Performance evaluation of gravel impact compaction piers (GICPs) in liquefiable soils

Abstract

A series of field tests were carried out to investigate the performance of gravel impact compaction piers (GICPs) system–supported multilayer coastal soil under liquefiable condition. The influence of the standard penetration test, relative density, and safety factor on the deformation behavior of GICPs were also assessed. Implementation of gravel impact compaction piers is a new generation of aggregate piers. GICPs are used as semi-deep foundations using two processes of substitution and displacement to improve the liquefiable soil layers and to increase the bearing capacity and hardness modulus and reduce subgrade settlement to withstand surface infrastructures. By implementing GICPs, through creating repeated radial compaction for the matrix soil in the process of hammering and feeding the gravel, the first time shuttle, hammering and feeding the gravel, and the second time, hammering and feeding the gravel repeatedly by the long tamper, and hammering and feeding of gravel are frequently done by a flat tamper device, with increasing pore-water pressure; the desired area is artificially liquefiable and highly unstable, and becomes stable and resistant within 8–14 days. In this research, the soil improved rapidly after 8–12 days. The results of the standard penetration test (SPT) in the matrix soil around the piers showed that the amount of (N₁)₆₀ in compacted soils was in the range of 24–32 and on average 3.10 times the amount of initial soil (7–16). Also, the relative density of the initial soil increased from 15–35% to about 71% after soil improvement. Accordingly, by relying merely on the compaction properties of the piers and without relying on other primary soil remediation factors, such as piers drainage and soil texture change, the safety factor of the improved soil is 2.2–2.85 times the minimum required according to two risk levels in the design.