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Direct shear tests of freezing strength at the interface between cast-in-situ concrete and frozen soil

JI Yanjun;JIA Kun;YU Qihao;JIN Huijun;GUO Lei;LUO Xiaoxiao;State Key Laboratory of Frozen Soil Engineering,Northwest Institute of Eco-Environment and Resources,Chinese Academy of Sciences;Gansu Electric Power Design Institute Co .,Ltd,Energy China;University of Chinese Academy of Sciences;Qinghai Electric Power Company,State Grid Corporation of China;  
Previous experimental study of interface strength between concrete pile and frozen soil has focused more on the mechanical properties of the interface between precast concrete block or specimen and frozen soil with less information about direct shear test of freezing strength between cast-in-situ concrete and frozen soil.Based on a new specimen preparation method,a series of laboratory direct shear tests of the interface between cast-in-situ and frozen soil were performed. The results show that because of difference in thermal parameters of concrete,the interface between cast-in-situ concrete and frozen soil appears irregular model. Freezing strength of rough interface will increase by 71. 9% as compared with that of smooth interface. Stress concentration occurs on the rough interface,resulting in stress intermittently increasing and jumping in the shear failure process. With the increase of roughness at the interface,φ contribution increase more than c contribution increase by degree. Thusφ can play more important role in the growth of freezing strength. When water cement ratio increases from 0. 4 to0. 6,with the thermal conductivity of concrete decreasing,the interface becomes smoother and the freezing strength will decrease; when water content increases from 15% to 30%,freezing strength will increase first and then decrease; when water content increases to 40%,freezing strength will decrease. Thus,it is recommended that 0. 4 ~ 0. 5 is a reasonable water cement ratio,according to this study.
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