Study On Mechanical Property Of Pile Anchor-Frame Anchor Combined Slope Supporting Structure And Its 0ptimum Design

With the gradual implementation and in-depth promotion of the national strategies of"western development"and"one belt and one road",a large number of high-steep slopes appear in the engineering.The pile anchor-frame anchor composite supporting structure is widely used in the reinforcement of high-steep slopes,especially under the condition of high limit of slope movement and limited engineering space,which is more advantageous.It is superior in the cases of higher limited displacement and engineering space limitations,because the tiebacks on slope surface can play an active reinforcement to limit slope displacement,as well as achieve a passive reinforcement of the stabilizing piles at slope toe to save space.However,how to allocate the residual sliding force of slope to the two structures has not been solved theoretically,which is likely to lead to engineering waste or design failure in practical application.Based on the slope treatment project of a certain section of Zengcheng to Conghua highway,relevant study on the distribution mechanism of residual sliding force of the slope aiming at the problem of unclear stress mechanism of pile anchor-frame anchor structure is carried out by theoretical analysis and numerical simulation.The main research results are as follows:?1?Study on mechanical properties of slope support structure.Based on the cooperative working principle,a mechanical calculation model of pile-anchor deformation coordination is proposed.Under the same condition of landslide thrust,the internal forces of two types of anti-slide piles are calculated in tension stage and working stage.The results show that:compared with the ordinary pile,the prestressed anchor cable anti-slide pile top horizontal displacement decrease about 54.83%,maximum shear decreases by about 26.17%,and the maximum pile bending moment decreases by about 50.31%.The negative bending moment is in pile body 1/3 place which makes the internal force distribution more reasonable.Taking the prestress of anchor cable as the concentrated force at the end of beam,the internal forces at each stage of prestressed anchor cable frame beam are calculated by using the inverted beam method and winkler elastic foundation beam method respectively.The results show that:The calculation result of internal force of beam on elastic foundation is small.Compared with the tension stage,the maximum shear force and maximum bending moment of the frame beam in the working stage increased by about24.67%and 53.34%respectively,and the maximum shear force and bending moment of the secondary frame beam were about 1/2 and 2/3 of that of the primary frame beam.?2?Study on the distribution mechanism of residual slope sliding force on composite structure.According to pre-set resistance to change simulation unit parameters and adjust the position and sequence of frame-pile-anchor structure layout,numerical simulation test is designed to use FLAC^3Dsoftware to analyze the slope displacement,stress,safety coefficient under various working conditions obtaining the structure combination meeting the test control conditions and determine the proportion of glide force distribution.The results show that the support ratio of pile anchor-frame anchor structure under the condition of unknown sliding surface and known sliding surface is about 7:3.When the support sequence is changed,the support ratio of pile anchor-frame anchor structure is about 6:4 from top to bottom when slope support is carried out.When there is a secondary sliding surface,the frame-anchor structure has a good limiting effect on the sliding body above the secondary sliding surface.Under the condition that the sum of sliding forces borne by pile-anchor and frame-anchor structure remains unchanged,the optimal design resistance ratios of prestressed anchor cables in the upper part of grade 3,4 and 5 slope are4:1:1,3:2:1:1,3:2:2:2:1:1,respectively.?3?Study on parameter optimization of pile anchor-frame anchor composite supporting structure.Based on the calculation model and the parameters of rock and soil mass of the slope in the section K8+280?K8+400,the value of each structural parameter is changed to study the relationship between the change trend of slope stability and the mechanical characteristics of the structure itself.The results show that the slope safety coefficient increases with the increase of the length of anti-slide pile,the size of pile section and the length of anchorage segment of anchor cable,but the change trend tends to be gentle when reaching a certain value.With the increase of the distance between anti-slide piles and the inclination Angle of anchor cables,it first increases and then decreases.From the perspective of economy,the structural optimization model is established.The constraint conditions is adjusted based on the above research results,and the preliminary design scheme is optimized with the engineering cost as the objective function.After optimization,the total cost is reduced by about 18.13%.?4?Application of research result in engineering practice.According to the engineering geological conditions of slope in a section of Zengcheng expressway and the optimization results of design parameters,the landslide thrust is distributed according to the ratio of 7:3 to calculate the resistance of pile-anchor-frame-anchoring.Long-term monitoring of slope state after the completion of construction shows that the reinforcement project after the implementation of regional slope deformation gradually convergence.The overall slope remaining basically stable and anti-slide pile top displacement value does not exceed allowable values of slope verifies validity of the research conclusion and the rationality of the optimal design scheme.