Study of lateral-pile-soil-interaction (LPSI) in seismically liquefiable soils

Lead Research Organisation: University of Surrey
Department Name: Civil and Environmental Engineering

Abstract

Pile foundations in liquefiable soil continue to fail during earthquakes despite being designed with required factor of safety against axial load bearing capacity (shaft resistance and end-bearing) and bending due to lateral loads. These lateral loads arise from the inertia of superstructure and kinematic loading of soil flowing past the pile (lateral spreading). Recent research discovered a fundamental omission in this design methodology. Essentially, when ground liquefies its reduction in lateral support allows slender piles to buckle under their axial load: there is an omission of this buckling mechanism or the P-delta effect (P is the axial load and delta is the pile head displacement) in the current design. The practical implications could be far reaching, requiring reassessment of existing structures in liquefiable soils as well as developing analysis methods to take better account of the effects of axial load. Piles are typically analysed using a Beam on Nonlinear Winkler Foundation (BNWF) model or p-y model due to its simplicity, mathematical convenience and ability to incorporate nonlinearity of soil. Essentially, the soil is modelled as a set of p-y springs assigned along the pile at discrete locations, where 'p' refers to the soil reaction to the pile deformation 'y' at a certain depth. While the p-y curves for sand (under non-liquefied condition), soft clay, stiff clay are well established, the profession still lacks a promising p-y curve for liquefiable soil. This research proposal aims to study the lateral loading of piles in liquefied soil, to understand the phenomena behind the interaction between pile and liquefied soil and to propose a p-y curve for liquefied soil based on back analysis of high quality model test data, element tests on liquefied soil, numerical modelling, and case records of pile foundation performance.

Publications

10 25 50

Related Projects

Project Reference Relationship Related To Start End Award Value
EP/H015345/1 01/09/2010 31/05/2013 £316,312
EP/H015345/2 Transfer EP/H015345/1 01/07/2013 30/09/2014 £106,470
 
Description The main findings are:
(1) Pile-supported structures continue to collapse in liquefiable soils during seismic liquefaction. This research showed that the current code based methods for design of piles in seismically liquefiable soils are inadequate. In particular, the dynamics of the whole system is ignored.
(2) Dynamics of the whole system plays an important role in the performance of pile-supported structures. In particular, the time period of the whole structure increases as soil liquefies. On the other hand, the damping of the whole also increases.This has design consequences.
(3) There is a need for seismic requalification of pile-supported structures in liquefiable soils.
Exploitation Route n/a
Sectors Construction

 
Description The main findings are: (1) Pile-supported structures continue to collapse in liquefiable soils during seismic liquefaction. This research showed that the current code based methods for design of piles in seismically liquefiable soils are inadequate. In particular, the dynamics of the whole system is ignored. (2) Dynamics of the whole system plays an important role in the performance of pile-supported structures. In particular, the time period of the whole structure increases as soil liquefies. On the other hand, the damping of the whole also increases.This has design consequences. (3) There is a need for seismic requalification of pile-supported structures in liquefiable soils.
First Year Of Impact 2014
Sector Construction
Impact Types Societal,Economic