1. Analysis of Laterally Loaded Drilled Shafts and Piles Using LPILE
Shin-Tower Wang, Ph.D., P.E.
Ensoft, Inc./Lymon C. Reese & Associates
Austin, Texas
April 3, 2009

2. 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

3. Piles are used in a variety of ways to support super-structures

4. Drilled Shafts with Lateral LoadQ M P
Ultimate earth pressure
(strength fully mobilized)
Ultimate earth pressure
(strength fully mobilized)
Actual earth pressure
Actual earth pressure

5. 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, )
has been developed extensively to take into account the soil-structure interaction and nonlinear resistance of soils.
3-D Finite-Element method

6. Soil Failure Patterns
Wedge Failure
Plane-Strain Failure

9. Nonlinear Model for Lateral Soil Resistance

10. Differential Equation
EI = pile stiffness
y = pile deflection
x = distance along pile
Px = axial load on pile and
Epy = slope of secant to p-y curve at point on pile
W = distributed lateral loading

11. Illustration of Numerical Solution ProcedureV y y
Epy
Epy p p x

13. p-y Curves Developed From Static-Load Tests on 24-in. Diameter Pile.

14. 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 b. a.

15. 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-f Soil (Evans and Duncan*, 1982)
Strong Rock (Reese & Nyman, 1978)
Weak Rock (Reese, 1997)
(* Concept only, not the full model)

16. Common Input Values Effective Unit Weight Shear Strength
Cohesion, c
Friction Angle, f
Soil Stiffness, e50
Initial Stiffness of p-y Curve, k
Rock Properties, RQD, qu, etc.

17. Soft Clay
Cyclic Loading
Static Loading

18. Stiff Clay with Free Water
Static Loading
Cyclic Loading

19. Stiff Clay without Free Water
Cyclic Loading
Static Loading

20. Sand (Reese Criteria)
Static & Cyclic Coefficients

21. Liquefied Sand (Rollins et al.)
Rollins model is limited to relative densities
Between 45 and 55 percent
Pile diameter = 324 mm

22. Cemented c-f Soil y p b/60 3b/80 m u ym yu pm pu ks k pk yk
Pult=Pu( f ) + Pu ( c )
Use of this p-y curve is not recommended without a load test to establish k

23. Vuggy Limestone p pu = b su y 0.0004b 0.0024b Perform proof test if
deflection is in this range
pu = b su
Assume brittle fracture if
deflection is in this range
Es = 100su
Es = 2000su
NOT TO SCALE y
0.0004b
0.0024b

24. Weak Rock Required rock properties
Uniaxial 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) y p A
pur
Kir ya

25. Soil Layering Effects
Georgiadis’ Method for Equivalent Depth (1983)

26. Georgiadis’ Method for Equivalent Depth (1983)

27. Pile-Head Conditions: Shear and MomentQt Mt Pt
Distance to Ground Surface
Layer 1
Layer 2
Pile Length
Layer 3
Note: Origin of Coordinate System for Pile and Soil Layers is Located at the Pile Head

28. Pile-Head Conditions: Displacement and SlopeQt qt yt
Distance to Ground Surface
Layer 1
Layer 2
Pile Length
Layer 3
Note: Origin of Coordinate System for Pile and Soil Layers is Located at the Pile Head

29. Effect of Side Friction and Tip Resistance on Large-Diameter Piers
Contact friction (maybe small) M Fs B
0.2” H
Tip rotation bearing, Fb
(need large mobilization) Fb
Contact friction, Fs
0.05B
Tip rotation bearing, Fb

30. Size Effect
For linear elastic portion of the p-y curves the size effect is not significant on initial k values.
For ultimate soil resistance Pu is a function of the pile diameter.
Most correlation coefficients in current p-y criteria were derived based on pile diameter of 2 ft to 4 ft.

32. Using service load to check deflection criteria
Using factored load to check bending moment and shear

33. Uncrack/Crack EI’s

34. 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.

35. Top Deflection vs. Length

36. Pile Subjected to Lateral Spreading due to Liquefaction of Soils

38. Slope Stabilized by Drilled Shafts
Fs is derived from p-y curves

39. Adjust the Passive Earth Pressure Not Over The Bending Capacity

40. Slope-Stability Analysis with Resistance from vertical piles

41. Main Window for LRFD
Load Combos
Unfactored Loads
Factored Loads

42. Unfactored Load Definitions

43. Load Factors, Resistance Factors, and Combinations

44. Load Summary Report (1)

45. Load Summary Report (3)

48. Concrete Properties

49. Reinforcing Bar Properties
Bar bundling options
Warning message for cage spacing and percent steel

50. 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

51. Thank You