Analysis of Laterally Loaded Drilled Shafts and Piles Using LPILE

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 Load Q 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, 1958-1975) 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 Procedure V y y Epy Epy p x p

13. p-y Curves Developed From Static-Load Tests on24-in. Diameter Pile.

14. Characteristic Shape of p-y Curves c. a. Initial Linear-elastic section b. Transition from linear to nonlinear section c. Yield section into limit state or plasticity failure b. a.

15. 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) p-yCurve Criteria

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 Cyclic Loading Static 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. p m pm k pk u ym pu yk yu ks y b/60 3b/80 Cemented c-f Soil 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 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. p pur A y 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) 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 Moment Qt Mt Pt Distance to Ground Surface Layer 1 Pile Length Layer 2 Layer 3 Note: Origin of Coordinate System for Pile and Soil Layers is Located at the Pile Head

28. Pile-Head Conditions:Displacement and Slope Qt qt yt Distance to Ground Surface Layer 1 Pile Length Layer 2 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 messagefor cage spacingand 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. 1998.