Study On The Collapse Mechanism Of Jointed Loess Steep Slope Under Infiltration Condition

Vertical joints are widely developed in loess steep slopes,which is a common geological phenomenon.The collapse of loess steep slope poses a great threat to people’s property and life safety.Therefore,the study of loess steep slope collapse has attracted wide attention in the engineering field.There are many factors affecting the collapse of loess steep slope,among which joint and water are important factors.Water infiltration will increase the water content of loess steep slope and reduce the safety factor of loess steep slope.The joints in loess constitute weak structural planes,which cut the loess into unstable structures.The rapid infiltration of water along the joints will further reduce the stability of the loess steep slope,which is an important factor for the collapse of the loess steep slope.However,the collapse mechanism of the loess steep slope with joint development under infiltration conditions is not clear.Based on this,this paper studies the collapse mechanism of jointed loess steep slope under infiltration conditions.The main research results are as follows :(1)Through the loess joint water infiltration test,the water infiltration law under different joint opening conditions is obtained.According to the different laws of water infiltration,the joints are divided into three modes : large opening,small opening and medium opening.Among them,the large opening joints have the most obvious effect on water infiltration and have the characteristics of high permeability.According to the parallel plate model combined with fluid mechanics,the permeability coefficient of the large opening joint is modified,and the water infiltration model of the large opening joint loess is given.The water field obtained by numerical simulation is basically consistent with the indoor model test.(2)Based on the water infiltration model of large opening jointed loess,considering the change of mechanical parameters of loess with water content,the calculation model of water infiltration and collapse of loess steep slope is given.Based on the calculation results,the relationship between the sliding surface and the joint development conditions(location and depth)is summarized.According to the characteristics of the sliding surface and the characteristics of stress and displacement,the loess steep slope slump is divided into four modes : sliding slump mode,bulging slump mode,traction slump mode and staggered slump mode.Based on the corresponding relationship between joint development conditions and collapse mode,the judgment diagram of loess steep slope collapse mode is obtained.(3)The water field,stress field,displacement field and plastic zone evolution law of loess steep slope under water infiltration condition are obtained by calculating and analyzing the water infiltration collapse calculation model of loess steep slope.The differences of the influencing factors in the four sliding modes are analyzed.It is revealed that the joint development conditions are the main influencing factors affecting the evolution of water field,stress field,displacement field and plastic zone.There is a corresponding relationship between the joint development conditions and the loess steep slope sliding mode.(4)According to the judgment diagram of loess steep slope collapse mode,the joint development conditions corresponding to different collapse modes are drawn up,and the indoor loess steep slope model test pattern is made.Based on the indoor model test,the water infiltration depth,sliding surface position and collapse mode of loess steep slope under different joint development conditions were measured.The calculation results of the loess steep slope water infiltration slump calculation model are basically consistent with the indoor test results.The slump mode obtained according to the loess steep slope slump mode judgment diagram is also consistent with the slump mode given by the test,thus verifying the reliability of the slump calculation model and the loess steep slope slump mode judgment diagram.(5)Based on the field data of 9·17 Bailuyuan,the joint development and soil conditions of Bailuyuan were obtained,and the sliding characteristics and sliding mode of Bailuyuan were given.The sliding mode and sliding surface position of Bailuyuan are obtained by using the sliding mode judgment diagram in this dissertation,which is basically consistent with the field data.