Study On Factors Influencing Drainage Of Water-induced Landslide And Optimal Design Of Drainage Hole

Landslide is one of the most common and devastating geological disasters in China,the southwestern region is particularly serious.The causes of landslide are complex and extremely harmful.Rainfall and groundwater are the most important factors influencing the deformation and failure of landslide.According to statistics,almost 45%of landslides deformation instability are caused by rainfall.The study on the evolution law of seepage field and stability evolution law of landslide under the action of rainfall and groundwater and the optimization design of the drainage control engineering are not only of theoretical value in related academic research fields,but also have important engineering guiding significance in the field of landslide drainage control.In this paper,a typical water-induced landslide—Qingganglin landslide,is selected as the research object.Based on rainfall infiltration theory and saturated-unsaturated seepage theory,The finite element software Geo-Studio is used to simulate and analyze the mechanism of rainfall infiltration affecting the seepage field and stability of landslide,and the evolution law of seepage field and stability of landslide before and after laying inclined drainage holes is analyzed,and the influence of the distribution parameters of each drainage hole on the seepage field and stability evolution of the landslide is applied.The sensitivity analysis of the drainage hole layout parameters is made by using the grey correlation theory,and the importance of the drainage hole drainage pressure is determined,selects the main influencing factors of drainage hole drainage and reduces the drainage effect,and 16 kinds of drainage hole layout schemes are designed by the orthogonal design principle,Then perform simulation calculation,and based on the basic principle of GA-BP neural network,the drainage hole layout parameters are taken as input parameters,the landslide drainage prevention project cost M?that is the total length of the drainage hole L?and the landslide stability after drainage prevention F_s as the output parameter,accurately establish the complexity nonlinear mapping relationship between them by setting reasonable structural parameters.The landslide drainage prevention project cost M?that is the total length of the drainage hole L?and the stability of landslide F_s?1.25 after the drainage prevention and control are output as the objective function and constraints respectively.By using the parallel genetic algorithm,the optimal value of the layout parameters of the drainage holes can be accurately and quickly solved within the fixed search range,and the optimization of the design scheme of the landslide drainage hole is completed.Based on the above research,using the loading-unloading response ratio theory,this paper studies the evolution rule of the loading and unloading response of the landslide under the condition of the inclined drainage hole,and the relationship between the landslide stability,and discusses the prevention and control effect of the optimal drainage scheme of the drainage hole on the landslide of Qingganglin was discussed.The main research results of this paper are summarized as follows:?1?The effect of landslide body on drainage and anti-pressure treatment and enhanced landslide stability is very significant;the drainage pressure-reducing effect and influence range of the inclined drainage hole increases with the increase of the hole length,however,it is necessary to consider the requirement of the depth range and the engineering geology condition of landslide in the reasonable economic hole length;the tilting drainage hole aperture and elevation angle changes have little effect on the drainage and pressure reduction effect,but the aperture is too large and not economical,and the slope of the large disturbance,the aperture is too small and easy to form a full pipe phenomenon,resulting in less drainage efficiency.The elevation is too big to cause the construction difficulty to increase,the construction cost increases,comprehensively considers the landslide actual groundwater's total water head and the project to drop the depth scope request.It is recommended that the diameter of the drainage hole of the landslide should be R=0.20m,and the elevation angle?=6°¹0°;when the drainage hole is buried at a lower elevation,it is easier to contact the rising groundwater,and the contact time with the groundwater is longer,and the displacement of the drainage hole is longer.More,the drainage and anti-pressure effect of the landslide body and the stability of the landslide are more obvious.It is recommended that the landslide drainage hole be reasonably buried in the vicinity of H=22m;Drainage hole number and spacing there is an optimal value,larger or smaller is not conducive to the drainage pressure reduction and improve stability of the landslide.The recommended drainage hole row number of the Qingganglin landslide is N=2³,and the best hole distance is recommended for D=7⁹m.?2?Based on the finite element software Geo-Studio,the simulation results of landslide stability under different drainage hole layout schemes are obtained,the sensitivity analysis of the drainage hole layout parameters is carried out by using the grey correlation theory,and the drainage drop of the enhanced drainage hole is obtained.The effects of pressure effect and landslide stability are dominant:drainage hole row,drainage hole length,drainage hole embedding elevation,drainage hole distance,based on genetic algorithm and neural network principle,a reasonable drainage hole design can be selected.The evolutionary neural network calculation model finally finds the optimal solution:the drainage hole row number N is 2 rows,the drainage hole length l is37.75m,the drainage hole embedding elevation H is 23m,and the drainage hole spacing D is 8m.?3?Using the loading and unloading response ratio theory,the difference between the rainfall and the total drainage of the slope from the drainage and drainage holes?and positive value?,that is the weekly effective rainfall is regarded as the loading amount R_+,and the corresponding monitoring point the displacement rate value V₊is used as the loading response;the difference between the rainfall and the total drainage of the slope from the drainage and drainage holes?and when it is negative?is regarded as the unloading amount R_-,and the corresponding displacement point velocity value V_-As an unloading response,a load-to-load response ratio calculation model suitable for a landslide with a drain hole is established.Through the study of the parameter evolution rule of the landslide under the condition of inclined drainage hole,the comprehensive evolution of the landslide stability evolution law shows that when the landslide stability coefficient is greater than 1,the loading and unloading response ratio of the landslide is1 fluctuations in the vicinity;when the stability coefficient of the landslide continues to decrease,the load-unload response ratio of the landslide continues to increase;when the landslide is about to destabilize,the load-unload response ratio of the landslide increases sharply and is much greater than 1.The results show that the optimal layout scheme of the drainage holes is effective for the prevention and control of Qingganglin landslide and meets the initial design requirements.