Experimental study on tackifying-frost resistance of tunnel surrounding rock-spray interface in cold region
LIU Hui1，XU Hainan1，REN Jianxi1，SHEN Yanjun2，3，JIA Hailiang1，XI Jiami1，TANG Liyun1，YU Jinjie1，WEI Yao4
(1. College of Architecture and Civil Engineering，Xi'an University of Science and Technology，Xi?an，Shaanxi 710054，China；
2. Department of Geological Engineering and Geomatics，Chang?an University，Xi?an，Shaanxi 710054，China；3. State Key Laboratory of Loess Science，Chang?an University，Xi?an，Shaanxi 710054，China；4. Laboratory of Road Engineering Safety and Health in Cold and High-Altitude Regions，CCCC First Highway Consultants Co. Ltd.，Xi'an，Shaanxi 710065，China)
Abstract：Tunnels in cold regions are generally affected by freeze-thaw action，which is prone to damage and debonding along the interface between concrete lining structure and surrounding rock，which seriously affects the construction quality and safe of tunnel engineering operation. In order to improve the bonding strength and frost resistance of the tunnel surrounding rock-spray layer interface，the surrounding rock-spray layer interface is simplified into a rock-concrete binary body. The cement-based interfacial agent is developed for improving the adhesion and frost resistance of the spray layer interface. A comparative test of the bonding strength and frost resistance of the sandstone-concrete interface was carried out before and after the spraying of the cement-based interface agent. The test results show that：(1) The main chain fracture parallel to the silicon-oxygen tetrahedron in the rock-concrete interface caused by freeze-thaw action is the core reason for the decrease of the bonding performance of the rock-concrete interface. (2) Through the test and development，the optimal mix ratio of cement-based interfacial agent suitable for improving the interfacial adhesion and frost resistance of tunnel spray layer in cold regions is proposed as follows∶cement∶water∶silica powder∶silane coupling agent∶polymer cementitious material(water-based acrylate peritoneal gel + bamboo liquefied phenolic resin) = 10∶4.4∶0.8∶0.2∶1∶0.5；(3) Due to the polymer hydration of the cement-based interfacial agent，the 'root pile' effect generated at the interface of the spray layer expands the degree of plugging on the contact surface between the rock and the concrete. At the same time，the chemical bonding of the silane coupling agent enhances the mechanical bite force between the interfaces. The coupling enhancement of the two improves the bond shear strength and splitting strength of the rock-concrete interface. Through comparative tests，it is found that after 30 freeze-thaw cycles，the shear strength of the rock-concrete interface can be increased by 109% compared with the untreated sample，and the bond splitting strength is increased by 78%. (4) The silicon-oxygen bond produced by the hydrolysis and condensation of siloxane in the cement-based interfacial agent is adsorbed on the hydrophobic layer formed at the rock-concrete interface，which inhibits the expansion of the interface water-rich zone；the silicon gel generated by the combined reaction releases heat by phase change，which reduces the freeze-thaw damage of the rock-concrete interface and inhibits the initiation and propagation of cracks at the rock-concrete interface. (5) The developed cement-based interfacial agent itself has good frost resistance，especially in the freeze-thaw environment of －10 ℃–10 ℃，it can effectively improve the adhesion and frost resistance of the surrounding rock-spray layer interface. This paper provides a new solution for the thickening and frost resistance treatment of tunnel surrounding rock-spray interface in cold region.
