Disintegration of granite residual soils with varying degrees of weathering

Abstract

Although rock disintegration has been well studied, much less is known for the residual soils decomposed from the parent rocks. Weathering affects every aspect of residual soil properties; however, how it controls soil disintegration behavior is yet to be established. In this study, laboratory disintegration tests were performed using a self-developed device on natural granite residual soil (GRS) collected at various depths (3.5–17.5 m). The remolded soil was also tested to investigate the effects of the soil structure. The disintegration process was quantitatively traced through several parameters that reflected soil disintegration degree and rate. A new classification system for soil disintegration behavior was proposed accordingly. It was found that the weathering degree (WD) significantly affected the disintegration behavior of GRS, with more weathered GRS being more susceptible to disintegration. The time required to initiate complete soil disintegration increased from 1.9 min (3.5 m deep soil) to 140 min (12.5 m deep soil), and the GRS at the depth of 17.5 m exhibited incomplete disintegration behavior, with an ultimate disintegration ratio of 62%. The disintegration rates v10, v30, and v50 for 17.5-m-deep GRS were ~97% lower than the values for soil at the depth of 3.5 m. In addition, the variations in particle composition caused by the degree of weathering did not control soil disintegration while cementation played a critical role. Soil disintegration was likely triggered by cementation damage upon soaking which broke up the soil aggregates and reduced soil stability. This study not only establishes a framework for studying the disintegration behavior of residual soils as affected by weathering but also provides a comprehensive dataset of GRS.