Abstract:

Focusing on the research hotspot of large-span tunnel passing through coal seams, and taking Chongqing Huanshanping tunnel for example, some works on defining the large-span tunnel and the mechanism of interaction between surrounding rock and support structure was primary conducted, and then on-site monitoring and numerical simulation of the stability of large-span tunnel passing through coal seams were carried out. The results show that the effect of equivalent stress concentration in different part of the tunnel structure has different sensitivities to the change of flat rate, the most sensitive is arch spring, and the crown is the least. Due to sharp stress redistribution when the tunnel is excavated through coal soft rock mass, tunnel crown settlement increases greatly; and the plastic zone can also quickly expand along the coal seam. Specially when the weak coal layer is intersected by the tunnel, the effect of bias pressure becomes much larger and the bias pressure increases with the coal seam steepens, so as to easily lead to the failure of surrounding rock and support structure. Therefore, it should be dealt with carefully during the design and construction.

Key words: coal seams, large-span tunnel, bias pressure, stability of surrounding rock