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Application of computedtomography to investigate
strain fields caused by conepenetration in sands
27 February, 2004
Jeroen van Nes
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• Drilling• Sampling and laboratory testing• Penetration testing• Geophysics• etc.
CPT : Relatively cheap, fast, easy and reliable.
CPT field data geotechnical soil parameters
Planning Construction
Site investigation
Intro
Application of computed tomography to investigate strain fields caused by cone penetration in sands
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Intro
Application of computed tomography to investigate strain fields caused by cone penetration in sands
OBJECTIVEto investigate if the relationships betweencone parameters and geotechnicalparameters can be improved by studyingstrain fields caused by cone penetration insands.
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Presentation overview
• Background information
• Tests Descriptions
• Test results
• Conclusions
• Applications & Recommendations
Introduction ConclusionsTestresults
Testsdescriptions
Backgroundinformation
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Applications &Recommendation
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CPTApplication of computed tomography to investigate strain fields caused by cone penetration in sands
The CPT probe• long tube• cone tip.
Pushed into the ground
Resistance/Friction
Conclusions (kind of soil & Some engineering properties)
Key parameters: Relative density, effective stress level and compressibility
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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Deformation Types
Shearing
– dilation
– compaction
High compressive stresses
– grain crushing/compaction
• Not-influenced area
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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•Medical background
Difference in X-Ray intensity
Attenuation of X-ray beam
Attenuation value of every pixel
Absolute density
Application of computed tomography to investigate strain fields caused by cone penetration in sands
CT scanner (1)
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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CT scanner (2)3D representation
MOVIE
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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Crossections
CT scanner (3)Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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Sand sample (1)Application of computed tomography to investigate strain fields caused by cone penetration in sands
Sand: Baskarpsand
• Fine sand• Well sorted• No contamination• >80 % SiO2 (Quartzitic)
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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A
B
D
C
H
Preparation: Pluviation
• Homogenous density• Different densities
1,481,501,521,541,561,581,601,621,641,661,681,70
0 20 40 60 80 100 120height [cm]
dens
ity [g
/cm
3]
set1set2Lineair (all)
Introduction ConclusionsTestresults
Applications &Recommendation
Sand sample (2)
Testsdescriptions
Backgroundinformation
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Calibration chamber
Scale effects• Boundary effects (cone size diameter - sand sample diameter)• Grain size effects (cone size diameter - mean grain size diameter)
Probe• Standard: diameter 35.7 mm• Miniature cone: diameter 6 mm
Introduction
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Applications &Recommendation
Testsdescriptions
Backgroundinformation
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CPT-tests (1)
CPT-tests with different
• Horizontal Swelling
• Penetration Resistance
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Applications &Recommendation
Testsdescriptions
Backgroundinformation
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02468
101214161820
0 20 40 60 80 100 120Penetration depth (mm)
Res
ista
nce
(MP
a)
DenseModerate denseLoose
Different sanddensities
High repetability ofmeasured resistance
Introduction ConclusionsTestresults
Applications &Recommendation
CPT-tests (2)
Testsdescriptions
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Scanned CPT testsTest 1: Reference testTest 2: Lower confining pressureTest 3: Lower densityTest 4: Rigid boundaries
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Test Density [g/cm3] Confining pressure [KPa] BoundryTest 1 1,61 78-82 Flexible membraneTest 2 1,61 38-42 Flexible membraneTest 3 1,54 78-42 Flexible membraneTest 4 1,61 78-82 Rigid alumium mould
Test at multiple stages
Introduction ConclusionsTestresults
Applications &Recommendation
Testsdescriptions
Backgroundinformation
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Density-Attenuation relation
Estimation sand density
Relation is determined forBaskarp sand, 100 mm.
