Abstract: In order to identify construction risk of small-diameter deep drainage tunnel shields and accurately evaluate risk level, a HAZOP-based risk identification method and an evaluation method based on rough sets and cloud models were proposed. Firstly, construction risks were identified comprehensively by using HAZOP and an evaluation index system was established according to attribute reduction theory of rough sets. Then, a risk assessment model for small-diameter tunnel shield construction was established by combining rough sets and cloud model. Finally, the model was verified with deep tunnel project of East Lake as an example. The results show that evaluations of the model are basically consistent with actual situation, and major factors causing high- level construction risks include delayed adjustment of tunneling parameters, deficient training and evaluation, clogged grouting pipes, falling down of hoisting equipment, and unspecific engineering geological and hydrogeological surveys, and they should be checked and avoided.

Key words: small-diameter shield tunnel, deep diainage tunnel, construction safety risk, hazard and operability study (HAZOP), rough sets, cloud model