Non-plastic silty sand liquefaction, screening, and remediation

Abstract

Assessing liquefaction potential, in situ screening using cone penetration resistance, and liquefaction-remediation of non-plastic silty soils are difficult problems. Presence of silt particles among the sand grains in silty soils alter the moduli, shear strength, and flow characteristics of silty soils compared to clean host sand at the same global void ratio. Cyclic resistance (CRR) and normalized cone penetration resistance (qc1N) are each affected by silt content in a different way. Therefore, a unique correlation between cyclic resistance and cone resistance is not possible for sands and silty sands. Likewise, the response of silty soils subjected to traditional deep dynamic compaction (DC) and vibro-stone column (SC) densification techniques is influenced by the presence of silt particles, compared to the response in sand. Silty soils require drainage-modifications to make them amenable for dynamic densification techniques. The first part of this paper addresses the effects of silt content on cyclic resistance CRR, hydraulic conductivity k, and coefficient of consolidation Cv of silty soils compared to clean sand. The second part of the paper assesses the effectiveness of equivalent intergranular void ratio (ec)eq concept to approximately account for the effects of silt content on CRR. The third part of the paper explores the combined effects of silt content (viz effects of (ec)eq, k, and Cv) on qc1N using laboratory model cone tests and preliminary numerical simulation experiments. A possible inter-relationship between qc1N, CRR, accommodating the different degrees of influence of (ec)eq, k, and Cv on qc1N and CRR, is discussed. The fourth part of the paper focuses on the detrimental effects of silt content on the effectiveness of DC and SC techniques to densify silty soils for liquefaction-mitigation. Finally, the effectiveness of supplemental wick drains to aid drainage and facilitate densification and liquefaction mitigation of silty sands using DC and SC techniques is discussed.