Study On Shear Mechanics Properties Of Freezing Rock Joint

Along with western development strategy and the strategy to rejuvenate northeast old industrial bases of China,more and more engineering construction projects are being developed in the permafrost regions.In these tunneling projects,there are more than 70% of the varying degrees of vaulting leaking ice,pavement bulging ice,lining cracking,hole slope support structure frost heaving cracking and other frost damage,threatening tunnel rock and slope stability.Through the investigation,it was found that the site of frost damage of tunnel lining in permafrost region is mostly developed.At the same time,the frost damage of the retaining slope of the entrance slope is also caused by the geologic conditions of the joint rock mass with controlled structural plane.It can be seen that the difference in shear mechanical properties of rock joint surface under freezing conditions is the root cause of frost damage in tunnel and tunnel slope of permafrost zone.In this paper,the tuff joint of Jiangluling section of G214 national highway in Qinghai Province is taken as the research object.Four groups of rock joints with different roughness were selected.The peak shear strength of the frozen joint surface under different normal stress and opening conditions was obtained.The variation law of normal stress,opening and peak shear strength were summarized and analyzed.And the effect of roughness on shear strength was analyzed.By observing the failure form of the specimen,the failure mechanism is analyzed from the angle of mechanics and the bond strength of ice.Finally,the criterion of peak shear strength of frozen joint surface is proposed.The main achievements of this paper are as follows:(1)According to the shear stress-shear displacement curve obtained by shear test under different normal stress conditions.In general,the whole test process is divided into four stages: instantaneous deformation stage,stress increasing stage,yield stage and residual shear stage.(2)It is concluded that the peak shear strength of the frozen joint surface is negatively correlated with the opening degree.The shear displacement at the peak shear strength also has a negative correlation with the opening degree.(3)The effect of joint surface morphology on the peak shear strength of frozen joint surface is analyzed,which is concluded that the larger the roughness of rock joint surface is,the smaller the peak shear strength is.(4)By observing the test specimen after damage,it is found that the failure modes of the joint surface under different opening conditions are very different.Thus,the damage mechanism of the whole experiment is analyzed from the angle of mechanics and ice bond strength theory.According to the different forms of failure of the specimen,three kinds of failure modes are obtained,such as ice breaking failure,ice shear failure and ice rock shear failure.(5)The peak shear strength values obtained by the shear test and the failure modes of the specimens after the test.The peak shear strength criterion under different opening conditions is obtained.