Site
Investigation
in the
21st Century?
Chris Clayton
FOR PERSONAL USE ONLY (c) Chris Clayton
Issues
Site Investigation in the 21st Century
•
•
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Background
Aims
Constraints
Urbanization
Essential components
2
FOR PERSONAL USE ONLY (c) Chris Clayton
Issues
Site Investigation in the 21st Century
•
•
•
•
•
Background
Aims
Constraints
Urbanization
Essential components
3
FOR PERSONAL USE ONLY (c) Chris Clayton
Terzaghi oedometer 1923
CPT Delft Grondmechanika 1945
SPT 1902-1947
BRE laboratory 1945
Most of the techniques we
routinely use are between
60 and 100 years old
4
Bishop with U4 1944-45
FOR PERSONAL USE ONLY (c) Chris Clayton
1906
2006
5
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Background
“… engineers imagined that the science of foundations
would consist in carrying out the following program:
1. Drill a hole into the ground.
2. Send the soil samples obtained from the hole
through a laboratory with standardized apparatus
served by conscientious human automatons.
3. Collect the figures, introduce them into the
equations, and compute the result”
“Unfortunately, soils are made by nature and not by
man, and the products of nature are always
complex.”
Terzaghi, 1936
6
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Total increase in construction
cost (%)
Cost over-run on UK highway projects
Background
100
? current spend
25
0
0
1
10
5
SI cost / construction tender cost (%)
7
(from TRL Project Report 60)
FOR PERSONAL USE ONLY (c) Chris Clayton
Background
Cause of cost over-runs on 12 highway projects
interpretation of SI
project planning
site investigation planning
additional work
amended work
quality control
variation in quantities
bills of quantities
specification
60
100
% net additional cost
200
8
(Tyrrell, Lake and Parsons, 1985)
FOR PERSONAL USE ONLY (c) Chris Clayton
Issues
Site Investigation in the 21st Century
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•
•
•
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Background
Aims
Constraints
Urbanization
Essential components
9
FOR PERSONAL USE ONLY (c) Chris Clayton
“Subsurface projects
present an enormous risk
for the primary project
“stakeholders”, i.e. the
owner and contractor.
Realistically, not all risk for
subsurface conditions can
be entirely avoided or
eliminated. “
• Ground geometry
• Groundwater
• Ground properties
Aims
and
• Hazards and risks
– Geologic hazards
– Geomaterial hazards
– Geotechnical hazards
– Land use hazards
Hatem, 1998
health and
safety
cost
and
• Residual uncertainties
following GI
geotechnical
risk
quality
environment
programme
10
FOR PERSONAL USE ONLY (c) Chris Clayton
Aims
Ground geometry
11
(A ‘geological model’ from Fookes, 1997)
FOR PERSONAL USE ONLY (c) Chris Clayton
Ground hazards and risks
Aims
• Geologic hazards
• Geomaterial hazards
• Geotechnical
engineering hazards
Risks
Vulnerability
• Land use hazards
12
FOR PERSONAL USE ONLY (c) Chris Clayton
Geotechnical problems during construction
5%
Soil boundaries
4%
6%
22%
Aims
Soil properties
Ground water
9%
Contamination
Obstructions
Planning of SI
10%
Services
20%
Detailed design
Other
11%
13%
From a survey of 28 construction projects (Clayton, 2001)
13
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Example of risk analysis
14
(see the ICE/DETR Report on ‘Managing Geotechnical Risk’)
FOR PERSONAL USE ONLY (c) Chris Clayton
Issues
•
•
•
•
•
Background
Aims
Constraints
Urbanization
Essential components
15
FOR PERSONAL USE ONLY (c) Chris Clayton
Constraints
•
•
•
•
Ground conditions
Equipment
Supervision
Knowledge and experience (in
local conditions)
• Education
• Computation techniques
• Conditions of contract (?)
• Money (?)
16
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Constraints
SPT hammers
U100 disturbance
Most data used in design are not
fundamental - variations in the ways
drilling, sampling and testing are done
make the results very variable
17
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observed / predicted
settlement
Constraints
Predicted and observed settlements
for spread footings on sand
20
10
5
1
0.2
0.1
0.05
0.1
1.0
10
100
predicted settlement (mm)
18
Clayton, Simons and Instone, 1988
FOR PERSONAL USE ONLY (c) Chris Clayton
Predicted v. observed pile capacities
shaft capacity base capacity
Constraints
observed pile performance
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
predictions of pile performance
0
1000
2000
3000
4000
pile capacity (kN)
5000
6000
19
Wheeler, 1999
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Constraints
The need for experience
Building on dolomite
damaged by
subsidence
(courtesy Prof. G.
