Laboratory Geotechnical Samples, Quality and/or Quantity?
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01/07/2021
Laboratory Geotechnical Samples,
Quality and/or Quantity?
JOHN J M POWELL
TECHNICAL ADVISOR GEOLABS LIMITED
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Geotechnical Design
We need information and parameters for
Design – BSEN 1997
Ultimate Limit State
Serviceability Limit State
Safe, Reliable, Economic and environmentally friendly
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Why do we need to test the soil?
To design foundations we use shear strength and settlement
tests.
Permeability is required to assess consolidation etc, design
drainage, dewatering and underground structures.
We need to know the soil profile and stress history
In order to assess soil structure interaction with the use of finite
elements or other analyses we need soil stiffness and strength
parameters including Cyclic Loading!
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What happens if we do not get the right information?
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Static and Dynamic
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Modes of failure
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So
You want to get reliable parameters for your design using laboratory testing!
You need samples, but not just any old samples, they need to be representative
in terms of structure and composition
Sample Quality! (the right sample quality for the test)
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Something about Getting the Samples
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01/07/2021
Guidance
Eurocodes & ISO standards
No
British Standards
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Geotechnical Suite of Documents
BS EN 1997-2 is concerned with ground investigation and
testing.
BS EN 1997-2 is supported by NEW ‘Testing Standards’
(Standards) and Technical Specifications (TS) – CEN TC341,
ISO TC182
BS EN 1997-2 IS affecting all our GI practice as it impinges on
many of our codes and standards – BS5930 and BS1377 fully aligned
Also CEN TC 288 - ‘Execution of Special Geotechnical Works’
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Supporting Documents
Sampling and Drilling 1 & 2 No 3 & 0
Field (in situ) tests 12 & 2
Geo-hydraulic tests 6 & 0
Laboratory tests 12!!
Soil and rock description and classification 3 & 0
Piles, anchorages, nails, reinforced earth etc 8 & 0 ???
Geotechnical works 14 & 0
Some 60+ documents
And soon Earthworks
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Supporting Documents
Sampling and Drilling 1 & 2 No 3 & 0 under review BS ISO 22475-1, 2 and 3
Field (in situ) tests 12 & 2
Geo-hydraulic tests 6 & 0
Laboratory tests 12!! BS ISO 17892- 1 to 12
Soil and rock description and classification 3 & 0 new versions
Piles, anchorages, nails, reinforced earth etc 8 & 0 ???
Geotechnical works 14 & 0
Some 60+ documents
And of course BS 5930
And soon Earthworks
Plus of course remaining BS1377
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Sample Quality
Samples can be obtained in many ways. The testing which may be
carried out is dependant on the method used and the type of
sample obtained.
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Sample types
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Stages in sampling and preparing soil specimen for laboratory test
What
chance
has a
sample
got?
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Sources of tube sampling disturbance
Open drive and piston
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Sampling
BS EN 1997-2 tells us how we need to go about establishing the
geotechnical parameters for use at the design stage
It tells us about the quality of samples needed to be used in various
test methods to establish parameters. (and also numbers of specimens)
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Table 3.1 — Quality classes of soil samples for laboratory testing
Soil properties / quality class 1 2 3 4 5
Unchanged soil properties
particle size * * * *
water content * * *
density, density index, permeability * *
compressibility, shear strength *
Properties that can be determined
sequence of layers * * * * *
boundaries of strata – broad * * * *
boundaries of strata – fine * *
Atterberg limits, particle density, organic content * * * *
water content * * *
density, density index, porosity, permeability * *
compressibility, shear strength *
Nothing new really
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EN ISO 22475- 1: Technical principles for execution
Sampling techniques, sample handling, sample transportation and
storage procedures shall be selected on the basis of the required
sample quality class according to EN 1997-2;
sample mass;
Good guidance -shall
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Table 3.1 — Quality classes of soil samples for laboratory testing and sampling categories to be used
Soil properties / quality class 1 2 3 4 5
Unchanged soil properties
particle size * * * *
water content * * *
density, density index, permeability * *
compressibility, shear strength *
Properties that can be determined
sequence of layers * * * * *
boundaries of strata – broad * * * *
boundaries of strata – fine * *
Atterberg limits, particle density, organic content * * * *
water content * * *
density, density index, porosity, permeability * *
compressibility, shear strength *
Sampling category according to EN ISO 22475-1
A B
A
B
C C
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1001/07/2021
Sampling by drilling EN ISO 22475- 1:
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Sampling
using
samplers
Cutting
angle etc
UT100 X
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QUALITY in EN 1997 & 22475-1
Quality of investigation services
Required quality classes of samples
Achieved quality - before laboratory test?
