Triaxial Shearing Experimental Study On Strength And Deformation Behaviors Of Lightweight Soil Cemented By MICP

As a new geotechnical filling material,expanded polystyrene(EPS)lightweight mixtures over recent years have been used in bridge abutment backfill,roadbed of railway,weak foundation of roads,slope engineering and so on.This material has advantages of low unit weight and high intensity,energy conservation and environmental protection,the convenience for construction.In order to research the expanded polystyrene(EPS)lightweight soil,a series of indoor consolidation drainage triaxial shear tests were carried out aim to sand-EPS beads mixtures to investigate the strength and deformation characteristics of unreinforced and microorganism reinforced lightweight soil,these tests analyze the effects of EPS content,confining pressure and cementation degrees on the mechanical properties of lightweight soil.The major research contents and conclusions of this paper are as follows:(1)For lightweight soil without cementation,four different EPS volume contents(0,5%,10%,15%)were selected to carry on consolidated drained triaxial test under four different effective confining pressures(0.1,0.2,0.3,0.4MPa).The test results show that the dilatancy,maximum dilatancy angle,secant modulus,elastic modulus,peak and residual deviatoric stress of lightweight soil decrease with increasing the content of EPS,the fitting equations of deviatoric stress and mean effective stress in peak and residual state with EPS content and confining pressure are also derived.(2)For microorganism reinforced lightweight soil,we cemented the specimens by the microbially induced calcite precipitation(MICP)on the basic of unreinforced lightweight soil,which the content of calcium carbonate reach 5% to investigate the effects of EPS content and confining pressure on strength and deformation characteristics of reinforced lightweight soil,and by comparing with the unreinforced lightweight soil,it is concluded that the volume dilatancy,the maximum dilatancy angle,secant modulus,elastic modulus,peak and residual state deviatoric stress of reinforced lightweight soil decreased with increasing the EPS content.The strength of lightweight soil was significantly improved at the same confining pressure and EPS content after cementation by MICP,and the improvement was more obvious when the confining pressure was higher and EPS content was lower,it is also concluded that the volume dilatancy tendency of reinforced lightweight soil was more obvious in the same condition.The equations of deviatoric stress,mean effective stress and stress ratio at peak and residual state with EPS content and confining pressure are also given in this paper.(3)For lightweight soil with different cementation degrees,this paper selected the lightweight soil at 5% EPS content to cement by MICP,which the calcium carbonate content reach different degrees(0,1%,3%,5%)to investigate the influence of confining pressure and reinforcement degrees on the strength and deformation characteristics.It was found that the volume dilatancy,the maximum dilatancy angle,secant modulus,peak and residual devaiteric stress of lightweight soil increased with increasing the calcium carbonate content.This paper also gave the equations of deviatoric stress,mean effective stress and stress ratio at peak and residual state with confining pressure and calcium carbonate content.