Thrust Calculation Method for Earth Pressure Balance Shield in Compound Strata

The total thrust is difficult to be determined during the design and construction of an earth pressure balance shield tunnel in compound strata. Based on the mechanical analysis of a shield machine, a thrust calculation method of the shield tunneling machine in compound strata was proposed by taking the upper-soft and lower-hard strata as an example. The ground composition, the cutting tool form, the penetration per revolution, the opening rate of the cutterhead were considered in this method. The reliability of the proposed method was verified by the application in a project. The results show that the average error of the proposed method is -11.88%, and the accuracy is much higher than the Krause empirical model. The influences of different factors on the total thrust force of the shield and the components were analyzed. It is found that with the increase of buried depth, the soil arching effect is brought into play, and the total thrust of the shield increases at first and then slows down. The total thrust increases significantly with the increase of rock ratio in the tunnel face, the penetration per revolution and rock strength. And the total thrust of the shield varies little with the opening ratio.