Reasearch On Interface Characteristics Between Inner Pile And Outer Carbonized Soils Of The Carbonized Composite Pile

The carbon composite pile（GCP）technology is a new type of composite pile which is formed by mixing active MgO with soil and then carbonizing it by inserting porous pipe pile.In this paper,three representative soils,silty soil,clay and silty clay,are selected to systematically study the interfacial characteristics of inner and outer core of carbonized composite piles through laboratory tests and theoretical analysis.The main research contents and achievements of this paper are as follows:（1）The effects of soil properties,carbonization time,magnesium oxide content,initial water content and normal stress on the interface shear strength of carbonized soil-permeable concrete were studied by laboratory shear test.The results show that the soil around the pervious concrete can be effectively carbonized by CO₂,and the bond strength between pile and soil can be generated.Carbonization time,magnesium oxide content and initial water content of soil are the important factors affecting the shear strength of the interfacial between inner and outer core of the carbonized pile,and the optimal values exist.The optimum initial water content of silt sample is 25%,and the maximum interfacial shear strength is 572k Pa.The best mg oxide content of clay samples is 20%,and the maximum interfacial shear strength is 342k Pa.The optimum magnesium oxide content of silty clay carbide pile is 20%,the optimum initial water content is 25%,and the interfacial shear strength can reach 311k Pa.（2）The interfacial shear stress-shear displacement curve（τ-（35）curve）has folded and hyperbolic lines.When the normal stress is 400k Pa,theτ-（35）curve of silty clay samples changes from fold to hyperbola and then to fold with the increase of carbonization time,which is different from that of silty clay and clay tests.With the increase of initial water content,the curve changes from folded to hyperbolic.With the increase of MgO content,the curve changes from folded to hyperbolic.The shear stress of silty clay decreased more than 60%,and the maximum stress decreased more than that of silty clay and clay.（3）Through unconfined compression test,the relationship between interfacial shear strength,internal friction Angle,cohesion and unconfined compressive strength（q_u）was studied under different soil properties,normal stress,carbonization time,magnesium oxide content and initial water content.The results show that within a certain range of unconfined compressive strength,cohesion is positively correlated with unconfined compressive strength,but internal friction Angle has little correlation with unconfined compressive strength.Finally,a prediction model of interfacial shear strengthτ_f=Aq_u+B based on unconfined compressive strength is established.（4）The relationship between different soil properties,normal stress,carbonization time,magnesium oxide content,interfacial shear strength,internal friction Angle,cohesion of initial water content and change value of water content（difference of water content before and after carbonization）was studied by using CURVE estimation method of SPSS software and water content test.The results show that within a certain range of water content variation,the cohesion increases with the increase,while the internal friction Angle has little correlation with the water content variation.Finally,a strength prediction model τ_f=CΔw+D based on moisture content variation value is obtained.（5）Through multiple linear regression analysis,the effects of normal stress,carbonization time,magnesium oxide content and initial water content on the shear strength and strength of different carbonized soil-permeable concrete interface were studied.The results show that in a certain range,the interfacial shear strength of silt sample is most affected by the content of magnesium oxide,the interfacial shear strength of clay sample is most affected by the normal stress,and the interfacial shear strength of silty clay sample is most affected by the normal stress.