Near Shore Land Formation – Importance of...
Transcript of Near Shore Land Formation – Importance of...
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Near Shore Land Formation –Importance of Specifications
Dr Suraj De SilvaSMEC Asia Ltd. Hong Kong
Hong Kong - 31st October 2013
Jesper S. DamgaardSMEC International Pty. Jakarta
and
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• BACKGROUND
• IMPROVEMENT OF INDIGENOUS SOILS
• Focus on PVD
• IMPROVEMENT OF FILL MATERIAL
• Focus on vibrocompaction
CONTENT
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• Widespread use of coastal reclamations,
especially in Asia Pacific and the Middle East,
• Ground improvement (GI) almost always
required,
• Not necessarily rocket science but there are
pitfalls
• If these pitfalls are not properly addressed the
result is often delays and claims
MOTIVATION
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RECLAMATION PROJECTS
Largest artificial islands according to their size
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The World Islands
- DubaiThe Pearl Qatar
Jebel Ali Palm -Dubai
Land Reclamation in Hong Kong
Grey (built) red (proposed or under development)
RECLAMATION PROJECTS
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IMPROVEMENT OF INDIGENOUS SOIL
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• Land formation techniques
• Ground Improvement techniques (PVDs)
• Problems/Issues of recent reclamations
(Settlement)
• Causes for such issues
• Approach to avoid/mitigate them
• Clauses required in Engineer’s
Specifications
Introduction
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5-2
0m
10
-25
m~
5m
Up
to
20
mV
ari
ab
le
Very Soft to Soft Marine Mud
Soft Alluvial Clay
Firm to Stiff Alluvium (Clay, Silt and Sand)
Completely Decomposed Granite (CDG)
Granite Bedrock
Water Depth of about 5m to 25m
General Sub-seabed Ground Conditions
in Hong Kong
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Engineered Reclamation Approach
in The Recent Past
Fully Dredged Reclamation
• Kwai Chung Container Terminals CT8 and CT9
• Chek Lap Kok Airport Platform
• Penny’s Bay Reclamation for Disneyland
Firm to Stiff Alluvium
Reclamation Fill
(Sandfill and Public Fill)
Marine Mud Marine Mud
Soft Alluvial Clay
Decomposed Granite
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Engineered Reclamation Approach
in Recent Years
Dredged Seawall and Non-dredged Reclamation
• Tseung Kwan O New Town
• Tseung Kwan O Industrial Area
• Ma On Shan New Town
• Tuen Mun Area 131
Firm to Stiff Alluvium
Marine Mud
Reclamation Fill
(Sandfill and Public Fill)
Marine Mud
Marine Mud treated
with PVDs
Surcharge over roads and utility corridors
Dredged Seawall
Soft Alluvial Clay
Decomposed Granite
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Engineered Reclamations Today
in Hong Kong
Soft Marine Mud
Reclamation Fill – Sand fill and Public Fill
Soft Alluvial Clay
Firm to Stiff Alluvium
Decomposed Granite
Improved Ground Improved Ground Improved Ground
Non-dredged Reclamation
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Detailing the Al Raha Beach
Development in Abu Dhabi
in the UAE
Dr Suraj De Silva
AECOM
Tseung Kwan O Reclamation in
Progress in late 1990s
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Construction of Container Terminal 9 (CT9),
Hong Kong
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Marine Installation of PVDs
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Prefabricated Vertical Band Drain
Installation Areas in Hong Kong
Total Area of Reclamation: >1710 ha
Total Length of Seawall: >36 km
Total Length of Berths: >7.1 km
HKBCF
Penny Bay
IWMF
Hong Kong Boundary Cross
Facilities
Chek Lap Kok Airport
Penny’s Bay Development for
Disney Theme ParkIntegrated Waste
Management FacilitiesContainer Terminal No. 9
Container Terminal No 6, 7
& 8 Cyberport
Wan Chai Development
Central Wan Chai
Development
Tseung Kwan O New Town
Shatin Ma On Shan New
Town
Tai Po New Town
HZMB
Man-made Island
Prefabricated
Vertical Band
Drain Installation
Areas
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Typical Measured Settlement
in a Recent Reclamation
-400
-350
-300
-250
-200
-150
-100
-50
0
Oct-0
0
De
c-0
0
Feb
-01
Apr-0
1
Jun-0
1
Aug-0
1
Oct-0
1
De
c-0
1
Feb
-02
Apr-0
2
Jun-0
2
Aug-0
2
Oct-0
2
De
c-0
2
Feb
-03
Apr-0
3
Jun-0
3
Aug-0
3
Oct-0
3
De
c-0
3
Feb
-04
Apr-0
4
Jun-0
4
Aug-0
4
Oct-0
4
De
c-0
4
Feb
-05
Apr-0
5
Jun-0
5
Dif
f.(m
m)
Month
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Impact of Large on-going Settlement on
Structures – Areas Treated with Band
Drains but no Surcharge
400 – 500 mm
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Impact of Large on-going Settlement on
Structures – Areas Treated with Band
Drains but no Surcharge
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Impact of Large on-going Settlement on
Structures in Shatin– Areas Treated with
Band Drains but no Surcharge
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Reclamation Sandfill
Reclamation Settlement
Contributing Factors to On-going Settlement
• Residual Primary Consolidation
Settlement arising from
• Marine Mud
• Underlying Firm to Stiff Alluvial
Clays
