Lateral Loads on Long Piles and Piers in Granular Soils: Fid-Bau Portal

Lateral Loads on Long Piles and Piers in Granular Soils

Vennalaganti, K. Mohan / Endley, Shailendra N. / Rao, Pramod M.

Piles and piers are extensively used as laterally loaded structural members, especially for offshore platforms, chemical plants and communication tower foundation structures. Engineers are often confronted with the task of determining the maximum deflections and moments of laterally loaded pile or piers. The problem is complex because it involves bending of the piles or piers along with the soil movements. Several researchers have tried various methods to estimate the laterally loaded pile response ranging from closed form solutions using a constant value of "reaction modulus" to linearly varying reaction modulus using a finite element elastic approach or finite difference, `p-y' type approach. Finite difference techniques or `p-y' methodology involves defining the soil resistance (p) along the length of the pile as a non-linear function of lateral pile deflection (y). The analysis involves generating a set of `p-y' curves and solving a fourth order differential equation to determine the pile response. The computer program LPILE developed by Lymon C. Reese and Shin-Tower Wang is available to perform such an analysis. The program utilizes `p-y' criteria developed for different kinds of soils by various researchers. The present study includes the analyses of different pile types with lateral load and moment (i.e., lateral load at an eccentricity from the ground surface) applied to the pile head at the ground surface in uniform granular soil deposits. Utilizing the LPILE program, pile head deflections and maximum bending moments were determined for various pile types and pile sizes. A total of about 720 runs were performed. The results of the computer runs were then normalized to obtain simple equations. The equations can be easily used to determine the pile-head deflection at the ground surface and the bending moment given the applied load and moment on a pile-head, soil friction angle (φ) and diameter of the pile. Findings of this study are limited to pile and pier-head deflections of about 50 mm (2 in.) at the ground surface. The equations presented herein should be utilized for preliminary design purposes only. For an accurate determination of pile behavior, LPILE program or such other routines should be used Similar study was performed for uniform clay profile and is reported elsewhere by Endley et al, Vennalaganti et al., and Vennalaganti et al. Similar research was performed by Duncan, et al. The results of that research proposes method known as "CLM" method to determine the deflection and moment of the laterally loaded piles and piers. In Duncan's CLM method, for a pile or pier applied with a combined load and moment, a series of steps (about 6 steps) are required to compute pile head deflection. These series of steps are associated with nonlinear superimposition as the independent load induced deflection and the isolated moment induced deflection cannot be simply added. The present research has eliminated these steps and a unique closed form solution is established. The required nonlinear superimposition is simplified and this can be seen from the findings of the present research.