| The topography is complex,and the embankment filling material consists mostly of soil-rock mixtures in the mountainous area of Southwest China.It is inevitable that the highway construction will encounter sections that require high levels of fill in this area.In order to ensure the smooth passage of the highway through the valley without hindering the traffic,and to quickly drain the surface water along the highway,the number of culverts were set up under the high fill embankment is increasing.At present,the research on soil arching effect of high fillings soil-rock mixture at the top of culvert and the interaction mechanism between embankment and culvert is not well understood,which leads to appear a variety of issues in high filling embankment culvert.In order to improve the earth pressure calculation theory of high filling around culverts,it is necessary to seek the optimal and most reasonable culvert load reduction scheme,improve the safety of high filling culvert structure and reduce the probability of culvert engineering diseases.Combined with indoor model test,numerical simulation and theoretical derivation,the mechanical characteristics of soil-rock mixture filling and the influence of culvert parameters on soil arching effect at culvert top has been studied.At the same time,the paper has proposed the earth pressure calculation method of high filling soil-rock mixture embankment culvert,and studied the load reduction mode of vertical earth pressure at the top of culvert,and studied the influence of culvert soil contact parameters and the shape of unloading area on the vertical earth pressure reduction effect at the top of culvert.The specific research work is as follows:(1)The mechanical properties of soil rock mixtures with five different rock block proportions has been studied.Through particle screening,compaction test and direct shear test of coarse-grained soil,the particle crushing characteristics and shear failure characteristics of soil-rock mixture has been studied.The particle breakage characteristics of soil-rock mixture under the standard heavy compaction test II-1,the shear failure characteristics and mechanical characteristics of soil-rock mixture under the direct shear test of coarse-grained soil has been revealed.(2)By the indoor model test of embankment culvert of soil-rock mixture,the variation law of culvert mechanical characteristics with filling height has been studied.The results show that with the increase of filling height at culvert top,the vertical earth pressure calculated by model test and soil column method increases,and the difference between them was also increasing.When the top fillings of soil-rock mixture reaches a certain height,soil arching effect occurs inside the fillings.Due to the influence of additional pressure on the top of culvert,the vertical earth pressure at the top of the culvert in high fill embankment is obviously higher than the vertical earth pressure calculated by the soil column method.(3)The variation law of soil arching effect in culvert top filling under different structural parameters has been studied.The influence of rock block proportion,filling height,Poisson's ratio of soil-rock mixture,culvert slab thickness,foundation stiffness and ratio of culvert width to culvert height on soil arching effect of top filling of upper buried slab culvert were studied by numerical simulation method.Based on the calculation results of the vertical earth pressure at the top of the culvert under the influence of the above parameters,the design chart and fitting equation of the earth pressure were established,which were used to evaluate the vertical earth pressure and bending moment on the top of the same type of slab culvert.(4)A modified equation of vertical earth pressure at the top of culvert was proposed,which can consider the stone content of filling and non limit stress state.Based on the nonlinear regression analysis of the numerical simulation results,a modified equation of vertical earth pressure at the top of culvert was proposed,which can consider the stone content of filling and the state of non limit stress.The modified theoretical model can more accurately calculate the vertical earth pressure concentration factor of embankment culvert top of high fill of soil rock mixture.The results show that the difference between the modified calculation results and the numerical simulation results was less than 5%.(5)The variation laws of vertical earth pressure on the top of the culvert under load reduction condition was studied,and the design methods of vertical earth pressure reduction at the top of culvert-embankment with soil-rock mixture under load reduction condition were improved.When the thickness and the density of expanded polystyrene(EPS)geofoam blocks on the top of culvert top EPS plate were changed,the variation of vertical earth pressure and vertical earth pressure load reduction rate of culvert top with filling height has been discussed.The results show that with the thickness of EPS slab increases,the vertical earth pressure at the top of culvert decreases and the load shedding rate increases.When the thickness of EPS slab at the top of culvert is more than 0.6m,the vertical earth pressure at the top of culvert does not decrease obviously.By considering the influence of foundation stiffness on the load reduction characteristics of culverts,the existing simplified design method of EPS slab on culvert top has been supplemented and modified.At the same time,the "neutral point" theory was applied to the calculation process of vertical earth pressure at the top of culvert under the condition of load reduction,and the accuracy of the vertical earth pressure concentration factor at the top of culvert and the vertical pressure at the bottom of culvert calculated by "neutral point" theory has been verified.(6)The influence of culvert-soil interface parameters and the unloading zone geometry on the earth pressure reduction rate of the culvert has been studied.The influence of contact interface parameters and filling height above culvert top on vertical friction force between side wall and side fill of slab culvert has been discussed under the condition of load shedding and without load shedding.The direction of the vertical friction force on the side wall and the variation law of the vertical friction distribution curve has been analyzed.The contribution rate of vertical friction to the vertical load of bottom slab has been calculated when the side fill was compacted or not.The results show that,under the condition of load shedding,the contribution rate of vertical friction to the total vertical pressure of the bottom slab was greater than the contribution rate of the culvert without load reduction.In addition,the load reduction rates of vertical friction force at culvert side,vertical earth pressure at culvert top and vertical earth pressure at culvert bottom has been compared under different geometric shapes of load shedding area,and an optimal geometric shape of load shedding zone has been proposed.(7)The influence of culvert-soil interface parameters and the geometry of the unloading area on the load shedding rate of the culvert earth pressure has been studied.Based on the optimal geometry of load shedding zone,the variation of vertical load reduction rate between the culvert top and the bottom with the elastic modulus of lightweight load reduction material and friction coefficient of culvert-soil interface has been analyzed under the conditions of compaction and uncompaction of side fill.The results show that,with the increase of elastic modulus of lightweight load shedding material(EPS),the vertical earth pressure reduction rate of culvert top decreases under the compaction condition.Compared with the case of uncompacted filling,the vertical earth pressure reduction rate of culvert top under the compaction condition of culvert side fill was greater.Moreover,the prediction equation of vertical load reduction rate and the calculation equation of vertical earth pressure concentration factor under the condition of load reduction has been established. |
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