Analysis of Laterally Loaded Piles in Liquefiable Soils
with a Frozen Crust
1
Zhang ,
1
Ph.D.
Xiaoyu
Zhaohui (Joey)Yang,
1. Dept. of Civil Engineering, University of Alaska Anchorage, Anchorage, Alaska
Conclusion
5
The Open System for Earthquake Engineering Simulation platform (OpenSees) was used to
conduct pile-soil interaction analyses. Based on general Alaska soil conditions, an idealized soil
profile with an embedded pile and a surface inclination angle of 3° was used. A reinforced
concrete-filled steel-pipe pile, commonly used in constructing Alaskan highway bridge foundations,
was chosen for study.
Shear
Depth
(m)
Soil
Type
Mass
density
(kg/m3)
Frozen
1.8x103
Unfrozen
Frozen
1.8x103
Unfrozen
Frozen
1.8x103
Unfrozen
wave
velocity,
VS (m/s)
500
200
1,000
200
500
200
180
Status
0-0.2
Silt
0.2-1.8
Silt
1.8-2.0
Silt
2.0-8.0
Loose
Sand
Unfrozen 1.9x103
Medium
Dense Sand
Unfrozen 1.9x103
8.0-14.0
27
33
27
33
27
33
100
0
100
0
100
0
6.6 x10-5
29
0
-5
-10
Frozen Crust
Frozen Crust
Loose Sand
Loose Sand
0 sec
10 sec
20 sec
30 sec
40 sec
50 sec
60 sec
70 sec
82 sec
Medium
Dense Sand
-15
Dense
Sand
-0.4
-0.2
0
0.2
0.4
0.6
6.6 x10-5
37
Dense
Sand
-0.4
-0.2
0
0.2
0.4
0.6
5
0
0
Frozen Crust
-5
Loose Sand
-10
Medium
Dense Sand
-20
Frozen Crust
Loose Sand
-5
-10
0 sec
Medium
10 sec
Dense Sand
20 sec
30 sec
40 sec -15
50 sec
Dense
60 sec
70 sec
Sand
82 sec
-15
0
BNWF model
Deflection, (m)
5
Dense
Sand
200
Medium
Dense Sand
3D model
-20
Permeabili Friction
Cohesio
ty
Angle
n (kPa)
(m/s)
(deg)
1.0 x10-8
1.0 x10-7
1.0 x10-9
1.0 x10-7
1.0 x10-8
1.0 x10-7
These figures are
comparisons of pile
performance
evaluated from both
models. The graphs
on the left were
obtained from 3-D
modeling, the ones
on the right from a
BNWF process (the
final step in a
Pushover analysis.)
As can be seen, the
simplified method
provides accurate
data and has the
potential to be used
in design practices.
Summary: A 3-D Finite Element simulation of
a single bridge pile embedded in liquefiable
soils overlain by a frozen crust was carried out
using OpenSees. The BNWF Pushover
method was used to evaluate the pile
performance with a newly developed frozen
soil p-y curve. The simplified BNWF model
generated accurate results and can be used to
develop guidelines for engineers.
0
Depth (m)
Liquefaction and associated ground failures are
common in major earthquakes in Alaska and
have caused extensive infrastructure damage.
To model ground failures in cold regions and
their effects on infrastructure, it is necessary to
account for frozen ground crusts, which have
drastically different physical properties (including
stiffness, shear strength and permeability) than
unfrozen ground. How can we predict the impact
to a bridge pile foundation when there is a
frozen ground crust that is resting on top of the
liquefied soil?
3-D Dynamic Base Shaking Model
Depth, (m)
Abstract
BNWF model
3D model -20
-4
-2
0
2
4
6 -4
-2
0
3
2
4
6
Shear Force (kN, x10 )
5
14.0-24.0
6.6
40
x103
0
0
-5
Frozen Crust
Frozen Crust
Loose Sand
Loose Sand
0 sec
10 sec
20 sec
30 sec
40 sec
50 sec
60 sec
70 sec
82 sec
Medium
Dense Sand
-10
-15
Dense
Sand
BNWF model
3D model
-20
-10 -8
Medium
Dense Sand
-6
-4
-2
0
2
4
6
8
10 -10 -8
-6
-4
-2
0
2
4
6
8
10
Bending Moment (kN-m, x10 3)
2-D Static BNWF Pushover Model
The BNWF (Beam on Nonlinear Winker Foundation) Pushover method is a simplified approach to
analyzing piles in laterally spreading ground, which has the potential to serve as a practical tool for
engineers. Using BNWF, a model for frozen soil were developed and implemented into OpenSees.
P-y, t-z and q-z springs were used to represent
soil lateral behavior, friction in soil-pile interface,
and
end-bearing
capacity,
respectively.
Displacement was imposed on a frozen crust
spring. (Brandenberg et al. 2007; OpenSees
Example Page)
1/ 3
pu  y

p
2  y m




p 
u
p
p u  q u b (1 . 5  0 . 25
p u  4 .5 q u b
for y<= yu
for y>yu
xr
b
)
for 0 ≤ xr≤2b
for xr>12b
ym  kmb
Damage from the 1964 Alaska Earthquake
250
x10-5
Time histories recorded during the 2002 Denali earthquake at
Trans-Alaska Pipeline System Pump Station #10 were input at
the base in X direction. The record has an 82 second duration
and peak acceleration of 0.3g.
Introduction
In March 1964, Alaska experienced one of the
largest earthquakes in recorded history. In
November 2002, the Denali Earthquake struck
Interior Alaska. These two winter earthquakes
caused extensive ground failure and structural
damage, including substantial damage to
bridges. Alaska’s population has increased from
226,167 in 1960 to 710,231 in 2010 (2010
Census), making the topic of potential
earthquake damage more important than ever.
Unfrozen
2.1x103
Depth, m
Numerical simulations were used to address this
issue. A simplified method to account for frozen
crust was developed and evaluated.
Dense
Sand
A frozen soil p-y model was proposed based on an experiment
conducted in Fairbanks, Alaska.
To approximate liquefaction effects on
p-y behavior one must apply a pmultiplier to drained p-y resistance.
A p-y curve for frozen silt was proposed
based on the p-y curve model for weak
rock (Reese, 1997) and clay (Matlock,
1970) and calibrated by field test data
(Li, 2011). This was used in a 2-D
Static BNWF Pushover Model.
Represented Theme:: This poster is entered
in the Water/Environment, as it deals with
naturally occurrence elements and processes
(i.e. frozen soil and earthquakes.)
Acknowledgement: This research was
supported from Alaska EPSCoR NSF award
#EPS-07011898.
References
Brandenberg S J. and Boulanger R W. (2007). "Static Pushover Analyses of Pile Groups in Liquefied and Laterally
Spreading Ground in Centrifuge Tests." Journal of Geotechnical and Geoenvironmental Engineering 133: 9.
OpenSees Example Page, http://opensees.berkeley.edu/wiki/index.php/Laterally-Loaded_Pile_Foundation,
Retrieved on 2011-05-01.
Reese, L. C. (1997). "Analysis of laterally loaded piles in weak rock." Journal of Geotechnical and
Geoenvironmental Engineering 123: 1010-1017.
Matlock, H. (1970). "Correlations of design of laterally loaded piles in soft clay." Proc., Offshore Technology
Conf. 1: 577–594.
“Resident Population Data – 2010 Census” (2010.) http://www.census.gov. Retrieved on 2011-05-29.
22nd National NSF EPSCoR Conference, Coeur d’Alene, Idaho October 24-27, 2011. Theme: Water/Environment.