Model Test And Numerical Analysis Of Bearing And Deformation Performance Of Encaesd Steel Slag Column Under Cyclic Loading

In railway construction,it is necessary to conduct foundation treatment in soft soil area.The encased slag column,a unique foundation treatment technology,can speed up the rate of the consolidation of soft soil.Composite foundations need to performed excellently in the aspect of bearing capacity and deformation under cyclic loads induced by trains or vehicles,but the mechanical behavior of geosynthetic encased slag column subjected to sustained cyclic loading is a complex interaction involving soil,geosynthetic encased slag column and load characteristics.Therefore,it is very crucial to understand the mechanical behavior of the encased slag column under such loading conditions for the structural design of the soft foundation soil improved by the encased slag column.In consideration of the economical reuse of steel slag as industrial waste,the environmental protection of steel slag as column filler was determined through leaching test in this paper.This study mainly analyses the relationship between settlement and loads of geosynthetic encased steel slag column composite foundation,stress deformation regularity of column,stress transfer relations and accumulation regularity of pore water pressure.Furthermore,through the indoor model test of composite foundation,the study discusses the working performance of geosynthetic steel slag column in saturated soft soil foundation with different end bearing and encased reinforcement lengths under static and dynamic loads.Based on the test results and considering the change of plastic modulus of soil under cyclic loads,the parameters affecting the load-settlement response of composite foundation with a floating fully encased steel slag column are further analyzed by using ABAQUS software.(1)Model test on composite foundation with an encased steel slag column(1)In the floating columns,the column-soil synergy of partially encased steel slag column is better than that of fully encased steel slag column.Under long-term cyclic load,the radially expanded unencased steel slag column will have a certain cushioning effect.(2)The cyclic loading has little effect on the radial bulging deformation of fully encased steel slag column.Among the floating column,the radial deformation of partially encased steel slag column is larger than that of fully encased steel slag column,and the radial deformation of partially encased steel slag column is basically the same as that of fully encased steel slag column in the depth range.The bulging deformation of the end bearing encased steel slag column is larger in the range of 1.5d to 2.5d.(3)Under the short-term low amplitude cyclic load,the excess pore water pressure of the composite foundation continues to increase,while under the long-term high amplitude cyclic load,the excess pore water pressure of the composite foundation will appear a peak,and it will be stable or a trend of dissipation after reaching the peak.(4)After consolidation,the undrained shear strength of the composite foundation with an encased steel slag column is improved obviously,the permeability coefficient of the soil around the column is significantly reduced,and the water content of the composite foundation with an end bearing encased steel slag column decreases more than that with a floating encased steel slag column.(2)Numerical simulation of steel slag column composite foundation(1)For the numerical simulation of dynamic response of composite foundation under cyclic load,it is feasible to consider the change of plastic modulus,and it can effectively simulate the accumulated settlement and shakedown characteristic of composite foundation under cyclic load.(2)With the increase of loading amplitude and the decrease of loading frequency,the cumulative settlement of composite foundation will increase.(3)The ultimate bearing capacity of floating steel slag column composite foundation increases with the stiffness of geotechnical reinforced material.Nevertheless,when it is over a certain stiffness,it can be shown that the ultimate bearing capacity of composite foundation has little increase.(4)The bearing capacity of the composite foundation of floating fully encased steel slag column increase with the column length,but after reaching the critical column length,the increase of the column length has limited improvement on the stability of the settlement of the composite foundation.Thus,considering the load settlement behavior of the composite foundation in the static load and cyclic load stage,it is suggested that critical length of floating fully encased steel slag column should be 9d.