| With the rapid development of transportation infrastructure, a great many tunnels will be built in elevations areas or circumpolar areas in the Big West. Compared with traditional tunnels in the cold area, these tunnels require higher technology with bad geologic conditions. However, frost damage theory of tunnel is not perfect; less attention has been given to plateau climate characteristics, monitoring of the temperature field and analysis on frost deformation, which is generally interested problem in the study of tunnel in cold regions. Moreover most of the studies are based on the background of permafrost, and less attention to the seasonally frozen. Meanwhile, China’s current tunnel design specifications were not considered the impact of relaxed rock mass on surrounding rock pressure after the earthquake, the engineering characteristics of relaxed rock mass has also not been mentioned. In this paper, this issue was raised alone as a new research direction alone. The main research content containing some aspects as following:(1) Through field monitoring, got the annual change law of ambient temperature and the Development Law of frozen soil; using scanning electron microscopy proved frost heave may cause degradation damage on rock microstructure;Meanwhile, mudstone uniaxial compressive strength test at different freezing temperatures indicate that frost heave have a greater effect on the mechanical properties of the rock mass.(2) Based on long-term field testing and finite difference software explores the surrounding rock temperature variation at different depths, obtained the maximum frost depth of surrounding rock under different conditions. Analysis on variation law of rock temperature in the radial direction showed that surrounding rock was influenced to different degrees by the ambient temperature, and temperature trends are inconsistent at different depths.(3) Based on studying the frost heave deformation mechanism,the article put forward the analysis of frost heaving deformation of tunnel should include two aspects, namely rock and surrounding rock-support system. And the development of the freezing front was simulated and analyzed,using the finite difference software FLAC3D,during the freezing process.(4) Using the finite difference software FLAC3D, the stability of surrounding rock was analyzed under different freezing time and freezing temperatures. The results showed that when the freezing temperature is lower, the freezing time is longer and the frost heave deformation is larger. In addition, the frost heave deformation is also related to the excavation time of tunnel section, the more heat energy will be stored before the arrival of the cold season, by prolonging exposure periods in the warm season, and the frost heave deformation will be also smaller.(5) Based on wave theory and mohr-coulomb failure criterion, the limiting failure depth of rock masses was explored. Using the derived analytical formulas, the failure depth of rock masses was calculated, and the division of loose depth was analyzed through in-situ wave velocity tests and comparative analysis of different results. Finally, surrounding rock pressure of tunnel under earthquake force was analyzed.(6) The judgement standard of loose rock was put forward from two aspects:the mass elastic wave velocity and density. The judgement standard is decrease amplitude of density> 7%and rock longitudinal wave velocity ≤3000m/s after 5.12 earthquake in Beichuan Area. While, the loose rock was divided into three grades, with decline for every additional 5%, namely:(1)Slight loose (2500m/s<Vp<3000m/s,7.4%<a<13%); (2)Moderately loose (2000m/s<Vp<2500m/s,13%<a<18%); (3)Strong loose (Vp<2000m/s, a>18%).(7) Proposed two methods to determine the depth range of different loosening grades: First, analyze the range of longitudinal wave velocity and rockmass density to determine, by conducting wave test. Secondly, combined with the depth proportion, which was based on the early related researches, it can be determined by the analytical formula of limiting failure depth. The percentage of different degree of loosening was 20%,30% and 50% under earthquake force.(8) A new mechanics concept of load form, that all the deadweight of strong loose rockmass acting on the tunnel lining, was put forward. Loose rock mass has great influence on the loose pressure of surrounding rock, and the change of critical buried depth of tunnel is the major reason for this.(9) The loose rockmass have some influence on frost damage in tunnels. It mainly reflects on two aspects:firstly, the frozen-heave rate will increase because of loose rockmass; secondly, joint fissure provides a convenient migration path to water migration, when the aqueous phase turns the ice. |
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