Research On Static,Dynamic Deformation And Strength Characteristics Of Contact Surface Between Coarse Grain Soil And Geogrid

The development of reinforced soil has a history of decades.Due to the advantages of improving the economic efficiency,high construction efficiency,beautiful appearance,and reduced use of building area,it has been widely used in engineering.In order to strengthen the seismic effect of earth and rockfill dams,some projects(Qingfengling,Yele,Shiziping,Lianghekou,etc.)have applied geogrids for seismic reinforcement at the dam crest.For the stability analysis of the dam slope,there are two main types of failure on the arc fracture surface,namely,the top reinforcement material is pulled out or broken which leads to fail,and the bottom reinforcement material horizontally slides with the soil body to exceed the maximum bearing capacity of reinforced soil interface then leads to the failure,and the existing research mainly focus on the static characteristics of the interface between clay,sand and the static and dynamic tests on the interface characteristics of coarse-grained soil with large particles and geogrid carrying on Less research.Therefore,large-scale direct shear and pull tests for coarse-grained soil should be carried out to study the deformation and strength characteristics of the interface between coarse-grained soil and geogrid under static and dynamic loads to clarify the mechanism of geogrid reinforcement.In this paper,the joint pullout tester and the large direct shear tester are first improved.On the basis of this new equipment,a series of studies on the interface characteristics of coarse-grained soil and geogrid reinforcement are carried out.(1)Firstly,the shear box of the drawing tester was improved to ensure that the interface area of the test piece remains unchanged during the drawing process and improve the accuracy of the experimental measurement.Developed a new grid fixture to enhance the embedding of the grid to improve the accuracy of the test measurement;for the direct shear test,a pulley was added between the upper and lower box shear surfaces to reduce measurement errors.(2)Through the indoor pull-out test,the influence of the cross-ribbed and longitudinal ribs of the polyester warp-knit geogrid on the interface properties of the reinforced soil in the pull-out test was studied.The results show that the combined effect of longitudinal ribs and transverse ribs affects the tensile strength of geogrid,while longitudinal ribs have a greater influence on tensile strength than transverse ribs.A larger grid element with transverse ribs is the key factor leading to a significant reduction in the pull-out strength of the reinforced soil interface.(3)Large-scale direct-shear test equipment was used to conduct monotonic direct-shear test to study the influence of different types of geogrids on the interface characteristics of reinforced soil,and further analyze the test results through the shear strength curve.The results show that the interface of plain coarse-grained soil without reinforced material has stronger softening characteristics than the interface of geogrid.By adding reinforcement to the Lianghekou rockfill material,the friction angle at the soil interface can be increased and the overall shear strength can be improved.In the relationship between the normal displacementand shear displacement of the warp knitted geogrid of polyester,the overall condition of the curve is the law of shearing then dilatation.(4)In order to study the dynamic characteristics of the interface between the polyester warp knitting geogrid and coarse-grained soil,a cyclic direct shear test was carried out by indoor large-scale direct shear test equipment to study different normal stresses,cyclic shear amplitudes,cycle times,etc which influence the shear strength and body deformation of the reinforced soil interface.The test results show that at the interface of the reinforced soil under different vertical stresses the cyclic shearing phenomenon is characterized by the increase and decrease of normal displacement alternately,and the overall performance is the characteristic of shearing.As the amplitude of the cyclic displacement increases,the peak shear stress of the monotonic straight shear test after the cyclic test gradually increases.Cyclic shear cycles also have an effect on the dynamic properties of the rockfill reinforced-soil interface.Under the same normal stress,as the number of cycles increase,the reinforced-soil interface hardens,the intersecting force between the transverse rib and the grid increases,and the reinforced-soil interface shear strength also increased accordingly.