Abstract 3-D Dynamic Base Shaking Model Conclusion

Introduction

References

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.

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.

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.

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)

for y<= yu

To approximate liquefaction effects on p-y behavior one must apply a p-multiplier 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.

3/1

2

m

u

y

ypp

upp

)25.05.1(b

xbqp r

uu

bqp uu 5.4

for y>yu for 0 ≤ xr≤2b

for xr>12b

bky mm A frozen soil p-y model was proposed based on an experiment conducted in Fairbanks, Alaska.

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.

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.

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?

Numerical simulations were used to address this issue. A simplified method to account for frozen crust was developed and evaluated.

Depth(m)

SoilType

StatusMass

density(kg/m3)

Shear wave

velocity, VS (m/s)

Permeability

(m/s)

Friction Angle(deg)

Cohesion (kPa)

0-0.2 SiltFrozen

1.8x103 500 1.0 x10-8 27 100Unfrozen 200 1.0 x10-7 33 0

0.2-1.8 SiltFrozen

1.8x103 1,000 1.0 x10-9 27 100Unfrozen 200 1.0 x10-7 33 0

1.8-2.0 SiltFrozen

1.8x103 500 1.0 x10-8 27 100Unfrozen 200 1.0 x10-7 33 0

2.0-8.0LooseSand

Unfrozen 1.9x103 180 6.6 x10-5 29 0

8.0-14.0Medium

Dense SandUnfrozen 1.9x103 200 6.6 x10-5 37 0

14.0-24.0DenseSand

Unfrozen 2.1x103 250 6.6 x10-5 40 0

Damage from the 1964 Alaska Earthquake

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.

-0.4 -0.2 0 0.2 0.4 0.6

Deflection, (m)

Frozen Crust

Loose Sand

Medium Dense Sand

DenseSand

-0.4 -0.2 0 0.2 0.4 0.6

-20

-15

-10

-5

0

5

Frozen Crust

Loose Sand

Medium Dense Sand

DenseSand

Dep

th (

m)

0 sec10 sec20 sec30 sec40 sec50 sec60 sec70 sec82 sec

BNWF model3D model

-4 -2 0 2 4 6

-20

-15

-10

-5

0

5

Shear Force (kN, x103)

Loose Sand

Frozen Crust

Medium Dense Sand

Dense Sand

-4 -2 0 2 4 6

-20

-15

-10

-5

0

5

Dep

th, (

m)

x103

Frozen Crust

Loose Sand

Medium Dense Sand

Dense Sand

0 sec10 sec20 sec30 sec40 sec50 sec60 sec70 sec82 sec

3D model BNWF model

-10 -8 -6 -4 -2 0 2 4 6 8 10

Medium Dense Sand

Loose Sand

Frozen Crust

-10 -8 -6 -4 -2 0 2 4 6 8 10

-20

-15

-10

-5

0

5

Bending Moment (kN-m, x103)

Frozen Crust

Loose Sand

Medium Dense Sand

Dense Sand

Dep

th, m

0 sec10 sec20 sec30 sec40 sec50 sec60 sec70 sec82 sec

3D model BNWF model

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.

Acknowledgement: This research was supported from Alaska EPSCoR NSF award #EPS-07011898.

22nd National NSF EPSCoR Conference, Coeur d’Alene, Idaho October 24-27, 2011. Theme: Water/Environment.

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.)

Analysis of Laterally Loaded Piles in Liquefiable Soils with a Frozen Crust

Xiaoyu Zhang1, Zhaohui (Joey)Yang, Ph.D.1

1. Dept. of Civil Engineering, University of Alaska Anchorage, Anchorage, Alaska