies for London Clay ...... 13

10 Index test summary for London Clay ...... 13

11 Summary of geotechnical properties for Blackheath Beds...... 14

12 Index test summary for Blackheath Beds ...... 14

13 Summary of geotechnical properties for Upper Shelly Clay ...... 14

14 Index test summary for Upper Shelly Clay ...... 15

15 Summary of geotechnical properties for Upper Mottled Clay ...... 15

16 Index test summary for Upper Mottled Clay ...... 16

17 Summary of geotechnical properies for Laminated Beds ...... 16

18 Index test summary for Laminated Beds ...... 16

19 Summary of geotechnical properties for Lower Shelly Clay ...... 17

20 Index test summary for Lower Shelly Clay ...... 17

21 Summary of geotechnical properties for Lower Mottled Clay ...... 18

22 Index test summary for Lower Mottled Clay ...... 18

23 Summary of geotechnical properties for Pebble Bed ...... 18

24 Index test summary for Pebble Bed ...... 19

25 Summary of geotechnical properties for Glauconitic Sands ...... 19

26 Index test summary for Glauconitic Sands ...... 20

27 Summary of geotechnical properties for Thanet Bed ...... 20

28 Index test summary for Thanet Bed ...... 20

29 Summary of geotechnical properties for Bullhead Bed ...... 21

30 Summary of geotechnical properties for Upper Chalk ...... 21

1.0 INTRODUCTION

A site investigation was undertaken in 1990 by Soil Mechanics Ltd. in accordance with the Department of Transport who published specifications for Ground Investigation in 1987 relating to tunnelling projects (Attewell, 1995). These works involved Package 4 of the Jubilee Line Extension in which 20 boreholes (18 Cable Percussive and 2 Rotary) were drilled in the area between London Bridge and Canada Water, London. The work was completed on the 16th November 1990 for London Underground.

The purpose of the investigation was to report the ground conditions prior to the proposed engineering work (tunnelling) in the area.

This interpretative and factual report follows the work undertaken for Package 4 of the proposed Jubilee Line Extension and includes copies of the test data obtained during the site investigation.

2.0 THE SITE

2.1 Topography

The site area at street level is considered to be relatively flat, ranging from 3.6 mOD in the east to 1.9 mOD in the west. Generally the low and rolling topography is a result of the composition of the London Clay Formation being homogenous, as well as the overlying superficial units which were subject to erosion in the Thames Valley. Beginning just past London Bridge tube station, the line follows a south-easterly direction, while being known to remain approximately 400m from the bank of the River Thames. The line continues for approximately 600m towards Bermondsey tube station eventually curving eastwards and continuing in an easterly direction underlying the borough of Southwark.

2.2 Geology

Table 1: A summary of the geological strata of the London Basin (Ellison et al., 2004).

Period Group Formation Thickness (m) Palaeogene Bagshot Formation: sand, fine grained with thin clay 10-25 beds Thames London Clay Formation: clay, silty; fine sand clay at 90-130 base. Claygate member: interbedded sand and clay at top

Harwich Formation: sand, clayey fine-grained sand 0-10 and pebble beds

Lambeth Reading, Woolwich, and Upnor 10-20 Formations: clay mottled with fine-grained sand, laminated clay, flint pebble beds and shelly clay

Thanet Sand Formation: sand, fine-grained 0-30

Cretaceous Chalk Undivided mainly Seaford Chalk Formation: chalk, Up to 70 soft, white with flint courses

Lewes Chalk Formation: chalk, white with hard, 25-35 nodular beds New Pit Chalk Formation: chalk, white to grey with 30-40 few flints Holywell Chalk Formation: chalk white to grey, shelly, 13-18 hard and nodular Undivided Zig Zag Chalk 65-70 Formation and West Melbury Marly Chalk Formation (formerly Lower Chalk): chalk, pale grey with thin marls; glauconitic at the base

The site is said by Ellison et al., (2004) to be located on a series of superficial and bedrock geological units which are at or near ground level. The geological units described below range in depth across the site and are likely to be encountered during the site investigation.

2.2.1 Stratigraphy The main lithologies and strata which make up the London Basin consist of several groups of formations and structures (Table 1) which have been summarised and presented by detailed geological mapping from the British Geological Survey (Royse et al., 2012). The Thames and Lambeth groups are underlain by the Chalk (Mortimore et al., 2011), all of which are presented in a geological map (Figure 3). The main geological strata of significant importance concerning the Jubilee Line Extension include the London Clay

(Burnett & Fookes, 1974), the Lambeth Group (Entwisle et al., 2013), and the Thanet Sand (Page, 1995). A cross section of all strata is presented in Figure 4.

2.2.2 Groundwater Because of its nature to flood, groundwater plays an essential role in tunnel engineering projects (Head, 1986). However, there is a general lack of information from literature in this specific area, which has been suggested because disruption of water supplies is not very significant, and these problems are of major importance to groups of people who may be involved (Brassington, 1986). Significantly, groundwater abstraction must be considered because rising and falling groundwater levels will have an effect on the engineering properties due to pore pressures. Simpson et al., (1989) identifies that groundwater levels in London are rising and could have potential long term effects on the proposed work for the Jubilee Line Extension, particularly towards the base of the London Clay.

There are two confined aquifers in the London Basin: the upper aquifer within the Kempton Park Gravel and a lower aquifer in the Upper Chalk, Thanet Sand and Upnor Formations. These aquifers are separated by the impermeable London Clay Formation. Perched aquifers also occur within the London Clay and Lambeth Group where the composition is coarser or sandier (Linney & Page, 1996).

