Study On Mechanical Properties Of Collapsible Loess-Concrete Interface

With the advancement of social development in China,projects such as Fengshan Road Opening,Water Crossing Bridge,and West-East Gas Pipeline Project in the Great Northwest have also been rapidly developed.Stable operation has become a topic that engineers and technicians generally pay attention to.Therefore,the problems involving the interaction of special soil-loess and structures are common in civil engineering,hydraulic engineering,and geotechnical engineering.In addition,considering that the strength of the soil and the structure is significantly different,the deformation characteristics of the part in contact with each other also become cumbersome,so correctly evaluate and describe the soil and the structure The interaction is particularly important.This subject relies on the major scientific and technological special project of Gansu Province-"Complete Technology Research on Highway Construction in Collapsible Loess Areas of Gansu Province",and aims at the sub-project-"Research on the Influence Law of Collapsibility of Loess on Bridge Pile Foundation".The mechanical properties of the collapsible loess-concrete structure interface are analyzed by combining the Shear-III geotechnical large-scale shear test research,theoretical research and numerical simulation.The conclusion is as follows:?1?The loess-concrete interface characteristics are studied using the Shear-III geotechnical large-scale shear tester's indoor direct shear test,using the rotation factor method and the single-factor control variable method to affect the factors affecting the soil and structure,such as moisture content Comparative analysis was carried out on the directional stress and interface roughness.Direct shear test results show that:under the condition that the roughness and water content of the loess-concrete interface are constant,the normal stress increases with the increase of the maximum shear stress and residual stress;under a certain normal stress and interface roughness,The peak shear stress increases first and then decreases as the water content increases;at rough contact surfaces,the rate of change of residual strength changes from small to large,while at the smooth contact surface,the rate of change of residual strength changes from large to small;in loess-concrete When the roughness and water content of the contact surface are constant,the normal stress and the shear stress will change obviously when the shear displacement increases to the peak shear stress.Normal stress,the relationship curve is hyperbolic,the shear stress increases to the peak Shear stress gradually decreases,and finally tends to a horizontal straight line;when the normal stress and water content are the same,the peak shear stress of the collapsible loess-concrete structure interface increases with the roughness level;the rough contact surface The coefficient of friction is 12.6%higher than that of the smooth contact surface.?2?In the research and analysis of the change law of shear stress-shear displacement in the direct shear test,for fitting the bi-fold shear stress-shear displacement curve,the fitted loess-concrete shear stress-The effect of the shear displacement curve is better;the BoxLucas2 function in the exponential model in the OriginPro function library is used,and it is improved.The generalized hyperbolic model is adapted to the softening analysis.It is difficult to find one for all shear displacements.-Mathematical models that are suitable for shear stress curves,so it is necessary to analyze the constitutive model suitable for itself.The study found that each constitutive model has a good fit and the complex correlation coefficient is above 0.95.?3?In the theory of contact surface constitutive model and contact surface element,write the form of the contact surface element and select the appropriate structural surface element;Study the contact surface constitutive model.?4?In order to describe the deformation characteristics of collapsible loess-concrete during shearing in a practical,reliable and appropriate manner,the size of concrete in this article is 505mm×305mm×102mm,the size of loess is 305mm×305mm×102mm,using MATLAB-CAD-ANSYS-FLAC^3D method established a numerical model of concrete surface and loess,and analyzed the influence of two normal conditions on the shear slip zone and the logarithmic value under different normal stresses and different moisture contents during the shearing process The relationship between the simulated shear stress-displacement relationship curve and the relationship curve obtained by the direct shear instrument is compared and analyzed.It can be seen that the two relationship curves are basically consistent,and the simulation effect is good.It shows that the simulation results of the finite difference software FLAC^3D are suitable for the indoor direct shear test in this paper.