Applied Mechanics and Materials Vols. 256-259

Abstract: Accompanying the enforcement of strategy to develop western regions, transport and other infrastructures of western China expand substantially and long tunnel in karst zones increases dramatically. Geological hazard of water inrush and mud outburst often occur in the process of karst tunnel construction, which often lead to equipment destroyed and construction period bungled, even serious casualty and economic loss. The influence of large-scale concealed caverns with high pressurized water on top of tunnel on the stability of rock pillar between them is researched in this paper. According to the actual conditions, rock pillar is simplified into beam with both ends built-in. Utilizing the conception of classic structural mechanics, a model is developed to calculate the minimum thickness of rock pillar in order to evaluate its stability by use of the criteria of shear strength and tensile strength of rock pillar. As a example, the proposed model is applied to predict the stability of rock pillar between karst tunnel on Yi-wan rail line and concealed cave with high pressurized water, the result illuminates that this methods is feasible to supply basis for evaluating the stability of rock pillar during construction period of karst tunnel.

Abstract: With the implementation of Western Development, West-to-East Electricity Transmission Project and South-to-North Water Diversion Project, a large number of hydro-power stations have been built in the west middleland regions of China. Because of the complexity of terrain, geological and physical-mechanical conditions, the stability of large underground structures becomes one of the most important problems during the engineering design, construction and operation. This paper will take Tianchi hydro-power station as an example, according to the measured stresses at several points, the in-situ stress field is feedback analyzed by using the combination of the genetic algorithm and 3D finite element method. Then, the rheological model of bolted joint rock and nonlinear finite element method are adopted to calculate the displacement field, stress field and D-P point safety factor of the underground structure. The stability of the underground structure is discussed, the excavating and supporting scheme are also presented, and the supporting effect is evaluated. The achievements in this paper can not only be taken as the reference to the design, but also provide some design experiences for other underground structures.

Abstract: On the basis of the three-dimensional ,unsteady-state , viscous N-S Equation and k-ε two equation turbulence model , the simulation calculation is made with the finite volume method on the aerodynamic effect of a high-speed train passing a tunnel.The numerical computation simulates the pressure change in the tunnel,analysises regularity of the the initial compression wave and the pressure gradient wave,compares the mitigation effect of the two hoods on the pressure gradient.The following conclusions have been drawn from the research: The amplitude of the initial compression wave is not significantly reduced with hood,however,the amplitude of the pressure gradient is significantly reduced with hood.And the mitigation effect of the vented hood is better than the unvented one.

Abstract: Underground water is a big problem for tunneling under rivers or oceans. So it’s practical method to consider pore pressure for determination minimum value of surface support pressure. What’s more, the earth thickness above excavation tunnel changes because of the riverbed existence, which makes surface support pressure more difficult to set. Active earth pressure theory, Murayama formula and fluid-structure interaction theory are used to analysis the minimum value of surface support pressure. Relationship between support pressure and horizontal displacement, which is supporting characteristic curve, is established. The determination principle for minimum value of surface support pressure is comprehensive analysis of plastic zone development and the level of face horizontal displacement. The results suggest that: the active earth pressure can be used as the lower limit for surface support pressure set in horizontal excavation section; but it can’t meet the requirements for the uphill section of notching section. But minimum value of surface support pressure for the slurry can be determined by supporting characteristic curve.

Abstract: A two-dimensional RSM turbulence model combined with enhanced wall function method is used to solve Naviar-Stokes equations，and Fourth Order of Runge-Kutta method is embedded in FLUENT’ UDF for Solving vortex-induced vibration equation of the cable of the submerged floating tunnel .The weakly coupled fluid-structure interaction algorithm is applied to solve the vibration equation and Naviar-Stokes equations, respectively,and the structure systems and fluid systems are combined with the lift coefficient, drag coefficient and dynamic mesh technology. The following conclusions: submerged floating tunnel cable presents non-locking and locking the two phenomena with the increase of the reduced velocity; In the non-locking region, the cable vibration beat phenomenon; in the locked region, vortex frequency is closed to the natural frequency of the cable and vortex-induced resonance leads to a significant increase of the cable displacement and the lift and drag.

Abstract: Rock burst is one of the main geological disasters in deep-buried long and large tunnels, therefore rock burst prediction is necessary to ensure the safety of tunnel construction. Measuring the geostress in Yaojia tunnel, and using the Turchaninov and Russenes to conduct comprehensive evaluation, it turned out that the maximum horizontal stress is 3.6~12.5MPa and the minimum horizontal stress is 2.1~7.8MPa in the surveyed area, the dominant direction of the maximum horizontal stress is about N34 W, the angle between the maximum horizontal stress and the tunnel axis is about 83°. And these results showed Yaojia tunnel may occur slight rock burst within 400m of its length and it is adverse to the stability of tunnel surrounding rock.

Abstract: An analysis is made of the compression wave generated when a high-speed train enters a tunnel with hood. The purpose of the hood is to reduce as much as practicable the maximum gradient of the compression wave. In this paper the numerical computation simulates the pressure change in the tunnel,analysises regularity of the the initial compression wave and the pressure gradient wave,compares the mitigation effect of the two hoods which have different cross section on the pressure gradient.The following conclusions have been drawn from the research: The amplitude of the first compression wave is not significantly reduced with hood,however,the amplitude of the pressure gradient is significantly reduced with hood.And the mitigation effect of the enlarged-transect hood is better than the equal-transect one.

Abstract: Aiming at the problems in construction for a shallow-buried and unsymmetrical loading portal in Banzhulin Tunnel in Yu-Xiang expressway, the finite element simulation were carried on to study the behavior for bench excavation method. Main results of numerical analysis as follows:the displacement of surrounding rock of right tunnel(as AR)at the horizontal direction is large and may larger than that of the left tunnel(as AL) at the vertical direction,and the largest deformation is 22.63mm,occuring at the key point DL. Compared with the data of monitoring measurement, the correctness of this simulation was proved.The behavior for deformation and stress of mountain tunnels as Banzhulin is basically mastered,and the displacement of rockmass is the key factor in tunnelling.

Abstract: The shape and properties of the sliding wedge in the three models, DIN4085, Jancsecz and Anagnostou/Kovari, are systematically explained, based on the simple and applied properties by using the analytic method to calculate the earth pressure in the tunnel project with shield machine. Combining with the Silotheory proposed by Janssen and the Terzaghi formula, the three pre-add models are applied to calculate the earth pressure in the projects of the Westerschelde tunnel in Holland, the Metro Line 1 in Düsseldorf and the Mostoles railway in Spain, in comparison with the actual earth pressure data of shield machine. The suitable using conditions of the three models in different situations as the shield type, the buried depth, the soil type, the water pressure and the part of the face are summarized, in which the water pressure, the friction angle and the cohesion of the soil are taking a crucial role in the value of the support pressure.

Abstract: The slope effects on the movement of internal smoke cannot be ignored. Fire experiments in a small scale tunnel are conducted in order to observe the smoke movement in a tunnel with three kinds of slope (0%, 3% and 5%) under different longitudinal ventilation velocity, then find the correlation between smoke diffusion velocity and longitudinal ventilation velocity, and slope in tunnel by numerical fitting and dimensional analyses, finally conclude:(1) as longitudinal ventilation velocity increases, smoke diffusion velocity gradually decreases; (2) when longitudinal ventilation velocity is smaller, with the increase of slope, smoke diffusion velocity is gradually increasing; (3) when longitudinal ventilation velocity is large, slope to smoke diffusion velocity is not affected. These quantitative conclusions provide fire Prevention of the tunnel in city with a reference.