EXPERIMENTAL STUDY ON THE INFLUENCE OF DIFFERENT WATER CONTENT CHARACTERISTICS OF SANDSTONE ON ULTRA-LOW FRICTION EFFECT

To reveal the influence mechanism of water-bearing characteristics of tunnel sandstone on ultra-low friction type impact ground pressure under stress disturbance, a self-made ultra-low friction test device was used. Taking the sandstone in Shenyang as the research object, The whole and layered water-bearing characteristics of deep rock mass are simulated by changing the water content and immersion height of sandstone block. Taking the intermediate sandstone as the working block, the peak horizontal displacement and the friction force of rock-rock interface were used to characterize the strength and resistance of ultra-low friction effect respectively, and experimental study on the influence of different water content characteristics of sandstone on ultra-low friction effect was carried out. The results show that: (1) The displacement time history curves of working blocks with different water content and immersion height have three stages of preparation, impact and oscillation. At the same time, the peak horizontal displacement has obvious zoning characteristics with the increase of vertical disturbance frequency. The average value of peak horizontal displacement at the boundary of strong influence zone and weak influence zone of ultra-low friction effect is 0.232 and 0.368 mm respectively. (2) The average strength of ultra-low friction effect under dry and saturated water content of working block is 165% and 89.7% higher than that under natural water content, respectively. The average maximum reduction in friction due to increased moisture content is 16.6%, indicating that the water content of rock mass continues to increase from natural state, which is prone to ultra-low friction effect but the strength is weakened. (3) The average increase in the strength of the ultra-low friction effect of the working block immersion height of 75 mm is 146%, and the maximum decrease in friction is 12.1%, indicating that the ultra-low friction effect is prone to occur currently and the strength is high. (4) When the water content of sandstone block is 1.05% and the immersion height is 75 mm, the strength of ultra-low friction effect is the highest. In the actual working conditions, the water content and immersion height of rock mass should be reasonably controlled to prevent the occurrence of ultra-low friction rock burst disaster.