Experimental study on unloading failure strength of red sandstone
FAN Pengxian1，2，LI Ying1，ZHAO Yuetang1，WANG Mingyang1，WANG Derong1，SHI Yehui2
(1. State Key Laboratory of Disaster Prevention and Mitigation of Explosion and Impact，Army University of Engineering，Nanjing，Jiangsu 210007，China；2. Tunnel and Underground Engineering Research Center of Jiangsu Province，
Nanjing，Jiangsu 210018，China)
Abstract：Excavation is routine operation in underground rock engineering. The unloading behavior of high stress rock differs from the rock under the loading conditions and results in engineering disasters such as large deformation or rockburst. In order to reveal the unloading effect，triaxial tests are conducted and the strengths of cubic red sandstone samples under loading/unloading conditions are measured. According to the tests，the samples firstly split in the adjacent area of unloading surface several seconds after the unloading，and then lose the bearing capacity as a whole. The test results indicate that under the rapid unloading condition，the unloading strength is 8.4% to 27.2% lower than the loading strength. The higher the confining stress is，the bigger the strength declines. When the confining stress is the same，the strength under double-direction unloading condition is lower than that of under one-direction unloading condition. A dynamic damping vibration model is established and the influence factors of unloading failure are discussed. The negative unloading effect of the rock strength revealed by the tests is of great importance for evaluating the rock parameters under unloading conditions reasonably.
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2018, Vol. 37 
