Geophysical techniques reduce geotechnical risks

qusanssori@infratechgeo.com
IEM 27th July 2020
Innovative Site investigation
techniques to reduce project
geotechnical risks
By Qusanssori Noor Bin Rusli
B.Sc. (Hons) Civil Engineering, M.Sc Geotechnical Engineering
Technical Talk on
“Advances in Geotechnical and Pavement Engineering for Transport
infrastructure”
HIGHWAY & TRANSPORTATION ENGINEERING DIVISION, IEM

Presentation Outline
 Implications of inadequate site investigations
 Basic theory of geophysical techniques
 Combination with conventional techniques
 Benefits of this approach
 Concluding thoughts on how these techniques can
add value and reduce risk.

Site Investigations
 Is not just a SOIL INVESTIGATION
 Geotechnical Hazards present a major project risk.
Site investigation a key part of any
development
Detail of investigation directed by the client
Understanding of possible and likely risks and
variability is key in reducing risk

Objectives of Investigation
 Sub soil strata – type of soils, depth to bedrock,
compressibility, strength, collapsing, swelling
 Geo hazards – earthquake related liquefaction, cavities,
faults
 Ground water – depth to ground water, flow direction,
flow volumes, quality
Able to combine geotechnical and hydro-geology
investigations for reduced cost of ground water wells, etc.

Philosophy of Approach
To provide the client with the most comprehensive
geotechnical report the most likely risks must first to
analysed. This requires a highly targeted approach
The investigation techniques used must be appropriate
for the geotechnical hazards to be addressed
Therefore it is important to discuss the geotechnical
issues that affect infrastructure developments before we
analysis the geophysical techniques of investigation

Implications of inadequate SI
Soft sub-surface leads to
slope failures
Sinkholes and Voids can be
missed caused major damage
Differential settlement can occur
causing significant damage - even
to piled structures

 Geophysics is ideally suited
to geotechnical site
investigations
 Provides Engineering
Parameters from non-
invasive site investigation.
 Quickly and cheaply maps
variability – allows refined
and reduced drilling
Geophysical Site Investigation

 Multi Channel Analysis of Surface
Waves – MASW
 Measures 2D profile of
compressibility / strength /
thickness of soils and rocks
 Continuous analysis of surface
waves – CSWS
compressibility in high resolution
 Ground Penetrating Radar – GPR
 High resolution 2D scans that
quickly highlight depth to
features as well as voids.
Geophysical Techniques

 Electrical Resistivity
Tomography (ERT)
resistivity of sub surface
materials
 Ground Conductivity – EM
 Magnetics
 Seismic Reflection /
Refraction
Geophysical Techniques

1st Method – MASW (Multichannel Analysis of
Surface Waves)
 The MASW Technique utilises surface
waves elastic condition (stiffness) of the
ground for geotechnical engineering
purposes.
 A 2D Map of ground stiffness – in terms of
sear-wave velocity (Vs) is created

Multiple lines used to create a 3D
MASW survey
Fence diagram
shows clear
band of rock
material

Advantages
 Quick and cheap – 1 km a day at medium resolution
 Can be built up with multiple lines
 Good agreement with invasive testing
Disadvantages
 Depth of investigation with sledge hammer limited to around 30m depth
(can be increased)
 Resolution of survey must match estimated size of hazards (voids etc)
Multiple lines used to create a 3D
MASW survey

2nd Method – SASW (Spectral Analysis of
Surface Waves)
 Non-Destructive and Non-Intrusive Geophysical
method
 Utilizes the dispersive nature of Rayleigh-Type
surface waves
 Measures the shear wave velocity profile of a
material
 Dispersion of the waves occurs when material
varies in stiffness (Perfect for Geotechnical
Investigation)

 Sledge hammer is used to create
the surface waves.
 Recorded by geophones at known
spacing
 Saved onto computer in the field
SASW

 Sledge hammer is
replaced by vibrator
 Frequency of wave is
controlled.
 Allows operator to
focus on depths
 Requires power – a
generator is used
3rd Method - CSWS (Continuous
Surface Waves System)

