Estimation of liquefaction-induced ground deformations by CPT and SPT-based approaches.

摘要

Earthquake shaking may result in the liquefaction of saturated sandy soils in the ground. Both ground settlements and lateral spreads are the pervasive types of liquefaction-induced ground deformations for level to gently sloping sites. Currently, the estimations of liquefaction-induced ground deformations are less successful than the evaluations of liquefaction potential. In particular, no CPT-based method is available to estimate ground settlements and lateral displacements.; The objective of this thesis was to develop approaches to estimate liquefaction-induced ground deformations using either CPT or SPT data. First, a CPT-based approach is proposed to estimate liquefaction-induced ground settlements for level ground. The approach combines a CPT-based method to estimate liquefaction resistance with laboratory test results on clean sand to evaluate liquefaction-induced volumetric strains for sandy and silty soils. The approach was used to estimate the ground settlements at two case history sites. Good agreement between the calculated and measured ground settlements was found. Second, three simple, semi-empirical approaches are proposed to estimate lateral displacements in liquefaction-induced lateral spreads for gently sloping ground without a free face, level ground with a free face, and gently sloping ground with a free face respectively. The proposed approaches combine available results from laboratory tests with data from sixteen case histories associated with past thirteen major earthquakes, capture the mechanisms of liquefaction-induced lateral spreads, and characterize the major factors (soil properties, earthquake characteristics, and ground geometry) influencing lateral displacements. Either SPT or CPT data can be used in the proposed approaches to estimate lateral displacements. Generally, the calculated lateral displacements using the proposed approaches showed variations between 50% and 200% of measured values for the available case histories studied in this research. The proposed approaches may be used to estimate both the magnitude and distribution of liquefaction-induced lateral displacements for gentle slopes and/or ground with a free face for low to medium-risk projects or to provide preliminary estimates for high-risk projects using either SPT or CPT data. The proposed approaches are relatively simple and can be applied with only a few additional calculations following an SPT- or CPT-based liquefaction-potential analysis.