Anqiang Chen

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.

Determination of purple soil loss tolerance based on soil productivity in southwest China

Soil loss tolerance (the T value) is generally defined as the maximum acceptable soil loss that allows a high level of productivity to be maintained for a long period while considering the soil fertility and productivity. The T value is both the basic criterion for determining whether erosion control measures are necessary to conserve the soil and the index used to classify the degree of soil erosion. Therefore, soil loss tolerance must be determined scientifically and rationally. In this study, the ultimate objective was to determine the T value that could sustainably satisfy the needs of local development with regard to regional social progress based on the productivity of the soil. Artificially established plots with soil depths of 10, 20, 40 and 60 cm (4, 8, 16, and 24 in), representing 50, 40, 20 and 0 cm (20, 16, 8, and 0 in) of eroded soil depth, respectively, were used to determine quantitatively the effect of soil erosion on soil productivity. The crops planted within the plots were corn (Zea mays L.) and wheat (Triticum aestivum L.) for summer and winter, respectively, and their yields were used as the proxy measure of the productivity of the soil. The T value was determined by the permissible reduction rate of soil productivity that satisfies the requirements of local sustainable development in the long term and the relationship between the eroded soil depth and soil productivity. The results demonstrated that the crop yield decreased at an exponential rate with an eroded soil depth: with a 1% reduction in crop yield, the soils planted with corn were eroded by 0.92 cm (0.36 in), and those planted with wheat were eroded by 0.94 cm (0.37 in). After analyzing the increase in the local soil productivity and the requirements for sustainable social development, the soil productivity reduction tolerance was found to be 0.1%, and the T value of the studied region was determined to be 11 Mg ha−1 y−1 (4.91 tn ac−1 yr−1).