CSWS
 Vibrator is ‘run’
through set
frequencies – usually at
5hz intervals
 A display is given of
depth against Shear
Modulus (G)
 Areas of interest can
be focused on by
repeating test with
controlled frequencies

CSWS Results
 Results used to
create graphs like
this
 At this location a
depth of -35m was
reached
 Seen to have a
shear modulus of
approximately
800MPa
-40.00
-35.00
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
0 200 400 600 800 1000
Depth
(m)
Shear Modulus, Gmax (MPa)
Soil
Stiff Soil
Dense Soil
or
Weathered
Rock
Solid Rock

4th Method – Electrical Resistivity Method
 The resistivity technique measures
the bulk resistivity of the
subsurface.
 The resistivity of the material is
measured in unit ohm meter (Ω.m)
 It began with 1-D technique and
later developed into 2-D (electrical
tomography) & 3-D investigations.

2. Cable 100m x 2
1. Abem Sas 1000 and
Abem Selector
4. Battery 12v
6. 42 Clip
3. Measuring tape
5. 41 electrode
Resistivity Method
 41 electrode connected
to 100m ( x2) cable
 inject current into soil
 Source of the current is
by 12v battery
 Data is saved in field
 Data then processed in
the office using RES2DINV
to produce 2D profiles
1
1
5
6
2
2
3 4

Detection of limestone using
resistivity method
at Air Panas, Setapak, Kuala Lumpur.

Zone A – Contamination area ( 1m )
Zone B – Uncontaminated zone (1m – 7m)
Detection of oil contamination at Shah alam

Detection Of Cavity in Limestone area
using resistivity method
Cavity

Detection Of source of water which will
lead to geotechnical risk to slope and sub
base

 High resolution 2D scans that quickly highlight
depth to features as well as voids.
5th Method – GPR (Ground
Penetrating Radar)

Innovation in Investigations – GPR in
shallow water
GPR Scan
showing
lake bottom
and
sediments
beneath
(Freshwater
lake)
Freshwater
river and
lakebed
profiling
Bedrock
Sediments
Freshwater

Combination with Conventional techniques
• Undertake geophysical
scanning of the entire site
• Develop 3 dimensional
ground model
• Calibration with SPTs
SPT N-Values from
subsequent drilling
investigation
Compressible
layers lead to
rapid
reduction in
SPT n

Example Profile
Faster, Stronger, Cheaper, Safer, Greener

Geophysical Investigation to Assess Risks
Involved with Karstic Limestone Formation
Including Presence of Cavities & Pinnacles

Example Project

Typical Conventional SI profile

Comprehensive SI profile

Benefits
 A quick and cheap investigation of
site variability is undertaken before
a site is cleared and without
breaking the soil
 Huge areas can be covered – a
scalable technique
 A range of different types of
geophysical targets mean that
techniques can be picked and
chosen to best suit every challenge
 Invasive investigation can be
targeted and refined based on the
results of the non-invasive
investigation

Adding Value
 Cost of investigation is reduced
 Speed of investigation is increased
 Investigation is scalable in terms of
resolution and depth
 Flexibility with staged processing
 2D and 3D ground models created to
inform decision makers
 Risk of site investigation is reduced

Reducing risk
 Location and measurement of voids /
sinkholes
 Identify geohazards that may be
missed in conventional investigations
 Better predict development costs
with better understanding of site
variability
 Assess features such as contamination
or perched water tables without
problematic invasive investigation
 Identity buried services and
uncontrolled fill

Presentation Summary
 Inadequate site investigations can lead to project
failure (or worse)
 Geophysical techniques provide a cheap and quick
way to gather information
 Add value by:
 Reducing Risk – better site understanding
 Reducing drilling cost
 Creating more accurate ground models

qusanssori@infratechgeo.com
Land and Infrastructure Development on Marginal Soils
IEM 27th July 2020
Technical Talk on
“Advances in Geotechnical and Pavement Engineering for Transport
infrastructure”
HIGHWAY & TRANSPORTATION ENGINEERING DIVISION, IEM

