Liquefaction Characteristics of Gravelly Soils Prepared by Water Sedimentation Method

L. Wang, G. Chiaro & S. Rees
Department of Civil and Natural Resource Engineering, University of Canterbury, Christchurch
C. Cappellaro
Tonkin & Taylor, Christchurch
A. Pokhrel
Beca Limited, Christchurch

ABSTRACT
Field observations and evaluations from 32 case histories of liquefaction in gravelly soils worldwide, including three in New Zealand, have indicated that gravelly soils in alluvial deposits are the most susceptible to liquefaction. However, replicating these conditions in laboratory tests remains a challenge, particularly in achieving uniform specimen preparation for reliable liquefaction assessment. This study addresses these challenges by using a newly developed water-sedimentation (WS) method for gravelly soil specimens that can reproduce as much as possible the anisotropy and fabric of naturally deposited alluvial sand, enabling a better assessment of liquefaction potential. Notably, this WS method enhances density uniformity and minimises the inherent segregation between small sand and large gravel particles. A series of stress-controlled undrained cyclic triaxial tests were conducted on WS gravelly soil specimens reconstituted at relative densities (Dr) between 20% and 60% and isotropically consolidated at 100 kPa effective confining stress. The specimens were then subjected to cyclic stress ratios (CSR) ranging from 0.14 to 0.45. Comparisons with specimens prepared by the moist tamping (MT) method showed that soil fabric significantly influences liquefaction resistance, with the WS specimens generally less resistant to liquefaction. In addition, density and gravel content also play a critical role, with liquefaction resistance increasing with both density and gravel content. This study indicates that for a better evaluation of the liquefaction resistance of alluvial gravelly soils, the combined effects of fabric, density state and gravel content must be considered together.