Study On Shear Behavior And Reinforcement Effect Of Vibroflotation Gravel Piles Composite Foundation In High-fill Embankment

The stability of gravel piles composite foundation is very important in the filling process of high embankment at soft soil area.In general design,the formulas given in the standard are used to calculate the shear strength parameters of composite foundation,which are used to obtain the stability coefficient of composite foundation.However,this method only consider the factor of piles area replacement.In practice,gravel piles would form drainage channels in composite foundation,which accelerates the consolidation of foundation soil and improves the shear strength of composite foundation.Therefore,it is necessary to study the shear characteristics of the gravel piles composite foundation.In this paper,after reading a large number of papers,the research process and obtained results of domestic and foreign scholars for the stability of composite foundation are summarized.On this basis,the model experiment of vibroflotation gravel piles composite foundation was innovatively carried out for the first time.The results of two ways of shear strength parameters of composite foundation are compared,which are obtained by test method,calculated by standard method and Priebe method.The numerical calculation of two-dimensional section of high embankment filling is carried out by using the soil hardening model.The characteristics of deformation and dissipation of excess pore water pressure in two kinds of piles distance’s composite foundation are analyzed.Using the strength reduction method,the difference of two way’s results of filling stability coefficient is compared,which are calculated by the way of normal algorithm considering the drainage effect and the way of standard algorithm only considering the area replacement factor.The following conclusions are drawn:1、During the shear process of composite foundation,piles and soil have a good deformation coordination.With the increase of piles’ replacement rate,the shear deformation of composite foundation is restrained.2、The standard method result is smaller than the test method result in two piles’ replacement rate composite foundation.Therefore,The standard method which only consider the factor of piles area replacement rate to calculate the shear strength parameters of composite foundation is insufficient.The improvement of shear strength of composite foundation due to the drainage effect of piles should also be considered.3、Two different piles distances of 1.5m and 2.0m composite foundation are selected to calculate.in the filling process.The results show that the deformation and dissipation of excess pore water pressure of piles distance of 1.5m and 2.0m of composite foundation have a little difference.It also shows that after selecting an appropriate pile distance,shorten the piles distance has a little effect on deformation and dissipation of excess pore water pressure in the high embankment filling.4、There are obvious differences in the stability of high embankment filling in soft soil area between the methods of normal algorithm and standard algorithm.The standard method results which only consider the geometric elements of the permutation is smaller than the normal algorithm results.It indicates that the standard method is conservative in the calculation of stability of embankment filling.5、The preliminary research of this paper suggests that there are some deficiencies in the calculation of shear strength parameters of gravel piles composite foundation and the stability coefficient of high embankment filling by the standard algorithm.Further researches will be done in the theory of drainage consolidation.