• Occasionally, consolidation of clay/silt
Residual soils and Completely
decomposed Granite(DG)
• Secondary Consolidation Settlement of
• After End of Primary (EOP)
consolidation secondary
consolidation of marine mud
• Alluvial clays
• Some small contribution from
silt/clay residual soil and CDG
• Creep Settlement of sand
• Arising from reclamation Sandfill
and public fill
• Underlying Alluvial sand and gravel
layers (small)
Marine Mud
Alluvial Clay
Decomposed Rock
TimeS
oil
Pro
file
1
1
2
3
4
5
Se
ttle
me
nt
EOP
EOP
2
3
4
5
Handover of Site
Total Settlement Curve
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Primary Consolidation Settlement
(Of Soft Sediments)
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Accelerating Consolidation with PVDs
Marine Mud
Alluvial Clay
Sand fill
Geotextile
PVDs
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Typical View of a Prefabricated Band Drain
PVD Core
PVD Filter
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Forces and Stresses on Band
Drains during Installation
The tensile forces imposed will stretch the filter fabric of the drain and change the filter characteristics allowing fines to flow in clogging the drain
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Microscopic View of Non-
woven Filter Fabric
Normal After Stretching
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Impact of Stretching Stresses
on Filter Fabrics
Geosynthetics International, 1995 Vol 2 No.2
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6m+6mPD
+2.5mPD
-10mPDReclamation Fill
Marine Mud
Alluvium
-25mPD
-22.5mPD
Water Pressure inside Band Drain=245kPa
σv=596kPa
σp= 556kPa
Effective Pressure applied on Band Drain
=311kPaσv= 12.5*16.0+(12+10)*18
= 596 kPa
σp= σv-2Cu
= 596-2*20
= 556 kPa
Water pressure inside band drain
= (22.5+2.5)*9.8
= 245 KPa
Pressure applied on band drain
= 556-245 KPa
= 311 KPa
Band Drains
Lateral Pressures Imposed on
Band Drains reducing Flow
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Stretching of Filter Fabric
due to High Lateral Soil
Dual Core Integrated PVD
Stretched Filter membrane will Allow fines into the Core resulting in clogging
Sagging of Membrane reduces flow capacity of core
Membrane creep over time will further reduce flow capacity with time
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H
Settlement
Reclamation Fill
Alluvium
The bends will reduce the
flow capacity of the band drains
Marine Mud
Settlement can be as large as 15 % to 25 % of mud thickness (H)
Reduced Vertical Transmissivity
due to Folding of Drains
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Smear Zone
Undisturbed
Marine Mud
Vertical Band
Drains
Reduction of Lateral Permeability due
to Smear Effect during Installation
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Residual Settlement Impact
of Poor Performance of PVDs
EOP
Time
Se
ttle
me
nt
Primary Consolidation Settlement
EOP
Handover of Completed Reclamation
With poor quality PVDs
With good quality PVDs
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Testing Requirements for PVDs
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NUS Buckling PVD Tests for Discharge Capacity
Determination(1)
(After Victor Choa, 1994)
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NUS Buckling PVD Tests for Discharge Capacity
Determination(2)
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NUS Buckling PVD Tests for Discharge Capacity
Determination(3)
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NUS Test Method for Discharge Capacity
Determination – Performance Testing
Test Simulating the true installation conditions of the PVDs in field has a
significant effect on the flow capacities of the drains
Important to adopt the Performance based PVD tests like in Singapore
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Secondary Consolidation Settlements from
Soft Sediments
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Measures to Reduce Secondary Consolidation
Settlements in Soft Marine Mud
End of Primary (EOP)
Secondary Consolidation
Cαε
Time
Sett
lem
ent
Cc
Cαε
Cc= Constant
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Overconsolidation to Reduce Secondary
Consolidation Settlements
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Decrease of Coefficient of
Secondary Consolidation with OCR
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Overconsolidation to Reduce Secondary
Settlements
• Consolidate the soft clays to ensure it is
overconsolidated under working load
conditions
• Achieve an overconsolidation ratio
(OCR) of at least over 1.2
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Summary Measures/Specifications to Minimise Settlements
• PVDS
• Use good quality band drains – appropriate performance specifications are
required to ensure them
• Best to determine PVD make at Tender Stage
• At construction stage - confirmatory performance tests on band drains before
accepting
• Tests shall simulate field installation conditions and the soils encountered
• QA/QC - carry out tests regularly on samples retrieved from consignments
• Instrumentation and Monitoring
• Include extensive instrumentation in the reclamation.
