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

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 Q M P Ultimate earth pressure (strength fully mobilized) Ultimate earth pressure (strength fully mobilized) Actual earth pressure 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

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

Illustration of Numerical Solution Procedure V y y Epy Epy p p x

p-y Curves Developed From Static-Load Tests on 24-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 b. a.

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)

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.

Soft Clay Cyclic Loading Static Loading

Stiff Clay with Free Water Static Loading Cyclic Loading

Stiff Clay without Free Water Cyclic Loading Static Loading

Sand (Reese Criteria) Static & Cyclic Coefficients

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

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

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

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

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

Georgiadis’ Method for Equivalent Depth (1983)

Pile-Head Conditions: Shear and Moment Qt 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

Pile-Head Conditions: Displacement and Slope Qt 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

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

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.

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. Length

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 Combos Unfactored Loads Factored Loads

Unfactored Load Definitions

Load Factors, Resistance Factors, and Combinations

Load Summary Report (1)

Load Summary Report (3)

Concrete Properties

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

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