Evolution Mode And Mechanical Characteristics Of Multi-sliding Zones Landslide-Stabilizing Pile System

Multi-sliding zones landslides(MSZ landslides)are widely developed in the world and multi-sliding zones are one of the important characteristics of large landslides.Due to the lack of in-depth research on the MSZ landslides,the inaccurate judgment of evolution behavior of the MSZ landslides,and the prevention methods of the MSZ landslides are lagging behind,leading to the failure of engineering decision-making and prevention engineering.In order to ensure the successful implementation and safe operation of large water conservancy and hydropower projects,efficient prevention and scientific evaluation of multi-sliding zones landslides is important.Stabilizing piles are one of the most commonly utilized landslide control structures.The evolution behavior of the MSZ landslides is changed and a new landslide-stabilizing pile system is produced when the piles are implanted into the landslide.It is important to further study the evolution mechanism of the MSZ landslide-stabilizing pile system.The MSZ landslides have special dynamics behavior,the current stabilizing pile design method doesn’t account for the relative motion of multi-sliding zones and is therefore inappropriate for the pile structure design of multi-sliding zones landslide.Therefore,it is of great theoretical significance and application value to conduct the studies concerning the evolution mode and mechanical characteristics of the MSZ landslidestabilizing pile system.In this dissertation,the Majiagou landslide-stabilizing pile in the Three Gorges reservoir area is chosen as the research object.Based on field investigation and in-situ monitoring platform,the distribution characteristics of a typical MSZ reservoir landslide in the Zigui-Badong section are studied,the sliding behavior and genetic mechanisms of the Majiagou landslide are revealed,the spatiotemporal deformation behavior and relative motion main control factors of the Majiagou landslide are studied,and the multiple sliding zones landslide is studied.The mechanical features and deformation modes of the MSZ landslide-stabilizing pile system are discovered.Simultaneously,based on the physical model test,the deformation evolution characteristics and failure modes of the MSZ landslide-stabilizing pile system are investigated under various working conditions,and the relative motion law and mechanical characteristics of the MSZ landslide-stabilizing pile system were revealed under various movement modes.In addition,the effects of piles design parameters on the reinforcement effect of the MSZ stabilizing piles under different movement modes are explored using numerical simulation test.Finally the mechanical model and internal force calculation method of the MSZ stabilizing pile is proposed,the theoretical calculation and model test results are compared and verified.Based on the above research content,the primary research results and conclusions of this dissertation are as follows.(1)The development characteristics of the typical MSZ landslides in Zigui-Badong section of the Three Gorges reservoir area were summarized and the basic characteristics of Majiagou landslide are determined.The typical MSZ landslides in this section are basically developed in the Jurassic and Triassic Badong Formation.The landslides are usually large-scale,and mainly divided into two types: soil interface +base-cover interface type and base-cover interface + weak interlayer type.The soft and hard layered structure developed by joints and fissures,which is very unfavorable for slope stability;reservoir impoundment and rainfall induced the Majiagou landslide to revive deformation and relative sliding.The soil shear surface of the deep sliding zone,which is the main sliding zone of the Majiagou landslide,has visible abrasion and polishing surface,and its clay mineral particles have obvious directional arrangement characteristics.(2)Based on field monitoring results,the relative motion law and mechanical pattern of the landslide-stabilizing pile system of the Majiagou landslide are disclosed.The deformation of the Majiagou landslide exhibits the step-type increase under the combined effect of reservoir water level and rainfall.The deep sliding zone having the largest relative displacement and velocity and enters the accelerated deformation stage about one month before the slope surface displacement.Apriori algorithm shows that the main control factor for the relative movement of the deep sliding zone and the slope surface displacement is reservoir water level decline,the main controlling factor for the relative movement of the shallow sliding zone is the heavy rainfall.The monitoring laws of the strain,axial force and bending moment of the test piles are relatively consistent,and there are three extreme values.Due to the local blocking effect of the engineering piles on the shallow sliding zone,the test piles has a reverse bending point below the shallow slip zone.Due to the relative motion of the middle and deep sliding zone,the bending moment(axial force)extreme point appear below the middle and deep sliding zone.Cooperative deformation occurs between the test pile and the soil around it,and deformation of the test pile appear step-type increase.(3)Based on the model test platform,the multiple field evolution characteristics of the MSZ landslides are revealed.Under the same thrust,the landslide evolution process demonstrated four stages,initial deformation,constant deformation,accelerative deformation and failure,with the main deformation location of the landslide varying in different evolution stages.Under the action of trailing edge thrust and gravity,the MSZ landslides undergoes translational sliding,local shear damage occurs at the leading edge of the landslide,and the main sliding zone is the shallow sliding zone.There is a good correlation between the deep relative displacement and the soil pressure.The soil pressure evolution process can also be divided into four evolutionary stages: initial accumulation of stress potential energy,constant accumulation,accelerative accumulation,and stress potential energy conversion,with a complex multi-level trapezoidal distribution of soil pressure.The abrupt drop in soil pressure value can be utilized as a criterion for landslide critical damage.(4)The MSZ landslide-stabilizing pile system evolution process and mode are exposed,and the mechanical characteristics of the piles are investigated.The MSZ landslide-stabilizing pile system may be separated into three evolution stages based on the multi-field evolution characteristics of the pile-soil: initial,synergistic,and nonsynergistic deformation.In the non-synergistic deformation stage,the landslide displacement,soil pressure and pile bending moment increase rapidly.The landslidestabilizing pile system presents the instability mode: the soil between the shallow and middle piles extrudes and the soil behind the shallow pile is destroyed over the top,and the three shear surfaces of the leading edge develop continuously and connect to the overall sliding.After the implantation of the piles,the landslide damage limit load and elapsed time both increased significantly.Multiple extremum points of bending moment are distributed in the MSZ pile and the shear appears negative.The maximum bending moment and shear force are larger than those of the single sliding zone piles and the piles are easier to fail.(5)The relative motion law and mechanical characteristics of the piles under different motion modes of the MSZ landslides are revealed.With the increase of relative displacement of the shallow sliding zone,the system undergoes non-synergistic deformation,there is a bending moment(strain)extreme value point and shear negative region below the shallow sliding zone,and the reinforcement effect of the piles is continuously reduced.There is a two-way multi-level soil arch distribution phenomenon of "soil arch behind the pile-soil arch in front of the pile-soil arch behind the pile" and the soil arch effect of the MSZ landslides shows different patterns at different evolution stages.In different motion modes,the changes of the pile design parameters differ in the effect of reinforcement effect.When the shallow sliding zone is dominant,changing the pile spacing can better improve the reinforcement effect.When the deep sliding zone is dominant,increasing the embedment depth and reducing the pile spacing can improve the reinforcement effect,which changing the pile spacing is more economical and reasonable.(6)Based on the Winkler elastic foundation beam model,the stabilizing pile is divided into three sections of shallow loaded segment,deep loaded segment,and socketed segment.The mechanical model and "multi-segment" elastic foundation beam model control equations of the MSZ landslide-stabilizing pile are established.The internal force calculation method of the MSZ stabilizing pile is proposed,and the theoretical calculation and model test results are compared and verified.The two laws are basically consistent which means that the internal force calculation method is reliable,can provide theoretical basis for internal force calculation and structural optimization design of the MSZ stabilizing pile.