Heymann)
“There are known knowns. These are things that we
know that we know. There are known unknowns.
That is to say, there are things that we know we
don’t know.
But there are also unknown unknowns. There are
things we don’t know we don’t know.” Donald Rumsfeld 20
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Constraints
Growing problems with UK education and
training
•Very small proportion of civil engineering graduates
now take a soil mechanics or geotechnical
engineering MSc
•Civil Engineering MEng/PhD graduates are not
adequately trained (ab initio) to practice as
geotechnical engineers
•Engineering geology postgraduate courses are not
valued by leading geology departments
•Very difficult to identify the next generation of senior
geotechnical laboratory technicians
•Are the working conditions of the light percussion
driller compatible with high quality technical output?
21
FOR PERSONAL USE ONLY (c) Chris Clayton
Constraints
Growing problems with knowledge and
experience
• Few consultants (or SI engineers / geologists)
understand the details of drilling and testing
techniques.
• Specification of more complex work can be poor.
• Consultant supervision is pointless unless informed
and rigorous.
• GI contractors cannot afford to supervise fieldwork
unless paid.
• Drillers and technicians are a most important
resource. They need to be trained, and feel part of
the team.
22
FOR PERSONAL USE ONLY (c) Chris Clayton
Issues
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•
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Background
Aims
Constraints
Urbanization
Essential components
23
FOR PERSONAL USE ONLY (c) Chris Clayton
Urbanization
Urbanization
• At the beginning of the 20th century 7%
of the world’s population could be
considered ‘urban’. Most urban dwellers
lived in developed countries.
• By 1950 30% of the population lived in
urban areas, and by 2000 47% was
urban
24
FOR PERSONAL USE ONLY (c) Chris Clayton
Urbanization
Urbanization
• At the beginning of the 20th century 7%
of the world’s population could be
considered ‘urban’. Most urban dwellers
lived in developed countries.
• By 1950 30% of the population lived in
urban areas, and by 2000 47% was
urban
• By 2030 it is expected that >60% of the
world’s population will live in an urban
world.
• Most of the new urban areas will be in
25
developing countries.
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Predicted Asian population growth
URBAN
RURAL
2
1
19
50
19
75
20
00
20
30
0
19
50
19
75
20
00
20
30
Population (billions)
Urbanization
3
From Zlotnik (2003) 26
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Urbanization
Anyone who believes that India is an
‘economic powerhouse’ should ‘try living
there’. ‘The shortcomings of infrastructure
are a huge problem. In Delhi ‘some areas are
blighted by daily four-hour power cuts’. ‘A
report last week highlighted a 73km rail
project in East Bengal that is still unfinished
after 32 years.’
(Justin Huggler in The Independent, Sept
2006)
27
FOR PERSONAL USE ONLY (c) Chris Clayton
Urbanization
Urban vulnerability
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Instability of natural slopes
Mining impacts
Damage to infrastructure
Effects of construction on nearby
structures
28
FOR PERSONAL USE ONLY (c) Chris Clayton
Hong Kong, Po Shan Road
Slide, 1972
• Rainfall of 700mm in 3 days
prior to slide
• Main slide involved 25,000m3
debris, moving 280m in 1
minute
• 1 block of flats pushed off
foundations onto another
• 67 people died
29
FOR PERSONAL USE ONLY (c) Chris Clayton
Merriespruit tailings dam failure, South Africa
28m high tailings dam, failed 21 February 1994, 17 died30
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Kinzie Street
Bridge,
Chicago
13 April 1992
Downtown
basements
flooded as a
result of piling
work.
President
signs disaster
declaration.
31
FOR PERSONAL USE ONLY (c) Chris Clayton
Heathrow Airport Central
Terminal Area collapse
20
October
1994
32
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The Straits Times 2004
33
FOR PERSONAL USE ONLY (c) Chris Clayton
Urbanization
Urban ‘ground’ - London
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Made ground
Archaeological heritage
Contaminated land
Infrastructure
Obstructions
Ordnance
34
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Reconstruction of Southwark’s topography c.
