Applied Mechanics and Materials Vols. 90-93

Abstract: In this paper the distribution of shear stress along the anchoring section of prestressed bolt was presented. The distribution of shear stress along the anchoring section of prestressed bolt was analyzed with the plane elastic theory. The analytical solution of shear stress along the anchoring section was deduced. Several cases of shear stresses were analyzed with the analytical solution. The results show that shear stress of prestressed bolt are not uniform distribution along the anchoring section; it is has no relations with the prestress value where the shear stress peak value is; the shear stress is at a certain range along the anchoring section; the shear stress peak value increases with the increase of prestress value;the larger the diameter of the anchoring section is, the less of shear stress peak value is.

Abstract: For the high-speed railway tunnel concrete lining, there have been some such initial damages as initial pores or cracks, therefore the initial damages will be expanded gradually under aerodynamic fatigue loads resulting from the high-speed train passing by tunnel, elastic module attenuation laws of concrete was adopted to reflect the effects of fatigue loads on the tunnel lining mesoscopic concrete, taking the second stage of the elastic module attenuation as the main research stage, the mesoscopic damage mechanism and fatigue damage cracks developing-and-changing laws of high-speed railway lining concrete were simulated under the repetitive aerodynamic loads. Study indicates: for the concrete lining with initial damages, under the repeated aerodynamic fatigue loads, the mechanical properties of the tunnel lining concrete will gradually deteriorate to the whole damage of the concrete structure, which will cause serious inference on the durability of the tunnel especially during the middle and later periods of the high-speed railway tunnel serving.

Abstract: The changing rule of excess pore water pressure during dynamic compaction is important for construction. The following conclusions could be drawn by observing and analyzing the excess pore water pressure in test area. Under ramming strike energy of 2000kN•m, the best hit number during the 1~2 times is 8~9, the best hit number during the third time is 6~8. After compaction, the shallow excess pore water pressure is basically larger than the deep. The shallow excess pore water pressure needs more time to dissipate. The horizontal distance of the shallow excess pore water pressure is larger than that of the deep. During the dissipating process of the pore water pressure, we should pay attention to avoid vibration interference of load in the surface and prevent liquefaction of the powder soil. Under ramming strike energy of 2000kN•m, the biggest influence depth of dynamic compaction is 8～9m, the effective reinforcement depth is 6～8m. The conclusions can provide the theoretical basis for dynamic compaction construction.

Abstract: We have done a survey about the surface crack of the loess tunnel of Zheng-xi passenger railway by field survey, geophysical exploration test and pit detection and also have researched the produced regularity of the surface crack of the loess tunnel, especially about in the depth. The result of the survey and the detection indicates that: (1)The surface crack is mostly visible in the shallow area of the loess tunnel entrance. The visible width of the surface is extensive (0.2~200mm) and it is mostly visible in the tunnel, the depth of which is below 60m. The visible or wide cracks mostly appear in the area whose surface settlement is above 80mm. The width of the surface crack of the tunnel, which has a more shallow depth and a larger settlement, is much wider. (2)The effect of the High-density electrical method reflecting the development of the surface crack is obvious. The method of seismic reflection wave and seismic imaging is more accurate than Rayleigh wave in interpreting depth development of the crack. (3)There are two kinds of performance of the surface crack: longitudinal crack that inclines to the inside on both side of the tunnel and circumferential crack perpendicular to the axis of the tunnel. (4)The visible crack depth of the surface crack is limited, which is about 3.0~10m and it always doesn't reach the top of the tunnel. The depth by the geophysical exploration test is much more depth, which is about 10~15m.

Abstract: Slope is the wide range of large in channel works to ensure the safety of critical infrastructure.The actual project—the Bird Island Park in Shenyang, an example of hinge joint concrete block revetment ,using the FLAC analysis software, and the finite difference method percolation theory to calculate the 29 slope angle the role of a 45kg block under the action of the seepage stability of the slope. Variation in water level discussed in further detail and the role of the different blocks on the slope stability of the quality of the impact of the slope to provide a reference design and application.

Abstract: A new algorithm is presented for the finite element analysis of fracture mechanics. The algorithm allows crack propagation in any direction, and guarantees the crack path smoothly. This is achieved by tracking the path of the crack tip and by introducing a new remeshing method. Examples show that this algorithm is efficient for 2D problems.

Abstract: The failure conditions of tunnel surrounding rock under different cross section after full face excavation were studied through a number of model tests. The simulation of unsupported tunnel failure process under gravitational stress is carried out successfully in the tests. The test results show that failure of surrounding rock initiates from the upper part of the tunnel and develops upward progressively. Failure form of tunnel is different under different cross section type. Comparing with two-lane tunnel, the surrounding rock of three-lane tunnel keeps shorter stabilization, failure develops to the ground surface more rapidly, the stress changing amplitude of those beside tunnel is larger, and the rock mass on the top of the tunnel slides downward more clearly.

Abstract: Artificial neural network has been widely used in displacement back analysis, but it has the problems of large sample, over-fitting, local optimization and poor generalization performance, so it has the poor adaptability in the Geotechnical Engineering. Support Vector Machines algorithm has the advantages of small sample, global optimization and generalization performance. A direct optimization method based on genetic algorithm and the improved support vector regression algorithm (GA-SVR) is applied in order to identify multinomial parameters intelligently and forecast displacements fast and exactly, combined with an unsymmetrical pressure tunnel with shallow depth section of the left line of import in BEIKOU Tunnel on Zhangjiakou-Shijiazhuang highway. The application result shows the new type of intelligent displacement back analysis could obtain accurately the parameters of rock mechanics and initial stress in limited monitoring data and provide parameters for ahead-forecast of rock deformation.

Abstract: This paper will introduce the basic methods of soil-structure dynamic interaction at home and abroad, and analysis the advantages and disadvantages of these methods. Finally, the paper will put forward opinions on the research tendency of soil-structure dynamic interaction.

Abstract: The characteristics of smoke flow in natural ventilation shaft are studied in this paper, Using the computational fluid dynamics software FDS5.0 to build a 3D model of an urban tunnel with a smoking shaft, Large Eddy Simulation model was used to obtain the structure of flow field and the mass flow rate of natural ventilation at different shaft height, The results show that when the shaft height is low, the driving force of exhaust is weak and the exhaust capacity reduces rapidly, the flow state in shaft is controlled by horizontal inertia force; when the shaft height increase to a critical height, the exhaust effect enhance significantly, the flow state in shaft will change to stack effect control.