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OT5206 Offshore Foundations
Pile Driveability Analysis - Tutorial
Prof Chow Yean Khow
Email : chowyk@nus.edu.sg
Phone : 6516 2161
Office : E1A-07-07
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
GRLWEAP Installation
2
 Installation
• Download the GRLWEAP 2010 installation file and the background manual at
http://downloads.pile.com/GRLWEAPUniversity
• Enter user name and password below:
• User name: PDI-user2
• Password : drEp7esw
• Copy the GRLWEAP_2010_Univ.exe file to your computer. Double click on the file to install
it onto your computer. When the window appears that asks for the company name and
serial number, enter the following:
• Company : NU Singapore-NOT FOR COMMERCIAL USE
• Serial number: 8GCTCN2-6008-7NYT5ZK
• The first time you run the GRLWEAP program right click on
the GRLWEAP icon and select “Run as Administrator”.
You will get a dialog box saying that it is a Demo version
and how many days you have left. Click “OK” to start
using the program.
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
GRLWEAP Overview
3
 A Quick Overview
• One-dimensional wave equation analysis of pile driving
• Extensive library of pile driving hammer and cushion
information
• It can be used for developing:
• Bearing graph
• Ultimate capacity vs blow count for a specific pile depth
• Inspector chart
• Stroke vs blow count for a specific pile ultimate capacity
• Pile driveability
• Pile depth vs blow count and pile stresses during driving
• Despite its complete features and user-friendliness,
geotechnical expertise is required to ensure correctness
of the geotechnical input parameters and sensibility of
the analysis outcomes
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Various Usage
GRLWEAP Overview
4
Bearing graph
For a specific pile depth Inspector chart
For a specific pile ultimate capacity Pile driveability
For a specific or varying hammer stroke
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Main Input Window
GRLWEAP Input
5
Hammer library
and user input
parameters
Cushion input
parameters
General pile
geometry
[Length can be
modified]
Gain/ loss factor
for unit soil
resistance
[see next slide for
details]
Schematic of
key input
parameters
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Hammer Parameters
• Hammer Model
• To select a suitable model from the list
• Double click the list at the main input for hammer details
• Stroke
• Defined as equivalent stroke instead of physical stroke;
automatically calculated from rated hammer energy
over ram weight
• Default value can be used unless a lower stroke is required;
varying strokes can be defined [see advanced features]
• Efficiency
• For design, the recommended value can be used which
was based on measurements. Alternatively, a specific value
may be assigned to suit a pile driving plan.
• Varying efficiency as a function of pile penetration depth can be
input using depth modified function [see advanced features]
GRLWEAP Input
6
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile Parameters
• Geometry
• Cross sectional properties must be entered
• Total pile length is to be defined and consists of design
penetration depth plus length above the seabed;
temporary pile length can also be set in “Depth Modifier”
[see advanced feature]
• Penetration refers to design penetration depth of the pile
• Non-uniform piles can be entered in “Pile Type” drop down
menu and select “Non Uniform Pile”
• Batter/inclination of pile can be set in “Pile Parameter”
• Material properties
• Default elastic modulus of steel piles is 210 000 MPa
• Default unit weight of steel piles is 77.5 kN/m3
• Resulting pile stresses has to be checked against
allowable stress manually
GRLWEAP Input
7
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Soil Parameters
• Unit shaft resistance
• Total resistance from external
and internal shaft
• Unit toe resistance
• “Unplugged” is the default option
• For “plugged” pile during driving
at specific layers, [Toe Area] is to
be modified to full bearing area
• Skin and toe quakes
• Typically 2.5mm (0.1 inch) for
unplugged driving
• Skin and toe damping
• Each soil has its values (refer to
the table for the standard values
for impact driven piles)
GRLWEAP Input
8
Soil type Shaft Damping* Toe Damping
Non cohesive (“Sand”) 0.16 s/m 0.50 s/m
Cohesive (“Clay”) 0.65 s/m 0.50 s/m
Note: * for mixed soils, intermediate values may be appropriate; for
example, a sandy silt or clayey sand may be modeled with 0.33 s/m
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Soil Parameters
• Setup factor
• Conversion from long-term static
resistance (LTSR) to static resistance
to driving (SRD)
• Only applicable for shaft resistance
and the value may vary for each layer
• Generally equivalent to sensitivity
(undisturbed and remolded strength
ratio) for clay soils
• Input shaft resistance must be
compatible with the setup factor
• Input shaft resistance is LTSR  set fs ≠
1.0 (SRD will be computed accordingly)
• Input shaft resistance is SRD  set fs = 1.0
(simplest approach)
GRLWEAP Input
9
= ⁄
Soil type Setup factor Remarks
Clay 3.0 Range of 2 – 5 is possible
Sand 1.2
For loose to medium dense sand;
dense to very dense sand may
result in relaxation and thus fs <
1.0
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Soil Parameters - Advanced Features
• Variable setup factor [setup time, limit distance]
• If pile driving is interrupted, soil may gain strength
which magnitude is a function of elapse time since
the driving is halted.
