The Mechanical Mechanism And Calculation Methods For The Structural Load Of Tunnels Excavated With Mining Methods

Because the excavation is often processed in steps during the twin-arch tunnels and tunnels with small spacing construction, the load of supporting structure changes frequently. Meanwhile rock stress and the interaction between rock and structure is complex. The existing theories are based on single tunnel not the double-arch tunnel. The influenced zone and mechanics mechanism of support and structure of double-arch tunnel is different from the single tunnel, so the existing theories are not right to the different style of structure.The load's computational methods of different constructer style are suggested by numerical simulation and theory computation. Through numerical simulation, compact the plastic zone and rock pressure between double-arch tunnels, tunnels with small spaing and single-span tunnels.By comparing different net distance, analysis and summarize the relationship between net distance and stress. The research results are suggested as follows:1. The stratum displacement, plastic zone and rock pressure of tunnels with small spacing are all superimposed when the net distance is very small.The plastic zone of soil between the tunnels with small spacing is obvious and the strain value is tall.2. For the tunnels with small spacing, the tunnel excavated later would cause additional stress to the tunnel excavated before through the results calculated by numerical simulation. The influence is significant when the net distance is small. Based on the calculation theorise of rock pressure for single tunnels and the calculation results obtained by numerical cauculation, the calculation methods of rock pressure for tunnels with small spacing are summarized in different depth and net distance.3. The plastic zone of double-arch tunnels distributes the arch hance, skewback, the bottom and top of mid-partition. Because of the mid-partition, the plastic zone of double-arch tunnels is obviously small than the single tunnels with the same span length.4. The rock pressure of double-arch tunnels is larger than the results obtained by single tunnels with half-span while smaller than results obtained by single tunnels with the same span. The question is researched and analysised through the existing theories and formulas of formation pressure. Assume the double-arch tunnel is excavated by mid-cavatity method, so we should consider the span excavated of mid-pilot heading and its influence to the rock pressure of whole double-arch tunnel. By comparing to the results of numerical simulation, we can know the relationship of rock pressure between the double-arch tunnels and single span tunnel. Assume the rock pressure is well distributed, we can conclude the calculation methods of double-arch tunnels in different depth.