Keywords: pile-soil-structure interaction, pile dynamics, impact loading, boundary element method, finite element method, nonlinear analysis.

Since analytical complexity involved in pile-soil-structure interaction problem, time domain analysis had studied relatively less. Real practical problem often has the transient loads with high degree of material nonlinearity in the domain, therefore it is necessary to implement a nonlinear transient analysis of the physical problem. The transient dynamic formulations are more complicated and often pose a number of problems involving numerical accuracy and stability.

Available approaches that have been used for transient problem are categorized in two main types: 1) Finite and/or Boundary element method formulations and 2) Dynamic Winkler type formulations.

In this paper, nonlinear pile-soil-structure interaction is formulated by using finite element and boundary element methods. The main idea in using this technique is to get computationally efficient results when comparing with 3D boundary element elastodynamic formulations. Linear beam column finite elements are used to model the piles and structural elements. The continuum is assumed to be elastic and an efficient step by step time integration scheme is implemented by using half space integral formulation. Nonlinear modeling of soil media is done by introducing a rational approximation to continuum with nonlinear interface springs along the piles. Modified Özdemir's nonlinear model [1,2] is implemented and systems of equations are coupled for piles and pile groups. By using this mixed type of formulation, it is possible to get computationally most efficient and accurate results.

In order to verify the proposed formulation, the result of a full-scale statnamic load tests performed by Rollins et al. [3] are compared. A series of dynamic load tests were performed on a 3x3 pile group in soft clay. These tests were on full scale and well instrumented pile and pile groups under lateral loads.

The dynamic loads were applied using an innovative technique which applies a dynamic impulse load to the pile group using the newly developed statnamic method. The statnamic device was initially developed for vertical load tests on pile. However, the ability of the statnamic device to apply an impulse load similar in duration to many of natural phenomena makes it useful for lateral load testing of pile group foundations. A description of the statnamic device and the associated test method can be found in Rollins [3] with more details.

It was seen that results are reasonably agrees with those of experiment results. The key to the successful prediction of piles/pile groups settlements are the method used and the proper assessment of the soil parameters and in particular, the magnitude and the distribution of Young's modulus of the soil.

1

H. Özdemir, "Nonlinear transient dynamic analysis of yielding structures.", PhD dissertation, University of California. Berkeley, CA, 1976.

2

S. Küçükarslan, "Linear and nonlinear soil-pile-structure interaction under static and transient impact loading." PhD dissertation, State University of New York, Buffalo, 1999.

3

K. Rollins, K. Peterson, T. Weaver, "Full-scale pile group lateral load testing in soft clay." Technical Report. National Center for Earthquake Engineering Research, Brigham Young University, 1996.

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