Research On Reinforcement Effect Of Anti-slide Pile-soil Nail Wall On High Cut Slope Under Rainfall And Earthquake

In recent years,with the proposal of the strategy of building a transportation power,China’s railway construction is in full swing.However,China is a mountainous country with complex and rugged terrain.While transforming the natural environment to form a railway network,there are bound to be some complex slope problems.It is difficult to ensure the stability of the slope only by the strength of the slope soil itself.In engineering,the way of setting retaining structure is often used to strengthen the slope.For railway slope,the design service life of retaining structure can reach 100 years.In order to ensure its working performance in the normal service life,the influence of natural conditions must be considered.In China,earthquake and rainfall are two important natural factors causing slope instability.Once the slope is unstable,it will not only directly cause great economic losses,but also cause human death.Therefore,it is very necessary to study the stress of supporting structure under rainfall and earthquake and evaluate its reinforcement effect.Relying on the project "Research on Long-term Stability and Monitoring and Evaluation Technology of High and Steep Cutting Slopes",this paper selects the slope section of Xingquan Railway Dehua Station as the research object.By combining the theoretical research of supporting structure,on-site measurement and numerical simulation and other methods,the mechanical characteristics and reinforcement effect of the anti-slide pile,soil-nail wall supporting structure of the slope under the action of rainfall and earthquake are deeply studied.The main research content and the results are as follows:(1)Based on the plane strain problem,the soil arch behind the pile is regarded as a statically indeterminate three-hinge arch to simplify the calculation,and the reasonable arch axis is taken as a parabola,and the ultimate bearing capacity formula of the soil arch is deduced.Through this formula,it is found that the ultimate bearing capacity of soil arch is only related to the width of anti-slide piles,the clear distance between piles,the cohesion of the soil and the friction angle in the soil.(2)Based on the calculation method of internal force of anti-slide pile and the calculation method of soil nail tension given in the existing specifications,the relationship formula between pile top displacement and pile internal force and the distribution formula of soil nail tension along the length under different post pile load distribution forms are deduced respectively.Compared with the measured data,it is found that the theoretical formula has good applicability and certain engineering application value.(3)Long-term on-site monitoring was carried out on the high cutting slopes of DK371+315～DK371+525 in the Ningquan section of Xingquan Railway,and the force changes and internal force distribution characteristics of the anti-slide pile,soil-nail wall supporting structure were obtained.The force variation law of the retaining structure is closely related to the slope construction.When the soil in front of the pile is excavated,the internal force of the anti-slide pile begins to increase,while the internal forces at both ends of the pile are almost unchanged.With the completion of soil excavation in front of the pile,the internal force of the anti-slide pile is basically in a stable state.According to the measured results of soil nail reinforcement stress,it is found that the distribution of soil nail tensile force first increases and then decreases.(4)The on-site slope model is established by using FLAC3 D finite difference software to study the influence of the change of pile spacing and pile section size on the behavior of soil arch behind pile,the stress of anti-slide pile and the reinforcement effect of slope under no rainfall,no earthquake,rainfall and earthquake conditions.The results show that the behavior of soil arch behind pile is greatly affected by pile spacing and less by pile section size.For the anti-slide pile itself,rainfall and earthquake will cause the stress of the anti-slide pile to rise significantly.The smaller the pile spacing is,the larger the pile section size is,and the better the support effect is.Combined with the soil arch behind the pile,the stress of the pile body and the reinforcement effect on the slope,it is finally determined that the reasonable pile layout method is the pile spacing of 6m and the section size of 1.75 * 2.75 m.(5)On the basis of determining that the pile spacing is 6m and the section size is1.75*2.75 m,the parameter sensitivity analysis of soil nailing between piles under no rainfall,no earthquake conditions,rainfall conditions and earthquake conditions is carried out.It is found that the displacement of soil between the piles can be effectively limited after the arrangement of soil nails between the piles.On this basis,changing the length of the soil nail and the inclination angle of the soil nail has little effect on the displacement.The change of soil nail length and inclination mainly affects the force of soil nail.The longer the length and the greater the inclination angle,the greater the load borne by the soil nails,which is more conducive to the reinforcement of the soil between the piles.Besides,the arrangement of soil nails can also share the load of anti-sliding piles,so that the internal force of the pile body is reduced.The longer the soil nail,the larger the inclination angle,and the better the load sharing effect against the sliding pile.