Research On Anti-sliding Mechanism Of The New Micropi1e-anchor Composite Structure

Slope engineering relates to the road, railway, mining, water conservancy andhydropower, nuclear power and other engineering field.Some slope diseases,such as slopefailure induced by rain and the traffic discrupted by landslide, need to be cured rapidly,but theconstruction site and method are limited. The traditional large-scale prevention structures,suchas anti-sliding piles and prestressed anchor, need long construction period and large amount ofmasonry, so they are unable to meet the requirements of rapid treatment. Therefore, based onthe need for emergency rescue and inviromental protection, the anti-sliding structures aregradually tended to the development direction of the light, fast and mechanization. the slopeengineering has been developing light support system and the combination of retainingstructure actively.Due to non excavation and strong applicability to soil layer, flexible layout,fast construction speed, small disturbance on the slide and other advantages, micropiles hasgot more and more applications in landslide control in recent years. But because the ratio oflength to diameter is big and flexural bearing capacity is insufficient, micropile structures areeasy to appear lateral deflection under the action of external force. When reinforced bymicropiles independently, the slope deformation is easy to exceed the allowable displacementrequired by stability or security, such as the tunnel-landslide system. In engineering practice,the micropiles are usually combined with other retaining technology to achieve the purpose ofprevention and treatment of landslide. Therefore, on basis of the research and application ofexisting micropile structures, it is of great significance to develop new micropilereinforcement forms of high bearing capacity.Relying on the Special Research Fund For Technology Development of ResearchInstitute Supplied By the Ministry of science and Technology,《New Rapid GovernanceStructure and Protection Technology For Slope Disease After Disaster》（2009E123201）,Thepaper researches on a micropile-anchor composite anti-sliding structure proposed by the topicgroup. On the basis of research at home and abroad, combined with three kinds of typicallandslide including accumulated layer landslide and homogeneous soil landslide induced byload and loess landslide, this paper studies on the reinforcement effect and mechanicalmechanism of common micropile structures and micropile-anchor composite structures bycombined method,which is consist of field investigation, theoretical analysis, numericalsimulation, laboratory model test. The study has confirmed that micropile-anchor composite structure is feasible to landslide control. The main results obtained are as follows:(1)On the basis of summarizing commonly used micropile structure types in practice, thethesis puts forward a new micropile-anchor composite anti-sliding structure through theresearch ideas of combineing advantages of pile frame structure and anchored retainingstructure. Prestressed anchor is set up on the structure as outer pull system to formate anactive reinforcement system, one end is connected with the micropile through the tie beam atthe top of piles, the other end is anchored in the stabilized soil. The improvements ofanti-sliding mechanisms are: on the one hand, it increases the lateral stiffness of rigid-frameretaining structure, limiting the lateral deformation of the whole structure effectively; on theother hand, a part of landslide load is dispersed to stablized soil through anchorage, makingfull use of the load bearing capacity of structure and layer.(2) Selecting a typical line-type colluvial landslide as the subjects, the paper usesFLAC3D finite difference software to study the suitability of the new composite structure inlandslide prevention. It calculates natural conditions, common plane rigid-frame micropilestructure and micropile-anchor composite structure separately, analyses deformation andstress-strain characteristics of the slope and the force distribution law and deformationcharactaristics of the structure. Comparative analysis shows that displacement field, stressfield, strain field of the slope reinforced by the new structure are more stable, topdisplacement of new structure is smaller than the commen, the coordinate deformation withslope is better, force distribution is more even and peak of force is smaller.(3) Through geomechanical model test, the paper studies the retaining effect andmechanism of5kinds of structures i.e. individual piles, vertical rigid-frame planar structure,inclined rigid-frame planar structure, vertical and inclined structure under the action ofprestressed anchor cable. The experimental results show that:the anti-sliding mechanism ofsingle pile is provided by its flexural capacity, shearing capacity and unique tensile capacity;tie beam on the top of pile group can enhance the integrity of the structure, formating thesoil-pile composite structure; the shear and flexural strength can be increased when the pileaxis tilted to the vertical angle with sliding surface, therefore selecting right axis angle in viewof the morphology and layout of different sliding surface can improve the anti-sliding effect;the prestressed anchor added on the top of the frame structure can increase the overallstiffness effectively, limit the lateral deformation and top displacement, uniform stress distribution and reduce the peak of internal force.(4) Based on the assumption that the new structure is a composite pile under lateral load,according to the calculation method of ransversely restraint Winkler elastic foundation beamand the principle of coordinate deformation, the article deduces the calculation formula of theprestress of anchor and internal force and deformation of pile. Based on the above,the paperputs forwards complete design steps and calculation methods.(5)Taking a subgrade losses slope located in Provincial highway316line of xinjiangprovince as the engineering background, the paper introduces the design procedures and thecalculation methods of the new structure in detail. Firstly,it predicts the most dangeroussliding face according to the calculation results of analysis module of slope stability ofLizheng software; then it calculates the landslide thrust;and after drawing up the cross sectionof the pile, it determines the spacing between combined structure through the calculation ofsoil arching effect and disturbing flow between piles; based on the engineering practice andthe requirements of related codes,it determines the form and size of connection beam;according to the design load on base of the anchor-pile load sharing ratio, it calculates theanchorage length; lastly, according to the ultimate resistance of cross section, the length ofpile is calculated through the analytical formula.