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Evaluation of dynamic frictional behavior of rock joints through shaking table test
Tunnelling and Underground Space Technology incorporating Trenchless Technology Research
Tunnelling and Underground Space Technology 21 (2006) 427
www.elsevier.com/locate/tust
Evaluation of dynamic frictional behavior of rock joints through shaking table test B.K. Park, S. Jeon, C.S. Lee School of Civil, Urban and Geosystem Engineering, Seoul National University, Republic of Korea
In order to characterize the frictional behavior of rock joints that substantially affects the stability of underground structures in rock mass, a number of experimental researches have been carried out. Those previous studies have generally focused on determining the peak shear strength of rock joints under monotonic and static conditions. However, recently, not only the frequency of occurrence but also the magnitude of earthquakes in Korea are on an increasing trend and other sources of dynamic events including large-scale construction, operation of high-speed railway and explosives blasting have been increasing. Besides, the probability of exposure for rock joints to free faces gets higher as the scale of rock mass structures becomes larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be thoroughly investigated. Therefore, in this study, an inclined plane shaking table test system which enables sliding block test was set up and a series of shaking table test was carried out to examine dynamic frictional behavior of rock joints under dynamic loading conditions. Saw-cut granite joints were used in the test. During dynamic tests, accelerations of a sliding rock block both in perpendicular and parallel to the inclined plane were obtained using 3 accelerometers. The relative displacement of the rock block was measured by a laser-type displacement sensor. The static friction angle was back-calculated by measuring yield acceleration at the onset of slide. The dynamic friction angle was estimated by closely approximating the experimental results to the program-simulated displacement and acceleration-time histories. In addition, tilt angle was measured prior to every dynamic test in order to compare with friction angles obtained under dynamic conditions. As a result of dynamic testing, the static friction angle calculated under dynamic condition was significantly lower than the tilt angle in spite of the same method of determination. This means that the rock joints in blocky rock mass structures under dynamic environment can move more easily than as expected without considering dynamic effect. Therefore, great care should be taken in the design of rock mass structure considering dynamic loading. The difference between the tilt angle and the static friction angle was influenced by the amplitude of base acceleration and inclination angle. The difference was much greater when the inclination angle was set to 10° rather than 15° and when the amplitude of base motion was 4.6 mm rather than 7.2 mm. The back-calculated dynamic friction angle was also lower than the tilt angle, and the difference between the tilt angle and the dynamic friction angle tended to be smaller according to increasing base acceleration and amplitude of base motion. Keywords: Dynamic friction; Shaking table test; Rock joints
doi:10.1016/j.tust.2005.12.069
Tunnelling and Underground Space Technology 21 (2006) 427
www.elsevier.com/locate/tust
Evaluation of dynamic frictional behavior of rock joints through shaking table test B.K. Park, S. Jeon, C.S. Lee School of Civil, Urban and Geosystem Engineering, Seoul National University, Republic of Korea
In order to characterize the frictional behavior of rock joints that substantially affects the stability of underground structures in rock mass, a number of experimental researches have been carried out. Those previous studies have generally focused on determining the peak shear strength of rock joints under monotonic and static conditions. However, recently, not only the frequency of occurrence but also the magnitude of earthquakes in Korea are on an increasing trend and other sources of dynamic events including large-scale construction, operation of high-speed railway and explosives blasting have been increasing. Besides, the probability of exposure for rock joints to free faces gets higher as the scale of rock mass structures becomes larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be thoroughly investigated. Therefore, in this study, an inclined plane shaking table test system which enables sliding block test was set up and a series of shaking table test was carried out to examine dynamic frictional behavior of rock joints under dynamic loading conditions. Saw-cut granite joints were used in the test. During dynamic tests, accelerations of a sliding rock block both in perpendicular and parallel to the inclined plane were obtained using 3 accelerometers. The relative displacement of the rock block was measured by a laser-type displacement sensor. The static friction angle was back-calculated by measuring yield acceleration at the onset of slide. The dynamic friction angle was estimated by closely approximating the experimental results to the program-simulated displacement and acceleration-time histories. In addition, tilt angle was measured prior to every dynamic test in order to compare with friction angles obtained under dynamic conditions. As a result of dynamic testing, the static friction angle calculated under dynamic condition was significantly lower than the tilt angle in spite of the same method of determination. This means that the rock joints in blocky rock mass structures under dynamic environment can move more easily than as expected without considering dynamic effect. Therefore, great care should be taken in the design of rock mass structure considering dynamic loading. The difference between the tilt angle and the static friction angle was influenced by the amplitude of base acceleration and inclination angle. The difference was much greater when the inclination angle was set to 10° rather than 15° and when the amplitude of base motion was 4.6 mm rather than 7.2 mm. The back-calculated dynamic friction angle was also lower than the tilt angle, and the difference between the tilt angle and the dynamic friction angle tended to be smaller according to increasing base acceleration and amplitude of base motion. Keywords: Dynamic friction; Shaking table test; Rock joints
doi:10.1016/j.tust.2005.12.069