y = 9 7 3 ,4 1 x - 7 7 7 ,6 5R2 = 0 ,9 9 1 7
6 5 0 ,0
7 0 0 ,0
7 5 0 ,0
8 0 0 ,0
8 5 0 ,0
9 0 0 ,0
1 ,4 5 1 ,5 1 ,5 5 1 ,6 1 ,6 5 1 ,7
S a n d d e n s ity [g /c m3]
Hou
nsfi
eld
unit
val
ues
[H
M eas urem entpoints
Sand grain size < resolution of theCT-scanner
Sand sample scanned with multipledensities
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Applications &Recommendation
Testsdescriptions
Backgroundinformation
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Processing of the data
Processing programs• Amira:
• Q-win
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
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Testsdescriptions
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Absolute density
Homogenity• marker lines• Density variation
Loosening
Densification
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTest
resultsTests
descriptionsApplications &
RecommendationBackgroundinformation
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• 100 mm cone penetration
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Density-changes (1)
Introduction ConclusionsTestsdescriptions
Applications &Recommendation
Testresults
Reference test Lower confiningpressure
Lower sanddensity
Rigidboundaries
Backgroundinformation
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• 6 mm cone penetration
Density-changes (2)Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestsdescriptions
Applications &Recommendation
Testresults
Reference test Lower confiningpressure
Lower sanddensity
Rigidboundaries
Backgroundinformation
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Measuring the sizes of the dilating areasApplication of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Theoreticalbackground
Applications &Recommendation
Introduction ConclusionsTestsdescriptions
Applications &Recommendation
Testresults
6 mm under the cone tip
-0,3-0,2
-0,10
0,1
0,20,3
-60 -40 -20 0 20 40 60
Horizontal distance (mm)
Den
sity
cha
nge
(g/c
m3)1,4
1,5
1,6
1,7
1,8
1,9
-60 -40 -20 0 20 40 60
Horizontal distance (mm)
Den
sity
[g/c
m3]
NOPEN PEN
At the cone tip
-0,3
-0,2
-0,1
0
0,1
0,2
0,3
-60 -40 -20 0 20 40 60
Horizontal distance (mm)Den
sity
cha
nge
(g/c
m3)
1,4
1,5
1,6
1,7
1,8
1,9
-60 -40 -20 0 20 40 60Horizontal distance (mm)
Den
sity
[g/c
m3] NOPEN PEN
Above cone
-0,3
-0,2
-0,1
0
0,1
0,2
0,3
-60 -10 40
Horizontal distance (mm)Den
sity
cha
nge
(g/c
m3)1,4
1,5
1,6
1,7
1,8
1,9
-60 -40 -20 0 20 40 60
Horizontal distance (mm)
Den
sity
[g/c
m3]
NOPEN PEN
1,1
1,3
1,5
1,7
1,9
0 20 40 60 80 100 120
Vertical distance (mm)
Den
sity
(g/c
m3)
Pen No Pen
Backgroundinformation
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Dilating areas
• Inside: dilating areas
• Outside: No changes & Compression
III III
IV
Application of computed tomography to investigate strain fields caused by cone penetration in sands
IV
Introduction ConclusionsTestsdescriptions
Applications &Recommendation
Testresults
Backgroundinformation
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• Sand sample created by pluviation are not perfect homogenous.
• CT is a suitable technique to investigate the deformations in sand by a CPT test
• The degree of dilation and the extend of the dilating zones are dependent on thetest conditions
– Large difference: change of density.
– Small difference: change of boundaries & confining pressure.
Conclusions (I)
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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Conclusions (II)
• 3 Different deformation zones are believed to be created by the conepenetration test
Application of computed tomography to investigate strain fields caused by cone penetration in sands
A B C
Introduction Testresults
Testsdescriptions
Applications &RecommendationConclusionsBackground
information
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Conclusions (III)
No failure structures– Large failure plains– Shear bands
Difference• Large failure structures• Defined zones
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction Testresults
Testsdescriptions
Applications &RecommendationConclusionsBackground
information
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• Better understanding of the CPT test
• Validation models– DEM (Distinct Element Models)– Cavity expansion theory
• Validation of other tests– pressuremeter test
Applications
Application of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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Recommendations
Test setup• Loading system around CT scanner.• a smaller cone.• a larger calibration chamber.
Processing• Replace interpretation by a computer program
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation
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QuestionsApplication of computed tomography to investigate strain fields caused by cone penetration in sands
Introduction ConclusionsTestresults
Testsdescriptions
Applications &Recommendation
Backgroundinformation