Instability Mechanism Of Unsaturated Coal Gangue Accumulated Slope By Considering Rainfall Infiltration As A Triggering Factor

The stability of slope is allied with variations in rainfall infiltration processes having peculiarity to reduction in shear strength and suction loss resulting failures.The occurrence of slope failures has mainly been observed during rainfall events or immediately after rainfall.Although the conditions causing these failures have been demonstrated as the rapid cause of increases in pore-water pressure due to rainfall infiltration,however,the important influencing factors that initiate slope failures have not been copiously addressed.The influence of rainfall intensity and rainfall duration on the stability of slope have been analyzed,but the effect of rainfall infiltration process on the stability of slope with coal gangue accumulation needs to evaluate.It is of great significance to explore the failure mechanism of multiple slopes and the displacement of their failure bodies for the safety of mountainous environment around the world.Rainfall characteristics(intensity and duration of rainfall)and hydraulic conductivity of soil may influence the mechanism of occurrence and failure type of slope.In general,damage can be caused by two mechanisms i.e.,the propagation of wetting front leads to the loss of matric suction and rise of ground water table.So far,there still have no clarified indicators to determine the dominant parameters controlling the failure types of such landslides.Therefore,rainfall infiltration process as an influencing factor for the instability of coal gangue accumulated slope was taken into consideration in Fuxin area,Northeast China in the present study.The recorded precipitation,measured soil parameters,geology of site and geometry of slope were utilized in both coupled and uncoupled finite element analysis to evaluate the failure mechanism in coal gangue accumulated slope.The influence of rainfall infiltration on the instability of slope based on different rainfall durations(1 day,2 days,3 days,4 days and5 days)with constant intensity of rainfall was analyzed through physical modelling and then authenticated by finite element numerical analysis for coupled and uncoupled responses.The experiment based on slope model with consideration of rainfall infiltration was performed and the comparison of obtained results were verified through analysis method of unsaturated slope instability.The variations in matric suction and volumetric water content due to rainfall infiltration were measured in the experiment and the time of occurrence of slope failure was determined.The high permeability coefficient of coal gangue and the maximum observed deformation due to water runoff near the slope toe further explained the movement of slope body in downward direction,which are in good agreement with the observations from field and physical model.Additionally,the observed variations in factor of safety values from the analysis for both hydraulic and hydro-mechanical analysis were compared and authenticated with slope model experiment.The results also show that the increase of infiltration rate cause hysteretic increase in pore-water pressure and decrease in stability factor.In conclusion from the presented study,the factor of safety value in coupled analysis(coupled effect of stress and pore-water pressure)was significantly reduced in comparison of uncoupled analysis(effect of hydraulic response).In order to prevent the slope from further failure and to prevent its affect on the traffic of road,the combination of anchoring and horizontal drainage design is adopted.It is suggested that anchors with concrete beam should be incorporated to reinforce the roadbed at the top of the slope while pile row should be set up near toe of the slope.The horizontal drainage system has been introduced to divert the rainfall water for protecting the slope and roads at top and bottom.The effect of pile coupled with anchor reinforcement is analyzed by Limit equilibrium Bishop method,and the influence of reinforcement scheme on the safety factor of the slope is evaluated.The results show that the safety factor of soil slope reinforced by pile and anchors is increased from 0.9 to 1.14.In addition,a horizontal drainage system is designed in the landslide area by using engineering value study to control the excessive rainfall infiltration within the landslide body,to protect the road at top and bottom of the slope and to divert the rainfall water.