Study On The Deterioration Characteristics Of Soil-rock Mixture Under The Action Of Periodic Saturated Water Cycle

Geological disasters occur frequently in the Three Gorges Reservoir area,among which the instability and damage of the wading slopes of the reservoir bank and the river bank is a frequently faced problem in the construction of various water wading projects in the Three Gorges Reservoir area.Because the wading slopes of reservoir banks and river banks are usually composed of a mixture of small-sized soil and large-sized boulders(referred to as soil-rock mixture),the mechanical model of wading slopes cannot be calculated strictly according to the soil slope.And under the action of the periodic rise and fall of the reservoir water level,the soil-rock mixture slope will be affected by the long-term erosion of the reservoir water,and the soil structure and structure will change.It is often manifested as intermittent gradation and low content of fine particles,and the rock is more easily broken under load,which affects the strength of the soil-rock mixture,and in severe cases will lead to the occurrence of landslide disasters.It is meaningful to supplement the corresponding scientific theories and guide the practical application of engineering to study the law of strength deterioration of soil-rock mixture under the action of periodic saturation of reservoir water.The Tuanshiban landslide in Wanzhou District is an old slump-slip accumulation.The material of the landslide is mainly composed of silty clay and rubble soil,and it has the characteristics of a typical soil-rock mixed landslide.Therefore,this paper takes the natural damaged soil-rock mixture below the reservoir water level and the soil-rock mixture at the top of the slope without periodic saturated water cycle taken from the Tuanshiban landslide in Wanzhou District,Chongqing as the research object.Particle analysis test,conventional triaxial test,and SEM scanning electron microscope test were carried out on soil-rock mixtures with different rock contents and different periodic water saturation times,and multi-scale deterioration studies of soil-rock mixtures were carried out,and their deterioration laws were clarified.Based on rock and soil damage mechanics,a deterioration model of soil-rock mixture under periodic water saturation is established.The research results of this paper have certain scientific and engineering significance.The main research results are as follows:(1)The strength of the soil-rock mixture is closely related to the number of cyclic saturation,and the peak deviatoric stress decreases with the increase of the number of cyclic saturation,and the peak deviatoric stress decreases significantly after the first saturation.In addition,the evolution equation for the deterioration of the strength parameters of soil-rock mixture under the action of periodic saturated water cycle is established,and the relationship between the number of periodic saturated water N and the shear strength index cohesion c and the internal friction angle?is analyzed.It is also pointed out that when N approaches infinity,the soil-rock mixture will be weathered and decomposed into silt soil with cohesion c=0 k Pa and angle of repose?=e?₀.(2)The mesoscopic and microscopic deterioration characteristics of periodic water-saturated soil-rock mixture are revealed.Periodic saturated water cycle results in a decrease in the fine particle content,a significant increase in the characteristic particle size and inhomogeneity coefficient in the soil-rock mixture,and a poorer continuity of the soil-rock mixture sample.The phenomenon of particle loss caused by latent erosion is more obvious in high rock content.In addition,the number of periodic water saturation has different degrees of influence on the microscopic parameters,and the geometric characteristics of pores change with the increase of the number of periodic water saturation.(3)An improved damaged binary medium model of soil-rock mixture is proposed,which verifies the reliability of the proposed model.The rock and soil in the soil-rock mixture were regarded as structural blocks and friction blocks,respectively,and the damage rates of soil-rock mixtures with different times of saturated water cycles and different rock contents were calculated according to the stress-strain curve obtained by the triaxial test.