2.2.3 Made Ground This unit forms the top superficial layer overlying the stratigraphy and is distributed throughout the London Basin and almost the entire length of the proposed Jubilee Line Extension. Made ground can consist of a wide range of rubble, brick material, concrete, and refuse which are incorporated with sands and gravels in a clay or silt matrix (Ellison et al., 2004). Difficulties in construction have risen due to the variability of this unit, particularly because industrialisation and urbanisation has a long history in London (Burland et al., 2001).

2.2.4 Alluvium Resting uncomfortably on the Kempton Park Gravel, this unconsolidated material forms a shallow layer on the surface and is a result of deposition by streams and rivers (Knappett et al., 2012). The unit is made up of clayey silt, silty clay and locally developed fine to coarse grained sand depending on abundance of grains. This unit is generally less than a metre thick and it also includes organic peat which becomes more extensive west of the Rotherhithe tunnel (Ellison et al., 2004).

2.2.5 Kempton Park Gravel Member This unit was deposited in a braided river system, approximately 5km across the River Thames floodplain, causing inconsistency within thickness and lateral distribution. However, this unit covers the entire length of the Jubilee Line Extension (Burland et al., 2001). Dominating this stratum are variable sands and gravels 1-6m thick. (Ellison et al., 2004).

2.2.6 Thames Group 2.2.6.1 London Clay Formation Of significant importance and more argillaceous towards the top, this stratum majorly (~60%) consists of overconsolidated, bioturbated, fissured blueish grey silty clay to very silty clay which is slightly calcareous. Pyrite and carbonate concretions such as claystone may occasionally occur. Towards the top and beneath the superficial deposits, the London Clay is weathered and oxidised to a brownish colour (Chandler, 2000), while siltier and sandier deposits are more abundant at the base (Ellison et al., 2004; Royse et al., 2012).

2.2.6.2 Blackheath Beds (Harwich Formation) This unit is generally less than a metre thick and lateral distribution varies, but sometimes is present underneath the London Clay. This unit consists of dense, rounded medium to coarse flint gravel within a dark brown or green silty/clayey sand matrix (Burland et al., 2001).

2.2.7 Lambeth Group The Lambeth Group geological system is considered to be complex (Entwisle et al., 2013; Hight, Ellison, & Page, 2004). The units are summarised below:

2.2.7.1 Woolwich Formation - The Lower Shelly Clay (LSC) is dominantly dark grey to black clay containing abundant shelly beds, becoming increasingly medium grained sand towards the east. At the base of this unit is a bed deposited with an abundance of oyster shells and is relatively sandy. Some beds are weak cemented shells, but fewer beds are brownish grey clay, with siderite cementation. Lignite (0.3m or less) is present at the base in the south-east. Overlying the LSC, there are laminated beds of thinly interbedded fine and medium sand, silt and clay with scattered bivalve shells. Cross laminated medium grained, well sorted pale olive brown sand (4m thickness) becomes extensive towards the east. On top of this unit, lies the Upper Shelly Clay (USC) 3m thick. It is comprised of interbedded grey shelly clay and interbedded grey brown silt and very fine sand with more shells than the Lower Shelly Clay and scattered glauconite grains. The sand is more abundant in the south-east. (Ellison et al., 2004; Entwisle et al., 2013) 2.2.7.2 Reading Beds Formation - The unit is dominated by unbedded colour-mottled fissured silty clay and Upper Mottled Clay (UMC) of pale brown and pale grey-blue, dark brown, pale green, red, brown and crimson in colour, depending on the state of oxidation. The fissures give rise to a blocky texture and this unit is thinly laminated. The Lower Mottled Clay (LMC) is somewhat similar to the Upper Mottled Clay except that purple is another colour within the deposit and the clay contains irregular

carbonate nodules 0.5m in diameter. Calcareous clayey sands become more abundant towards the east (Ellison et al., 2004). 2.2.7.3 Upnor Formation - Resting uncomformably on the Thanet Sand, this stratum is dominated by fine to medium grained sand and clayey sand with variable amounts of medium to coarse glauconite grains of fine to medium sand graded, and well-rounded, elongated flint pebbles. The Pebble Beds are approximately 3m in diameter, while the pebbles themselves vary between less than 30mm diameter and up to 200mm. The Glauconitic Sands are typically grey to greenish grey when fresh, and change to a range of brown, red, orange and purple when weathered. Like the London Clay, carbonate concretions of powdery patches, 0.5m diameter, and/or highly irregular masses are prominent (Ellison et al., 2004).

2.2.8 Thanet Sand Formation 2.2.8.1 Thanet Beds - This unit consists of fine to medium grained sub angular sand, with fine glauconitic sand and little clay or silt higher up as the sequence coarsens upwards. The sands are grey and heavily bioturbated, reaching a maximum thickness of 30m (Ellison et al., 2004).

2.2.8.2 Bullhead Bed - This stratum marks the bottom of the Thanet formation, comprising of sporadic rounded black pebbles (up to 50mm), and unworn nodular flints (up to 150mm across) within a dark greenish grey, clayey fine to coarse grained sand matrix. It is considered to be a conglomerate up to 0.5m thick (Ellison et al., 2004).

2.2.9. Upper Chalk Formation - This stratum is typically a fine grained and white limestone, made of skeletal remains (Cocoliths of planktonic algae, composed from calcium carbonate). It is mapped as the Lewes Chalk or Lewes Nodular Chalk in London and can be best described as hard to very hard chalk with interbedded soft-hard gritty chalks and bands of flint (Ellison et al., 2004; Mortimore et al., 2011).

