Study On Waterproof Technique And Supporting Structure Of Metro Tunnel Passing Through Water-inrich Fault Zone

With the continuous expansion of China's subway construction scale,urban subways will face a variety of complex geological conditions,and the construction of urban subways will inevitably cross the area of high-pressure water-rich faults and fracture zones.Under the current situation of increasing demand for environmental protection,the problem of groundwater can not be avoided and need to be paid great attention to,not only because increasingly stringent requirements of water drainage,and the impact of groundwater on the construction will also be a key issue in the construction of subway.This paper relies on China railway first survey and design institute group co.,LTD.The technology research and development plan key project “The research on the key technology of urban rail transit project”,using theoretical analysis and numerical simulation methods to study the relationships between the permeability coefficient,water inflow,and the external water pressure in the process of tunnel excavation and grouting reinforcement for the tunnel lining.And this paper study the influence of grouting reinforcement on the distribution of water pressure outside the tunnel lining and the internal force of the initial support structure;Study the change of the internal force with the increase of water pressure after the secondary lining is completed,and the design of the waterproof and drainage.The main results of this research are as follows:(1)Based on the classical seepage theory,a model of tunnel inflow is established,which is based on the theory of axisymmetrical symmetry,and the calculation formula of water inflow under the condition of applying grouting circle to the tunnel in the equivalent continuum medium is derived,the calculation formula of the external water pressure of the lining,groundwater seepage equations,and analysis of the method of using FLAC3 D to solve the seepage problem.(2)The numerical simulation of fluid-structure coupling method was used to study the influence of the thickness and permeability coefficient of different grouting circle on the seepage field and initial support of the tunnel site.It was concluded that the increase of the thickness of the grouting circle which decreases the range of seepage field,the initial support was reduced,but this effect diminished when the thickness exceeded 3m.With the decrease of permeability coefficient,the water pressure outside the grouting ring increases,and the value of the water pressure inside the grouting circle changes little,but it is not economical to reduce the water pressure on the supporting structure by reducing the permeability coefficient continuously when the permeability coefficient ratio is n>30.The optimal grouting circle thickness is 3m,and the optimal permeability coefficient ratio is 30.(3)The numerical simulation of load structure method was used to study the change of internal force and safety factors of the secondary lining during the continuous raising of water pressure to fullwater after completion of the secondary lining.It was concluded that the safety factor of the lining increases first and then decreases as the water level rises.Before the water level rises to the vault,the elevation of the water level can increase the lining safety factor.However,when the water level exceeds the vault,the safety factor of the lining decreases after the water level rises.The acceptable water pressure for the lining is 2.0 MPa?(4)Through the on-site hydraulic test,it was concluded that the water pressure gradually increases over time after the secondary lining was applied,grouting is the main cause of water pressure fluctuations,and the closure of the secondary lining is the main cause of the permanent increase of water pressure.