A quantitative determination of the effect of moisture on purple mudstone decay in Southwestern China

• Quantitative relationship between rock decay and its moisture content was studied.
• Rock decay rate exponentially increases with the increase of rock moisture content.
• The rank order of decay rate was J3t > K2m > J1l.

AimsThe moisture condition is well known to be a key factor that apparently influences rock decay, but little is known about the quantitative correlations between a rock's decay rate and its moisture content, which makes it difficult to quantitatively predict the rate of rock decay under varied moisture conditions. Thus, in this paper our aim is to observe the decay rates of various purple mudstones with different moisture contents and to develop an equation to calculate the decay rate.MethodsThree types of purple mudstones were sampled from the Tuodian group (J3t), Matoushan group (K2m), and Lufeng group (J1l), respectively, all located in the Chuxiong district of Yunnan province, southwestern China. All samples were manually cut into cubes of 50 mm × 50 mm × 50 mm, divided into nine groups, wetted on a sieve with 2 mm pores according to nine treatment levels, and then dried in an oven in the laboratory. Thirty-nine such wetting–drying cycles were carried out for each treatment. Decay rates were calculated by weighing the mass remaining on the sieve after each treatment cycle, and the average decay rates were estimated from the 39 cycles.ResultsThe results showed that the average decay rate of the tested rocks rose with increasing rock moisture content and that the rank order of the decay rate was J3t > K2m > J1l.ConclusionsA significant exponential relationship between the average rock decay rate and rock moisture content for all three purple rocks was found to quantitatively predict the decay rate of purple rock under varied moisture conditions.