Research On Pile Position Optimization Of Push Landslide Anti-slide Pile Based On Anti-slip Ratio Method

Anti-slide pile is an effective and common supporting measure for landslide.According to the sliding mechanism of driving landslide,the comprehensive supporting effect of anti-sliding piles at different pile positions is studied by using anti-sliding ratio method.Choosing the Pile Location with the Optimum Comprehensive Evaluation Effect to Set Anti-slide Piles,Therefore,it can not only ensure the stability of landslide,avoid casualties and economic losses caused by landslide,but also save engineering economy and avoid waste.According to the actual treatment project of Heitu landslide in Wenchuan,the sliding mechanism of the landslide is analyzed numerically,and the failure type of the landslide is distinguished based on the sliding mechanism of the landslide.Then,according to the characteristics of landslide failure types,the anti-slide ratio method is applied to determine the optimal pile position of anti-slide piles.The specific research process is as follows:Firstly,through the early investigation of relevant literature,consulting the research data of this area,and on-the-spot survey of the landslide area,we can grasp the topography,geological structure and hydrogeological conditions of this area.The stratum lithology in the landslide area is exposed through drilling holes and artificial grooves.Secondly,according to the anti-slide pile support scheme of the Heitu landslide in Wenchuan,after the anti-slide pile is set up,the displacement and deformation of the corresponding parts are monitored.Finally,based on the actual engineering geological conditions,a three-dimensional geological-mechanical-numerical model is established by means of ANSYS,and the elastic-plastic strength reduction method is used to calculate and analyze in FLAC3D.The results of calculation and analysis are compared with the actual monitoring results.The results show that:(1)Under two working conditions,the deformation and development process of the plastic zone of landslide without anti-slide pile support are analyzed in detail.Combining with the characteristics of the landslide mechanical failure,we can distinguish the Heitu slope of Wenchuan as a driving landslide.Plastic zone deformation.Under natural conditions,the upper and middle parts of the landslide are destroyed by shear,and there is a continuous plastic deformation zone.Due to the support of the lower part of the landslide,the plastic deformation zone does not completely penetrate the foot of the slope,which indicates that the landslide still has a certain safety reserve and is in a stable stage.Under rainfall conditions,the continuous plastic deformation zone of the upper and middle slippers has been further developed.Because the residual anti-sliding force of the lower slippers is insufficient to support the residual sliding force of the upper slippers,the plastic deformation zone continues to run through to the foot of the slope completely,and is currently in an unstable stage.The shear strength of the upper and middle landslides is insufficient,which leads to failure and instability.The upper unstable sliding body transfers the downward sliding thrust to the lower stable sliding body,which promotes the deformation and failure of the lower sliding body.The failure mode is consistent with the driving landslide.Displacement deformation.Under natural conditions,the landslide has a large displacement at the left back edge,the displacement value is about 0.06m,which indicates that the landslide will begin to deform from this position under natural conditions.Under rainfall conditions,the displacement at the left rear edge of the original landslide increased from 0.06m to 0.4m,and the increase multiple was 7 times.However,the maximum displacement of the sliding body occurs in the upper and middle parts of the boundary of the landslide,and the displacement value reaches 0.71m,which indicates that the sliding body will have the earliest slip in the upper and middle parts of the landslide.In the actual investigation results,a large number of tension cracks appear at the top and left and right rear edges of the landslide,which shows that the numerical results are in good agreement with the field survey results,and the landslide deformation and sliding will be carried out at the middle and rear edges.By comparing the real deformation of the whole landslide and the detailed distribution of cracks with the displacement and deformation nephogram calculated by numerical method,it is found that the displacement and deformation nephogram are consistent with the real deformation of the landslide,which further verifies that the landslide is a typical driving landslide.(2)Two working conditions of landslide after anti-slide pile treatment.Under natural conditions,the stress distribution of the landslide is uniform and the compressive stress in the boundary area of the landslide is smaller than that in other parts,that is,closer to the tensile stress.However,under rainfall conditions,there is no tension stress in landslide,so tension failure will not occur.Under natural conditions,the shear strain increment at the left and right rear edges of the landslide body is larger than that at other parts,so it can be seen that the landslide body will take the lead in deformation at the left and right rear edges.However,under rainfall conditions,the shear strain increment of the whole landslide is relatively small and uniformly distributed,and the maximum shear strain increment is also less than its own shear strength.Under natural conditions,the displacement of the whole landslide is small,but under rainfall conditions,the maximum local displacement of the landslide is 0.508m,and the safety factor is 1.05 calculated by elastic-plastic strength reduction method.The above points show that the landslide treated by anti-slide piles may have local deformation under rainfall conditions,but the whole is still in a basically stable state.The numerical simulation is basically consistent with the field investigation and analysis,which preliminarily verifies the rationality of the model.(3)Seven monitoring points are evenly set up on the main slip section to monitor the surface deformation.The monitoring can be divided into three stages:survey design,support construction and prevention effect monitoring.Analysis of monitoring data shows that the displacement of numerical simulation is in good agreement with the displacement of actual monitoring points,which further verifies the correctness of the three-dimensional model of landslide and lays a foundation for optimizing the pile position of anti-slide pile by anti-slide ratio method.(4)The anti-slide ratio method is proposed to optimize the anti-slide pile position.The part of Heitu landslide in Wenchuan where the sliding force is greater than the anti-sliding force is divided into the sliding section,and the part of anti-sliding force greater than the sliding force is divided into anti-sliding section.According to the mechanical characteristics of the sliding and anti-sliding sections of the propelled landslide,the leading edge of the sliding section not only has certain self-stabilization ability,but also can bear part of the residual sliding force of the sliding section.However,the residual sliding force that the anti-slide section can bear should be determined based on the comprehensive support evaluation score Br(taking into account the overall displacement of landslide,safety factor,displacement of anti-slide pile body,shear force of anti-slide pile body and shear force of embedded end of anti-slide pile).When the anti-slide ratio(Ar)is 3%?8%,the pile position is the best.Therefore,the anti-sliding section of the driving landslide can also bear 3%to 8%of its residual anti-sliding thrust.When choosing the pile position of driving landslide,the conclusion can be followed to set the pile position.Therefore,it can not only give full play to the self-stabilization of anti-slide section to achieve the purpose of optimizing the pile position of anti-slide pile,but also provide quantitative scientific basis for the design of pile position of driving landslide in the future.(5)The comprehensive evaluation of landslide prevention and control projects should consider the deformation of the sliding body,the stability of bedrock embedded in the end and the structural safety of the anti-slide pile itself.In order to quantify the three main bodies,it is subdivided into six factors:sliding displacement,safety factor,displacement of anti-sliding pile head,shear force of anti-sliding pile body,bending moment of anti-sliding pile body and lateral compressive stress of embedded end bedrock.When adjusting the position of anti-slide piles,the factors such as sliding thrust,anti-sliding resistance and embedded depth of anti-slide piles are different at different positions,so the six factors mentioned above will change accordingly.Through scientific comparative experiments,it can be seen that the pile position determined by anti-slide ratio method will not be affected by one or two factors especially well,but by other factors seriously poor.As a result,the whole prevention and control project is destroyed because of a special poor factor.Finally,it is concluded that only considering the influence of six factors comprehensively to evaluate the quality of landslide control project is a scientific and reasonable method.