QA system in field, laboratory and office
Quality of comparable (precedent) experience
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Quality and QA
Quality in sampling
Quality in transport and storage
Quality in preparation and testing
Quality of samples
Quality in reporting
Quality throughout!!
All rely on Quality in equipment and personnel!!!
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Practice
Our Practice has been questionable at times but now at the
top end we are second to none in delivering high quality
samples that can be tested with precision.
But the rest?????
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The Past?
Not always reliable?
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Maintain equipment – who inspects
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Disturbance
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1401/07/2021
Sampling
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Measured water content distributions across the
diameter of tube samples of soft clay
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1501/07/2021
Samples
Sealing
Wrapping
Waxing
Protecting
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Samples
Sealing
Wrapping
Waxing
Protecting
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1601/07/2021
Samples
Sealing
Wrapping
Waxing
Protecting
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Block sampling with
Sherbrooke sampler
Block sample cleaned
and wrapped in plastic
cling film
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1701/07/2021
Unconfined compression tests on
Ariake Clay (Tanaka and Tanaka, 1999)
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Shelby tube
Shelby tube
ELE 100
ELE100
NGI 54
NGI54
Japanese standard
Japanese Standardpiston
Piston
Compressive Stress (kPa)
30 Sherbrooke sampler
Sherbrooke
Laval sampler
Laval
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10
10m
0
0 2 4 6 8 10 12 14
Axial strain (%)
What are YOU trying to test??
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Results of CRS tests
Clearly block sample gives a
more stiff behaviour showing less
sample disturbance
Better definition of
preconsolidation stress, pc’
Lierstranda clay 12,3 m depth
Semilogarithmic scale
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1801/07/2021
Comparison of IL and CRS Consolidation Data
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P (b)
c’
σ'vo
Vertical Strain εv (%)
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Know the tests
CRS
IL 24 hr. Better definition of preconsolidation stress, pc’,
20 from CRS
Boston Blue Clay - Newbury
Depth = 7.3 m
w = 53%, PI = 21, LI = 1.4
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10 100 1000
Vertical Effective Stress σ'v (kPa)
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Results from shearing phase of CAUC tests
Similar failure envelopes?
Stress path diagram
(Lunne et al, 2001)
Lierstranda clay from 6.1 m depth
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Drammen low plasticity clay
Block 54 mm piston sample
sample
60 60
54mm, 17.35m
54mm, 16.35m 54mm, 17.35m
Shear stress, (σa-σr)/2, kPa
Shear stress, (σa-σr)/2, kPa
54mm, 16.35m
40 40
20 20 Block, 16.17m
Compression Block, 16.57m
Block, 16.17m Block, 16.57m
0 0
-20 -20
54mm, 16.45m
Extension 54mm, 16.45m
-40 -40
0.0 4.0 8.0 12.0 16.0 20.0 20 40 60 80 100 120
Axial strain, εa, % Effective mean stress, (σa'+σr')/2, kPa
Results of CAUC and CAUE tests contractant to dilatant
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Section 2: Planning of ground investigations
2.4.2 Laboratory tests
2.4.2.2 Visual inspection and preliminary ground profile
(1) Samples and trial pits should be inspected visually and compared with field
logs of the drillings so that the preliminary ground profile can be established.
