Abstract: The deformation of surrounding rock tunnelling by tunnel boring machine (TBM) is normally large when the tunnel passes through the deep and weak layer. The TBM shield is squeezed easily by the surrounding rock, which further results in the TBM jamming and influences the operation of TBM. By analyzing the mechanism of TBM shield jamming problems, two important conditions for forecasting TBM jamming are concluded. One is that the deformation of the surrounding rock is greater than the reserved space, and the other is that the rated thrust force cannot overcome the frictional resistance. For monitoring the jamming state of the actual TBM engineering, this study is to propose a scheme of monitoring the deformation of the TBM shield and a method of calculating the pressure of the shield. The extrusion force between the surrounding rock and the shield can be estimated, then the frictional resistance of TBM is calculated, and the state of the TBM jamming can be achieved. According to the relation between TBM frictional resistance force for excavating and the TBM rated thrust, the state of the TBM jamming can be divided into four grades: no jamming, minor jamming, jamming and severe jamming, and the corresponding treatment measures are suggested. At last, the flowchart of warning of the TBM jamming is developed by combining the monitoring scheme with the conditions of TBM jamming. The flowchart and the scheme of monitoring the deformation are successfully applied to Lanzhou water conveyance tunnel engineering, and it is found that the predicted jamming state is nearly the same as the actual state, and thus this method has certain reliability and attaches great importance to TBM tunnelling construction.

Key words: tunnel boring machine (TBM), shield stress, warning mechanism of the TBM jamming