G.R. Martin

Liquefaction in silty soils—screening and remediation issues

Abstract Current techniques for liquefaction screening, ground modification for liquefaction mitigation, and post-improvement verification rely on knowledge gained from extensive research on clean sands, field observations of liquefied ground, and judicial correlation of normalized penetration resistance [(N1)60,qc1N] or shear wave velocity (vs1) data with field liquefaction observations. Uncertainties prevail on the direct extrapolation of such techniques for silty soil sites. This paper examines laboratory data on liquefaction resistance, strength, and vs1 of sands and silty soils using grain contact density as the basis. Effect of silt content on cyclic resistance, strength, mv, and cv is examined in this light. Rational insights on effects of silt content on the current screening techniques based on (N1)60, qc1N, and vs1 to silty soils are offered. Recent advances and modifications to the traditional densification, drainage, and permeation grouting techniques to make them viable for silty soils are discussed.

Numerical Simulation of Soil Densification Using Vibro-Stone Columns

Saturated loose sand and non-plastic silty sand deposits are often vulnerable to liquefaction during earthquakes. Sand deposits densified by vibro-stone column (SC) are more resistant to liquefaction, and have performed well during earthquakes. Silty sand deposits appear to perform well when improved by SC supplemented with wick drains. Wick drains aid dissipation of excess pore pressure induced during SC installation in low-permeable silty soils enhancing densification. This paper presents a numerical model to simulate, and to analyze soil densification during SC installation with and without wick drains. Design charts for SC are developed based on this work. These numerical results are compared with field test data. Design guidelines are presented based on these design charts.