For soil samples, the visual inspection should be supported by simple manual
tests to identify the soil and to give a first impression of its consistency and
mechanical behaviour.
(3) Where practicable, the quality of the sample should be assessed before
laboratory tests are performed. Quality classes for soil samples are defined in
Table 3.1.
.
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2001/07/2021
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Who inspects the samples before sending to the laboratory
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Drying/sealing
/storage
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Samples – good!
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Quality
essential
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Sample quality – what can be achieved ?
0 0
• Transportation
• Onshore storage 5 5
conditions and time 14.1 m 18.0 m
• Lab testing equipment 10 10
Strain (%)
Strain (%)
and procedures 15 15
20 20
25 25 UMass CRS (Winter 2005)
UMass CRS (Summer 2005)
NGI CRS (Fall 2004) NGI CRS (Fall 2004)
30 30
10 100 1000 10 100 1000
Vertical Effective Stress (kPa) Vertical Effective Stress (kPa)
Onsøy block samples
Tested at NGI and at UMass No significant difference
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2301/07/2021
Confidence in your Laboratory
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What is Proficiency Testing?
Proficiency testing (PT) is defined as:
The determination of the testing performance of a laboratory
against pre-established criteria by means of interlaboratory
comparison (ILC).
The process involves the testing, preferably to a known standard
or procedure, of reference or other standardised specimens
provided by the scheme’s organiser.
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The AGS Position
Consistent with its aim of promoting best practice and improving
professional standards, the AGS supports the principle of proficiency
testing within the geotechnical and geo-environmental laboratory
community in the UK, and will:
1. promote the technical, quality and cost benefits of participation,
2. encourage both member and non-member laboratories to
participate in PT schemes,
3. consider endorsing suitable PT schemes as they arise, and
4. support UKAS initiatives to encourage accredited laboratories to
participate in suitable schemes.
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Proficiency / Interlaboratory
Comparison Testing Scheme
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Liquid Limit
4pt 1pt
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Plastic Limit
With 4pt LL With 1pt LL
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Plasticity Index
With 4pt LL With 1pt LL
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Laboratory Testing
The best personnel and equipment in the
world can’t overcome poor samples
(or poor preparation)
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2701/07/2021
Sample disturbance – which factors are most important ?
• Drilling – for drilling mode
• Sample tube penetration
• Stress relief
• (Temperature change)
• Preparing for storage on board
• Transportation
• Onshore storage conditions and time
• Onshore sample preparations
• Lab testing equipment and procedures
• Interpretation
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Sample disturbance – which factors are most important ?
• Drilling – for drilling mode In “normal” cases
• In situ tube sampling sample causes say 90 %
• Stress relief of SD
• Temperature change
Can be
• Preparing for storage on board
minimized if
• Transportation
sound and
• Onshore storage conditions and time
consistent
• Onshore sample preparations
procedures are
• Lab testing equipment and procedures*
used (ref. ISO
•(Interpretation)
standard)
* The lab can destroy anything!!
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Sampling effects
Sampling effects are understood
Equipment and techniques for taking high quality samples are
available
Difficulties remain with laminated clays, sands and residual soils
The engineer must decide when he is justified in adopting these
techniques
There are dangers in improving only sample quality
Essential to evaluate quality of samples
o by volume strains during consolidation
o by shear waves
o Etc?
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You Need to
Whether you are a consultant, contractor or client you need to know or ask the
questions -
What do I want from laboratory tests
Which tests give me what I want (know the tests)
How do I give the laboratory the samples they need to deliver the testing and
results I need (quality and quantity)
Do I know what the laboratory needs by way of instructions (handout)
How do you ensure quality throughout the operation of sampling,
transportation, storage and testing! (know your laboratory, contractor etc)
And more?? Polls!!!!
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2901/07/2021
Quality
Do you get what you pay for????
Rubbish in – Rubbish out
Quality in – Rubbish out
Quality in – Quality out
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GET ON WITH THE CHALLENGE
And good luck!!
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