Analysis Of The Stability And Dynamic Characteristics Of A Cross-river Tunnel Under High Pressure

With the increase of the urban population density and the rapid development of the metro technology,metro has been one of the transportation in many metropolises of China.Wuhan is one of the national central cities which located in the central China along the Yangtze River,the programme and construction of the metro lines have been developed in recent years.Cross-river metro tunnel as the new significant constructure that connecting the economic zones located in both sides of the river,the stability of excavation surface during shield driving and the dynamic characteristics of tunnel during metro train operation have become the focus that the domestic and foreign scholars focus on.In order to analyze the static and dynamic characteristics of a cross-river tunnel,in this dissertation,the systematic laboratory tests and numerical simulations have been conducted to reveal the soil stability near the excavation surface during tunnel construction process and the dynamic characteristics of the concrete lining and the surroundings under metro train operation.The main contents and conclusions are as follows:?1?The mixture tests of soil materials used in the scaled model were conducted based on the 1^st,2^nd similitude theorems.The mixture proportion of each material,such as silty-fine sand,coal ash,wood chip,coarse sand,and machine oil,was determined as 1.0:0.1:0.1:0.02:0.05 that the macro parameters were calibrated under a series of consolidation and direct shear tests with different mixture proportions.Meanwhile,a discrete element model of direct shear test was estabilished to calibrate the micro parameters of the mixed materials for the following numerical simulations of cross-river tunnel model.?2?Based on the conclusion of the research of excavation surface support pressure of shield tunnel in domestic and overseas,the laboratory test scaled model of limit support pressure of cross-river tunnel excavation surface was conducted.Two different depths of covering soil,such as 0.5D and D,were conducted to analyze the destroy model of soil in front of excavation surface.A calculation model of limit support pressure of cross-river tunnel excavation surface in sands was proposed preliminarily.The model was compared with different models proposed by the domestic and foreign scholars.In order to evaluate the micromechanism of the soil in front of the excavation surface,a discrete element model with the covering depth of 0.5 D was established.The shear strain,sliding fraction,coordination number,volumetric strain,and bond rupture zone of particles in front of the excavation surface were analyzed.Based on the numerical results,the preliminary proposed model of limit support pressure was amended.?3?A laboratory scaled model of cross-river shallow tunnel during shield driving was established.A spiral excavator as a simple shield machine was used,the theoretical support pressure determined by the calculation model was used,and the settlement of ground surface was measured during shield driving.Meanwhile,a discrete element model of cross-river shallow metro tunnel was proposed and the water pressure was executed on the top of the model by servomechanism.The buoyancy force and lateral earth pressure were considered.The settlement of ground surface and the coordination number,volumetric strain,vertical strain,shear strain and bond rupture zone of particles in front of the excavation surface were measured and analyzed by comparing with the laboratory results.?4?A large-section cross-river tunnel is established based on DEM which considering the dynamic load of metro train as Wuhan Metro 7^th line?combining the road and metro?a case study.Irregular vibration levels induced by metro train operation in 2D was proposed based on the methods of 3D and 2.5D.The vertical displacement of rail,the mechanics,deformation and dynamic characteristics of concrete layers between the road and metro line in the tunnel have been analyzed.Meanwhile,the dynamic charateristics of concrete lining at different angles under the irregular vibration levels have been revealed.Subsequently,the vibrational accelerations and deformation of granular elements in the surroundings with different distance from the outer edge of the concrete lining have been analyzed.?5?Numerical simulations of dynamic characteristics of a small-section cross-river tunnel under metro train load were conducted based on discrete element method and the geological situation of Wuhan metro 2^nd line was considered as a case study.Three conditions,such as different water levels,different train speeds,and different train loads were taken into account to analyze the dynamic characteristics of concrete lining and the surroundings of the cross-river tunnel induced by the train operation.The numerical results showed that the stress in concrete lining and the deformation of the surroundings increased with the water level increased;the deformation of concrete lining became asymmetric and the deformation of the soil layer above the tunnel vault was separated as the train speed increasing;the vertical displacement of rails and the hoop stress of concrete lining increased,the particle accelerations of the surroundings decreased gradually and their radial displacement was distributed symmetrically with the train load increased.