Effect of pore air escape and cement dissolution on granite residual soil disintegration, southeast China.

Granite residual soil in south and southeast China has obvious characteristic of disintegration, which induces collapse erosion and shallow landslide. Although the escape of pore air can be observed in the present hydrostatic water tests, and pore air and cementitious substance dissolution is qualitatively confirmed to promote soil disintegration, these two factors fail to be monitored in real time throughout the whole disintegration process. Therefore, this study utilized two self-developed instruments to monitor the volume of escaping pore air and the process of soil disintegration, and observe the current variations in the solution during the soil disintegration. The disintegration patterns and rates of residual soils with various compaction levels and initial moisture contents were analyzed. The intrinsic affecting mechanisms of pore air escape and cementitious substance dissolution on the soil disintegration were revealed. The results consist of three aspects. (1) The initial moisture content has a significant impact on disintegration pattern, completion time and velocity. (2) The variance in the effect of the increase in compaction degree on the completion time and speed of disintegration is governed by the initial moisture content. (3) The escape of pore air and the dissolution of cementitious substances constitute two principal phenomena during the entire disintegration process of granite residual soil. (4) The repulsive stress generated by the compressed and escaping pore air being greater than the sum of suction stress and viscous stress generated by capillary water and cementitious substance is one of the primary causes for granite residual soil disintegration.