Induced Partial Saturation (IPS) for soil liquefaction mitigation: Large-scale shake testing

PhD Student: Chunhui Zhao

Publication Year: 2014

Advisor: Sabanayagam Thevanayagam

Abstract: Due to the hazards of soil liquefaction and limitations of traditional liquefaction mitigation approaches, this research focuses to investigate of new liquefaction mitigation method----Induced Partial Saturation (IPS) which reduces the degree of soil saturation by introducing small amounts of gas and air into liquefaction-susceptible sand making sand partially saturated, an idea initially developed by researchers at Northeastern University. A large-scale 1-g geotechnical laminar box (6m height, 2.75m wide, 5m long) which can simulate the response of fully saturated sand and partially saturated sand up to 20ft (6m) depth subjected to base shaking has been developed by the Structural Engineering and Earthquake Simulation laboratory (SEESL), University at Buffalo. The laminar box system is made of 39 laminates vertically stacked together, shaking base, computer-controlled high-speed actuators, strong floor, advanced instrumentations, and a laboratory hydraulic filling for placing sand.

One large-scale fully saturated sand experiment (LG-1) and two large-scale partially saturated sand experiments (IPS-1 and IPS-2) were performed with two different treatment methods, involving nearly 16ft (5m) deep sand deposit, and the results are presented henceforth. One of the latter two experiments involved partially saturating the top 8 feet of sand (IPS-1), and the other involved partially saturating the full depth of sand in the laminar box (IPS-2). Tests were conducted using laminar box. Accelerometers, teompsonics, potentiometers, piezometers, conductivity probes and cameras were used to record soil response. Cone Penetration Test (CPT) was performed to assess the geotechnical engineering properties of soil.

A comparison between fully saturated sand responses, partially IPS treated induced partial saturation sand response and fully IPS treated induced partial saturation sand response reveal the effect of IPS on soil behavior due to strong shaking. Liquefaction, significant sand boils, and ground settlement occurred in fully saturated sand test. Soil didn't fully liquefy in IPS- treatment zone, although pore pressures and limited ground settlements occurred. Fully saturated sand (LG-1) liquefied at all depths throughout the experiment. Fully IPS treated induced partially saturation test (IPS-2) didn't liquefy and has a delay on pore water pressure development. The partially IPS treated induced partial saturation test (IPS-1) didn't liquefy in IPS treated zone and exhibited similar excess pore water pressure response. Further analysis of the work are presented in three other separate PhD dissertations at Northeastern University and another MS thesis report at University at Buffalo.

The experiment results presented demonstrate the IPS method can be further improved as an effective method to reduce the soil liquefaction potential and reducing liquefaction-induced ground settlement.