• Monitor progress of consolidation closely
• Allow provision in the specifications to take remedial action if required
• Overconsolidation
• Overconsolidate to OCR >1.2 Settlement sensitive areas by surcharging
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IMPROVEMENT OF FILL MATERIAL
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• Is ground improvement (GI) required? A
crucial question in the planning, design and
construction of coastal reclamation
projects
• Number of key-factors related to the
loading and functionality of the
development must be assessed carefully
• Need for comprehensive GI Specification
and in particular GI Performance Criteria
GROUND IMPROVEMENT: CHALLENGES
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PERFORMANCE CRITERIA
• Many design issues (particularly those related to liquefaction
assessment and seismic induced settlement) are not definitely
addressed (neither fully nor partially) in any design Codes commonly
used. [see BS-8002:1994, BS6349-7:1991 and BS6349-1:2000).
• In practice, there are many legitimate approaches that can be usually
adopted, yet with a wide variation in the final results.
• Different approaches can be used to fulfill the performance criteria
stated in the Project Specification. This always creates dilemma
between the Engineer and the Contractor.
GROUND IMPROVEMENT: CHALLENGES
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• “achieve an in-situ density not less than 90% of the Maximum Dry Density
(MDD) throughout the full thickness and lateral extent of the fill”
• “The uppermost zone of fill shall be placed and treated to ensure that the
top 900mm of the fill has an in situ density not less than 95% MDD”
• “shall establish a correlation between cone resistance and relative density
and shall prepare a relationship between cone resistance and depth for fill
having a Relative Density corresponding to 90% MDD. Once this relationship
has been agreed with the Engineer the cone resistance depth profile shall be
used to monitor the density of the whole fill”
• “The reclamation shall be accessible and have a bearing capacity of not less
than 80 kPa. This shall be proved by demonstrating the ability to drive freely
over any given area without leaving undue tracking, in a vehicle or item of
plant developing such a loading”
GROUND IMPROVEMENT: CHALLENGES
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Ground/fill condition
• Fill characteristics
• Natural ground conditions
Target design performance
• Settlement
• Structral stability
• Seismic hazards
Construction methodology
• Dredging/reclamation
Quality Assurance / Quality Control
• Testing
KEY ASPECTS TO ADDRESS
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Primary Factors Subsidiary Factors Design Parameters
Fill
characteristics
• Fine content
• Carbonate/shell
content
• Suitability for
target
improvement
technique
• Soil Behavior Type Index (Ic)
• Shell correction factor
• Suitability Number
Natural ground
conditions
• Ground
characteristics
• Natural hazards
• Drained and undrained soil modulus
• Creep coefficient
• Shear strength parameters
• Unforeseen problematic sub-soil
GROUND/FILL CONDITIONS
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Primary Factors
Subsidiary Factors Design Parameters
Settlement • Short term settlement
• Long term settlemen
• Method of analyses
• Allowable short and long term
settlement
Structral
Stability• Bearing capacity
• Other failure modes
(sliding, overturning,
deep-seated failure)
• Method of analyses
• Acceptable safety factors
• Material Properties
Seismic
hazards
• Liquefaction potential
• Seismic-induced
settlement
• Seismic Bearing capacity
and stability of retaining
structures
• Lateral spreading
• Method of analyses
• Acceptable safety factors
• Acceptable settlement criteria
• Peak ground acceleration
• Magnitude Scaling factor (MSF)
• Depth reduction factor (rd)
• Soil Behavior Type Index (Ic)
GROUND/FILL CONDITIONS
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GROUND/FILL CONDITIONS
LIQUEFACTION – EARTHQUAKE OR WAVE INDUCED
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Impact of Method of Analyses :Correlation between cone resistance
and relative density
TARGET DESIGN PERFORMANCE
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Impact of Material Properties -Testing of Max Density
TARGET DESIGN PERFORMANCE
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NCEER
Youd et al. (2001)
Idriss & Boulanger
(2008)
Moss et al. (2006)
Impact of Method of Analyses on Liquefaction Potential Assessment
TARGET DESIGN PERFORMANCE
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Primary factors Subsidiary factors
Dredging
Reclamation
• Type of dredging (suction,
cutter-suction, etc.)
• Type of placement (bottom
dumping, rainbowing,
pipelines, etc.)
CONSTRUCTION METHODOLOGY
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Primary factors
Subsidiary factors
Testing • Testing
methodology
• Inspection
regime
• Frequency &
distribution of
testing
• SPT-CPTu- SCPT-Vs –Pressuermeter –
DCPT, Geophysical Testing Methods,
etc.
