Study On Thixotropic Mechanical Properties Of Fiber-Reinforced Loess

The thixotropic property refers to the phenomenon that the strength of soil decreases after disturbance and gradually recovers with time after disturbance stops.In practical engineering,the soil disturbance will make the decrease of strength of foundation soil,the slope instability,produce the engineering disasters,such as post-construction settlement for old embankment engineering of thixotropic characteristics of soil due to its strength has a sharp growth,to master the law of strength increasing,to study the long-term stability of the embankment slope has important engineering application value.Based on many scholars at home and abroad on the basis of study of thixotropy,polypropylene reinforced loess as the research object,using homemade can separate pressure device preparation of different fiber content,moisture content,dry density,the different period of thixotropic reshape the soil specimen,through the indoor experimental research on the rule of the strength of soil under different influencing factors of recovery,and defines the thixotropic parameter,The thixotropic parameters can reflect the thixotropic strength of soil under different working conditions.The research results are as follows:(1)Through direct shear test,the results show that: under the condition that the fiber content,dry density and thixotropy period remain unchanged,the cohesion increases first and then decreases with the increase of moisture content,and reaches the peak at the optimal moisture content.The internal friction Angle fluctuates with the increase of moisture content,with little change.With the increase of dry density,the cohesion and internal friction Angle of the fiber-reinforced loess increase with the fiber content,water content and thixotropy period being constant.Under the condition of constant fiber content,moisture content and dry density,the shear strength parameters increased significantly from 0 to 40 days with the increase of thixotropic period,and gradually leveled off after 40 days.The shear strength thixotropic parameter Tτ,σ is defined as the ratio of the shear strength of the specimen at time T standing after disturbance to that at time 0 standing after disturbance.In this case,σ is selected as 100 kPa.The test results show that:Under the condition of constant dry density,fiber content and thixotropy period,the thixotropy parameter of shear strength changes slightly with the increase of water content.When the water content is 22%,the thixotropy parameter and thixotropy of shear strength are the largest.When water content,fiber content and thixotropy period remain unchanged,the thixotropy parameters of shear strength show an increasing trend with the increase of dry density.When the dry density is 1.7g·cm-3,the thixotropy parameters and thixotropy of shear strength are the highest.When dry density,water content and fiber content remain unchanged,the thixotropic parameters of shear strength increase rapidly during 0-40 d and tend to be flat during 40-120 d with the increase of thixotropic period.(2)Through the unconfined compressive strength test,the results show that the unconfined compressive strength increases with the increase of fiber content under the condition that the moisture content,dry density and thixotropy period remain unchanged.Under the condition of constant dry density,fiber content and thixotropy period,the unconfined compressive strength increases first and then decreases with the increasing of water content,and reaches the peak value at the optimum water content.At the same water content,fiber content and thixotropy period,the unconfined compressive strength increases with the increase of dry density.Under the same dry density,water content and fiber content,the unconfined compressive strength gradually increases with the increase of thixotropic period,and increases rapidly during 0-20 d and slowly during 20-120 d.The ratio of the unconfined compressive strength at time T after disturbance to the unconfined compressive strength at time 0 after disturbance is defined as the thixotropic parameter Tq of the unconfined compressive strength.The test results show that:When the moisture content,dry density and thixotropy period remain unchanged,the thixotropy parameter of unconfined compressive strength increases first and then decreases with the increase of fiber content.When the fiber content is 0.5%,the thixotropy parameter and thixotropy of unconfined compressive strength are the largest.Under the condition of constant dry density,fiber content and thixotropy period,the thixotropy parameter of unconfined compressive strength decreases slightly when the moisture content is 16%-18%,and gradually increases when the moisture content is 18%-22%,and the thixotropy is the strongest when the moisture content is 22%.When the moisture content,fiber content and thixotropy period remain unchanged,the thixotropy parameters of unconfined compressive strength show an increasing trend with the increase of dry density,and the thixotropy is the strongest when the dry density is1.7g·cm-3.When water content,dry density and fiber content remain unchanged,the thixotropic parameter of unconfined compressive strength increases continuously with the increase of thixotropic period,and increases rapidly during 0-20 d and slowly during 20-120 d.(3)The results of the undrained triaxial shear test show that the cohesion increases gradually with the increase of the fiber content under the same water content,dry density and thixotropy period,while the variation of the internal friction Angle is not obvious and the range is relatively small.When water content,dry density and fiber content remain unchanged,the cohesion tends to rise with the increase of thixotropic period,and the internal friction Angle fluctuates,with a small range within 3°.The triaxial thixotropic parameter Tτ,σ is defined as the ratio of the shear strength at time T after perturbation to the shear strength at time 0 after perturbation when σ is 100 kPa.The experimental results show that:When the moisture content,dry density and thixotropy period remain unchanged,the triaxial thixotropy parameter increases first and then decreases with the increase of the fiber content,and reaches the peak value when the fiber content is 0.35%,indicating that the thixotropy of the fiber content is the strongest.Under the condition of constant moisture content,dry density and fiber content,the triaxial thixotropy parameter increases continuously with the increase of thixotropy period,which increases rapidly during 0-40 d and tends to be flat during 40-120 d.