Some innovative studies on stability analysis, landslide mechanism and stabilization measure of soil slopes

Abstract

Slope stability analysis, landslide triggering mechanisms and the slope stabilization measure are three critical problems in slope engineering. The thesis aims to carry out innovative studies on the three significant problems. Firstly, a new depth plot technique based on limited equilibrium method (LEM) is proposed to study the critical slip in slope stability analysis. The combined and individual impacts of cohesion and internal friction angle on the FOS values of potential slips at various depths are investigated. The results reveal that the different contributions of cohesion and internal friction angle to FOS values of potential slips with respect to the slip depth cause the existence of the critical slip. The slip-depth plot also reveals the existence of a wide critical slip zone with similar minimum FOS values in soil slopes. Two solutions are proposed to obtain a representative critical slip in the critical slip zone. Secondly, a series of flume tests are performed to study the landslide in stable gentle soil slope triggered by pressurized gas and its combination of water. The triggering is performed by the injection of H2O2 into the cement powder core in the slope. An impermeable layer covering the cement powder core is employed to trap the generated gas. The flume tests demonstrate the landslide at the stable gentle soil slopes can be triggered by a small mass of pressurized gas. An original dynamic modelling method, including the flume test, dynamic mechanical model and calibration test for gas generation from the H2O2 in cement powder are presented to test and examine the minimum mass of gas for triggering the landslide. Meanwhile, the unique failure behaviors of the landslide triggered by pressurized gas or its combination of water, soil upheaval and fluid mixture penetration, are observed in the flume tests. Moreover, the influence of injection and distribution of gas generation zone on the failure behaviors of the slope with the gas and water triggering are studied. At last, the mechanical properties of cement-stabilized particles from public fill soil are studied as the stabilization measure of the fill slope. Two common geotechnical materials in HongKong, Completely Decomposed Granite (CDG) and Completely Decomposed Volcanic (CDV) are chosen to be converted to gravel+sand, silt and clay particles by extending wet sieving method. The three basic particle components are combined into four groups of particles, gravel+sand, gravel+sand+silt, clay and clay+silt. The four groups of particles and the original soil are employed as the raw material of the cement-stabilized soil. The strength, elastic modulus, durability and permeability of the five groups of stabilized soil particles are tested. The test results reveal that cement-stabilized gravel+sand and gravel+sand+silt from CDG soil have superior mechanical properties than the stabilized original natural soil and other stabilized particles from CDG and CDV soil. Therefore, the cement-stabilized gravel+sand and gravel+sand+silt from CDG soil are recommended as more suitable options for constructing fill slopes and as replacement materials in slope stabilization.