London Basin Forum

The Lambeth Group and Thanet Sand Formation

- also Palaeogene clay & whole rock mineralogy

Dr Jackie SkipperGeotechnical Consulting Group,

Natural History Museum

Dr Jenny HuggettPetroclays, NHM

London Basin Forum

Lambeth Group & Thanet

London Basin Forum

Achievements – past 15 years• Improved GI techniques• Improved construction techniques• Improved UNDERSTANDING of ground

• Clients with higher standards• Consultants with higher standards• Training in stratigraphy, logging and how to interpret• Better communications between projects

London Basin Forum

New New classification classification of lithologies of lithologies for Crossrail/for Crossrail/TidewayTideway

London Basin Forum

10

-100

0

-20

-30

-40

-50

-60

-70

-10

-80

-90

10

-100

0

-20

-30

-40

-50

-60

-70

-10

-80

-90

ELE

VA

TIO

N (m

OD

)

0042

6B/7

0042

6B/6

0042

6B/5

0042

6B/4

0042

6B/3

0042

6B/1

3A

0042

6B/1

0

0042

6B/9

0042

6B/8

0042

6B/1

1

0042

6B/1

2

0042

6A/1

0042

6B/2

A

0042

6B/2

D

0042

6B/1

C

0042

6B/1

A

?

RIV

ER T

HA

MES

BEC

KTO

N O

VER

FLO

W S

HAF

T

BEC

KTO

N P

UM

PIN

G S

HAF

T

ABB

EY M

ILLS

SH

AFT

THE GREENWICH FAULT ZONE

1+09

0

6+06

1

6+90

4

3+90

5

2+59

1

1+49

1

1+93

6

3+12

6

3+40

9

4+83

1

5+46

8

0+58

7

0+00

0

CHAINAGE

‘THE PLAISTOW GRABEN’

?

STRATA (DURATION IN m)

BEDWELL’S COLUMNAR (1200m) BEDWELL’S COLUMNAR FLINT (3120m)FAULTING

(300m)

CIRIA GRADE (AT TUNNEL HORIZON)

CHALK STRENGTH MPa(AT TUNNEL HORIZON)

0042

6B/1

D

60

HAVEN BROW BEDS (1250m) TSF (375m) HAVEN BROW BEDS (2030m) HAVEN BROW / CUCKMERE BEDS (2947m)

BELLE TOUT (300m)

A2 -3A1C3A2 - 3NO DATA YETA1 - 4A2 A1 - 3 PROBABLYC3

4.4 – 5.0 3.1 – 5.34.2 – 5.3 4.1 – 7.9 6.2 – 8.9NO DATA YETNO DATA YET

TIDEWAY LEE TUNNEL - GEOLOGICAL MODEL REV 6 - DETAILED CHALK STRATIGRAPHY (vertical exaggeration x 28.5)

HAVEN BROW BEDS CUCKMERE BEDS BELLE TOUT BEDS BEDWELL’S COLUMNAR FLINTSEAFORD CHALK FORMATION:

LEWIS NODULAR CHALK FORMATION UNDIFFERENTIATED WHITE CHALK SUBGROUP

GEOHAZARDS (DURATION IN m)

6.065.436.645.12

8.58

6.52

10.26.77

12.1

2.83

6.46

6.264.18

4.916.01

3.12

6.06

2.8 – 6.45.1 – 6.66.5 – 8.5NO DATA YET N/A

4.625.70

4.365.15

5.26

5.394.29

5.303.303.10

3.702.804.903.704.20

5.004.40

4.30

6.23

8.94

5.05

6.807.82

UCS test values & point of sample in red

?

The quality of the interpretation for the Lee Tunnel Site Investigation allowed

rapid, significant design and alignment modifications to be made, and was a

major contribution to the understanding of the structure of

London

London Basin Forum

‘Cartoon’ cross-section of Crossrail alignment showing general structure and

areas where more detailed analysis of faults has been, and will be, possible

London Basin Forum

Detailed analysis of geology for

design detail and risk

assessment

London Basin Forum

Faulting Examples of reactivated faulting in borehole from Farringdon (left) and growth fault from the Bean outlier,

near Gravesend Kent (right)

London Basin ForumAreas with > 5m total Upnor Fm pebbles

Upnor (/LMB) Fm pebbles present

Evidence of uplift during the deposition of the Upnor Formation –large, ?estuarine channels filled with flint pebbles which have been eroded out of Upnor or Chalk uplifted elsewhere in the London Basin

London Basin Forum

Mineralogical, especially clay data will be collected for the

London Basin to create a database for the whole area.

This can be used to civil engineering planning and to look at volcanic ash or other

origins of the original sediments

London Basin Forum

Woolwich Formation, Laminated BedsSand Channels

New data interpretation is leading to a better understanding of hydraulic continuity and lateral extent of depositional features such as sand channels in the Lambeth Group

London Basin Forum

Deoxygenation risks?An improved understanding of the structure of London Basin may

help in the prediction and remediation of hazards such as deoxygenated gases under pressure, which have been encountered in the sediments of the Lambeth Group in various places in London

London Basin Forum

Lambeth and Thanet - risks and hazards

• Classification• Unexpected ground conditions• Instability• Variable permeabilities/dewatering• Pyrite/acid water/de-

oxygenation/gases• Clay mineralogy – conditioning?• Lost data • Poor knowledge transfer between

projects

London Basin Forum

Challenges• Communication: where does data go?• Undercutting bids • Litigation as a cost recovery strategy• Secrecy about data even after project

complete• ‘Blame’ culture?• Lack of time and energy to overcome

these issues• LACK OF OVERVIEW AND ANALYSIS• NEED TO START FROM SCRATCH

EACH PROJECT

London Basin Forum

What can the LBF contribute?• Start joining up the dots• Synergy – bouncing ideas between

different specialities• Big picture overview

• Understanding of structure and influence on behaviours

• Clearer hazard prediction and planning?• Better communication for future projects

London Basin Forum

What will the Lambeth Gp contribute to the project?

• Vertical and horizontal variability means faults seen clearly, and measurable in the Lambeth Group

• Shallow environments of deposition mean small variations in depth (? Tectonic influence) lead to large changes in lithology, so easily seen

London Basin Forum

What don’t we know – and needmore data for?

• We have only the beginnings of understanding of the structural development of the London Basin

• Do tectonics drive change in the Lambeth Group lithologies?

• Implications for engineering design, petroleum geology, health and safety

London Basin Forum

Be involved! What is needed:

• Data• History• Knowledge• Enthusiasm• Support