Ring Shear Test On Shear Behavior Of Interface Between Saturated Silt And Concrete Structure

There are interactions between structures such as pile foundations,underground structures,dams,retaining walls and soil,mainly exist in a thin layer of shear zone of the soil near the interface,which we called the interface.The force and deformation properties of the interface determine the bearing behavior of the structure,which is mainly related to the size and nature of the load,the type of soil,the water content and the roughness of the structural surface.Since the underground structures are mostly below the groundwater level,studying the shear characteristics of the saturated silt interface is of great significance for the design of underground projects in Zhengzhou.In this paper,based on the improved SRS-150 ring shear apparatus,under monotonic shear and multiple cyclic shear modes,the interface ring shear test was conducted under monotonic shear and multiple cyclic shear modes,and the modified thin layer boundary surface model is used to simulate and analyze the test results.Mainly achieved the following results:(1)The ring-shaped rotary pressure plate and the load plate of SRS-150 ring shear apparatus are modified,and the mold for preparing the ring shear soil sample is designed.The mold overcomes the defects such as the inability to prepare the ring soil sample of different heights and the poor flatness of the soil sample.At the same time,the consolidation instrument was improved and designed to apply the sample preparation mold for initial consolidation.(2)The monotonic shear test of the saturated silt interface under the constant normal load(CNL)boundary conditions was completed.It was found that the shear strength of the interface increased with the increase of normal pressure,and the interface cohesion was significantly less than the cohesion of the silt itself.It shows that the shear failure surface occurs on the contact surface of the silt and cement mortar.Because the cohesive potential energy and friction potential energy cannot break through the restraint of normal stress,the interface appears to be a shearing phenomenon,and the peak value of normal compression increases with the increase of normal pressure.(3)Various cyclic shear mode tests were completed,A variety of cyclic loading and shearing tests were completed,and it was found that the cohesive force after different cyclic shears was slightly greater than when the interface was monotonously sheared,but its angle of internal friction was smaller than the angle of internal friction when the interface was monotonically sheared.For the closed-loop shear test,the normal shear stress during forward shear does not change with the cycle,while the negative shear stress during reverse shear increases with the number of cycles.The relationship between the shear displacement and the normal compression also shows that the normal compression is very small during forward shear,and a large normal compression occurs during reverse shear.The reason for this phenomenon is that the structure exerts a forced orientation constraint on the soil particles during the shear process.(4)By revising the existing thin layer boundary surface model,considering the CNL boundary conditions,and compared with the results of the interface ring shear test,the validity of this constitutive model was verified.The model can accurately describe the complex mechanical relationship of the interface including hardening and softening characteristics under the monotonic load,also can well simulate the relationship between shear displacement and shear stress under multiple cyclic shear modes.