Laboratory investigation of disintegration characteristics of purple mudstone under different hydrothermal conditions

Disintegration of rock is one of the primary processes of soil formation and geomorphology and is affected considerably by water and heat. This study focused on the disintegration characteristics under laboratory conditions of typical purple mudstone from the Tuodian group of Jurassic red beds (J₃t) in Tuodian Town, Shuangbai county, Yunnan Province of southern China. The fresh mudstone was subjected to alternating applications of water, heat and hydrothermal interaction during five treatments: wetting-drying (WD), saturation (ST), refrigeration-heating (RH), a combination of wettingdrying and refrigeration-heating (WDRH), and a combination of saturation and refrigeration-heating (STRH). Each treatment was run in twenty-four cycles. The results showed that there are three types of disintegration: collapsing disintegration, exfoliation disintegration and imperceptible disintegration. The cumulative disintegration rate (percentage of cumulative disintegrated mass to the initiative sample mass passed through a 2 mm sieve) produced a ‘S’-shape function when related to treatment cycle time and closely fit a logistic model (R² > 0.99). The rank order of the cumulative disintegration rate resulting from the five treatments was as the following: WDRH > STRH > ST > WD > RH. Because of alternating periods of moisture and dryness, WD caused the most disintegration, while RH alone resulted in imperceptible disintegration. Additionally, there was a negative correlation between the disintegration rate of each treatment cycle (percentage of disintegrated mass to the treated sample mass) and treatment cycle number. There was a positive correlation between this rate and temperature change under moist conditions, indicating that a change in temperature greatly accelerates the disintegration of parent rock when water was supplied.