• If a setup factor, fs, (indicating the maximum loss)
is defined, the change in the loss factor with time
is modeled in GRLWEAP with the following
exponential relationship, where
• t = wait time since driving halted (in hrs)
• tS = setup time to achieve full gain (in hrs)
• Wait time is to be input in “Depth Modifier” input
form [see advanced features]
• Limit distance defines the minimum driving
distance to effect maximum strength loss
• The limit distance must be input and can be
estimated as 2m.
GRLWEAP Input
10
= 1 + log 0.01
= 1 − 1
log 0.01
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Soil Parameters - Advanced Features
• Gain/Loss Factor (Shaft)
• The setup factor, fS, controls the maximum loss of soil resistance with respect to the
long term static resistance (LTSR) for individual soil layers.
• The Gain/Loss factor, fGL, allows variations in the static resistance to driving (SRD) for
the entire soil layers between minimum SRD and LTSR
• At maximum loss  fGL = 1/fs (SRD = SRDmin)
• At partial setup  1/fs < fGL < 1.0 (SRDmin< SRD < LTSR)
• At complete setup  fGL = 1.0 (SRD = LTSR)
• For multi-layered soils, the Gain/Loss factor will adjust
the reduction factor fRD proportional to the ratio of
setup factor for individual layers fS [fsx = max fS of all layers]
GRLWEAP Input
11

∗ = 1 − 11 − 1 = 1 − ∗ + ∗× 0.8 1.00.9
0.4 1.00.7fRD
fRD
Example for multi layers
G/L fGL = 0.4; 0.7; 1.0
Clay fS = 2.50 (fSX)
Sand fS = 1.25
0.4 1.00.7fGL
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
GRLWEAP Input
12
 Driving Process - Advanced Features
• This tutorial only covers
the advanced features for
hydraulic hammer
(typically used offshore)
• Depth Modifier Input
• Any changes/variation during pile driving can be entered using
“Depth Modifier Input” form. The modification is set according to
specific pile penetration depths.
• For hydraulic hammers, the parameters that can be modified include:
• Temporary pile length
• Wait time (in hrs)
• Stroke length
• Hammer efficiency
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile Installation
• Pile driving at 60m water depth
• Design pile depth of 100m
based on static capacity
• Assess hammer suitability
GRLWEAP Example Problem
13
C
la
y
Sa
nd
Te
m
p
pi
le
l
en
gt
h
3
Te
m
p
pi
le
l
en
gt
h
1
Te
m
p
pi
le
le
ng
th
2
Water level
Seabed level
Pile
segment 1
Pile
segment 2
Pi
le

se
gm
en
t 3
Varying
hammer
energy
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile driving at 60m water depth
• Hammer parameters
• Hammer model : Menck MHU-750T
• Stroke length : 1.84m (equivalent)
• Efficiency : 50% (0-50m depth) and 95% (50-100m depth)
• Cushion : Not used
GRLWEAP Example Problem
14
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile driving at 60m water depth
• Pile parameters
• Vertical pile
• Pile outer diameter : 1.524m (60in.)
