Experimental Studies On The Tensile And Interfacial Shear Mechanical Properties Of Geocell

With the "14th Five-Year" plan to speed up the construction of a strong transportation country,China’s transportation infrastructure construction has made rapid progress.Geosynthetics is an indispensable new type of engineering material to accelerate the construction of transportation infrastructure under the background of "double carbon".As a new type of three-dimensional honeycomb reinforced material,geocell plays an active role in geotechnical engineering construction due to its excellent engineering properties,significant economic advantages and successful performance.However,the current research on geocells mainly focuses on engineering applications,and there is few researches on the tensile failure mechanical properties of geocell strips,geocell junctions and the entire geocell units.In addition,the effect of geocell on the shear behavior of reinforced soil interface also needs to be further studied.Therefore,on the basis of the existing research,this thesis takes the geocell as the research object,and conducts an in-depth study on the tensile and interfacial shear mechanical properties of the geocell through a series of laboratory tests.The research results can provide reference for the performance evaluation of geocell and the design of reinforced structures.The main research contents and results obtained in this thesis are as follows.(1)A series of laboratory unaxial tensile tests were performed on the geocell strips made from high-density polyethlene(HDPE),polypropylene(PP)and polyester(PET).The effects of the shape and width of the spcimens on the tensile mechanical properties of geocell strips were studied.The effects of several factors including slit or not,slit position,slit length and specimen width on the tear mechanical properties of HDPE and PET strips at slope shoulder were studied by trapezoidal tear test.It was determined that the elongation of HDPE,PP and PET strips is sensitive to the specimen shape,and the type I dumbbell-shaped specimen is smaller than the type II rectangular.The influence of specimen width on the tensile strength of PP strip is greater than that of HDPE and PET strip.The damage degree of the slit to the tearing force of the PET trapezoid specimen is greater than that of the HDPE.The slit damage coefficients of PET and HDPE trapezoidal specimens are 0.69 and 0.38,respectively.The slit length and specimen width have significant effects on the peak tearing force of HDPE and PET trapezoidal specimens.(2)A series of laboratory tests were performed on the geocell junctions including welding,latching,riveting and injection junction.The effect of different junctions on the tensile mechanical properties of the supported strips was studied.The failure characteristics of the junctions under different loading modes were observed.The relative performance of junctions was evaluated by introducing "strip strength retention rate","strip deformation retention rate" and "junction strength exertion rate".It was determined that the welding junctions used in the test play the best role in maintaining the strength and deformation properties of the HDPE strips,as well as the coordination of properties.The failure characteristics of junctions depend on the material,tensile strength of the strip near the junction against the strength of the material making up the junction itself.The junction strength of welding and injection depends on peel strength and shear strength,respectively,while the strength of latching and riveting junction depends on both shear and peel strength.(3)A series of entire tensile tests were conducted on geocell.The effects of singlefactor and multi-factor interaction of geocell height,spacing of junction and tensile rate on the entire tensile mechanical properties of geocells were studied.The evolution of tensile mechanical properties of geocell after deformation was characterized and studied.The relationship of strength between the entire geocell and strips and junctions is constructed.It was observed that the geocell height has a significant effect on the entire tensile strength of welded by HDPE and latched by PP geocells,which increases with the increase of geocell height.The sensitivity of the entire tensile strength of the two types of geocells to the spacing of junction decreases with the increase of geocell height,while the sensitivity to the geocell height increases with the increase of the spacing of junction.The entire tensile strength of geocell decreases significantly after characterizing the deformation of the geocell.Under the test conditions of this paper,the biaxial entire tensile strength of welded by HDPE geocell can be 9.5% of the tensile strength of HDPE strip or 14.0% of the tensile strength of welding junction subjected to split.(4)A series of laboratory direct shear tests were carried out on geocell.The effects of type of reinforcement,normal stress,geocell size and characterization of geocell deformation on the interfacial shear mechanical characteristics of reinforced soil were studied.The effect of different influencing factors on the shear properties of reinforced soil was evaluated by introducing the "reinforced strength coefficient".It was determined that the geocell can indirectly improve the shear strength through circumferential constraints on the soil in the geocell and indirect constraints on the soil in a certain range around the geocell,and it has a significant effect on the apparent cohesion of interface.The shear strength of the geocell increases with the increase of the geocell height and the decrease of the spacing of junction.The contribution of geocell height to interfacial shear strength is more significant than that of spacing of junction.In the design of reinforced structure,not only the reduction factor should be considered for the strength of the geocell itself,but also the corresponding reduction factor should also be considered for the interfacial shear strength.