Experimental Study On Shear Mechanical Properties Of Frozen Soil-Concrete Interface

With the implementation of national " Belt and Road" strategy in the northeast China,a large number of cold area engineering structures are accelerating to be constructed.As the main engineering material of engineering construction,the cohesiveness and stability of concrete contact surface with permafrost are very important in cold region.Especially,When buildings(structures)are built in seasonal frozen soil area,the mechanical properties of the frozen soil concrete interface change,because of the seasonal frost heaving and thawing of soil,which leads to the instability of the buildings(structures)foundation,and has a serious impact on the function and safety of the buildings(structures).Therefore,It is of great scientific significance to study the variation of mechanical properties of the interface between frozen soil and concrete in cold region.With the support of The National Natural Science Foundation of China(41627801,41430642,51108207),China Postdoctoral Science Foundation Project(2015M581403)and open fund of National Key Laboratory of frozen soil engineering(SKLFSE201514),the mechanical properties of frozen soil concrete interface in Northeast China are studied.The main tests and theories are as follows:(1)Two kinds of soil with different frost heave sensitivity were selected,three kinds of water content were respectively arranged,three kinds of concrete samples with different roughness were made.The direct shear test was carried out under four normal stress conditions by using strain direct shear apparatus and the apparent failure patterns were observed.(2)The roughness has a significant effect on the physical state of the contact surface after shear failure,which shows that the rougher the contact surface is,the more soil remains on the concrete surface,and the deeper the shear failure surface is into the soil.After the shear test,the sample temperature rises.The temperature rise of sand group is faster than that of silty clay group.Some moisture is observed on the contact surface of silty clay and sand group concrete.(3)Through depth analysis of shear strength data,it is found that the shearstrength is significantly affected by the roughness and moisture content,and increases with the increase of moisture content and contact roughness.In the contact surface of frozen silty clay,the internal friction angle decreases with the increase of water content,When the water content is 21.8%,the internal friction angle first increases and then decreases with the increase of the roughness of the contact surface,When the water content is 27.6% and 33.0%,the internal friction angle decreases with the increase of the roughness of the contact surface.The cohesion increases with the increase of moisture content and roughness of contact surface.With the increase of water content,the internal friction angle of frozen sand increases first and then decreases,at last decreases with the increase of roughness.The cohesion of contact surface increases with the increase of moisture content and roughness of contact surface.(4)Based on the principle of conservation of energy and assumption of plastic limit,the failure mode of contact surface was analyzed.The results show that the plastic failure model fits well under different roughness,different moisture content and two soil conditions,which can provide a reference to predict the shear strength of contact under a certain normal pressure.