Study About Tunnel Excavation And Surppoting Technology In Soft Rock On Two Water Tunnel Of Lan Yu Raod

With the development of the western region gradually thorough, railway transportation has become the primary task to solve the wide staff distribution and transportation of materials, a large number of railway construction in the western areas rising. In the construction of railways in West China, geological disease of soft rock tunnel is a difficult engineering problem to solve, which has great detrimental effect on the whole railway engineering construction safety, construction period and investment. To solve the problem, many scholars and experts have made positive efforts and contributions in this respect.The Two Water Tunnel of Lan Yu Railway crosses through the carbonaceous phyllite, slate with sandwiched phyllite stratum. In the process of excavation, the surrounding rock appeared large deformation and subsidence showing the typical characteristics of soft rock. In this paper, on the basis of Two Water Tunnel construction, from the following aspects treatment method of soft rock tunnel are discussed.①Firstly, the research status at home and abroad about soft rock in the literature study, grasp the definition, properties of soft rock and mechanical characteristics, and then through the practice of construction site, to collect relevant technical data, preparing for the following research.②Under the stress of surrounding rock after excavation, tunnel has the trend of squeezing into the cave inside. The soft rock has obvious plastic deformation in this force and invades the building line. In order to achieve control of the deformation of soft rock tunnel, according to norms and past experience, designers put forward reasonable amount of deformation reserved and support parameters at the design stage, and then strengthen the support appropriately by classifying the deformation during the construction phase.③During excavation of two water tunnel, it mainly used these methods of three-bench seven-step excavation method, two-bench four-step excavation method, three-bench to expand the arch foot and milling digging method. All above methods have a good control effect on the deformation of soft rock, but a reasonable choice should be decided by the condition of surrounding rock.④In this paper, numerical simulation which works on two-bench four-step excavation method is reasonably simplified through using FLAC3D to work on two-bench method. By comparing simulation results of vault settlement and vertical stress, the two-bench four-step excavation method in accordance with the up-step length6m,the down-step length16m,and excavation cycle step length lm is more reasonable.⑤Double early support and double tunnel secondary lining both are new tunnel construction supporting ideas, and we discussed them based on the Two Water Tunnel test section. Two engineering methods for soft rock deformation have good control effect, but they are not easy to carry out for the technical difficulties. So we make a choice to use them, It should base on rock surroundings and construction conditions.