Model Test And Numerical Simulation Of Composite Foundation With Analogical Soil Fillings

The cushion is the core of the work of composite foundation.The deformation coordination and force transmission characteristics of the cushion are the key problems in the research of composite foundation.In order to explore the effect of the working performance of the composite foundation cushion,the research group uses multi trapdoor model test box device and uses analogical soil as test material.The research group arranges 9 sets of composite foundation cushion tests that two elements relative filling height h/(s-a)and relative distance between piles(s-a)/a are the two key elements.Comparing with the test results of sand,the rationality of the test is verified.The tests check the change of the displacement form of the particles in the cushion of the composite foundation and analyse the contact force of the base and the pile-soil stress ratio and pile efficacy.By using DEM to simulate the model test.Meanwhile,research group conducts tests of reinforced cushion for composite foundation,analyzing the influence of the reinforced cushion setting on deformation coordination.Through the analysis of the results of each test,the following conclusions are obtained below:(1)Monitor the displacement of particles in composite foundation cushion by using particle image testing(PIV),summarize the form of displacement.The particle displacement forms are divided into three modes by relative filling height h/(s-a).When h/(s-a)=1/3,the form is overall settlement pattern.When h/(s-a)=2/3,the form is triangle settlement pattern.When h/(s-a)=1,the form is equal settlement pattern.(2)When the base plate is subjected to unequal force,it will cause punching and cutting damage to the bottom plate.In order to prevent this problem,it is necessary to monitor contact force of base plate.Two times function fitting of base plate contact force is carried out,and two times function fitting parameter A is obtained.It is found that the larger the(s-a)/a between the relative piles is,the more uniform distribution of the contact force of the base plate and the smaller the A value of the fitting parameter.So the fitting parameter A can be used as the evaluation index of the deformation coordination of the cushion.(3)Pile-soil stress ratio and pile efficacy reflect the force transmission characteristics of the cushion in the composite foundation.Finding the influences of the change of h/(s-a)and(s-a)/a on the working characteristics of the composite foundation cushion and present the selection criteria for the height and the parameters of the spacing between the piles of the composite foundation.(4)By using DEM to simulate the model test and compare with the model test.The results agree well with each other,which verifies the rationality of the numerical simulation test process and the values of micro mechanical parameters.Analysing the angle contour and force chain figure,confirm the position of the slip surface and the relationship between the them.(5)Set 17 tests of composite foundation numerical simulation of reinforced cushion by using micro-parameters.The No.8 and No.9 test are set the conditions of the geogrid to be laid on 100 mm and 150 mm to make deeply research of the influence of the geogrid laying position on the deformation coordination of the cushion layer,comparing with the model test.It is known that the higher the laying position of geogrids is,the closer the numerical simulation results are to model tests.when the geogrid lay between 50mm~100mm,it can ensure that piles and soil both can develop its bearing capacity,and ensure the ability of deformation coordination.In this experiment,the small size model test box is carried out,which is inevitably limited by the model boundary conditions.And the tests only carried on the numerical simulation test of reinforced cushion,so the use of the test is different from the actual.In order to further explore,it is necessary to carry out study of the three-dimensional composite foundation cushion test.