Risk assessment method for fall-block hazards in mountain tunnels based on element-matter theory and block theory

To conduct a risk assessment on the frequent occurrence of rockfall disasters in mountain tunnels, a new risk assessment method for surrounding rockfall at the tunnel face is established by combining matter-element theory, block theory and statistical rock mechanics.Firstly,a calculation method for block formation probability is proposed based on the distribution law of structural plane trace lengths.Combined with the classification criteria of risk event probability and the characteristics of random blocks,a classification standard for rockfall probability is established.Using block theory, parameters such as the position,volume and safety factor of random blocks are calculated,and a rockfall loss calculation method based on matter-element theory is constructed.Integrated with the classification criteria of risk event loss, a classification standard for rockfall loss is set up.By combining the probability and loss calculation methods,a quantitative risk assessment method for tunnel rockfall is formed.The method is applied to the rockfall risk assessment of the left tunnel of Yanqian Tunnel on the Jingtai Expressway.The results show that the root cause of block collapse is the formation of blocks with low safety factors cut by structural planes,which lack self-stability.The direct cause is that no anchoring force was applied to the blocks after excavation to maintain their stability.The calculation results are consistent with actual engineering conditions,verifying the advancement and practicability of the proposed method.This research improves the safety risk assessment system for tunnel rockfall and provides technical guidance for the prevention and control of tunnel rockfall disasters.