Presentation Outline
 Introduction – Examples of Marginal Soils
 Development on Marginal Soils (Swampy Land, Former
Mining Land and Old Landfills)
 Hazards & Risks
 Geotechnical Issues
 Ground Improvement Approaches
 Case Studies
 Concluding remarks

Geology of
Peninsular
Malaysia

What are Marginal Soils
 Marginal Soils include:
 Soft soils
 Swampy land
 Swelling soils
 Collapsing soils
 Former mining ponds
 Old landfills
 Uncontrolled fill
 Sometimes residual soil area also can referred as marginal soils

Issue Effects Occurrence
Soft soils Settlement; differential
settlement; bearing
capacity; liquefaction
Coastal areas, inland
swamps, alluvial deposits
Loose sands Settlements; slope
stability; liquefaction;
wetting collapse
Aeolian deposits,
uncontrolled fills
Karst - cavities Subsidence; whole sale
collapse and loss of life
Lime stone areas,
burrowing by animals
Swelling/Reactive clays Swelling and shrinking ,
cracking; upheave, slope
stability
Associated with
earthquake and volcanic
zones
Collapsing soils Settlements when wet;
liquefaction
Aeolian deposits, alluvial
areas
Acid sulphate soils Acidification if exposed
to air; run off to streams
Swampy ground,
Brown field sites Mining ponds, tailings
ponds, old land fills,
quarries

Issues with filling over soft soil
Fill over soft clay settled while piled
house did not – sewer pipe broke,
cables broke, house demolished
Negative friction pulled the pile
out of pile cap
Fill placed over soft clay settled

Some thoughts on Geotechnical engineering
 Geologists can predict future issues based on knowledge of
the past
 Geophysics can be used to “scan” for the issues rapidly, non
invasively and cost effectively
 Geotechnical drilling can be done at chosen strategic
locations to log, sample, filed and lab test and confirm
 Geotechnical Engineers must have the skill sets to work
with geologists, geophysicists
 Geotechnical Engineers must articulate their findings and
recommendations in a manner civil, structural engineers
and developers or Project owners can understand.

Geotechnical Issues
 High of fluctuation of ground water table
 Drainage
 Wetting collapse
 Compression
 Soft & loose soils will compress
 Organic soils will induce long term creep and differential
settlements
 Bearing Capacity
 Variable bearing capacity
 Potential development of negative skin friction on piles
 Localise slope failure
 Rainfall infiltration induced settlement
 Soaking Effect

EFFECTIVE STRESS CONCEPT
Of Terzaghi (1936)
Karl von
Terzaghi
Father of
soil mechanics
’ =  - uw
log ’
e
(Terzaghi, 1943)
“… all the measurable effects of a
change in stress, such as
compression, distortion, and a change
in shearing resistance, are exclusively
due to changes in effective stress.”
(Terzaghi 1936).
Model cannot
explain wetting
collapse
behaviour.







 
+
+
=
0
0
0
log
1 p
p
p
e
H
C
S c

CONCEPT OF EFFECTIVE STRESS
Loading
Settlement due to effective
stress increase i.e. derived
from load increase
( ) p
i I
E
qB
or
s 2
1 
 −
=

 (Steinbrenner, 1934)







 
+
+
=
0
0
0
log
1 p
p
p
e
H
C
S c
(Terzaghi, 1943)
( )
2
1
1 


 −
=


u
o
i
E
qB
or
s (Janbu et al., 1956)
Settlement in CLAY
Settlement in SAND
De Beer and Martens (1951)
'
'
ln
o
o
C
H
s


 
+
= '
5
.
1
o
c
q
C

=
z
E
I
q
C
C
s z
n
i 
= 
2
1
(Schertmann et al., 1978)

INTERACTION BETWEEN MOBILISED SHEAR STRENGTH AND
EFFECTIVE STRESS DURING SOIL SETTLEMENT

( )
w
u
−

3

1

Settlement is governed by
applied state of effective
stress and the mobilised
shear strength
'
3
 '
1

