Research On Mechanical Properties Of Palm Fiber Reinforced Clay Based On GDS And DEM

In the process of tunnel excavation,the surrounding strata are often disturbed,and major disasters like tunnel collapse will happened when the control is adopted timely.The traditional stratum reinforcement methods are mainly grouting reinforcement and support protection etc,but these methods have many shortcomings in terms of environmental protection and economic costs.In order to explore a new stratum reinforcement methods,the 4 palm fiber lengths(5mm,10 mm,15mm,20mm)and 5palm fiber contents(0.1%,0.3%,0.5 %,0.7%,0.9%)were selected,a total of 20 kinds of fiber mix ratio.By the triaxial consolidation undrained test,the stress-strain curve,shear strength and soil failure form between fiber-reinforced soil and plain soil were compared.The reinforcement effect of palm fiber on soil was studied,and suggested the maximum value of fiber mix ratio,meanwhile,the reinforcement mechanism of palm fiber reinforced soil was analyzed by SEM test.At the same time,according to the stress in different areas of the tunnel during excavation,the GDS triaxial system was used to carry out palm fiber reinforcement experiments under different stress paths,and the influence of the actual stress path on the reinforcement effect was studied.The discrete element software PFC 3D is used to establish a fiber reinforced soil model,and the change law of the stress-strain curve is analyzed by changing the meso-parameters of the fiber-soil interface.Combined with particle velocity and displacement vector diagrams,the local failure mode of soil and the relationship between contact force and inter-particle bond distribution and stress-strain curve are studied.The main conclusions are as follows.(1)In the conventional triaxial test,the stress-strain curve of palm fiber reinforced soil showed a stress-hardening type,and its peak deviatoric stress and cohesion showed a trend of first increasing and then decreasing with the increase of fiber content and length.The best reinforcement effect was obtained when the fiber length was 10 mm and the fiber content was 0.7%.By comparing the failure forms of palm fiber reinforced soil and plain soil,it is found that the incorporation of fibers will limit the lateral deformation of the soil to a certain extent.(2)Under four stress paths of RTE,RTC,TC and CTC,the mechanical properties is improved by using of palm fiber reinforced.Compared with plain soil,the peak deviatoric stress strength of palm fiber reinforced soil increased by 14.13%,11.97%,16.73% and 8.9% on average,the cohesion of palm fiber reinforced soil increased by37.17%,35.37%,43.11% and 54.87% on average.The deformation of soil is limited by palm fiber under different stress paths,especially in RTC and TC paths.(3)During the loading process of the discrete element model,the particle velocity field and the displacement field both show axisymmetric distribution and point to both sides,so the sample is mainly deformed in the lateral direction,which explains the reason why the sample does not form a shear plane from a mesoscopic level.By changing the friction coefficient of the reinforced-soil interface,the influence of the fiber surface roughness on the reinforcement effect is analyzed.The results show that the peak strength of the reinforced soil increases with the increase of the friction coefficient of the reinforced-soil interface.By changing the friction coefficient of the reinforced-soil interface,the influence of the fiber surface roughness on the reinforcement effect is analyzed.The results show that the peak strength of the reinforced soil increases with the increase of the friction coefficient of the reinforced-soil interface.