Study On Interface Mechanical Properties Of Gravel Sand And Concrete Pipe

As a construction technology widely used in underground space,pipe jacking engineering has a high degree of nonlinearity and complex shearing mechanical properties at the interface between pipe body and soil,especially for the interface mechanical properties of soil,slurry and pipeline after thixotropic slurry injection,there are few related research results.Since the shearing action between soil and concrete structure is affected by many factors,the mechanical behavior of the contact surface is not yet determined,The empirical guidance is more than the theoretical analysis,therefore,the theoretical research lags behind the progress of the construction process,To some extent,it has restricted the further promotion and development of the pipe jacking technology.Therefore,it is necessary to study the interface mechanical properties between the pipe and the soil.In view of this,this paper develops a visual direct-shearing container that can be used in digital image correlation measurement technology.The experimental study on the shear mechanical properties of the interface between the pipe and the soil in the two states of the thixotropic mud and the non-thixotropic mud was carried out.The interface mechanical properties under the influence of normal pressure,relative density of soil,water content,mud content in soil samples and stagnation time of pipe jacking construction are investigated.Based on the digital image correlation technology,the distribution of displacement field and the mode of interface failure during shearing are analyzed.A constitutive model of the contact surface that is more in line with the pipe-soil interface is proposed.The main research results are as follows:Independently developed a visual direct shear container for 300kN servo shear testing machine.Using digital image correlation measurement technology,the interface shear failure process under normal normal stress loading conditions was measured,and the software analyzes the digital image before and after the surface deformation of the object,and the displacement field cloud diagram during the shearing process is obtained,and the horizontal displacement value is obtained to obtain the "shearing displacement zone" in the soil-structure shearing process,and the thickness is about 3 times the average particle diameter of the soil particles.The shear test study on the contact surface between gravel sand and structure under normal normal stress loading conditions was completed.The effects of normal pressure,soil relative density,water content,mud content,and pipe construction stagnation time on the mechanical properties of interface shear stress were revealed.Based on the results of interface shear test,the strength law,interface dilatancy(shrinkage),stress-strain curve characteristics and contact surface failure law were analyzed.In order to better analyze the soft hardening characteristics of the interface and the "hugging effect" caused by the different stoppage time of the pipe jacking construction,the concepts of "strong disability ratio" and "pipe-holding difference value" were proposed respectively.Mathematical calculation formulas for characterizing different interface mechanical properties are obtained.A four-stage model and a two-stage model describing the characteristics of stress-strain curves are proposed.The model parameters are few and the physical meaning is clear.The results of the study show that the predicted values of the model agree well with the experimental data.