Study Step Method Construction Of Small Spacing And Large Cross Double Tunnel On Surrounding Rock Stability

With rapid economic development of China, considering the large land area of the country, the terrain is rugged, to facilitate the exchange of local economic, physical, cultural, the tunnel become the first choice to solve such problems. Separate tunnel get better development in engineerings, but it is difficult to determined by norms.If tunnel spacing is too large, the area is occupied big and the maintenance is inconvenient, such small-distance tunnel and arch tunnel emerged. The arch tunnel of construction period has a long time and complicated process, the leakage and cracks in the wall of problems is existing, so the structure type of application has been widely questioned. Small-distance tunnel can solve double hole connection problems well, while it can effectively avoid arch tunnel, long duration, complex process, the problem of higher cost, so small-distance tunnel in the mountain tunnel construction has been widely used.In this paper, Daiyunshan tunnel is used as the background, numerical simulation method of double hole small clear distance tunnel construction method (step method), the rock wall thickness, different level of surrounding rock were studied by theoretical analysis.Using finite element simulation software MIDAS GTS NX of surrounding rock at the same level, different thickness of rock wall, double holes in different depth, to simulate the construction progress and so on through the activation and passivation unit, to simulate the excavation process, observation of the tunnel surrounding rock deformation, stress and strain, the plastic zone size, reasonably come to the excavation method, a reasonable interval. Through simulation, we found that in the arch at the waist generally larger stresses at the crown and invert occur at larger vertical displacement, vertical displacement is greater than the value at the invert of the dome; step method of construction in different confining under the rock conditions, no matter what changes a step length, the smaller the difference between the construction schedule two tunnels, the smaller the rock wall thickness, the greater the impact on the stability of surrounding rock deformation relative increase.