Experimental Study On Mechanical Properties Of Interface Between Triaxial Geogrid And Sand Cushion

Soil is a kind of geological material with almost no tensile strength.In order to make up for the defects of soil,reinforced soil technology came into being.With the construction of China's infrastructure,geogrid with excellent reinforced properties have been applied in large areas.The use of geogrid reinforcement technology in actual engineering has become a common phenomenon.Geogrid reinforced cushion is widely used and popularized in railway engineering,highwa y engineering,water transportation engineering,mining engineering and supporting structures of domestic and international due to its excellent reinforcement performance and engineering characteristics,and has achieved good results and markets repercussi ons.However,the research on the interaction characteristics between the geogrid and sand cushion is not mature enough,especially the research on the reinforcement mechanism and design theory is far behind the engineering practice.Therefore,it is urgen t to conduct in-depth research and analysis on the interface mechanical characteristics of the reinforced cushion.This paper focuses on the reinforced cushion composed of sand and triaxial geogrid,and studies the interface characteristics of the reinforc ed soil.Through the indoor pull-out test,the mechanical behavior,deformation characteristics and mechanism of the reinforced cushion under different working conditions and practical application environments are analyzed in-depth.The research contents and achievements of this article are composed of the following parts:(1)According to a large number of specifications,a large-scale pullout test apparatus suitable for geosynthetics and different soils was designed and processed.The maximum sample size of this apparatus is 0.8 m × 0.6 m × 0.6 m.An adjustable strain loading system is used in the horizontal direction,and a hydraulic loading is used in the vertical direction.It is more convenient to study the interface mechanical characteristics under static load.(2)The pull-out test was used to study the interface characteristics between the triaxial geogrid and the middle-sand cushion under different pullout directions,water contents,and vertical stresses.It is considered that the pullout process of the geogrid is a gradual behavior,and the water content,vertical stress,and pullout direction all have a significant effect on the pullout resistance,geogrid-soil interface displacement,geogrid deformation,and geogrid-soil interface parameters.(3)The method of independent longitudinal ribs pull-out test and theoretical analysis was used to study the change trend,effect and reinforcement mechanism of two equivalent friction,and the formulas of equivalent friction ratio based on different vertical stresses and water contents are proposed.The research found that the peak pullout resistance of independent longitudinal ribs pull-out test only accounted for 55% to 69% of the overall pull-out test,and the theoretical value of interface frictional resistance accounted for 23% to 55% of the test value;The passive resistance is obviously between general shear failure and punching failure,which increases with the increase of vertical stress and water content.With the increase of the water content,the passive resistance curve gradually approaches from the punching failure curve to the general shear failure curve;The passive resistance accounts for 70% to 86% of the pullout resistance.The proportion of passive resistance decreases with the increase of vertical stress,and increases with the increase of water content.