• Pile thickness : 38.1mm (1.5in.) and 50.8mm (2.0in)
• Total pile length : 190m
• Design pile penetration depth : 100m below seabed level
• Temporary pile length : 0-30m depth (120m long); 30-60m depth (150m long);
60-100m depth (190m long);
• Yield strength : 450 MPa
GRLWEAP Example Problem
15
Section Length (m) OD (m) Thickness (mm) Annulus (cm2) Perimeter (m)
1 0 – 60 1.524 38.1 1779 4.788
2 60 – 120 1.524 50.8 2351 4.788
3 120 –190 1.524 38.1 1779 4.788
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile driving at 60m water depth
• Soil Parameters
• Two layer soils consisting of clay overlying dense sand
• Clay sensitivity St = 2.5
• Sand interface friction angle δ = 30o, K = 0.8, Nq = 40 (refer to next slide)
• Unplugged driving, 50% internal shaft friction is assumed
• Calculated external unit shaft friction is to be multiplied by 1.5 for GRLWEAP input
• Fully remolded strength for clay shaft friction during driving, no soil setup is assumed
• Shaft friction and end bearing for sand during driving is capped by limiting values
(refer to next slide), no soil setup/relaxation
GRLWEAP Example Problem
16
Depth (m) Soil Strength parameters γ’ (kN/m3) Unit shaft friction Unit toe resistance
0.0 – 80.0 Clay Su (kPa) = 25T – 125B 8.0 Su / St 9 Su
80.0 – 150.0 Dense sand φ’ = 35o 10.0 Κ σ’v tan δ σ’v × Nq
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile driving at 60m water depth
• Soil Parameters
• API RP2A
GRLWEAP Example Problem
17
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile driving at 60m water depth
• Soil Parameters
• Effective vertical stress at 80m depth : σ’v = 80 x 8 = 640 kPa
• Effective vertical stress at 150m depth : σ’v = 640 + (70 x 10) = 1340 kPa
• Calculated shaft and toe resistance of the dense sand layer is capped by limiting values
(refer to API RP2A) *
• No limiting shaft friction for clay; the toe resistance is based on undisturbed strength
• Unit shaft friction for all layers is to be multiplied by 1.5 to account for 50% internal friction
• Input soil resistance directly corresponds to SRD; the setup factor is to be set to 1.0
GRLWEAP Example Problem
18
Depth (m) Soil Unit shaft friction
(kPa)
Unit toe resistance
(kPa)
Skin and toe
quake (mm)
Skin and toe
damping (s/m)
0.0 – 80.0 Clay 15T – 75B 225T – 1,125B 2.5; 2.5 0.65 ; 0.50
80.0 – 150.0 Dense sand* 144 9,600 2.5; 2.5 0.16 ; 0.50
(Original) 443T – 928B 25,600T – 53,600B
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Main input window
• Refer to main input parameters
• Hammer
• Total pile length
• Pile penetration
• Gain/Loss factor
• Model diagram
• etc
GRLWEAP Example Problem
19
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Pile parameters
• Pile segment
• 0 – 60m : 38.1mm
• 60 – 120m: 50.8mm
• 120 – 190m: 38.1mm
GRLWEAP Example Problem
20
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Soil parameters
• Soil profiles and input parameters
• Limiting shaft and toe resistance for sands
GRLWEAP Example Problem
21
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Depth modifier input
• Temporary length at
various penetration
depths:
• 0 – 30m : 120m
• 30 – 60m: 150m
• 60 – 100m: 190m
• Efficiency at various
penetration depths:
• 0 – 50m : 0.50
• 50 – 100m: 0.95
GRLWEAP Example Problem
22
© Copyright National University of Singapore. All Rights Reserved. OT5206 Offshore Foundations 2021/2022
 Analysis output
• Predicted blow counts
• SRD profiles
• Pile stresses
• Energy profile
 Acceptance Criteria
• Blow counts
• Refusal criteria is often taken to be
150 blows/0.3m
• Pile stresses
• Allowable compression and tension
stress for steel piles < 0.9 fy
GRLWEAP Example Problem
23
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QUESTIONS?
24