| With the continuous expansion of infrastructure construction areas such as line engineering,airports,water conservancy and mine to more complex and dangerous mountainous areas,engineering landslide disasters occur frequently,and pile projects are commonly used to stabilize landslides.Landslides are commonly characterized by progressive defornation and failure,and the interaction between this process and pile is complex.Physical simulation and numerical simulation methods are widely used to study the mechanism of progressive landslides and pile-soil interaction.However,the relevant theoretical analysis and calculation methods are still in constant exploration and need more deeply research.This paper takes "phenomenon and data analysis of generalized centrifugal model test ? theoretical method establishment and theoretical formula derivation ?validation analysis of theory and test results ? application analysis of typical engineering cases" as the research idea,takes the non-piled and piled cohesive landslides as the research object,and takes centrifugal model tests and theoretical analysis as the research means to analyze the progressive failure mechanism and pile-soil interaction of cohesive landslides.The major research results are as follows.(1)The results of centrifugal model tests of cohesive landslide revealed the whole process of the initial formation and development of the failure surface,and revealed the variously dadegration of shear strength paremeters of soils along the spatial failure surface with the varied shear strain is the fundamental reason for the progressive deformation and failure of landslide.According to the test phenomenon,considering the "three-stage" linear relationship between the shear displacement and the shear strength parameters,the proposed modified unbalanced lateral transfer method is proposed in this paper.In this method,the calculation formulas of residual strength and residual shear displacement are firstly established,the spatial variation characteristics of shear strength parameters of soil along the failure surface in the whole process of progressive deformation and failure of landslide can be thusly determined,and the physical meaning of corresponding stability calculation results is more clear and cosistent with the reality,which contributes to improving the accuray and relaiability of resluts of landslide monitoring and early warning.(2)Based on Mohr Coulomb strength theory,the calculation formula of angle of linear failure surface behind pile in cohesive landslide is established considering the influence of slope angle.Based on the rotation theory of maximum principal stress,the mohr circle coordinate translation method is conducted,and the analytic expressions of active earth pressure coefficient and active earth pressure between neighbouring piles are derived and established considering vertical soil arching effect,then,the analytical formula of lateral earth pressure acting on pile based on Ito horizontal soil arching effect is modified by taking the active earth pressure between neighbouring piles as the boundary condition.Compared with the centrifugal test results and previous results,the proposed theoretical solution is closer to the centrifugal test results,which proves the correctness of the theoretical solution in this paper,and shows that the proposed calculation method can provide a theoretical basis for the design of single row piles.Further parameter analysis shows that: the lateral earth pressure acting on pile decreases with the increase of pile spacing,increases with the increase of pile width,significantly increases with the increase of slope angle,and increases with the increase of pile-soil interface roughness,therefore,it is suggested that in the design of pile engineering,1)smaller pile spacing should be adopted near the central section of slope,while larger pile spacing should be adopted on both sides of slope;2)The width of piles can be increased and the number of piles can be reduced;3)the slope behind piles should be slowed down;4)the roughness of pile-soil interface should be increased.(3)Based on the modified Ito plastic theory,Winkler elastic foundation beam theory and soil strength theory,the nonlimit active earth pressure coefficient between neighbouring piles with finite pile row spacing is derived and established considering the vertical soil arching effect,and then the analytical formula of the nonlimit lateral earth pressure acting on the two rows of piles without coupling beam at pile top is established considering the horizontal soil arching effect;the analytical formula of the lateral earth pressure acting on the two rows of piles with the semi infinite pile row spacing is consistent with that of the single row piles.Compared with the centrifugal test results,the distribution of earth pressure is similar between the theoretical solution and the test value,and the error between them is 1.08% ? 12.2%,which to a certain extent shows the rationality and applicability of the proposed theoretical calculation method.The proposed calculation method can provide theoretical basis for the reasonable distribution of landslide driving forces undertaken by the double row piles.(4)Considering the consistence of deformation and forces of double row piles,this paper puts forward a comprehensive method to determine the reasonable pile row spacing between the two rows of piles without coupling beam at pile top based on the required threshold of ratio of lateral earth pressures acting on the front row pile to that on the rear row pile,the displacement ratio of the double-row piles at their top,the ratio of the sum of lateral earth pressures acting on the double-row piles to the limit lateral earth pressure acting on the single pile,and the landslide safety factor Fs.Taking the landslide safety factor Fs greater than 1.0 as the sufficient and necessary condition,pile row spacing of double-row piles installed in the prototype slope of centrifugal model is determined to be 6 ? 22 m by graphic method.(5)Baed on the proposed modified unbalanced lateral transfer method,the pile post-reinforced effect evaluation method considering the influence of deformation and pile-soil interaction is established.The pile post effect evaluation of the Panzhihua airport fill ladlisde and Badu secondary landslide along Nanning Kunming railway is carried out with this method.The theoretical results show that the ratio of landslide driving forces respectively undertaken by the front,middle and rear row of pile in the Panzhihua airport fill landslide is 1:0.26:2.96,showing the teamwork ability of the three rows of piles are poor to satbilize the landslide.The caculated value of landslide driving forces taken by the single pile is significantly greater than the designed value,and the safety factor Fs of landslide gradually decreases during the evolution process of creep deformation ? uniform deformation ? accelerated deformation ? critical deformation.The ratio of landslide driving forces respectively undertaken by the first,second and third rows of piles in Badu secondary landslide is 1:1.18:1.09,showing the teamwork ability of the three rows of piles are good to satbilize the landslide.The caculated value of landslide driving forces taken by the single pile is slightly less than the designed value,and the safety factor Fs of the landslide considering the design resistance of three pile rows is 1.105,which is nearly eaqual to the designed safety factor.The analysis results of the above two cases are in accordance with their respective field results,which shows that it is feasible to use the proposed method to validate the rationality of the designed landslide drving forces undertaken by single and multiple rows of piles without coupling beam at pile top and quantify the dynamic stability of the piled landslide. |
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