2.3 Potential Ground Hazards

2.3.1 Groundwater levels

Groundwater levels in London are currently on the rise. Sand and gravel in the Lambeth Group and Thames Groups could be subject to higher pore pressures, which will cause lateral and vertical ground movements in the London Clay (Simpson et al., 1989). Structural damage occurs when these pore

5 pressures increase in the clays, leading to a loss in shear strength and the swelling of clay minerals (Hight et al., 2004). The Upper Chalk is fissured which can lead to flooding from increased groundwater flow as a result of the higher permeability. These fissures could lead to artesian pore water pressures. (Ellison et al., 2004). On the other hand, when groundwater levels fall, the geological strata become consolidated and under drainage may occur (Entwisle et al., 2013). 2.3.2 Seepage and Chemical Damage

Acidic groundwater can lead to deterioration of tunnel linings, because sulphate forms in the surrounding sediments when pyrite comes into contact with air driven by pressure changes (Rainey & Rosenbaum, 1989). The Upper Shelly Clay, Lower Shelly Clay and Laminated Beds could be problematic in that the pyrite concentration is high due to organic material and calcium carbonate. To overcome this, cement tunnel linings penetrating these units would need to be sulphate resistant (Entwisle et al., 2013). 2.3.3 Subsidence

Ground subsidence may become problematic once tunnel construction has been complete. This is due to the overlying weight of the buildings such as St James’s Church and high rise blocks of flats which could lead to loss of shear strength within the soils. Monitoring of these buildings is therefore paramount as well as reinforcement of the tunnels underneath the buildings.

3.0 GROUND INVESTIGATION

The ground investigation was carried out according to appropriate standards (BS 5930:1999, 1999). This section documents the important features that were considered for the Jubilee Line extension.

3.1 General

To assess the soil succession in the area, a ground investigation was undertaken for London Underground east of London Bridge railway station and west of Canada Water between 24th September 1990 and 17th December 1990.

3.2 Boreholes

Twenty boreholes were drilled across the site in order to determine the consistency and composition of the underlying soils. Commencing on the 24th September 1990, this programme lasted just under two months, finishing on 14th November 1990. The final elevations ranged from -24.93mOD in Borehole 413P to a much deeper -49.84 in Borehole 404T, but the majority of excavations were drilled between 40-30 metres in depth.

14 of the boreholes were drilled using Cable Percussive techniques that used diameters ranging from 150-250mm. 2 other boreholes (404T and 407T) were excavated using open hole drilling. This consisted of the use of a tricone rock bit, followed by rotary drilling to the base of the boreholes. Boreholes 410T and 415T commenced excavation using Cable Percussive methods followed again by rotary drilling. The remaining two boreholes (403P and 413P) were also drilled with Cable Percussion, but with the addition of some Self Boring Pressuremeter (SBP) tests to test the London Clay, Upper Mottled Clay and the Thanet Sands.

3.3 In Situ Testing

Standard Penetration Tests (SPTs) were undertaken in the clay and silt horizons with Split spoon testing. This involved an initial number of blows to a 150mm depth from the test start datum, with an N value being generated from the number of blows required to drive the split spoon or cone a further 300m. Down-hole boring permeability tests were carried out within a number of boreholes (BH403, BH404T, BH409, BH411, BH413P, BH414, BH416, BH417, BH418, BH419). Self boring Pressuremeter (SBP) tests were undertaken in BH403P and BH413P enabling a variety of total and effective stresses to be determined in-situ for clays and silts.

3.4 Installations

Most of the boreholes drilled during this investigation were installed with one piezometer and sand filter to measure groundwater movements and fluctuations. This was not the case for BH402, BH403, BH407T, BH410T, BH415T and BH416 due to being dual installed with an upper and lower piezometer. BH403P had no installation carried out. On completion of the installations, the boreholes were backfilled with bentonite.

3.5 Sampling

More than 1200 samples were collected for testing, involving different sampling methodologies: - Undisturbed samples within clayey and silty horizons were obtained using either 100mm diameter tubes or push piston methods. - Small disturbed samples were obtained from SPT tests in clayey and silty horizons or taken at intervals depending on the drilling methodology. - Bulk disturbed samples were obtained from CPT tests on sand and gravel horizons. - Core samples were extracted from BH404T, BH407T, BH410T and BH415T which are rotary cored. - Water samples were extracted from boreholes where groundwater levels were occasionally noted.

3.6 Laboratory Testing

In order to give an appropriate and detailed spread of the site data, the following tests were conducted on a selection of the borehole samples: - Index property testing on clayey and silty samples to identify the Liquid and Plastic Limits, Plasticity Index and natural moisture content (Figures 6 and 7). - Undrained triaxial compression tests on disturbed clay and silt samples to calculate the undrained shear strength values (Figure 8).

- Soil and water pH testing was undertaken on a number of water, undisturbed and disturbed samples.

The results of all the laboratory tests can be found in Figures 5-9.

3.7 Groundwater Monitoring

The piezometers were monitored from 4th October 1990 to 17th December 1990 for the highest and lowest observed groundwater levels, except from BH403. Results in Table 2 have been plotted on the cross section (Figure 4).

