Disintegration characteristic of granite residual soil considering pore air escape and different initial states, southern China

Abstract

The disintegration and softening of the granite residual soil (GRS) often occur, and the resulting geological disasters pose a serious threat to the safety of human life and property. Soil disintegration is accompanied by the escape of pore air. However, the existing methods cannot monitor pore air escape in real time, nor can they reflect the actual disintegration process of the GRS. In this paper, a self-invented instrument was adopted to monitor the pore air escape and disintegration processes of the GRS. The formula of pore air escape rate was established and employed to modify the formula of the existing disintegration ratio. The influence mechanism of initial moisture content and dry density on the disintegration morphology, ratio, and process were revealed. The disturbance effect of pore air escape on soil structure causes the separation of surface fine particles from the parent, and the formation of micro-cracks, which is conducive to water infiltration. The main causes of GRS disintegration are the decrease of suction stress between soil particles, the dissolution of cement and the compression of pore air. The pore air escape rate changes rapidly at the beginning and gently at the end of the disintegration process. This results in rapid, incremental, and stable complete types of the disintegration behaviors. Increasing the initial water content from 5 to 25% can increase the average disintegration rate and shorten the disintegration time. When the initial dry density increases from 1.2 to 1.6 g·cm⁻³, the average disintegration rate decreases and the disintegration is delayed. In the early and middle stages of disintegration, GRS displays partial saturation and overall unsaturated state. In the late stage of disintegration, the soil reaches saturation state and shows slow disintegration. The above results can provide key scientific support for exploring the relationship between GRS disintegration and the formation time of shallow landslides and collapsing erosion.