Based on large volume data of site investigation and engineering data analysis of shield construction in Strengthened permeable grit stratum

a fault tree is built to obtain the risk sources and their weight.Then the method of risk evaluating is studied on the basis of fuzzy comprehensive evaluation in two steps:The factor sets of both probability and loss are given according to risk source;and by using trapezoidal membership functions

the probability and loss of each factor are calculated as a matrix of risk evaluation.After that

the level of risk is confirmed through the matrix of risk evaluation.Finally

on the basis of risk handling principle

the risk handling measures are proposed from the mechanism of level

which is proved in practical engineering in Guangzhou.The study shows that

risk of shield construction is consisted of segment crushing

tunnel floating

spewing and ground collapsing etc.And the probability of risk as well as the loss of risk can both be divided into five degrees.Moreover

the main risk of shield construction

such as segment crushing

tunnel floating and spewing

can be well controlled by using risk aversion strategy such as the improvement of segment installing quality and the stratum properties

and risks of ground collapsing can be controlled by using risk aversion strategy

retention strategy and risk transfer strategy and so on.