Table 2: A summary of groundwater piezometer data. Borehole Highest Date Lowest Date Piezometer tip (m.O.D) (m.O.D) depth (m.O.D) 401 Flood 12 Nov -1.41 09 Oct -32.04 402 (U) -2.19 07 Dec -6.57 13 Nov -24.55 402 (L) 2.75 07 Dec -8.89 07 Oct -32.05 404T -4.73 05 Oct -7.08 10 Dec -33.79 405 -13.61 10 Dec -14.02 16 Oct -31.49 406 -11 10 Dec -13.44 15 Oct -30.12 407T (U) 1.31 23 Oct -4.71 14 Nov -12.74 407T (L) -7.93 23 Oct -10.78 07 Dec -21.74 408 -1.09 12 Nov -8.44 16 Oct -22.09 409 -1.05 31 Oct -1.15 24 Oct -3.75 410T (U) -2.36 07 Dec -2.54 15 Nov -7.21 410T (L) -8.47 31 Oct -8.92 17 Dec -21.21 411 -1.38 10 Dec -9.05 17 Dec -14.58 412 -8.47 01 Nov -13.46 15 Oct -32.36 413P -8.53 10 Dec -8.89 17 Dec -23.33 414 -8.75 31 Oct -8.9 17 Dec -16.11 415T (U) -7.69 07 Dec -7.99 15 Nov -15.5 415T (L) -7.69 10 Dec -8.18 07 Dec -29.5 416 (U) -1.52 30 Oct -1.73 17 Dec -4.29 416 (L) -7.54 10 Dec -7.11 29 Oct -14.49 417 -5.85 10 Dec -7.35 04 Nov -19.05 418 -8.34 29 Oct -8.59 15 Nov -19.88 419 -7.81 30 Oct -8.95 17 Dec -14.46 8

4.0 GROUND CONDITIONS 4.1 Stratigraphy

Stratigraphy logging of all 20 boreholes determined the following soil succession (Table 3) underlying the site. Table 3: A summary of the soil succession strata 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 Kempton Park Terrace Gravel 0.96 -7.95 2.70 6.90 Gravel Member London Clay London Clay -4.21(-3.96) -35.84(-7.29) 0.30(0.50) 28.55(0.55) Formation (weathered Harwich Formation Blackheath -4.28 -32.15 0.20 0.70 Beds Upper Woolwich Upper Shelly -4.8 -36.54 0.55 2.50 Formation Clay Upper Reading Upper -4.18 -36.74 1.60 7.65 Formation Mottled Clay Lower Woolwich Laminated Beds -5.78 -32 1.10 2.98 Formation Lower Shelly -8.68 -32.98 0.33 4.57 Clay Lower Reading Lower -9.78 -34.8 0.25 1.75 Formation Mottled Clay Upnor Pebble Bed -10.28 -32.44 0.57 3.10 Formation Glauconitic -13.38 -37.94 2.00 6.80 Sand Thanet Sand Thanet Beds -19 -49.84 10.50 12.50 Formation Bullhead Bed -31.4 -38.51 0.26 0.60

Upper Chalk Upper Chalk -31.4 -47.11 (NP 2.65 (NP) 8.6 (NP) Formation

A cross section of the site is located in Figure 4. From the table and cross section, it can be appreciated that the Woolwich and Reading beds are interbedded, and that there is indication of a north-west dip from boreholes 401-408 where the cross section is following a south-easterly direction. However, this is less apparent in the other boreholes since

9 the direction changes from west to east as can be shown by the map. Deformation is also evident towards the east, indicating higher shear strength.

4.2 Groundwater Conditions

Within the piezometers the groundwater levels formed two phreatic surfaces present underneath the site (Figure). Upper surface is ~-1.00 mOD and a lower surface is -7.00 mOD. The upper surface corresponds to the permeable Kempton Park Gravel, overlying the relatively impermeable London Clay from boreholes 401-408, and continues east in boreholes 410T419 where the Kempton Park Gravel overlies the Upper Shelly Clay and Upper Mottled Clay which are less permeable. The lower surface could possibly be related to pore pressures in the Lambeth Group and Thanet Sands formations. It is suggested that pore pressures within the strata closely match hydrostatic pore pressures, despite fluctuations between boreholes. Borehole 401 for example indicated groundwater at 0 mbgl. There is no evidence to suggest that there is under-drainage of soils beneath the site. However, further monitoring could be undertaken to identify recent changes to groundwater conditions, since the monitoring here only extended for at most 3 months after installations. Piezometers installed in clay horizons can take weeks, months or even longer for the groundwater conditions to become stable after drilling. Results may suggest that the phreatic surfaces may have moved.

4.3. Results of the Laboratory and In Situ Testing.

The graphs on the following pages represent the findings of the laboratory and in situ testing for specific geotechnical properties. Standard Penetration (Figure 5) is presented as N values taken from samples in all 20 boreholes. Plastic index was plotted against liquid limit to determine different plastic limits for the geological units; the A and U lines have also been plotted since the majority of samples are clays and the other majority of samples are silts (Figure 6). Moisture content and undrained shear strength values were plotted against depth (Figures 7 and 8). Design lines deriving from Cu/N (Stroud & Butler, 1975) which plot as lines of best fit are also included in Figures 5 and 8.

4.4 Geotechnical Characterisation

Information for SPT and downhole permeability tests were not made available for this report, so this will not be discussed.

4.4.1 Made Ground Table 4: Summary of geotechnical properties for Made Ground. Encountered Thickness Chiselling SPT N’ No of index Plasticity Bulk Undrained Range (m) Value property tests density shear strength

All boreholes 0.30 (BH416) 6 boreholes 3-24 1 Silt - 15-70 5 (BH402) Intermediate

This layer consisted of topsoil (0.10-0.20m) tarmac (0.05-0.15m) or concrete (0.05-0.40m) depending on the borehole. These elements overlaid soft to firm brown, grey, green and black silty sandy CLAY with abundant fine to coarse angular-rounded brick fragments, concrete, ash, tile mortar, flint coal and chalk gravels and rare cobbles of tile, chalk, concrete and timber. Made Ground in Borehole 403 was noted as oily and 413 noted as having a pungent odour, both indicating contamination. This is however, beyond the scope of this report. Results of the index test (Table 4) plot below the A line (Figure 6) and is a silt of intermediate plasticity.

Table 5: Index test summary for Made Ground. LL (%) PL (%) PI (%) W (%) 42 30 12 33

Two pH tests were also undertaken, with results indicating a pH of 7.0 to 8.0 (Figure 9).

