Applied Mechanics and Materials Vols. 170-173

Abstract: Few researchers study on deformation of rock tunnel face. The tunnel face is stable for small section shallow tunnel, but it shouldn’t be ignored when tunnels for large diameter are driven in weak rock mass. In this paper, dilatancy angle taken into account, FLAC3D is used to do 100 groups of numerical tests which are designed by orthogonal design method. According to test results, the formula for maximum deformation of tunnel face and test parameters are fitted by nonlinear regression method. Test value and predictive value have good correlation.

Abstract: The tether used to balance a submersed floating tunnel under water current is definitely subject to greater pre-tension, and is simplified as a Bernoulli-Euler beam. The fatigure characteristics of vortex-induced multi-modal resonance of tether under traverse shear flow are analyzed. In terms of the principle of energy equilibrium, both the mean square root displacement and mean square root stress of the dynamic response of tether is derived.The reliability index of tether is obtained in combination with S-N curve and fatigure probability model.

Abstract: There is no engineering experience for metro station construction by the PBA (Pile-Beam-Arch) method to enlarge an existing large-size shield tunnel in China. During enlarging construction by the PBA method, the spatial mechanical and deformational characteristics of metro station structure are still not clear. In this paper, the Gaojiayuan station is taken as an engineering background to study the spatial mechanical and deformational characteristics during enlarging construction by the PBA method. Based on soil-structure interaction theory, a three-dimensional finite element model is built to simulate the enlarging construction by the PBA method. The three-dimensional numerical results can be regarded as a valuable reference for enlarging construction by the PBA method in Beijing metro line 14.

Abstract: Strict waterproof is the key to prevent frost damage to tunnel in the cold region. Improving drainage system has benefits to obtain good waterproof effect. Aim at the drain pipe freeze in cooling and warming period, we design a strip partial insulating layer to the drainage system :(1) The girth drainage pipe connects to the central drainage pipe directly, and the lengthways drainage pipe connects to the girth drainage pipe by tee. (2) Interval decorating insulation layer to the tunnel girth drainage pipe, using the strip insulation layer behind the lining and setting annular insulation around drainage pipe under the tunnel road. (3) The strip insulation layer is sandwiched by two layers of flashing; one of them forms a whole system with the tunnel flashing and the other posts on its surface. The temperature field finite element analysis of surrounding rock and lining concrete show that: As the girth drainage pipe if there is insulation layer is placed with a certain interval between each other. Two kinds of drain pipe's freeze-thaw state has a time gap. It is beneficial to solve the problem of the poor drainage after the lining in the cooling and warming period.

Abstract: Jet grouting piles were used to reinforce overlying soil of shallow buried tunnel under unsymmetrical pressure. Displacement and strain was simulated during tunnelling with three steps excavation method under condition of reinforcement and unreinforcement. The results show that larger vertical displacement and shear strain occur during excavation of upper bench, and it changes very little when center and subjacent bench was excavated. This is because upper bench is located in soil, part of center bench in rock, and the whole subjacent bench in rock. Largest shear strain occurs at the arch foot of upper bench. It is concluded that jet grouting piles can control surrounding rock deformation effectively.

Abstract: The research status of radon elimination techniques at home and abroad in recent years is introduced. The feasibility of electrostatic radon elimination in underground engineering is analyzed. The technical problems of reducing radon and its daughters and such harmful substances are analyzed. The type of cellular and flat field dual-zone in electrostatic radon elimination is investigated. The dual-zone radon elimination equipment is designed and related tests are done.

Abstract: Based on the centrifuge model test this study established a mathematical model in which the interaction of culvert, soil, and culvert base and foundation were incorporated and developed a new method for calculating the soil pressure on embankment culvert. Centrifuge model test was performed in varying conditions to determine the relation between vertical soil pressure and filling height and to find out the variation of displacement field nearby the culvert. The results indicate that the vertical soil pressure on trench culvert is not always lower than the theoretical calculation value instead, it is related to and varies in nonlinear manner with a number of elements including filling height, width and slope of trench, dimensions of culvert, physical properties of backfill material, and stiffness of foundation, etc. When fills go up to a certain height, soil arch effect may develop on top of the culvert, with limited stability, which can relieve the stress concentration in this area.

Abstract: The damage features of surrounding rock in the process of bottom excavation in deep hard rock tunnel were investigated, combining with the actual tunnel data of JinpingⅡHydropower Station and using numerical simulation approach. The evolution mechanism of microfractures initiation, growth and expansion in deep intact rock mass was performed. It’s shown that the fractures caused by bottom excavation develop to deeper surrounding rock due to stress adjustment, and the zone that have been supported also has some damage. The research results provide important references to understand the damage features of surrounding rock in deep hard rock under high geostress.

Abstract: Under the particular geological conditions of clay and sandy soil interbed, through numerical analysis and field monitoring, the surface settlement, horizontal deformation and the stress distribution were analyzed after the tunnel excavation in a metro station in Beijing, China. There are differences of surface deformation whether the backfill grouting behind arch during tunnel excavation. While the backfill grouting behind arch, the ground surface settlement and the horizontal displacement reach 9.36 mm and 2.16 mm respectively. But while no backfill grouting behind arch, the ground surface settlement and the horizontal displacement are 14.51 mm and 8.85 mm respectively. The maximum ground settlement induced by tunnel excavation is directly proportional to ground loss ratio. When the ground loss ratio is 1%, the result is well consistent with the field measurement value and the numerical simulation result.

Abstract: On the basis of working surroundings of submersed floating tunnel(SFT), a new type of connexion joint is designed to link its tubes, and its mechanical behavior and safety under water condition are also analyzed by means of finite element method(FEM). The analysis shows that the connection joint proposed in this paper satisfies the requirement of safety under water environment and will be a new option for future use of submersed floating tunnel.