Research On The Supporting Time Of Large Deformation In The Soft Rock Tunnel

Since the21st century, the speed of the economic construction of our country have significantly improved and obtained unprecedented development. The great development of economy leads to a higher demand of transportation, therefore, high speed railway construction in China developed rapidly in recent years. In the next decade, the development of high-speed railway construction in China will not slow down, It is predicted that the mileage of high speed railway construction in China in next ten years will be more than the existing total mileage constructed. Due to China’s vast and diversiform terrain, which has lots of complex terrains, such as mountains and hills, the high speed railway construction will inevitably need to build tunnels. In the actual project, due to the slow progress and the difficulties, tunnel construction will be the control project in the high-speed railway construction. Whether the tunnel project can be completed on time and ensuring quality plays an important role in the time and quality control of a high-speed railway construction. Although the time、quality and safety of the tunnel project will be guaranteed when the geological condition is good, in poor geological conditions, such as high stress soft rock large deformation, the period will extend, the safety will decrease and the cost will increase because of the deformation of surrounding rock.It is popular to use the preliminary full load as the secondary lining as safety stock. Primary support under full load means that the surrounding rocks can completely be stable under the function of primary support; As a safety reserve, secondary lining is not to say that two line does not force, but to said that the stress second lining carried can be ignored compared with its capacity of load bearing, the main function of the secondary lining is to improve the structure durability of the complex lining and to resist the possible deterioration of surrounding rocks.The bearing capacity of surrounding rocks gets more and more attention in nowadays design and construction of tunnel projects. Use surrounding rocks and supportings as an unity to bear the load. In order to fully carry out the bearing capability of wall rock, certain deformation of surrounding rocks is allowed when the tunnel excavation begin or in the late development process. It will mobilize the supporting function of the supporting system and the bearing capacity of surrounding rocks, which also decrease the function of supporting structure to surrounding rocks and effectively improve the stress state of surrounding rocks.In order to prevent the surrounding rocks get too much deformation which may loose it, and ensure the reasonable function of two lining at the same time, supporting timing must be reasonable. If the support is too early, surrounding rock stress can not released, the load on the second line of will be too large, which not only ask for higher stiffness and strength of secondary lining, but also leads to great potential safety hazard; if the support time is too late, the displacement of surrounding rocks can not be limited, which will put more pressure on secondary lining, or even cause insufficient building line due to the large displacement. As a result, choosing rational support time become the top priority in tunnel engineering.