| With the in-depth implementation of the national strategies of "One Belt,One Road" and "Western Development",there are many slope backfill projects and combined support structures in loess areas.The soil pressure is closely related to the deformation and displacement pattern of the support structure,and the combined support structure is more complicated than the single support structure.In this paper,according to the requirements of a loess slope backfill project and the characteristics of combined retaining structure,the optimal cement mixture and physical and mechanical properties of cement-improved loess are studied through indoor geotechnical tests,and the non-limiting active earth pressure and the simplified calculation method of active earth pressure of pile-bearing box-type retaining wall with finite fill width are studied through numerical simulation and theoretical analysis,and the main research contents and conclusions are as follows:(1)Indoor geotechnical tests were conducted to study the effects of three factors,namely,cement admixture,compaction degree and age,on the maximum dry density,shear strength and unconfined compressive strength of cement-amended loess.The test results show that the maximum dry density of cement-improved loess increases and then decreases with the increase of cement admixture;the maximum cohesion and unconfined compressive strength of cementimproved loess are the highest at 14% of cement admixture,and the compaction is linearly related to the angle of internal friction,cohesion and unconfined compressive strength at 7 d;the unconfined compressive strength of cement-improved loess is approximately logarithmic with the age,and the maximum cohesion and unconfined compressive strength of cementimproved loess are approximately logarithmic with the age.The unconfined compressive strength of cement-improved loess is approximately logarithmically related to the age and the cohesive force is approximately linear;the optimum cement mixture is 14% when cementimproved loess is used as slope backfill.(2)Based on the actual project,the numerical analysis model of the pile foundationbearing platform-box-type retaining wall combined support structure was established by using ABAQUS finite element software,and the influence law of backfill parameters on the lateral earth pressure of pile-bearing box-type retaining wall was studied,and the numerical calculation method of non-limiting active earth pressure of finite fill pile-bearing box-type retaining wall was proposed.The results show that the lateral earth pressure of the pile-bearing box-type retaining wall belongs to the non-limiting active earth pressure in actual operation,and the displacement mode of the retaining wall can be approximated as the rotation mode around the bottom of the wall(RB mode);the influence of the cohesion of the fill,the internal friction angle and Poisson’s ratio on the maximum earth pressure of the retaining wall is very small,and the maximum lateral earth pressure of the retaining wall increases linearly when the weight increases,and the earth pressure of the retaining wall is almost constant when the widthto-height ratio of the backfill is greater than 1.2.(3)According to the displacement mode(RB mode)of pile-bearing box-type retaining wall,ABAQUS finite element software was used to study the change law of backfill slip crack surface and earth pressure distribution of basement exterior wall when the retaining wall rotates around the bottom of the wall to reach the ultimate active state,and the analytical formula of active earth pressure of finite fill was established and the influence law of relevant parameters was discussed.The results show that: when the cohesion of fill,internal friction angle and wallsoil friction angle increase,the active earth pressure of this formula gradually decreases,and the error with Rankine theory also gradually decreases;when the backfill width-height ratio is greater than 0.9,the active earth pressure no longer increases. |
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