Further results from Burland et al., (2001) are included in Table 3 for undrained shear strength. Bulk density is not given because values for volume are not documented in the literature, possibly due to the variability of this stratum.

4.4.2 Alluvium Table 6: Summary of geotechnical properties for Alluvium.

Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property tests content density shear strength (Mg/m3) 14/20 boreholes 0.50 (BH401) 3-23 3 Clay: Low to Semi-solid 2.01 25-50 high 3.60 (BH405) Silt - intermediate

The 6 boreholes found not to contain alluvium were 402, 403P, 407T, 404, 414 and 419. Where encountered, it was situated below Made Ground. This layer can be described as a soft to firm, yellow to orange, brown and green slightly sandy (fine to medium) occasionally very sandy silty to very silty CLAY with occasional fine to coarse angular-sub rounded flint gravel with rare rootlets. Some beds are also predominantly sandy, consisting of loose to medium dense greyish yellow orange and brown clayey and silty SAND with occasional fine to medium angular-sub rounded flint gravel and occasional pockets of brown very clayey silt (<20mm). In Borehole 405, peat was encountered 0.50m thickness and -0.49 mOD.

This can be described as firm black SILT with abundant fragments of organic material. This organic material is dominated by decaying wood.

The results of the index testing (Table 6) show that the clays plot as clays with high to low plasticity while the silt plots within the intermediate plasticity (Figure 6). Two of the three moisture contents plot to the left of the plastic limit, suggesting the soils are in a semi solid state (Figure 7).

Table 7: Index test summary for Alluvium. LL (%) PL (%) PI (%) W (%) 24-58 15-28 9-31 10-24

Two pH tests were completed, giving a pH of 7.1 to 7.8 (Figure 9).

Further results from Burland et al., (2001) are included in Table 5 for undrained shear strength. 4.4.3 Kempton Park Gravel Member Table 8: Summary of geotechnical properties for Kempton Park Gravel.

Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property tests content density shear strength (Mg/m3) All boreholes 2.70 (BH411) BH409 4-79 between 6.90 (BH407T) Majorities 6.90 and 11-47. 7.70 mbgl

Underlying either alluvium or made ground, this stratum can be described as a medium dense to dense orange brown very sandy medium to coarse sub-angular-sub-rounded flint GRAVEL with occasional flint cobbles and pockets of brown silty clay. Plasticity index, triaxial and moisture content tests could not be carried out due to the sandy and gravelly nature of this stratum, as it is considered that these soils are non-plastic. pH tests were carried out on 15 water samples, giving a range of 7 to 9.7 (Figure 9). Undrained shear strength and bulk density values are not available for this stratum. A design line based on SPT values has been plotted in Figures 5 and 8.

4.4.4 London Clay Table 9: Summary of geotechnical properties for London Clay.

Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property tests content density shear strength (Mg/m3) (kN/m2)

12/20 boreholes 0.30 (BH410T) BH401 12-99 30 75% samples Plastic— 1.90- 66-394 between 29.65 (BH401) very high and semi solid 2.10. 16.501710 20% high. BH401 and = Silt – high to 22.5023.40 intermediate, mbgl due to BH403 = Silt – irregular very high. claystone layers

There is indication of a north-northwest dip of this strata. The top of the formation in Borehole 401 was found to be noticeably weathered at 0.55m depth and 0.50m in Borehole 412. The London Clay can be described 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. There are fissures randomly oriented and are clean planar-undulose smooth and occasionally polished. The upper weathered section differed from the main formation and was brown in colour. The base of the stratum is siltier with proportional amounts 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. There are fissures randomly oriented and are clean planar-undulose smooth to rough. Occasionally polished fissures in the London Clay suggest shear surfaces (Ellison et al., 2004).

75% of index test results (Table 9) plot as very high plasticity clays (Figure 6) and approximately 20% as high plasticity clays. Two other samples from the basal beds of the London Clay plotted as silts with intermediate to high and very high plasticity respectively. Stroud & Butler (1975) report Cu/N values of between 4.3 and 4.8. A design line using Cu/N was plotted in Figures 5 and 8.

Moisture contents suggest that the samples are at or less than the plastic limit, indicating the London Clay is in a plastic to semi-solid state.

Table 10: Index test summary for London Clay. LL (%) PL (%) PI (%) W (%) 50-86 19-43 21-58 8-35

10 pH tests were undertaken giving a range of 6.9 to 8.6 (Figure 9). It is suggested that the lower pH values are due to localised areas containing pyrite.

4.4.5 Blackheath Beds Table 11: Summary of geotechnical properties for Blackheath Beds.

Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property tests content density shear strength (Mg/m3) (kN/m2)

Majority 0.20 (BH413P) BH402, 39-214 3 Clays – high to BH402 at 34 1.93- 111-235 mbgl - 0.70 (BH411) BH403, very high. 2.01 BH403P, BH412, non- Semi solid BH405 plastic.

Underlying the London Clay or the Kempton Park Gravel are the Blackheath Beds. The base of the London Clay was not reached in Borehole 401 so the beds were not identified and Borehole 410T shows an error where this formation would be expected. Elsewhere this formation was not found because the succession dips to the north-northwest shown by the cross section. The Blackheath Beds 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.

The results of the three index tests (Table 11) indicate that two samples plot as clays with high to very high plasticity (Figure 6). One sample plots to the left of the plastic limit, indicating a semi-solid state.

One pH test gave a result of 6.3 (Figure 9).

Table 12: Index test summary for Blackheath Beds.

