Two aspects of seismically-induced liquefaction are discussed which are of vital engineering significance: the triggering condition and the consequences of liquefaction. The triggering condition is examined with respect to liquefaction analysis, note being taken of the onset condition which is governed by cyclic strength. Consequences of liquefaction are discussed with respect to post-seismic stability analysis, in which the residual strength plays a major role. Procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced, and the applicability of this method for estimating associated ground settlements is discussed. The evaluation of residual strength requires a better understanding of undrained sand behaviour. Results of extensive laboratory rests on Japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better. The results of laboratory tests on silty sands are examined in the same way. AH the results are...

Liquefaction and flow failure during earthquakes.

Soil liquefaction is a major concern for structures constructed with or on sandy soils. This paper describes the phenomena of soil liquefaction, reviews suitable definitions, and provides an update...

Evaluating cyclic liquefaction potential using the cone penetration test

A laboratory parametric study utilizing cyclic triaxial tests was performed to clarify the effects of nonplastic fines on the liquefaction susceptibility of sands. Studies previously published in the literature have reported what appear to be conflicting results as to the effects of silt content on the liquefaction susceptibility of sandy soils. The current study has shown that if the soil structure is composed of silt particles contained within a sand matrix, the resistance to liquefaction of the soil is controlled by the relative density of the soil and is independent of the silt content of the soil. For soils whose structure is composed of sand particles suspended within a silt matrix, the resistance to liquefaction is again controlled by the relative density of the soil, but is lower than for soils with sand-dominated matrices at similar relative densities. In this case, the resistance to liquefaction is essentially independent of the amount and type of sand. These findings suggest the need for further evaluation of the effects of nonplastic fines content upon penetration resistance, and the manner in which this relationship affects the simplified methods currently used in engineering practice to evaluate the liquefaction resistance of silty soils.

Effects of nonplastic fines on the liquefaction resistance of sands

The behavior of sand is affected by the content of nonplastic fine particles. How and to what degree the fines content affects the minimum and maximum void ratios has been studied in detail. A review is presented of previous theoretical and experimental studies of minimum and maximum void ratios of single spherical grains, packings of spheres of several discrete sizes, as well as optimum grain-size ratios to produce maximum densities. A systematic experimental study is performed of the variation of minimum and maximum void ratios with contents of fines for sands with smoothly varying particle size curves and a large variety of size distributions. It is shown that the fines content plays an important role in determining the sand structure and the consequent minimum and maximum void ratios. It is indicated how the fines content and sand structure affects the compressibility and the static liquefaction potential of the sand.

Effects of non-plastic fines on minimum and maximum void ratios of sand

An experimental study aimed at a direct comparison of the undrained behavior of sand using specimens reconstituted by different techniques is presented. It is shown that at identical initial void ratio and effective stress state, the moist-tamped sand is potentially liquefiable, but in the water-deposited state may even be dilative. Water-deposited specimens are shown to be very uniform in contrast to the large nonuniformities that usually occur on moist tamping, rendering their results questionable from the standpoint of laboratory element tests. A direct comparison of the behavior of truly undisturbed sand specimens retrieved by in-situ ground freezing and their corresponding reconstituted counterparts after consolidating to identical initial states is also presented in support of the contention that the fabric that ensues on water pluviation closely simulates that of the natural alluvial and hydraulic fill sands, enabling the use of reconstituted specimens as substitutes for the expensive undisturbed frozen specimens for material characterization.

Influence of Specimen-Reconstituting Method on the Undrained Response of Sand

The results of undrained stress controlled cyclic triaxial tests indicated that the dynamic strength of saturated sands, remolded to the same density by different compaction procedures, was significantly different. Variations in the dynamic strength of Monterey No.0 sand were found to be in the order of —100%; however, tests on other sands indicated that the magnitude of the effect of the method of preparation used may be a function of the type of sand. Fabric studies and electrical conductivity measurements indicated that the orientation and arrangement of the contacts between sand grains were probably the primary reasons for the observed differences in the dynamic strength of Monterey No.0 sand. Comparisons indicated that specimens prepared by moist tamping or moist vibratory compaction would exhibit dynamic strengths most similar to those of undisturbed samples; however, in most cases, the strength of undisturbed samples ranged from 0% to 45% higher than that of samples prepared by moist tamping.

Effects of Sample Preparation on Sand Liquefaction

It has long been recognized that clays increase in strength with time due to consolidation and secondary compression; however, the fact that sands can increase in strength after periods of sustained loading is not so well known. Recently several engineers have suggested that the liquefaction characteristics of in-situ sand deposits are influenced by the age of the deposit. Omote and Myamura presented data that showed a trend for less damage occurring in older sandy deposits during the Tokaido earthquake of December 7, 1944, and Casagrande has stated that, whenever possible, the age of a sand strata should be determined, since there are indications that young alluvial sands are much more susceptible to liquefaction than older sediments.

J. Paul Mulilis

Papers

Effects of Sample Preparation on Sand Liquefaction

Resistance to Liquefaction Due to Sustained Pressure