Reciprocating Shear Behavior And Strength Wea Kening Mechanism Of Coarse-grained Soil-Steel Interface

The upper reaches of the Yangtze River have steep slopes,steep flow,large water levels,and complex topography and geological conditions.For these problems,large-diameter steel rocK-socKeted rocK-socKeted pile foundations can meet the needs of deep-water wharf construction and have been used in the construction of deep-water wharfs in the upper reaches of the Yangtze River.The construction process determines that the depth of the steel casing embedded in the bedrocK is very limited,but it must pass through all the ground soil.The steel casing and the ground soil will form the steel-soil interface.The rocK-socKeted piles are subjected to cyclic loads such as ship impact force and mooring force for a long period of time in the process of use,causing reciprocal shear at the steel-soil interface,The mechanical properties of the steel-soil interface will inevitably affect the bearing behavior of the large-diameter steel rocK-socKeted piles,Therefore,this article selects mudstones that are used as bacKfill materials in Chongqing to conduct indoor experiments and incorporates discrete element software（PFC）to study the mechanical properties of reciprocating shear at the interface between steel and soil.The specific research content and research results are as follows:（1）Improved ZJ-type direct shear meter to meet coarse-grained soil-steel interface reciprocating shear system,Mainly added drive,normal,tangential displacement measurement multimeter,travel switch,replace shear box with steel plate with certain roughness,etc.The results show that the system can obtain more reliable test data.（2）The effects of initial normal stress,interface roughness,and sample moisture content on the reciprocating shear behavior at the steel-soil interface were revealed.Using improved test equipment,the shear stress-strain relationship,normal displacement,interface shear strength,and the variation of c and?in the specimen under various factors were studied.According to the analysis of the test results,the reciprocal shear strength attenuation of the coarse-grained soil-steel interface is mainly due to the redistribution of particles near the contact surface and particle breaKage.（3）Based on the principle of discrete elements,a uniaxial compression simulation system for rocK samples was established using PFC^2D.Sensitivity analysis was performed on the mesoscopic parameters of the built-in linear adhesive contact model of the PFC.The meso-parameters of mudstone were obtained by using the difference of the effect of different mesoscopic parameters on the macroscopic mechanical properties.（4）The mesoscopic parameters obtained by calibration were used to establish a steel-soil interface reciprocating shear simulation test system using PFC^2D.Using this simulation system,the variation law of shear band,stress distribution,particle energy and porosity near the interface of each sample was studied.Under the effect of reciprocating shear,the shear characteristics of particles near the contact surface have been further understood.