Settlement STOP when
stress equilibrium is
reinstated


Mobilised shear
strength envelope
just touches the
effective stress Mohr
circle

Occurrence of wetting collapse substantiated by
laboratory data
Pore air pressure
High air-entry
ceramic disk
Inundation
settlement
Pore
water
pressure
0.6
0.65
0.7
0.75
0.8
0 100 200 300 400 500
Net Pressure (kPa)
Void
Ratio,
e
Wetting at 200kPa Wetting at 400kPa
Inundation
Greater wetting collapse for
low stress level than at high
stress level
ANOTHER
SOIL COMPLEX SETTLEMENT
BEHAVIOUR

UNDULATION OF ROAD EMBANKMENTS
CAUSED BY WETTING COLLAPSE
BUMPY RIDES
SMOOTH RIDES
Uneven
settlement

72
WHAT IS THE PROBLEM
WITH CONVENTIONAL
SLOPE STABILITY METHOD
Always assume pore
water pressure zero
above GWT i.e. ignore
suction
Ignore the
effect of
infiltration
Always apply shear strength at
saturation despite the condition
being partially saturated
ANALYSIS
Apply linear shear
strength envelope of
Terzaghi (1936) OR
Fredlund et al., (1978)
?
Model landslide
by elevating
GWT
FOS < 1.0
Ok, failed
due to GWT
rise
They are no more
conservative
1
2
3
4
5

Wetting
front
GWT
In highland area the
groundwater is too far down
to have influence on the
failure at the top
(Brand, 1981; Othman, 1989)
“The association of failures with heavy rain is clear, but this
qualitative association must be quantified on a physical basis,
if at all possible, before reliable design methods can be
established. Some advances can be made in this direction if
infiltration is postulated as the dominating factor.”
(Lumb 1975)
Stability
decreases
Rainfall
continuously supply
water at the slope
surface.
Water infiltrates and
travel inwards.
Suction
diminishes.
Apparent shear
strength
decreases.
Resisting factor
decreases.
Bulk unit
weight
increases.
Disturbing
factor
increases.

Conventional “Ground
Improvement” Approaches
 Piling
 Fill will settle over soft clay
causing differential
settlement
 to incorporate the negative
friction forces into the
design
 Friction pile designs must
consider group settlement
 Surcharging
 Takes several decades before
appreciable improvements can be
seen in soft clays
 Evaporation is greatly limited by
tailing ponds forming crusts

Ground Improvement techniques
 PVD + surcharge
 Stone columns
 Dynamic Compaction
 Dynamic Replacement
 Soil Mixing
 CDYC
 HIEDYC
 Dynamic Consolidation
 Etc
CRITERIA
 Fit for purpose
 Methodology, Validation,
 Cost
 Time
 Who is responsible

Method Limitations
1. Consolidation Approaches
• Surcharge only Very lengthy surcharge period; requires large quantities of surcharge fill;
possibility of bearing failures with placement of excessive surcharge fill
• Surcharge + PVD Could be lengthy surcharge period between 4 – 12 months, requires
significant quantities of surcharge fill generally of between 1m to 3m;
difficulties associated with clogging of PVDs;
2. Strengthening Approaches
• Stone Columns Bulging of stone columns;
• Soil Cement Columns Cost implications
• Geosynthetic
Reinforcement
Generally only provide improvements in stability and bearing capacity.
May reduce potential for differential settlement but does not address
reduction in total compression.
3. Piled Foundations Downdrag forces; reduction in pile capacity; potential structural damage
to piles
4. Excavate & Replacement Limited to shallow excavations <3m depth; problematic with contaminated
soils

Embankment Fill
Surcharge
Sand Blanket
Drainage length, D = H
H
Surcharge Without PVD
Soft Clay

Soft Clay
Embankment Fill
Surcharge
PVD
Sand Blanket
S
Drainage length, D = S/2
Surcharge With PVD
Nonwoven
Geotextile

Controlled Dynamic Compaction (CDYC)

