Study On The Mechanism Of Red-bed Mudstone Slope Mudflow Induced By Rainfall In Longde County

There are four kinds of landforms in Longde county Ningxia Hui Autonomous Region, including low mountains, loess hilly, red-bed mudstone hilly and river valley. The area of red-bed Mudstone hilly is199.83km2,accounting for20.14%of the total area. The main lithology is red sandy mudstone of Neogene and Paleogene. From June to July2013, Longde experienced sustainable strong rainfall, resulting in the loose mudstone from slope moving and sliping. This phenomenon is slope mudflow, which is a threat to the safety of people’s life and property. Based on the geological conditions in Longde, choose red-bed mudstone slope mudflow as the research object and apply to the laboratory artificial rainfall model test as the main means to study on the preliminary mechanism of red-bed mudstone slope mudflow induced by rainfall. The results of the main contents are as follows:(1) This paper, based on the field observations and lots of hydrology, meteorology, geology and topography of Longde, analyzed and studied the environmental conditions of the formation, it demonstrated that the geological conditions in Longde were conductive to the formation of the mudflows on slope for red-bed mudstone.(2) Take the sample of red-bed mudstone from Longde, carried out X-ray spectral analysis, particle size analysis, specific gravity, water content, density tests and shear test under different saturation, which obtain the relationship between c,Φ and water content and make the foundation for laboratory artificial rainfall model test.(3) Conduct the laboratory artificial rainfall model test to form slope mudflow, under the antecedent rainfall intensity10.27mm/10min and short duration rainfall intensity21.30mm/10min. Through analysis of water content changes of surface and deep mudstone and the morphology changes while immersing in water, study on the mechanism of red-bed mudstone slope mudflow and also can provide reference for early warning and forecasting of mudstone slope mudflow.(4) From the results of laboratory model test, it was known that the formation of red-bed mudstone slope mudflow was worked by the antecedent rainfall and short duration rainfall intensity. By changing the water content of mudstone, they influence the stability of mudstone slope. In addition, using the experienced formulation between debris flow and rainfall intensity to analyse the rainfall index in Longde. It demonstrated that the rainfall intensity had reached the critical rainfall values what the slope mudflow needed. As a result, the analysis was consistent with the actual.(5) Thanks to the disintegration, mudstone becomes muddy while immersing in water. In order to study the disintegration process of mudstone under water action, the paper used X ray diffraction to analyse the composition of mudstone. The results show that the disintegration of mudstone is caused by the second porosity and wedging pressure in saturation process. Crack is formed by wedging pressure of porosity surface in the process of saturation. The sample is disintegrated because of crack penetration each other. Since the disintegration, mudstone becomes muddy. The shear strength of mudstone is decreasing rapidly. Then with the work of slope runoff, the slope mudflow will occur.