Study On Vertical Bearing Mechanism Of Cement-soil Composite Pile With Silica Fume

Cement-soil reinforced composite pile is a new type of composite pile formed by implanting high-strength core pile into the same core of cement-soil mixing pile before the initial setting of cement-soil.Compared with the single use of cement soil mixing pile,the pile type has higher engineering economic benefits.However,the production and use of cement need to consume a lot of energy and produce a lot of carbon dioxide and other pollutants.Silica fume is a kind of volcanic ash material with large specific surface area and high activity.It can refine the pore size by filling micropores and producing dense mixture,thus making the structure denser and improving the mechanical properties of soil.However,silica fume is an extensive industrial by-product in China,and many enterprises have not yet carried out reasonable resource recovery and reuse.Therefore,this paper uses silica fume instead of part of cement to make rigid composite piles,which provides a feasible new method and new idea for the recycling of silica fume while reducing the amount of cement.Based on the indoor model test,combined with the research method of finite element numerical simulation analysis,this paper studies and analyzes the vertical bearing mechanism of silica fume cement soil stiff composite pile.The main research results are as follows :(1)With the increase of cement content from 15% to 25%,the strength of pure cement soil test block increases by 15%～20%.When the proportion of silica fume in cementitious materials increases from 0% to 50%,the unconfined compressive strength of silica fume cement-soil test blocks increases first and then decreases.The test results show that when the proportion of silica fume in the cementitious material is 30%,the unconfined compressive strength of the silica fume cement-soil test block reaches the peak,which is 40%～60% higher than that of the pure cement-soil test block.(2)The results of MIP pore distribution test show that when the proportion of silica fume in the cementitious material continues to increase,the maximum mercury intake continues to decline,and the pore volume of the silica fume cement soil test block decreases accordingly.This shows that the cementitious products generated inside the test block are increasing,and the pore-filling effect is more significant.(3)Under the same pile top load,the axial force of the core pile of the silica fume cementsoil composite pile is less than that of the core pile of the pure cement-soil composite pile.The pile tip resistance of silica fume cement soil composite pile is less than that of pure cement soil composite pile.When the curing age is 7 d and the pile top load is 5.88 k N,the tip resistance of the silica fume cement-soil composite pile is 3.4% lower than that of the pure cement-soil composite pile.When the curing age is 28 d and the pile top load is 5.88 k N,the tip resistance of the silica fume cement-soil composite pile is 6.8% lower than that of the pure cement-soil composite pile.(4)Through ABAQUS finite element numerical simulation analysis,it can be obtained that when the curing age is the same and the load applied to the pile top is the same,the side friction resistance of the silica fume cement soil pile-core pile is smaller than that of the pure cement soil pile-core pile.When the pile depth is the same and the pile top load is the same,the axial force of the silica fume cement soil composite pile is smaller than that of the pure cement soil composite pile.When the pile top load is the same,the ratio of the core pile load of the pure cement soil composite pile to the load of the cement soil pile is greater than the ratio of the core pile load of the silica fume cement soil composite pile to the load of the silica fume cement soil pile.