CDYC Swampy ground
improvement
Sub Division at Lake Coogee, WA
 Swamp site (class P)
 Combination of CDYC (12m
depth of influence) and
HIEDYC™ techniques
 Result = Class S Site

High Impact Dynamic Compaction
( HIEDYC)
HIEDYC Tria HIEDYC Qadra
HIEDYC Penta

0
1
2
3
4
5
6
0 20 40 60 80
Depth
(m)
Elastic Modulus, E (MPa)
CSWS001-POST
CSWS002-POST
CSWS003-POST
CSWS004-POST
CSWS005-POST
CSWS001-PRE
CSWS002-PRE
CSWS003-PRE
CSWS004-PRE
CSWS005-PRE
GROUND IMPROVEMENT BY HIEDYC AT ELIZABETH
QUAY

Suitability of HIEDYC:
• Partially saturated soil
• Fill and embankment
• Coarse grain soil
• For fully saturated soft clay – need PVD to allow the dissipation of
excess pore water pressure and need surcharge to accelerate the
consolidation process

An Overview of Dynamic Consolidation
 Involves applying dynamic energy to pressurise the pore water and to
accelerate consolidation of the underlying soft ground using one of the
dynamic compaction methods and in combination of vertical drains
 Research with application of HIEDYC dynamic compaction on a soft
clayey soil where piezometers were installed at depths of 3m, 6m and
12m has been conducted
 These results to demonstrate that dynamic consolidation can work,
with installation of PVDs, to:
 accelerate the consolidation of soft soils
 reduce the need for placement of high surcharge fills
 create solid raft fill to accommodate high bearing capacity requirement

Deformation is primarily due to
the distortion of the soil particles
and sometimes can be recovered
on unloading
Deformation which is due to the slippage
between the soil particles as the soil
skeleton rearranges itself to accommodate
higher loads. This component of
deformation is irrecoverable or plastic
Will trigger development
of excess pore water pressure
instantly
By providing the drainage path
will accelerate the dissipation of
excess pore water pressure…
Hence will accelerate the
CONSOLIDATION!!

Case Study
 Dynamic Consolidation (DYCON)
approach was utilised in accelerating
the consolidation of soft marine clay.
 The project site is a located in Batu
Kawan, Penang where a Sales Gallery
and show houses for a housing
development are required to be
constructed on a fast track basis.
 Geology map shows that the site is
underlain by a quaternary deposit
 Subsoil properties of the site
Site Location

Earthwork and Ground
Improvement Process
1. Site clearing
2. Lay separator geotextile
3. Prepare working platform
4. Install PVD and geotechnical instrument
5. Lay geosynthetic strip drains
6. Fill 1m thick soil cover and carry out
DYCON
7. Fill in layer to surcharge level and carry
out DYCON
8. Settlement monitoring analysis and
validation testing
~RL
1.0
~300m
m

Settlement Monitoring Results
RSG1 at Sales Gallery
RSG2 at Show Unit

Projects Deliverable
PBT at Sales Gallery

Projects Deliverable
PBT at Show Unit

Pictorial Illustration of Project Activities
PVD and platform preparation

Geosynthetic strip drain installation

Filling in progress

HIEDYC Dynamic Compaction in progress

Sales Gallery and Show Unit under construction

Finish Product

Case Study
Runway Extension at Kota
Kinabalu Airport

Challenges and constraints:
• Reclaimed land with underlying soft clay
thickness of up to 3m
• High water table
• Limited availability of fill material for
surcharge

Soft Silty Clay
Soft Silty Clay

Original Design
1.Install pvd @ 1m c/c
2.Place 5m height of surcharge
3.Surcharge period of 5 months
4.Minimum of 90% degree of consolidation
Alternative
1.Install pvd @ 1m c/c
2.Place 1.5m height of surcharge
3.Apply HIEDYC deep lift compaction
4.Achieve a minimum of 90% degree of consolidation

Surcharge
Fill

0.5m
1.0m
1.5m
Ht
of
Fill

Conceptual Representation of Electro Osmosis in Soil
(from Jones et al, 2008)

