near shore land formation – importance of...

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

• BACKGROUND

• IMPROVEMENT OF INDIGENOUS SOILS

• Focus on PVD

• IMPROVEMENT OF FILL MATERIAL

• Focus on vibrocompaction

CONTENT

• 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

RECLAMATION PROJECTS

Largest artificial islands according to their size

The World Islands

- DubaiThe Pearl Qatar

Jebel Ali Palm -Dubai

Land Reclamation in Hong Kong

Grey (built) red (proposed or under development)

RECLAMATION PROJECTS

IMPROVEMENT OF INDIGENOUS SOIL

• 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

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

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

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

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

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

Construction of Container Terminal 9 (CT9),

Hong Kong

Marine Installation of PVDs

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

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

Impact of Large on-going Settlement on

Structures – Areas Treated with Band

Drains but no Surcharge

400 – 500 mm

Impact of Large on-going Settlement on

Structures – Areas Treated with Band

Drains but no Surcharge

Impact of Large on-going Settlement on

Structures in Shatin– Areas Treated with

Band Drains but no Surcharge

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

Primary Consolidation Settlement

(Of Soft Sediments)

Accelerating Consolidation with PVDs

Marine Mud

Alluvial Clay

Sand fill

Geotextile

PVDs

Typical View of a Prefabricated Band Drain

PVD Core

PVD Filter

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

Microscopic View of Non-

woven Filter Fabric

Normal After Stretching

Impact of Stretching Stresses

on Filter Fabrics

Geosynthetics International, 1995 Vol 2 No.2

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

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

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

Smear Zone

Undisturbed

Marine Mud

Vertical Band

Drains

Reduction of Lateral Permeability due

to Smear Effect during Installation

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

Testing Requirements for PVDs

NUS Buckling PVD Tests for Discharge Capacity

Determination(1)

(After Victor Choa, 1994)

NUS Buckling PVD Tests for Discharge Capacity

Determination(2)

NUS Buckling PVD Tests for Discharge Capacity

Determination(3)

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

Secondary Consolidation Settlements from

Soft Sediments

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

Overconsolidation to Reduce Secondary

Consolidation Settlements

Decrease of Coefficient of

Secondary Consolidation with OCR

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

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

IMPROVEMENT OF FILL MATERIAL

• 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

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

• “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

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

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

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

GROUND/FILL CONDITIONS

LIQUEFACTION – EARTHQUAKE OR WAVE INDUCED

Impact of Method of Analyses :Correlation between cone resistance

and relative density

TARGET DESIGN PERFORMANCE

Impact of Material Properties -Testing of Max Density

TARGET DESIGN PERFORMANCE

NCEER

Youd et al. (2001)

Idriss & Boulanger

(2008)

Moss et al. (2006)

Impact of Method of Analyses on Liquefaction Potential Assessment

TARGET DESIGN PERFORMANCE

Primary factors Subsidiary factors

Dredging

Reclamation

• Type of dredging (suction,

cutter-suction, etc.)

• Type of placement (bottom

dumping, rainbowing,

pipelines, etc.)

CONSTRUCTION METHODOLOGY

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

• 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

• 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

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

-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

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

• 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

• 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

• 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

• 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

-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

Thank You

Schematic Layout of ASTM 4716-08

PVD Discharge Test

Compacted clayPVD Test Specimen