AD50 on modern street plan
London Bridge
South Bank of
River Thames
(2008)
200m
35
Yule (1988)
FOR PERSONAL USE ONLY (c) Chris Clayton
London Bridge Hotel lift shaft excavation
http://www.londonbridgehotel.com/p_geology.html 36
FOR PERSONAL USE ONLY (c) Chris Clayton
Archaeological
heritage
Rediscovery of
the Rose
Theatre in
1989
37
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Grand Buildings, Trafalgar Square, London
London Underground tunnels
38
FOR PERSONAL USE ONLY (c) Chris Clayton
39
FOR PERSONAL USE ONLY (c) Chris Clayton
Redevelopment London Bridge area
John Dugleby’s
map of 1792
superimposed
on a 1:1250
Ordnance
Survey Map of
1950
40
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Battersea Power Station - existing
foundations
41
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Battersea
foundations
Desk study
42
Exhumation, examination and testing
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Bomb damage to London Bridge area
Total destruction
Damage beyond repair
Seriously damaged, doubtful if repairable
Seriously damaged but repairable at cost
General blast damage, not structural
Blast damage, minor in area
Clearance areas
Post-war 1:1250 bomb damage map
43
FOR PERSONAL USE ONLY (c) Chris Clayton
Issues
•
•
•
•
•
Background
Aims
Constraints
Urbanization
Essential components
44
FOR PERSONAL USE ONLY (c) Chris Clayton
Components
Essential components
• Competence / registration
–
–
–
–
–
Engineers
Geologists
SILC
Technicians
Drillers
(AGS, 2006)
• Early involvement of geotechnical experts
(hazard + risk assessment, conceptual design)
• Desk study and walkover survey
• Geological, geotechnical and land use ground
models.
• Targetted planning of ground investigation
45
FOR PERSONAL USE ONLY (c) Chris Clayton
Geotechnical and contaminated land models
46
FOR PERSONAL USE ONLY (c) Chris Clayton
Components
Essential components
• Targetted direct investigation
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Accurate identification of soil boundary locations
Groundwater positions / conditions
Contaminated land investigation
Repeatable test results
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Supervision
Informed interpretation
Appropriate analysis
Hand-over of residual risks
(risk registers)
• Contribution to CDM
47
FOR PERSONAL USE ONLY (c) Chris Clayton
The way forward?
Summary
• Definitions of content (essential
components), to define negligence.
• Definitions of education, training,
experience for all levels of staff, to define
necessary levels of competence.
• Quality driven by site investigation
industry, perhaps by peer review.
Distinct geotechnical design strategies for
• ‘Routine’ construction
• Major projects or ‘difficult ground’
48
FOR PERSONAL USE ONLY (c) Chris Clayton
The way forward?
Design strategy - Routine construction
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Recognise and understand current GI inadequacies.
Make great use of desk study information
Develop ground and land-use models (esp. cities)
Proper planning and informed interpretation of site
investigations
Use local and company experience, and material
performance database (case records)
Hazard identification and risk analysis
Conceptual design to avoid or mitigate risks
Limited, basic, quick, repeatable ground
investigation?
Conservative and simple analyses
Observation (and possibly monitoring) during
construction
49
FOR PERSONAL USE ONLY (c) Chris Clayton
Windowless
sampler
100mm ID
70mm ID
47mm ID
Drive sampling
rig
48% AR
81% AR
116% AR
50
(courtesy Dando and Archway)
FOR PERSONAL USE ONLY (c) Chris Clayton
Cone truck and Mostap sampler
(courtesy Lankelma) 51
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The growth
of web
sources of
information
High-resolution
vertical and
oblique air
photography of
University of
Southampton
From www.maps.live.com
52
FOR PERSONAL USE ONLY (c) Chris Clayton
British Geological Survey borehole database
(www.bgs.ac.uk/geoindex)
53
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Merging geotechnical & geological data
Borehole data
Land use
Archaeology
Contamination
Obstructions
Superficial geology
Solid geology
Hydrogeology
Fence model
3D model
54
GSI3D from www.lithosphere.de
FOR PERSONAL USE ONLY (c) Chris Clayton
The way forward?
Design strategy – Major projects
“Project owners must recognise that there are
certain types of projects that simply cry out for a
more sophisticated approach to doing the
subsurface portion of the work.”
(from Brierley, 1998)
• Use only when advanced geotechnical
computation can yield major savings / gains.
• Need for sophisticated sampling and testing
• Advanced numerical modelling
• International and flexible approach to
procurement.
• Partnering with ground investigation specialists.
• University collaboration?
55
FOR PERSONAL USE ONLY (c) Chris Clayton
Download a free copy of “Site Investigation” by Clayton,
Matthews and Simons from www.geotechnique.info
FOR PERSONAL USE ONLY (c) Chris Clayton