Static Pushover Analyses of Pile Groups in Liquefied and Laterally Spreading Ground in Centrifuge Tests

Abstract

Monotonic, static beam on nonlinear Winkler foundation ͑BNWF͒ methods are used to analyze a suite of dynamic centrifuge model tests involving pile group foundations embedded in a mildly sloping soil profile that develops liquefaction-induced lateral spreading during earthquake shaking. A single set of recommended design guidelines was used for a baseline set of analyses. When lateral spreading demands were modeled by imposing free-field soil displacements to the free ends of the soil springs ͑BNWF_SD͒, bending moments were predicted within −8% to +69 ͑16th to 84th percentile values͒ and pile cap displacements were predicted within −6 to +38%, with the accuracy being similar for small, medium, and large motions. When lateral spreading demands were modeled by imposing limit pressures directly to the pile nodes ͑BNWF_LP͒, bending moments and cap displacements were greatly overpredicted for small and medium motions where the lateral spreading displacements were not large enough to mobilize limit pressures, and pile cap displacements were greatly underpredicted for large motions. The effects of various parameter relations and alternative design guidelines on the accuracy of the BNWF analyses were evaluated. Sources of bias and dispersion in the BNWF predictions and the issues of greatest importance to foundation performance are discussed. The results of these comparisons indicate that certain guidelines and assumptions that are common in engineering design can produce significantly conservative or unconservative BNWF predictions, whereas the guidelines recommended herein can produce reasonably accurate predictions.

Lateral response of pile foundations in liquefiable soils

“…This can be explained by the fact that the lateral spreading displacements were not large enough to mobilize limit pressures and actual pressures are smaller than limit pressures. However, for large motions, the pile cap displacements were considerably underpredicted (Brandenberg et al, 2007). In this paper, the free-field soil movement was used as an input.…”

“…The third method for the simulation of pile response in liquefiable soils is the use of reduction factors, called pmultipliers. The p-y curves in liquefiable sand are multiplied by a factor usually between 0.01 and 0.3 to decrease the strength of sand due to liquefaction (Rollins et al, 2005;Brandenberg et al, 2007;Varun, 2010). In this paper, the third method (p-multipliers) was used.…”

Reducing Seismic Risk to Highway Mobility: Assessment and Design Examples for Pile Foundations Affected by Lateral Spreading

“…In CALTRANS (2011), the maximum displacement to mobilize the lateral earth pressure in the crust layer is estimated using the procedure recommended by Brandenberg et al (2007). In this example, due to the lack of guidelines in the literature to estimate the displacement to mobilize earth pressure in drilled shaft, CALTRANS (2011) procedure is adopted.…”

Effects of structural characterizations on fragility functions of bridges subject to seismic shaking and lateral spreading

“…Due to extraordinary diffi culties both in theoretical and computational efforts involved in three-dimensional continuum fi nite element modeling, the dynamic simulation of the liquefaction and lateral spreading process, which is intuitively appropriate, is not feasible for bridge fragility analysis. Instead, an equivalent static analysis procedure proposed by Brandenberg et al (2007b) is employed to simulate the bridge response under liquefaction-induced lateral spreading. In this procedure, free-fi eld lateral spreading demands are imposed as displacements on the free ends of p-y springs attached to the bridge foundation, as shown in Fig.…”