LL (%) PL (%) PI (%) W (%) 63-72 25-27 38-45 22-25

4.4.6 Upper Shelly Clay Table 13: Summary of geotechnical properties for Upper Shelly Clay.

Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property tests content density shear strength (Mg/m3) (kN/m2)

13/20 boreholes 0.55 (BH412) BH402, 32-273 5 Clays – low to Plastic— 1.71- 26-132. Lower value 2.50 (BH408) BH403, intermediate. semi solid 2.18 BH405 BH407T clay – in BH408 due due to high. to silty nature. limestone and flint gravel bands

The Upper Shelly Clay rests beneath the Blackheath Beds or the Kempton Park Gravel, and the geology is gently dipping due to interbedding of the Reading and Woolwich formation resulting in no appearance of the USC in BH403P. 14

The USC can be described as 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.

The results of the five index tests (Table 13) are summarised. Three samples plot as clays of low to intermediate plasticity with one other sample corresponding to a clay of high plasticity. Figure 7 suggests that moisture contents are at or less than the plastic limit, indicating the USC is in a plastic to semi-solid state.

Table 14: Index test summary for Upper Shelly Clay.

LL (%) PL (%) PI (%) W (%) 29-62 14-26 14-36 17-30

Stroud & Butler (1975) report Cu/N values of between 4.3 and 6 although their data shows values between 3 and 3.5. Based on this, a design line using Cu/N was plotted in Figures 5 and 8. One pH test gave a result of 6.3 (Figure 9).

4.4.7 Upper Mottled Clay Table 15: Summary of geotechnical properties for Upper Mottled Clay. Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property tests content density shear strength (Mg/m3) (kN/m2)

19/20 1.60 (BH419) 5 boreholes 15-333 24 Clays – low to Plastic 1.88- 22-277. Lower high. boreholes. 7.65 (BH403) due to hard 2.15 value due to BH402 not nature BH411 and polished encountered. BH415 silts – fissure. intermediate to high.

Situated beneath the USC or the Kempton Park Gravel or Blackheath Beds, the Upper Mottled Clay can be described as 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 encountered. Slickenlines and polished surfaces suggest shear surfaces in some of the fissures on this layer (Ellison et al., 2004). The samples from index tests (Table 15) plot from low plasticity to very high plasticity clays (Figure 6) but mainly centred around high to very high plasticity sections. Two samples plot as intermediate and high 15 plasticity silts. Natural moisture contents show that samples plot at or higher than the plastic limit, indicating this stratum is plastic.

Stroud & Butler (1975) report Cu/N values of between 4.3 and 7. A design line using Cu/N was plotted in Figures 5 and 8.

Table 16: Index test summary for Upper Mottled Clay.

LL (%) PL (%) PI (%) W (%) 20-80 11-31 9-50 11-35

Nine pH tests were undertaken, given a range of 6.4 to 8.4 (Figure 9). 4.4.8 Laminated Beds Table 17: Summary of geotechnical properties for Laminated Beds. Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property content density shear strength tests (Mg/m3) (kN/m2)

18/20 1.10 (BH405) BH409 due 25-300. 15 Clays – low to Plastic 2-2.20 102-314. Lower Majority 25- high. boreholes. 2.98 (BH418) to very stiff values due to BH401 and nature of 82. Greater BH407T at 16.73 silt. BH402 not clay. values due mbgl silt – low. encountered. to dense sand and very stiff silt

Situated below the UMC, the Laminated Beds can be described as 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. There was a void in 410T -28.29 mOD to -29.30 mOD from groundwater flow.

Results from the index tests (Table 17) show that the samples plot from low to very high plasticity clays (Figure 6). One sample plots as a low plasticity silt. Natural moisture contents suggest that samples plot within or on the plastic limit, suggesting a plastic state for this stratum.

Stroud & Butler (1975) report Cu/N values of between 4.3 and 7. A design line using Cu/N was plotted in Figures 5 and 8.

Six pH tests gave results of 6.2 to 8.6 (Figure 9).

Table 18: Index test summary for Laminated Beds. LL (%) PL (%) PI (%) W (%) 27-85 14-35 5-62 20-35

4.4.9 Lower Shelly Clay Table 19: Summary of geotechnical properties for the Lower Shelly Clay. Encountered Thickness Range Chiselling SPT N’ Value No of index Plasticity Moisture Bulk Undrained (m) property content density shear strength tests (Mg/m3) (kN/m2)

18/20 boreholes. 0.33 (BH404T) 9 boreholes 22-750. 19 Clays – Plastic-semi 2.01- 112-310. Lower due to very intermediate to BH401 and 4.57 (BH407T) Majority 22- solid state 2.23 values due to BH402 not stiff hard 76. Higher high. Majority – in situ silty nature. encountered. nature of values due intermediate Remaining LSC. to stiff and to high samples of clay possibly BH417 at plotted at and above 200. hard clays. 13.30 mbgl silt – high

Situated beneath the Laminated Beds, this stratum is described as 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. Polished surfaces on fissures suggest shear surfaces (Ellison et al., 2004).

Results from the index tests (Table 19) show that samples plot from intermediate to high plasticity clays (Figure 6) with the majority as intermediate to high plasticity and one sample plotted as a high plasticity silt. Natural moisture contents plot at or below the plastic limit, indicating that the soils are in the plastic to semi-solid state in-situ.

Stroud & Butler (1975) report Cu/N values of between 4.3 and 5.3. A design line using Cu/N was plotted in Figures 5 and 8.

Table 20: Index test summary for Lower Shelly Clay. LL (%) PL (%) PI (%) W (%) 37-71 18-28 19-45 18-36

Four pH tests were carried out, giving a range of 6.6 to 8.9 (Figure 9).

