Research On The Development Of Composite Solidifying Agent For Shield Slag And Mechanical Properties Of Solidified Soi

The construction of urban rail transit in China produces hundreds of millions of cubic meters of shield residual soil every year.Due to the high moisture content,high compressibility,insufficient shear strength and poor engineering characteristics of shield residual soil,it cannot be applied to engineering construction.At present,the main treatment of shield residual soil is landfill,which requires a large amount of land and high cost of treatment,moreover,it is prone to landslides,debris flows and other geological disasters after extensive accumulation.Therefore,it is necessary to solidify the shield residual soil to provide necessary conditions for the application of shield residual soil in engineering construction.In this paper,the shield residual soil of Xinting Road station(D5-XK04)of Nanjing Metro Line 5 is taking as the research object.Based on the theory of silt solidification combined with the composition analysis of shield residual soil,the composite curing agent which can improve mechanical properties of the soil is developing.A series of physical and mechanical tests are carring out on shield residual soil with the composite curing agent,and the physical and mechanical parameters of solidified soil are measuring.Meanwhile,the strength of solidified soil is analyzing by X-ray diffraction(XRD)and scanning electron microscopy(SEM).Finally,the feasibility of solidified soil as subgrade filler is analyzing by finite element method.Through the above research,the main results are as follows:(1)The composite curing agent is developing to improve the physical and mechanical properties of shield residual soil.The optimal ratio of curing agent is portland cement: fly ash : calcium oxide : calcium sulfate : sodium polyacrylate =35:35:15:9:6.On the premise that the solidified soil meets the subgrade filling,it is the most economical when the agent is 8%.(2)The microstructure and mineral composition of solidified soil are analyzing by SEM and XRD,and the strength of solidified soil are analyzing by combining the macroscopic mechanical properties of shield residual soil and solidified soil.The results shows that the strength of solidified soil includes the hydration reaction of curing agent and the internal transformation of soil structure.(3)It is found that the compressive strength of solidified soil gradually increases with the curing age,and finally tends to be stable.The compressive strength of solidified soil increases significantly with the curing agent content increasing;the moisture content affects the final strength of solidified soil.By establishing the function of unconfined compressive strength with curing age,moisture content and composite curing agent,it provides a reliable reference for engineering practice.(4)The maximum compressive strength of the solidified soil improved by the composite curing agent can be more than 4 MPa.The mechanical and engineering properties of the solidified shield residual soil are able to meet the requirements of the specifications for subgrades.The solidified soil as the subgrade material has excellent performance in the finite element analysis,and can replace the soil-stone mixture as subgrade filler.