Post on 16-Jan-2016
Analysis of Laterally Loaded Drilled Shafts and Piles Using
LPILE
Shin-Tower Wang, Ph.D., P.E. Ensoft, Inc./Lymon C. Reese &
AssociatesAustin, Texas
April 3, 2009
Outlines Introduction Basic theory of the p-y curve method
Numerical solution for soil-structure interaction
Characteristic Shape of p-y Curves Available p-y Curve Criteria Common Input Values
Special consideration for large-diameter piers Effect of nonlinear EI on deflection Special features in LPILE
Piles are used in a variety of ways to support super-structures
Drilled Shafts with Lateral Load
PM
Q
Ultimate earth pressure
(strength fully mobilized)
Actual earth pressure
Ultimate earth pressure
(strength fully mobilized)
Actual earth pressure
Methods of Solution
Linearly elastic solution (Poulos and Davis, 1980) emphasizes the condition of continuity although the soil cannot be characterized as a linearly elastic material.
Limit-equilibrium solution (Broms, 1965)
finds the ultimate lateral load at failure, but soil-structure interaction at lesser loads is not addressed.
The p-y method with beam-column model (McClelland, Matlock, Reese, 1958-1975)
has been developed extensively to take into account the soil-structure interaction and nonlinear resistance of soils.
3-D Finite-Element method
Soil Failure Patterns
Wedge Failure
Plane-Strain Failure
Nonlinear Model for Lateral Soil Resistance
EI = pile stiffnessy = pile deflectionx = distance along pilePx = axial load on pile andEpy = slope of secant to p-y curve at point on pileW = distributed lateral loading
02
2
4
4
WyEdx
ydP
dx
ydEI pyx
Differential Equation
Illustration of Numerical Solution Procedure
Epy
x
p
yV
y
p
Epy
p-y Curves Developed From Static-Load Tests on24-in. Diameter Pile.
Characteristic Shape of p-y Curves
a. Initial Linear-elastic section
b. Transition from linear to nonlinear section
c. Yield section into limit state or plasticity failure
a.
b.
c.
p-y Curve Criteria Soft Clay (Matlock, 1970) Stiff Clay
(1). with free water (Reese et al., 1975) (2). Without free water (Reese & Welch, 1975)
Sand (Reese model & API Model) Liquefied Sand (Rollins et al., 2005) c- Soil (Evans and Duncan*, 1982) Strong Rock (Reese & Nyman, 1978) Weak Rock (Reese, 1997)
(* Concept only, not the full model)
Common Input Values Effective Unit Weight Shear Strength
Cohesion, c Friction Angle,
Soil Stiffness, 50
Initial Stiffness of p-y Curve, k Rock Properties, RQD, qu, etc.
Soft Clay
Static Loading
Cyclic Loading
Stiff Clay with Free Water
Static Loading
Cyclic Loading
Stiff Clay without Free Water
Static Loading Cyclic Loading
Sand (Reese Criteria)
Static & Cyclic Coefficients
Liquefied Sand (Rollins et al.)
Rollins model is limited to relative densitiesBetween 45 and 55 percent
Pile diameter = 324 mm
Cemented c- Soil
Use of this p-y curve is not recommended without a load test to establish k
y
p
b/60 3b/80
m
uym
yu
pm
pu
ks
k pk
yk
Pult=Pu( ) + Pu ( c )
Vuggy Limestone
y
p
0.0004b
pu = b su
Es = 2000su
Perform proof test if deflection is in this range
Assume brittle fracture if deflection is in this range
Es = 100su
NOT TO SCALE
0.0024b
Weak Rock
y
p
A
pur
Required rock propertiesUniaxial Compressive Strength, su (from lab tests)RQD (from field investigation records)Rock Mass Modulus (interpreted)krm (from lab tests or estimated)Effective Unit Weight (from lab tests)
Kir
ya
Soil Layering Effects
Georgiadis’ Method for Equivalent Depth (1983)
Georgiadis’ Method for Equivalent Depth (1983)
Pile-Head Conditions:Shear and Moment
Mt
Pt
Qt
Note: Origin of Coordinate System for Pile and Soil Layers is Located at the Pile Head
Layer 1
Layer 2
Layer 3
Pile Length
Distance to Ground Surface
Pile-Head Conditions:Displacement and Slope
Qt
Note: Origin of Coordinate System for Pile and Soil Layers is Located at the Pile Head
Layer 1
Layer 2
Layer 3
Pile Length
Distance to Ground Surface yt
t
Effect of Side Friction and Tip Resistance on Large-Diameter Piers
Contact friction, Fs
Tip rotation bearing, Fb
Contact friction (maybe small)
B
H
Fs
0.2”
Tip rotation bearing, Fb
(need large mobilization)
Fb
0.05B
M
Size Effect
1. For linear elastic portion of the p-y curves the size effect is not significant on initial k values.
2. For ultimate soil resistance Pu is a function of the pile diameter.
3. Most correlation coefficients in current p-y criteria were derived based on pile diameter of 2 ft to 4 ft.
Using service load to check deflection criteria
Using factored load to check bending moment and shear
Uncrack/Crack EI’s
Effect of Nonlinear EI on Deflection
Comparison of pile-head deflections computed for same load using elastic and nonlinear EI values.
It is possible to under-predict pile-head deflections if only elastic EI values are used.
Top Deflection vs. LengthTop Deflection vs. Embedment Depth
LPILE Plus 5.0, (c) 2004 by Ensoft, Inc.
Embedment Depth, meters121110987
Top D
efle
ctio
n, m
0.05
0.045
0.04
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
Pile Subjected to Lateral Spreading due to Liquefaction of Soils
Slope Stabilized by Drilled Shafts
Fs is derived from p-y curves
Adjust the Passive Earth Pressure Not Over The Bending Capacity
Slope-Stability Analysis with Resistance from vertical piles
Main Window for LRFD
Load CombosUnfactored LoadsFactored Loads
Unfactored Load Definitions
Load Factors, Resistance Factors, and Combinations
Load Summary Report (1)
Load Summary Report (3)
Concrete Properties
Reinforcing Bar Properties
Warning messagefor cage spacingand percent steel
Bar bundling options
Recent Publications by Others Using LPILE
Rollins, K.M., Peterson, K.T., and Weaver, T.J.,”Lateral Load Behavior of Full-Scale Pile Group in Clay”, J. Geotech. & GeoEnviro. Eng. ASCE Vol 124, No.6, June, 1988. Anderson, J.B., Townsend, F.C., and Grajales, B.,”Case History Evaluation of Laterally Loaded Piles”, J. Geotech. & GeoEnvir. Eng. ASCE Vol 129, No.3, March, 2003. Davidson, W.A, McCabe, R.J., and Soydemir, C.,”Below Boston’s new Bridge”, Civil Engineering, Dec. 1998.
Thank You