4.4.10 Lower Mottled Clay Table 21: Summary of geotechnical properties for the Lower Mottled Clay. Encountered Thickness Range Chiselling SPT N’ Value No of index Plasticity Moisture Bulk Undrained (m) property content density shear strength tests (Mg/m3) (kN/m2)

18/20 boreholes. 0.25 (BH417) 10 boreholes 44-500. 8 Clays – low to Semi solid 1.89- 27-251. Lower due to very BH401 and 1.75 (BH404T) 11/12 high. Majority – state in situ 2.21 value BH402 not stiff hard samples – high. at BH417 due to encountered. nature of 44-250. High silty nature. clay. values due to stiff clay.

Situated underneath the LSC, this stratum can be described as 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. Polished and striated surfaces = shear. There were 2 voids in 407T -19.11- -20.08 mOD and -20.56 to -21.11 mOD either side of a silt bed, suggesting flow in the LMC. Results from the index tests (Table 21) show that samples plot as low to high plasticity clays (Figure 6) with the majority plotting in the high plasticity range. Natural moisture contents plot to the left of the plastic limit, indicating the LMC is in a semi-solid state in-situ. Stroud & Butler (1975) report Cu/N values of between 4.3 and 6.2. A design line using Cu/N was plotted in Figures 5 and 8. One pH test gave a result of 7.3 (Figure 9).

Table 22: Index test summary for Lower Mottled Clay. LL (%) PL (%) PI (%) W (%) 33-70 17-29 14-44 13-29

4.3.11 Pebble Bed Table 23: Summary of geotechnical properties for the Pebble Bed. Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property content density shear strength tests (Mg/m3) (kN/m2)

BH404TBH419 0.57 (BH404T) 12 36-390. 3 Clays – low. 2/3 samples 2.16 3.10 (BH419) boreholes Majority Third sample – equal to PL. due to 108-375. high. Last one dense One test – 0 lower. In pebble after 50 situ clay beds. blows. soils plastic or semi solid.

Situated underneath the LMC, this stratum can be described as 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. A value for bulk density has been considered from Ellison et al., (2004). Undrained shear strength values have not been found in the literature for this stratum.

The results of the index tests (Table 23) show that two samples plot as low plasticity clays and the third plotting as a high plasticity clay. Natural moisture contents of two of the three samples equal the plastic limit suggesting the in-situ clay soils are in a plastic or semi-solid state.

Stroud & Butler (1975) report Cu/N values of between 4.4 and 7. A design line using Cu/N was plotted in Figures 5 and 8.

Three pH tests were carried out, giving a range of 7.3 to 9.0 (Figure 9).

Table 24: Index test summary for Pebble Bed. LL (%) PL (%) PI (%) W (%) 25-51 13-22 12-32 10-22

4.4.12 Glauconitic Sands Table 25: Summary of geotechnical properties for Glauconitic Sands. Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property content density shear strength tests (Mg/m3) (kN/m2)

17/20 2 (BH406) 6 boreholes 30-750. 12 Clays – low to Majority of 2-2.18 13-118. boreholes. fine grained 6.80 (BH412) due to very Majority 60- intermediate. 2 Lower values BH401, dense 250. samples of silt – sand – (13, 45) due to BH402, BH403P sands or low. plastic. very sandy not weak 25% clays and encountered. limestone samples – higher values bands. semi solid. due to sandy clays.

This stratum can be described as 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.

Results of the index tests (Table 25) show that samples plot as low to intermediate plasticity clays with two samples plotting as low plasticity silts (Figure 6). Natural moisture contents plot close to and within

19 the plastic limit. The fine grained part of this stratum is considered to be in a plastic state while approximately 25% of the samples are semi-solid.

Stroud & Butler (1975) report Cu/N values of between 5 and 7. A design line using Cu/N was plotted in Figures 5 and 8.

Two pH tests gave a range of 6.3 to 8.7 (Figure 9).

Table 26: Index test summary for Glauconitic Sands. LL (%) PL (%) PI (%) W (%) 29-41 16-23 6-23 15-33

4.4.13 Thanet Bed Table 27: Summary of the geotechnical properties for the Thanet Bed. Encountered Thickness Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained Range (m) Value property content density shear strength tests (Mg/m3) (kN/m2)

404T-419. 10.5 (BH411) 94-1000. 2 Clays – low Plastic 2.24 49-92 12.50 (BH417) Majority 94- not proved 300. 2 tests – 0.

Underlying the Glauconitic Sands, this stratum can described as 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. There were no bulk density or undrained shear strength results because of the sandy nature. Values for bulk density and undrained shear strength have been considered from Ellison et al., (2004).

Index test results (Table 27) show that samples plot as low plasticity clays (Figure 6). Moisture contents plot at the same percentage of the plastic limits, indicating a plastic state for this stratum.

Two pH tests were carried out, giving a range of 8.2 to 8.4 (Figure 9).

Table 28: Index test summary for Thanet Bed. LL (%) PL (%) PI (%) W (%) 26-31 14-15 11-17 14-15

4.4.14 Bullhead Bed Table 29: Summary of geotechnical properties for the Bullhead Bed. Encountered Thickness Range Chiselling SPT N’ Value No of index Plasticity Moisture Bulk Undrained (m) property content density shear strength tests (Mg/m3) (kN/m2)

6/20 boreholes. 0.26 (BH418) BH414 138-300 (BH4047, 0.60 (BH415T) (37-37.30 BH410T, mbgl) due BH411, to flint BH414, cobbles in BH415T, clay matrix. BH418)

Situated beneath the Thanet Bed, this thin stratum can be described as 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. There were no index property, plasticity, moisture content bulk density, or triaxial compression tests for this stratum

4.4.15 Upper Chalk

Table 30: Summary of geotechnical properties for Upper Chalk.

