Study On Model Test And Calculation Theory Of Single Column Bearing Characteristics Of Concrete Construction Waste Encased Column

Recycled concrete aggregates are used to replace the gravel core material of the encased stone columns.Forming a new foundation treatment method---recycled concrete aggregate encased column,which can be used to solve the problem that the gravel strength can not be fully used when the encased stone column is used to treat liquefied and soft soil foundations.In order to explore the bearing characteristics of concrete construction waste encased columns,a physical model test of the bearing characteristics of a single concrete construction waste encased columns was carried out.The effects of the encasement’s length,stiffness,and diameter on the bearing characteristics,deformation characteristics and the influence of the law of column’s stress transfer have been investigated.After analyzing the test results,it is found that the load-bearing characteristics of concrete construction waste encased columns are closely related to the crushing characteristics of the core material.In order to explore the breaking rules of the core material of concrete construction waste encased columns,this paper further carried out the confined compression test of the core material to study the relationship between its crushing characteristics and load-bearing characteristics.Finally,Based on the model test results of concrete construction waste encased columns,the calculation formula of bearing capacity of single column is derived by using limit equilibrium theory and elastoplastic theory.Through the above research,the following conclusions can be drawn through the above research.(1)When the encasement’s length of the column is 20%～90% of the column’s length,the bearing capacity of the columns can be significantly increased by extending the length of the geosynthetic,and the optimal encased length is about 6 times the pile diameter;The critical encasement’s stiffness of column is about 100 k N/m.The stiffness of the geosynthetic is less than the critical stiffness,the ultimate load of column can be significantly increased by increasing the encasing stiffness,When it is greater than the critical stiffness,increasing the stiffness has no obvious effect on improving the ultimate bearing capacity of the columns.When the diameter of the column is less than 10,local bending failures will occur within the depth of the column at the range of 10～30cm.In engineering applications,it should be ensured that the encased column has a reasonable diameter to avoid this phenomenon.(2)The bulging deformation zone of unencased and full-length encased columns are distributed in the depth of 0 to 5 times the diameter;Below this depth,the bulging deformation rate of the unencased column is almost 0,andthe full-length encased column is about 0.5%;The bulging deformation of partially encased column mainly occurs at the transition position between the encased and unencased sections;Increasing the encasement’s stiffness can effectively restrain the bulging deformation of the column.When the stiffness of the geosynthetic reaches 49 k N/m and above,the radial deformation rate of the columns with different encasement’s stiffness is almost equal in the region below 4d.(3)The stress ratio of column’s bottom to top(Pb/P0)can be significantly increased by using geosynthetic to encased the oncrete construction waste columns.When the encasement’s stiffness reaches 73.81 k N/m,the Pb/P0 ratio reaches 44%,and increasing the stiffness of encasement almost can not improve the ratio of Pb/P0.The maximum variation of Pb/P0 of unencased column with the settlement of column top is only 1.6%.The difference in Pb/P0 of partially encased columns is not obvious,and finally only about10%,which indicates that the bearing characteristics of full-length encased and partially encased columns are different.The former is a friction end bearing column,and the unencased column is a friction column,the bearing mechanism of partially encased columns lies between them.(4)The core material of the concrete construction waste encased columns was damaged during the bearing capacity of the column.Through the confined compression test of the core material,it is found that the failure modes of the core material are broken(30%),ruptured(20%)and fraied(25%).Increasing the relative density of the core material and improving the gradation can reduce the breakage rate of core material,during the construction and bearing of the column,the corresponding load should be less than14 k N to avoid excessive crushing of the core material due to excessive load.