Electro Osmotic
Consolidation
 Removal of water from the cathode results in:
 Changes in soil material properties
 Increase in shear strength
 Electrochemical hardening of soil
 Reduction in volume

Electro Osmotic
Consolidation
Relationship between Shear Strength and Water Content
(from Jones et al, 2008)

Difficulties in
Application of E-O
 Metallic Electrodes are expensive to use and to install
to depths
 Electro-chemical corrosion during E-O process

Electrode
Requirements
 Electrically Efficient
 Drainage Capacity
 Not subject to Electro-Chemical Corrosion
 Rapid and Low Cost Installation
 Preferably with Existing Equipment

Copper Foil
PP Core
Filter
Electrically Conductive
Prefabricated Vertical
Drains

Conceptual Application of
Electro Osmotic Consolidation

Completed road open to traffic

Benefits from Electro
Osmotic Consolidation
 Ideal for fast-track projects requiring ground
improvement.
 Technology sells time.
 Attractive option for locations with no easy access to
surcharge supply.
 Quick gains in shear strength enable ground to
support high embankments

Chemical/Cement
/Lime Soil
Stabiliser

Chemical / Cement / Lime Soil Stabiliser
 Most of the stabiliser product aims to:
 Stabilise at least 300mm of subgrade to increase CBR and
to reduce sand, crusher run and binder course

Typical work sequence
Process 3: Adding stabiliser agent
to calculated value
Process 4: Mixing and stabilize
the material
Process 6: Adding stabiliser agent
to calculated value

Secugrid® Geogrid & COMBIGRID® Geogrids – Function for
Road Application
Biaxial laid geogrid made of stretched,
monolithic flat polymer (polypropylene)
bars with welded junctions (patented
process)
Provide superior soil reinforcement and
stabilization for base reinforcements
Reinfor
cement
Stabili
sation
Combigrid®
Geogrids
A Geocomposite for soil
reinforcement,
separation, drainage and filtration in 1
product

Secugrid® & Combigrid® - interlocking, confinement
Lateral
restraint
Load
Secugrid®
Subgrade Layer
Secugrid® - how does it work?
Granular / soil material interlocks with the geogrid bars (MD & CMD)
Geogrid bars provide confinement to the overlaying gravel/soil

Soft
Subgrade
Base
• Prevent soft subgrade intruding into
aggregate base, and vice versa
• Combigrid® restrict soil movement,
yet allow water to move from the
filtered soil to the coarser soil →
Cost savings !
Pumped Fine
Soils
Intruded Coarse
Aggregates
Combigrid®
Soft
Subgrade
Base
▪ Reduced strength, stiffness
and drainage characteristics
of base aggregate
▪ Greater risk of heave →
Problem!
Secugrid® Combigrid® - separation, filtration,
drainage

Concluding Remarks
 The dwindling supply of land for infrastructure development
around the world has pushed development into marginal
land ranging from Soft Ground to Former Mining Ponds, etc.
 These marginal lands require specific investigation to fully
characterise the geotechnical properties.
 It is important to understand the rheology of formation of
these marginal lands in order to predict its engineering
behaviour.
 Geophysical investigation methods have proved to be useful
as investigation tools.
 Specialist geotechnical knowledge has to be utilised with
geology and geophysics for effective outcomes

PERFORMANCE BASED PAVEMENT DESIGN AND
CONSTRUCTION
Secugrid®
Reinforced with Secugrid® 30/30 Q1,
CBR < 3%
Unreinforced, CBR < 3%
No Pavement
Description
Alternative Design 1 Alternative Design 2 Alternative Design 3 Conventional
Standand Design
ESAL 5 Million 5 Million 5 Million 5 Million
Design
300 Subgrade With
Soaked CBR > 5%
20mm Chipseal
(Double layer)
300 Subgrade With
Soaked CBR > 5%
50mm ACW
(Wearing Course)
Soil Stabilise
Pavement 300 mm
Soil Stabilise
Pavement 300 mm
300 Subgrade With
Soaked CBR > 5%
50mm ACW 20
(Wearing Course)
Soil Stabilise
Pavement 300 mm
60mm ACB 28
(Binder Coarse)
300 Subgrade With
Soaked CBR > 5%
50mm ACW 20
(Wearing Course)
150 mm Crushed Aggregate
60mm ACB 28
(Binder Coarse)
150 mm Compacted Sub Base

