Movement Mechanism And Safety Protection Of Rockfall On The Slope With Tunnel Below

Railway and road tunnels, which are commonly seen in the southwestern mountainous area, is the key to the transportation construction. The mountainous terrain condition has caused numerous tunnels below slopes,leading to the formation of high and steep slope with precipitous terrain, broken rock mass and exposed crag at the entrance and exit of tunnels. Therefore, the construction of open cut tunnel structure is a necessary means to ensure traffic safety. Affected by weathering of rocks, earthquakes, heavy rainfall and other natural factors, crag at the top of slopes will have a direct impact on the open cut tunnel section once collapsed, even leading to fracture and collapse of tunnel structure and posing a great threat to the safety during road and rail transport. Therefore, it provides a strong theoretical reference for the protection against rollfall in the open cut section to fully analyze movement patterns, movement mechanism and rules of the rockfall on the slope with tunnels below in order to understand the impact of the rockfall on open cut tunnel, which is of great research significance.Based on railway tunnels in the southwestern mountainous area and through methods such as theoretical analysis, model test and numerical calculation, this paper studies movement patterns, movement mechanism of the rockfall and the impact of it on the open cut tunnel below and conducts simulation of rockfall movement locus by combining engineering practice, providing reference frame for design of protection against rockfall.First of all, the impact patterns of rockfall on the entrance to a tunnel are classified to analyze their cause. Impact energy and destructive effect should be contrasted in order to conduct targeted engineering protection according to different impact patterns of rockfall.Secondly, testing system of collapse movement mechanism model of crag on the slope with tunnels below is developed. Mechanical model is built based on different impact patterns of rockfall and theoretical analysis is conducted to grasp the motion law of rockfall, model tests of impact movement of vertical, rolling and bouncing rockfall are done to analyze the change law of recovery coefficient of impact speed on open cut tunnels, study the effect of variation of mass and shape on rolling movement feature of rockfall and draw the effect law of different impact patterns on open cut tunneLThirdly, by combining test results with engineering practice, risk assessment model of impact of rockfall on open cut tunnels based on extension method is built. Impact risk of six groups of crag on site is assessed to provide reference for protection against rockfall.Finally, numerical analysis model is built according to profiles of three locuses with relatively higher impact risk on the site to calculate the movement locus of rockfall under 18 working conditions and analyze the effect of rockfall mass, collapse position and slope feature on coefficients of open cut tunnel impact such as speed, energy and impact height, position, range, height and impact energy level of passive safety net of the rockfall are designed based on the results, and the protective effect is checked. The results show the layout of passive safety net can effectively prevent the impact of the rockfall collapse on tunnel structure, providing strong guarantee reduction of construction risks and traffic safety.