The Lambeth Group and Thanet Sand Formation€¦ · London Basin Forum The Lambeth Group and Thanet...
Transcript of The Lambeth Group and Thanet Sand Formation€¦ · London Basin Forum The Lambeth Group and Thanet...
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
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New New classification classification of lithologies of lithologies for Crossrail/for Crossrail/TidewayTideway
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10
-100
0
-20
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-50
-60
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-10
-80
-90
10
-100
0
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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
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‘Cartoon’ cross-section of Crossrail alignment showing general structure and
areas where more detailed analysis of faults has been, and will be, possible
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Detailed analysis of geology for
design detail and risk
assessment
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Be involved! What is needed:
• Data• History• Knowledge• Enthusiasm• Support