AASHTO Road
Test (Empirical
Design Method)
 AASHTO is solely depending
on the AASHTO Road Test
carried out in Ottawa, IL
from 1956 – 1961.
 Only the specified material
(granite) shall be used in
pavement design.
 Crushed rock and sandy
gravel sub base.
 In tropics, Australia and also
in USA known to produce
thicker than required
pavement.
 Freeze–thaw conditions.

AASHTO Road Test
(Empirical Design Method)
Following points need to be pointed in relation to empirical
pavement designs:
 The AASHO road test was conducted to less than 2million
ESA. Extrapolation for higher axle numbers has been shown
to give higher pavement thickness
 The empirical pavement thickness derived from the
AASHTO guidelines allow for freeze thaw and frost heave
effects and hence naturally lead to a thicker pavement. In
the tropics such as Malaysia and many parts of Australia this
does not happen. Therefore, pavements need not the as
thick as per AASHTO guidelines
 The empirical approach constrains the designer to use the
same type of materials used for the original road test.
Stabilised materials, geo synthetics etc cannot be reliably
modelled in the empirical designs

 The main consideration in mechanistic-empirical method is
the actual response of the pavement when it is subjected
to load.
 The most special value of the mechanistic design method is
it allows a rapid analysis of the impact of changes in input
items such as changes in traffic and materials.
 This method also can accurately characterize in situ
material using the portable device that is called Falling
Weight Deflectometer (FWD).
Mechanistic Pavement Design
Developments
D0 = maximum deflection for a test point
D0 - D200 = deflection measured where the test load
is 200mm from the point of maximum deflection
(in the direction of travel).

Mechanistic
Pavement Design
Developments
 The deflection (D0)
of the pavement
represents the
strength, while the
curvature (D0 - D200)
represent the
asphalt fatigue.
 The smaller value
of the D0, the
stiffer the
pavement it can
be.
 D0 and D0 - D200
against ESA can be
estimated based on
the graph 1 & 2
(Austroads, 2004).
Graph 1 : D0 vs ESA
Graph 2 : (D0 – D200) vs ESA

Pavement performance
parameters
No Performance
Criteria
Descriptions
1 Rutting Rutting is when pavement deform due to sub grade strain and mix
design
2 Skid Resistance The friction force developed between tyre and pavement to prevent the
vehicles from sliding - TRRL Pendulum to Laser Profilometer Test.
3 Surface Texture Pavement surface texture is texture wavelength. Adequate surface
texture will provide proper drainage of tyre grooves and reduce water
spray when moving at high speed – Sand Patch Test and Laser
Profilometer Test
4 Roughness Pavement roughness is defined as microscopic undulating of the
pavement that affect the ride quality of vehicles – Bump Integrator and
Lase Profilometer Test.
5 Strength The maximum deflection (D0) is noted as the strength of the subgrade -
Benkelman Beam and Falling Weight Deflectometer Test
6 Stiffness Deflection ratio (D250/D0) is used to indicate the stiffness of the
pavement structure - Benkelman Beam and Falling Weight
Deflectometer Test.
➢ > 0.8 indicates CTB or CTSB bound pavement
➢ 0.6 – 0.8 indicates good quality unbound pavement
➢ < 0.6 indicates a possible weakness in the pavement materials
7 Fatigue Pavement fatigue is determined from the curvature function (D0 – D200)
to predict the fatigue life of an applied asphalt surfacing overlay or an
existing asphalt surfacing - Benkelman Beam and Falling Weight
Deflectometer Test.
Unlike the empirical design method, the mechanistic design method can be
evaluated using the in-situ testing.
Rutting
Fatigue
Surface Texture

