Study On The Influence Of Matric Suction On The Stability Of Tailings Dam Under The Condition Of Rainfall Infiltration

Rainfall infiltration has a direct bearing on soil moisture content of tailings dam.The change of water content will change the matric suction of soil.The matric suction is closely related to the shear strength and stability of unsaturated dams.At present,the rainfall infiltration is seldom considered in the stability analysis of tailings dam.Most of the existing slope stability analysis is based on the traditional theory of saturated soil mechanics.The method considers only the three-phase of solid-liquid-gas,and lacks the matric suction produced by the contraction film on the fourth phase of gas-liquid interface.Tailings dam is a kind of special unsaturated soil slope.Matric suction is the basic characteristic of unsaturated soil,which is different from that of saturated soil.Therefore,the influence of matric suction can not be neglected in the calculation and analysis of tailings dam stability.Based on this,this paper takes a tailings dam as the object of study.Firstly,the influence mechanism of matric suction on slope stability is systematically analyzed.Phosphorus tailings were used as the main test materials to test.The 13 physical properties such as water content,density and plastic limit of the sample are determined by laboratory soil test,and 4 mechanical properties,such as cohesion,internal friction angle and permeability coefficient,are measured.The above tests were conducted to select tailings sand materials for later tests.Secondly,the model similarity test of tailings dam is carried out.The law of infiltration and physical and mechanical characteristics of tailings dam under different rainfall intensities are studied.Then,the contact filter paper method was used to study the change law of matric suction with water content during the rainfall infiltration process.According to the Fredlund-Xing model,the soil water characteristic curve(SWCC)of tailings is drawn.The main factors affecting matric suction and SWCC are analyzed from two aspects of soil self factor and external environment condition.Finally,on the basis of the traditional Mohr-Coulomb strength failure criterion,according to the Fredlund double stress variable theory,the matric suction is taken as a stress variable alone,and the shear strength calculation is taken into account.To avoid the inconvenience caused by the matric suction friction angle φb and effective stress parameter ? in the calculation of shear strength,it is also convenient for the calculation of limit equilibrium analysis software Slide.Based on the combination and optimization of Bishop and Fredlund unsaturated soil strength formula,the " microscopic Mohr-Coulomb strength formula" for tailings dam is established on the basis of water content.According to the lattice Boltzmann model,the experimental results of matric suction and shear strength parameters are fitted and analyzed.The relationship between the stability safety factor and matric suction of unsaturated tailings dam is obtained.At the same time,the variation law of the safety factor of the dam before and after considering the matric suction is analyzed.The results show that the safety factor of dam slope decreases with the increase of soil moisture content in the process of rainfall.From the dry state of the dam to the saturated state,the safety factor calculated by the traditional saturated soil mechanics method is reduced by 43%.According to the new method after considering the matric suction,the safety factor is reduced by 61%.And the degree of change is more significant than the traditional calculation method.When the water content is in the low saturation stage before the plastic limit(16.1%),the calculated safety factor of the traditional method is about 14.7% smaller than that of the new method.The safety factor calculated by the traditional method is about 26.2% when the water content reaches the high saturation stage after the plastic limit is reached.Therefore,the effect of matric suction on the enhancement or weakening of the safety factor of tailings dam stability is very obvious.In the tailings dam stability calculation and analysis should be fully considered.