Encountered Thickness Range Chiselling SPT N’ No of index Plasticity Moisture Bulk Undrained (m) Value property content density shear strength tests (Mg/m3) (kN/m2)

5/20 boreholes 8.60 (BH407T) BH411 61-260. 7 25-37% 1.97- 2600 (BH407T, Not proven (37.8038.20 tests – 1.82 BH410T, mbgl) due 6185. BH411, to flint BH415T, nodules. BH418)

Situated below the Bullhead Bead this stratum can be described as 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. CIRA documentation states that the chalk is between C4 and A3, but predominantly of C3 to C4 (Spink, 2002). Table 29 shows that there were no values generated from index property, plasticity, moisture content, bulk density or triaxial compression tests for this stratum. Values considered derive from Ellison et al., (2004).

5.0 CONCLUSION

Ground conditions in the site area indicate that the succession of consolidated soils are gently dipping to the north-north west and deformation is evident towards the east. The London Clay is present more towards the west while the Lambeth Group dominates the east. An upper phreatic surface between the Kempton Park Gravel and London Clay is identified at approximately -1.00 mOD while a second, lower surface within the Lambeth Group and the underlying strata is also existent at approximately -7.00 mOD. The lower surface in these units is representative of the pore pressures governing the engineering behaviour. The water tables are connected where the London Clay is eroded out. Seepage and swelling of the clay should be monitored as excavation will increase phreatic connectivity between the water tables.

The Lambeth Group is considered to be complex in geotechnical characterisation, indicating that excavation in the site area will not be simple. The stiffness of the shelly and mottled clays together with coarse basal units of the Upnor Formation and Thanet Sand Formation may mean difficult excavation conditions.

6.0 REFERENCES

Attewell, P. B. (1995). Tunnelling contracts and site investigation. E & FN Spon.

Brassington, F. C. (1986). The inter-relationship between changes in groundwater conditions and engineering construction. Geological Society, London, Engineering Geology Special Publications, 3(1), 47–50. https://doi.org/10.1144/GSL.ENG.1986.003.01.04 BS 5930:1999. (1999). Code of practice for site investigations. British Standard, 3(March), 192. https://doi.org/10.1016/0148-9062(81)90248-5

Burland, J. B., Standing, J. R., & Jardine, F. M. (Finlay M. . (2001). Building response to tunnelling : case studies from construction of the Jubilee Line Extension, London. T. Telford Burnett, A. D., & Fookes, P. G. (1974). A Regional Engineering Geological Study of the London Clay in the London and Hampshire Basins. Quarterly Journal of Engineering Geology and Hydrogeology, 7(3), 257–295. https://doi.org/10.1144/GSL.QJEG.1974.007.03.02 Ellison, R. A., Woods, M. A., Allen, D. J., Forster, A., Pharaoh, T. C., & King, C. (2004). Geology of London : special memoir for 1:50000 geological sheets 256 (north London), 257 (Romford), 270 (south London), and 271 (Dartford) (England and Wales). Entwisle, D. C., Hobbs, P. R. N., Northmore, K. J., Skipper, J., Raines, M. G., Self, S. J., … Jones, L. D. (2013). Engineering geology of British rocks and soils : Lambeth Group. Head, J. M. (1986). Planning and Design of Site Investigations. Geological Society, London, Engineering Geology Special Publications, 2(1), 1–5. https://doi.org/10.1144/GSL.ENG.1986.002.01.01 Hight, D. W., Ellison, R. A., & Page, D. P. (2004). Engineering in the Lambeth Group. Ciria (Vol. C583). Knappett, J., Craig, R. F. (Robert F. ., & Craig, R. F. (Robert F. . (2012). Craig’s soil mechanics. Spon Press. Mortimore, R. N., Newman, T. G., Royse, K. R., Scholes, H., & Lawrence, U. (2011). Chalk: its stratigraphy, structure and engineering geology in east London and the Thames Gateway. Quarterly Journal of Engineering Geology and Hydrogeology, 44(4), 419–444. https://doi.org/10.1144/1470-9236/10-013 Page, D. P. (1995). Jubilee Line Extension. Quarterly Journal of Engineering Geology and Hydrogeology, 28(2), 97–104. https://doi.org/10.1144/GSL.QJEGH.1995.028.P2.02

Rainey, T. P., & Rosenbaum, M. S. (1989). The adverse influence of geology and groundwater on the behaviour of London Underground railway tunnels near Old Street Station. Proceedings of the Geologists’ Association, 100(1), 123–134. https://doi.org/10.1016/S0016-7878(89)80071-9 Royse, K. R., De Freitas, M., Burgess, W. G., Cosgrove, J., Ghail, R. C., Gibbard, P., … Skipper, J. (2012). Geology of London, UK. Proceedings of the Geologists’ Association. https://doi.org/10.1016/j.pgeola.2011.07.005

Simpson, B., Blower, T., Craig, R. N., Wilkinson, W. B., & Construction Industry Research and Information Association. (1989). The engineering implications of rising groundwater levels in the deep aquifer beneath London. CIRIA SPECIAL PUBLICATION. Construction industry Research and Information Association.

Spink, T. W. (2002). The CIRIA Chalk description and classification scheme. Quarterly Journal of Engineering Geology and Hydrogeology, 35(4), 363–369. https://doi.org/10.1144/14709236/00045

Stroud, M. A., & Butler, F. G. (1975). The standard penetration test and the engineering properties of glacial materials. In Symposium on Engineering Properties of Glacial Materials, Midland Geotechnical Society.

Figure

4:Interpreted Geological Cross Section

Figure

8: Undrained8: shear strengthversus depth

APPENDIX 1 – 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.

Kempton Park Gravel - 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- rounded flint gravel and occasional pockets of light brown silty sand. Fissures are random to sub-vertical planar smooth and 33 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 Bed - 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.