Pavement performance
parameters
 Based on specifications from Main Road Western Australia – Contract 89/13
[10], the pavement condition is measured based on criteria specified in table
below.
Pavement
Category
Component Measure Acceptable Standard
New
construction
Structural
Capacity
Pavement deflection –
FWD
(at 700 kPa)
For granular Pavements: mean
Segment value ≤ 0.60mm
Pavement curvature –
FWD
(at 700 kPa)
For granular Pavements: mean
Segment value ≤ 0.23mm
Functional
Capability
Pavement roughness 95th percentile lane value < 40
counts/km and no segment value >
50 counts/km
Surface shape 3mm maximum
Texture Index Segment value not greater than 0
Texture depth Measured at any point on the surface
must be greater than 1.0 mm
Table 2: Performance Measure requirements prior to Practical Completion (Main
Roads Western Australia – Contract 89/13)

Advantages of
Mechanistic
Pavement
Design
Enables the use of marginal materials with
modifications and the ability to model these modified
materials in the mechanistic design.
Saves cost by allowing local “non-standard” materials
to be used.
Reduces the risk of pavement life reduction due to
poor quality construction because stiffness can be
measured rapidly and economically by FWD testing.
Better long-term life can be obtained by specifying and
ensuring roughness.
Safer road (especially during rains) can be obtained by
measuring Surface texture and Friction as construction
acceptance testing.
This method can be used for both existing pavement
rehabilitation and new pavement construction.

Case History of
Performance-Based
Pavement (SDE)
Senai Desaru Expressway (SDE)
 SDE pavement for Package 1
and 2 was designed by Infra
Tech Projects using the
mechanistic design method.
 The trial pavements of various
thicknesses on subgrade which
was compacted by HIEDYC (High
Impact Energy Dynamic
Compaction)
 Original pavement designed
where the subgrade was
conventionally compacted as
per the JKR Design.

Case History of Performance-
Based Pavement (SDE)
Table 3: Trial pavements for SDE
These trial pavements were used to determine the stiffness and
resilience modulus, ER of each layer of the pavement. The validation
test using FWDT was carried by IKRAM and the result as shown in table
below.

Case History of Performance-
Based Pavement (SDE)
Table 4: Pavement deflection, D0 and strength modulus, MPa
Sub sequent to the trial, the pavements for SDE packages 1 and 2 were quality
controlled using the Falling Weight Deflectometer to validate the pavement stiffness
of each lane of the highway. The slow lane was tested at 50m intervals while the fast
lane was tested at 100m intervals with the 95th percentile deflection targeted to be
0.8mm or less.

Important
Factors in
Pavement
Design
In order to ensure the pavement condition
can be sustained for long period, several
factors need to be taken into account
during design and construction stage.
 Adequate assessment need to be
carried out on the subgrade conditions
especially when dealing with
problematic soil or rock material
(variably weathered soil subgrades,
swelling soils, collapsing soil, soft soil
and etc).
 Surface and subsurface drainage must
be looked into at the design stage and
then modified where necessary based
on site observations of geological
features and water seepage when the
site is opened up during construction
stage.
 Proper compaction needs to be done
to ensure the subgrade is highly
compacted and no major post-
construction settlement will occur
after the road is opened for public.

3 Important Causes of Pavement
Failure
 1. WATER – from the top (Precipitation)
 2. WATER – from the side (Slope)
 3. WATER – from the bottom (Seepage)
At design stage, it can be addressed by looking at the geology of the site.

Conclusion
 It is not only feasible for performance-based
specifications but also performance-based construction
and quality control of new works as well as maintenance
works.
 Based on past successful history of performance-based
pavement designs and construction there is a strong
case that pavement designs can be done by mechanistic
designs.
 However, important factors in pavement design need to
be considered.
 Other than that, good interaction among the highway
agency engineers to identify the proper input
parameters for the design is necessary.
 Even if the designs are done using empirical methods,
the pavement construction specifications should be
based on roughness, stiffness, friction, surface texture.

THANK YOU
FASTER, STRONGER, CHEAPER, SAFER, GREENER

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