Applied Mechanics and Materials Vols. 90-93

Abstract: In order to improve the mining benefit of coal resources, Chang Gouyu Coal Mine carried out the technology of mining without coal pillar in steep seam. The key of the technology was to ensure a long-term stability of the cross-entry roadway across the seam. Through the analysis of the nature of steep seam roof and floor rock, and based on the stability analysis and loose circle measured of surrounding rock of crosscut roadway, we brought forward adopting shotcrete rockbolt mesh and U-shaped steel complex support structure system. This complex support system could flex lengthways and compress in radial direction. The entirety integrated with the surrounding rock, and they formed into a whole. Application of the complex support system could effectively control the deformation of the surrounding rock collapse, and maintain the stability of the crosscut.

Abstract: The tunnel excavation destroys rock stress state and when concentrated stress exceeds the strength of surrounding rock, the tunnel periphery rocks will be destroyed. And the effective bearing ring will be soon instable and it needs to be supported. Blot-grouting support is an active support method which organically combines shotcreting support and grouting consolidation and its theoretical research achievements are less. This paper, starting from catastrophe theory, established catastrophe instability model of blot-grouting support body and it also obtained the mechanic judgment criterion of blot-grouting support body damage and the regular pattern of the point (N, q)’s motion tract in the controlling space, of which the influence to the rock stability. And the paper also judged the minimum thickness of blot-grouting support body in the point of catastrophe stability model to provide the basis for theoretical calculation and engineering application.

Abstract: Twin-bore tunnel is the better and useful structure form of wide span under complex conditions, and the Jiagar Tunnel is the Twin-bore tunnel of the expressway from Lhasa City to Gonggar International Airport. In the paper, we studied the deformation characteristic of the tunnel during two construction scheme, the sequential and whole excavation, by the numerical simulation of FLAC^3D code. We obtained that the key points deformation characteristic was similar, the obvious part of the x-displacement is the joint of the tunnel roof and the side wall and the y-displacement is the midpoint of the tunnel floor. And the sequential excavation is better than whole excavation.

Abstract: In view of certain areas of Guizhou are soft sandstone rock, where single block of rock's hardness is very low and easily crushed, complicated hydrogeology and low level of complex surrounding rock and geological conditions, geological radar prediction is used before the excavation of the tunnel, and New Austrian Tunneling Method was used in the construction. The process of construction segment had been monitored and measured, and the deformation of tunnel had been controlled. According to the situation during excavation and monitoring, the construction method was further improved. Through tracing and monitoring the tunnel construction of from zk40+430 to zk40+630 sections for two months, showed that the tunnel construction method is effective in this paper.

Abstract: The problem of disposing the soft soil foundation will appear inevitably during the construction of modem high way. There are many ways to dispose the soft foundation. One of those is CFG pile technology. Take the CFG pile technology in the GuangWu Expressway for example, the influence factors of embankment settlement were discussed in detai by numerical analysis, some useful conclusions are obtained from the computational results.

Abstract: In general, rock mass is anisotropic because of presence of stratification, foliation or joints in it. In this paper we considered how the angle of anisotropy influences the stability of tunnel. By using COMSOL Multiphysics, fluid and 2D plane models are coupled to analyze stress-strain state, failure shape and water flow characteristic around tunnel for angle range from 0° to 90° with a interval of 15°. Results show that in condition of vertical force of initial stress field larger than horizontal one, failure district is maximum for θ=40° and minimum for θ=90° where the strength of horizontal direction in anisotropic rock is smaller than the vertical one. In this case failure is mainly developed in roof and bottom. When the horizontal strength of anisotropic rock is larger than the vertical, results reverse. In anisotropic rock, the more the direction of larger permeability is coincident with one of source underground water acted, the more water flows into tunnel.

Abstract: Based on soil-structure interaction model, the seismic dynamic response of tunnel in karst areas were performed by using viscous-spring artificial boundary and time history analysis method. In combination with the Menglian tunnel engineering on the Bao-Teng Highway in Yunnan, in different sizes and sites karst caves conditions, the dynamic responses of displacement and internal force on control points of the tunnel structure were obtained. The results show that comparatively large interal forces, under the high-intensity earthquake conditions, will appear on the side wall of the tunnel which through karst areas, less ones on arch crown and inverted arch parts, and the differential displacements of arch crown reach to the maximum. When the karst caves are located in the side of the tunnel, it make the seismic dynamic response get more large, which make the surrounding rock must be strengthened treatment. The results provide useful reference for the aseismatic design of tunnel.

Abstract: Soil liquefaction due to the earthquake causes serious damages and engineering problems, such as the reduction of the soil strength, large settlement of the ground surface, the flow of liquefied soil and the uplift behavior to the underground structures, and the large deformation induced by the uplift force threatens the stability and safety of the structures. In this paper, a FE-FD coupled method is used in the simulation, the cyclic elasto-plastic constitutive model and the updated lagrangian formulation are applied to deal with the material and geometrical nonlinearity of liquefied soil. The results show that after the earthquake, the exceed pore water pressure will still exist for some time and the structure has an obvious vertical uplift displacement related to the liquefied area and the flow of liquefied soil. The uplift displacement will decrease as the thickness of the upper liquefiable soil layer is reduced. The results can be regarded as a guidance and reference for the design of the large underground structures.

Abstract: In order to keep the safety construction during TBM’S commencement and arrival more and avoid surface settlement and failure accidents happening at the joint areas of TBM’S commencement and arrival, according to mechanical properties and deformation modes of water-rich sand stratum, mechanical and mathematical models are established, and theoretical equations of longitudinal improvement scope based on strength and stability theory are deduced. At the same time, according to geometric structure of TBM and permeability requirement of improved stratum, geometric criterions are proposed. By monitoring and analyzing the whole process of stratum improvement at the joint areas of TBM’S commencement and arrival in line 2 lot 2202 of Shenzhen Metro, longitudinal improvement theory and stratum adaptability of various improvement methods are verified, it provides a reliable theoretical basis for stratum improvement in water-rich sand stratum.

Abstract: In the Yellow River crossing tunnel of the middle route project of South-to-North water diversion, its geological conditions are very complicated, so potential risks are much likely to occur in the construction. Based on the fault tree analysis, fuzzy comprehensive evaluation method is also used for the quantitative analysis on the risks during the departure and reception phase of the tunnel construction. And it turns out that, there are risks of collapse of working well, leakage and plasma leakage, mechanical equipment failure and large deviation from the designed axis during the construction. Finally, the measures available of risk aversion are put forward, which have achieved good field applications and also provided some reference value for similar projects in the future construction.