PORE WATER PRESSURE GENERATION AND DISSIPATION NEAR TO PILE AND FAR-FIELD IN LIQUEFIABLE SOILS

Abstract

The degree of liquefaction as characterised by the excess pore water pressure plays an important
role in defining soil strength and stiffness. The pile-soil interaction in liquefiable soil, if modelled using BNWF
model, the strength and stiffness of the soil springs can be suitably reduced by using a reduction factor. This
reduction mainly depends on the soil type, its SPT/CPT value and the degree of liquefaction. Ideally this reduction
should be based on the excess pore water pressure near the pile. However, it is difficult to estimate the degree of
liquefaction near the pile. Hence, the lateral resistance of liquefied soil at soil-pile interface is normally
characterized by the degree of liquefaction expected in the soil at the site without considering the influence of pile.
Though, excess pore pressure near to the pile could be the governing parameter of soil resistance, it is hard to
characterize the expected value of it in a field condition, as it depends on many parameters including soil type,
shear loading, pile dimension, gap formation near to pile that facilitates easy dissipation of excess pore water
pressure (EPWP), soil densification during pile driving, etc. Hence, to understand the difference between the farfield and near-pile response of liquefied soil, one high quality centrifuge test results are studied in this paper. The
pattern of excess pore water pressure generation and development has been compared for both near-pile and farfield. The results are critically reviewed and discussed in this paper.