• Independent Testing Labs
• Quality procedure
• Testing standards
• Tolerances
• Evaluation and acceptance procedure
• Number and frequency of tests
• Location of tests
QUALITY ASSURANCE /
QUALITY CONTROL
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• Reclamation in Dubai
• Extensive vibrocompaction works and CPT testing
• Two aspects are considered here as an example of sources of
disputes that can lead to claims and/or arbitration:
• Case 1: for the SBTn charts
• Case 2: Testing location
CASE STORY
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• CPT-based soil behaviour type (SBT) charts are a predictive (profiling) tool to classify soil behaviour
• different versions of the SBT charts exist including normalized and non-normalized charts
• used in general for ground profiling
• significantly sensitive to
• confining pressure, (compacted vs. non-compacted ground)
• evaluation of stress component (different methods)
• material type (siliceous vs. calcareous sands)
CASE 1: SBT charts
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Updated Soil Behaviour
Type(SBT) charts with 9 zones
based on either:
Non-normalized CPT-SBT or
Normalized CPT-SBTn
(A) (B)
(after Robertson, 2010)
CASE 1: SBT charts
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-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
0.50 1.50 2.50 3.50
Elevation
(m A
CD
)
Soil Behavior type, Ic
Pre-CPT
Post_Mid Point
Post_one-third point
Gravelly
San
ds
Sands
San
d
Mixtures
Silt Mixtures
Clays
1
10
100
1000
0.1 1 10
NO
RM
AL
IZE
D C
ON
E R
ES
IST
AN
CE
, Q
NORMALIZED FRICTION RATIO, F
Pre-CPT
Post-Centroid
Post-1/3 Point 2
1 3
4
5
6
7 8
9
Confining pressure
differs from un-
compacted to
compacted ground.
Ic may differs depending
on confining pressure
Ic values (hence soil
description) may differ
from pre-compaction
and post compaction
CPTu tests
Careful judgement must
be exercised!
post-CPT
centroid
pre-CPT
post-CPT
One-third
CASE 1: SBT charts
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Compaction point
CPTu at Centroid point (A)
CPTu at one-third point (B)
• Testing locations are often ignored in GI specifications.
• Significant differences are always noted between various testing locations.
• There is always a dispute over decision of selecting:
• (weighted )averaging of multiple testing location versus individual location .
• testing the weakest , intermediate and/or strongest locations versus random location.
CASE 2: CPT testing locations
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• Case study involving 305 boxes (25××××25 m-boxes) .
• 305 sets of CPT soundings done for a reclamation site of 19
m depth. Each set include two locations (Point A & Point
B)
• Assessment of relative differences between centroid
(Point A) and one-third points (Point B) along the testing
depth.
• Study considered the impact of the CPT rod system
inclination:
• Unlimited deviation
• 2.0 m maximum deviation
• 1.0 m maximum deviation
CASE 2: CPT testing locations
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• Centroid CPTs are always lower than one-third CPTs apart from the top 4 m.
• Rod inclinations , if not controlled, may impact the results.
Unlimited deviation 2.0 m Maximum deviation
limit
1.0 m maximum
deviation
CASE 2: CPT testing locations
Relative strength point B/A Relative strength point B/A Relative strength point B/A
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• Coastal reclamation projects require ground improvement
more often than not.
• The aim of the ground improvement is to achieve
competent foundation conditions.
• Sufficient time and efforts must be spent in formulating a
site- and project-specific ground improvement strategy.
• That includes tailor-made ground improvement
specifications
CONCLUSIONS 1/3
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• Proper estimation of parameters such as the SBT index (Ic)
is critical as it can have important commercial
consequences.
• Testing location is a key factor in the evaluation of ground
improvement works.
• More than one testing location must be considered,
particularly for vibro-compaction works.
CONCLUSIONS 2/3
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-12.0
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
0.0 2.0 4.0 6.0 8.0 10.0
EL
EV
AT
ION
(m
DM
D)
CONE RESISTANCE, qc (MPa)
-12.0
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
0.0 2.0 4.0 6.0 8.0 10.0
EL
EV
AT
ION
(m
DM
D)
CONE RESISTANCE, qc (MPa)
Performace Line FoS = 1.0
-12.0
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
0.0 2.0 4.0 6.0 8.0 10.0
EL
EV
AT
ION
(m
DM
D)
CONE RESISTANCE, qc (MPa)
Performace Line FoS = 1.0
The Engineer's Perspective The Contractor's Initial
Perspective
The Contractor's Final
Perspective
RECOMMENDATION: well defined CPT performance curves
CONCLUSIONS 3/3
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Thank You
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Schematic Layout of ASTM 4716-08
PVD Discharge Test
Compacted clayPVD Test Specimen