Response and Stability of Piles Subjected to Excavation Loading

Abstract

This paper develops new models and normalized solutions to capture the response of piles subjected to a mixed translation–rotational soil movement. A flexible pile is divided into upper and lower portions, which join together by a rotational spring. The upper (rigid) portion rotates about the depth of the maximum bending moment at a constant stiffness (BiP–kθ model), or a constant rotation ratio between the bi-portions (BiP–η model), or it is restrained by elastic lower portion (R–E model). The theoretical relationship between the stiffness (kθ) and the rotation ratio (η) is established, along with the limits of the stiffness and the ratio. Response amplification is detected for inward rotating bi-portions, and quantified by new singularity stiffness(s). The three BiP models are adopted to capture the response of piles subjected to excavation loading in centrifuge tests. The impact of the five input parameters [i.e., limiting force per unit length (FPUL), modulus of subgrade reaction, modulus ratio of stable over sliding layers, and rotational stiffness of each portion] on the predictions is elaborated. Use of reduced values of the modulus, modulus ratio, and limiting FPUL, in particular, the rigid-pile-based 2-layer model also captures well the response of flexible piles, while a variable stress factor is used to model response profiles. Inward rotating bi-portions may amplify the pile response, and pull the maximum bending moment up into weak layer(s), and incur an unexpected failure. Centrifuge tests on anchored-piles are modeled using the BiP–η model to show the impact of inward rotation of the bi-portions. The new models and solutions are useful for the design of piles adjacent to excavation.