Reliability Analysis Of Loess Slope In Jingyang South Tableland

Since 1976,the groundwater level has been rising due to diversion irrigation,landslides and other geological disasters occurred frequently in Jingyang South tableland,Shaanxi Province,which has continuously cannibalized farmland,endangered lives.So systematic measures to prevent landslides are urgently needed.Due to the formation process of loess is significantly affected by climate,the number of layer of loess and paleosol is large,and the spatial variability of soil strength parameters of slope is large,it is difficult to accurately determine the parameters,significant uncertainty is generated when adopting the traditional safety factor method to evaluate the stability of these slopes.Therefore,this paper takes Jingyang South tableland as the research area,and proposes a reliability analysis method of limit state slope considering engineering geological condition judgment experience based on Bayes theory,which to reduce the uncertainty of reliability calculation results.The proposed method is used to optimize the reliability results of the loess slope at the sewage outfall of the Xi'an Xianyang International Airport in Jingyang County,Shaanxi Province.In addition,irrigation is an important reason for the frequent occurrence of landslides in this area.Owing to the large number and wide distribution of landslides,it is unrealistic to take engineering measures to prevent landslides in the region.Therefore,this paper takes the loess slope at the sewage outfall of the Xi'an Xianyang International Airport as the research object,couples with unsaturated seepage and unsaturated strength,studies the law of irrigation infiltration in tableland and the change law of transient slope stability,and analyzes the influence of the width of the forbidden irrigation area and permeability coefficient on the transient slope stability.The results are as follows:(1)Filter paper method was used to measure the humidified soil water characteristic curves(SWCCs)of L₁,L₅ and L₉ loess.The Van Genuchten model was used to fit SWCCs,and the Van Genuchten unsaturated permeability equation was used to predict the unsaturated permeability coefficient of all the three loess.The results show that the higher the viscosity and the better the density of loess,the stronger the water holding capacity of SWCC and the weaker the permeability of soil.In unsaturated state,the phenomenon is opposite.(2)An optimization method of slope reliability calculation results is proposed based on Bayesian theory,which is used to evaluate the loess slope at the sewage outfall of the Xi'an Xianyang International Airport in Jingyang County,Shaanxi Province.The results show that the variance of the posterior distribution of the reliability is smaller,the accuracy is higher,and the evaluation results are more practical.In addition,the robustness analysis is performed on the posterior distribution of reliability.The results show that the calculation results are robust.Therefore,the method proposed in this paper can take the regional engineering geological experience into account to evaluate the stability of a specific loess slope more accurately.(3)Considering the influence of water diversion irrigation on the slope stability,the 70year transient reliability analysis of the slope is carried out under the actual irrigation mode,the pore water pressure profile and the slope stability change law are studied,and the influence of the width of the forbidden irrigation area and the Loess permeability on the slope stability is analyzed.The results show that firstly the changing of pore water pressure caused by irrigation infiltration is a slow process.The rising of groundwater level,the declining of safety factor and the increasing of failure probability are multi-stage and slow processes.The rising of groundwater level is closely related to the declining of safety factor and the increasing of failure probability.Secondly the longer the length of the forbidden irrigation area,the slower the groundwater level rises and the smaller the total amount of uplift;the slower the safety factor falls,the smaller the final decline range;the slower the failure probability increases,the smaller the final increase range.It is the most economical and scientific measure to prevent the regional landslides to set up 60 m forbidden irrigation area on Jingyang South tableland.Finally there is a dual nature of high permeability to slope stability.Due to higher permeability,the faster the water infiltration,and the earlier the stability decreases significantly.At the same time,the drainage of groundwater is increased,and the final stability is higher.