Abstract
To mitigate liquefaction and its associated soil deformations, ground improvement techniques were adopted in field to reinforce saturated sand deposits. Sand Compaction Pile (SCP) is one such popular proven treatment to improve liquefaction resistance of sandy deposits. Installation of sand compaction piles improves soil density and rigidity which further enhance seismic resistance against liquefaction and this was well evident from past field observations. However, studies involving SCP performance during repeated shaking events were not available/limited. In this study, using 1-g uniaxial shaking table, a series of shaking experiments were performed on SCP treated and untreated sand deposits having 40% and 60% relative density subjected to repeated incremental acceleration loading conditions (i.e., 0.1–0.4 g at 5 Hz frequency). Parameters such as improvement in soil resistance and relative density, generation and dissipation of excess pore water pressures, maximum observed foundation settlement and soil displacement and variation in cyclic stress ratio were evaluated and compared. Seismic response of liquefiable sand deposits was found to be improved significantly due to SCP installation together with occurrence of continuous soil densification under repeated loading. The experimental observations suggested that SCP can perform better even at repeated shaking events.
Highlights
Soil liquefaction and its associated deformations during earthquake incidence is one of the major threatsto the stability of infra-structures
Though field evidences highlighting the possible reasons for the occurrence of soil liquefaction and reliquefaction; no studies were available in investigating the performance of ground improvement techniques against repeated shaking events
The repeated incremental loading was applied to both Sand Compaction Pile (SCP) treated and untreated ground after complete dissipation of excess pore water pressure (EPWP) generated during previous loading i.e. after application of 0.1g acceleration loading, the time taken for generation and dissipation of EPWP was monitored continuously through glass tube piezometers
Summary
Soil liquefaction and its associated deformations during earthquake incidence is one of the major threatsto the stability of infra-structures. Though field evidences highlighting the possible reasons for the occurrence of soil liquefaction and reliquefaction; no studies were available in investigating the performance of ground improvement techniques against repeated shaking events. Through field investigations and undrained cyclic shear tests, Okamura et al (2006) found that, the liquefaction resistance of SCP treated deposits increased considerably for a slight reduction in degree of saturation irrespective of sand density. Factors such as grain size, pile depth, replacement ratio and distance from the sand pile influence the saturation of treated sand deposits. (2017) investigated the potential of SCP system prior earthquake events and events during 2003 Tokachi-Oki earthquake and 2004 Nemuro Hanto-Oki earthquake, and found limited soil liquefaction and reliquefaction occurrence in SCP treated areas compared to untreated deposits
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