Numerical and experimental method to determine the boring diameters of a two-stage TBM cutterhead to prevent rock burst

A two-stage tunnel boring machine (TBM) cutterhead with a pilot-enlargement boring method was presented to reduce the risk of rock bursts resulting from boring with a TBM with a large flat-face cutterhead. A reduced scale similarity experiment was designed on rock tunnel boring to determine the boring diameters of the two stages, and numerical simulation models were built. A micron X-ray computerized tomography system was adopted to examine the failure area of the excavated testing piece and validate the numerical models. Stress distribution and energy release rate (ERR) were used in the numerical simulations to evaluate the rock burst risk of the boring process. Experimental and numerical results show that rock burst is prone to occur in the upper, lower, and side areas of the surrounding rock around the tunnel, and risk increases with the lateral pressure coefficient and boring diameter. The optimal boring diameter ratio of stages 1 to 2 was determined between 0.55 and 0.59. Meanwhile, the ERR of the designed two-stage cutterhead is approximately 60% smaller than that of the flat-face cutterhead.