Applied Mechanics and Materials Vols. 638-640

Abstract: The factors resulted in the cracking of Xiao-wan arch dam are extremely complicated. A numerical analysis based on elastic-viscoplastic mechanics theory has been developed to study the cracks in the middle diversion pier of Xiaowan Arch Dam. This analysis aims to investigate the cause of cracks and the reliability and accuracy of the analysis model have been examined. By using this analysis and the obtained results, the following conclusions are drawn: 1) cracks were not induced by a single cause, but a multitude of various effect such as stresses induced by thermal movements, the bond between the anchor cables and the surrounding concrete and the pressure due to the impounded water, amongst which the thermal stress is the most significant reason; and 2) with the presence of water in cracks, if the drainage hole continues to run overflowing water, the stress intensity factor of a crack tip will exceed the fracture toughness of the concrete. With the hydraulic fracture effect, the crack will grow continuously. The findings derived from this study will provide useful information for future projects of the similar nature.

Abstract: In order to have a good understanding of the geotechnical behavior around underground opening excavated in stratified rock mass, numerical simulation of a gate-shaped cavern excavation was conducted by applying a transversely isotropic model base on microstructure tensor method. The simulations were performed under the assumption that both the beddings and the in-situ middle stress vector run parallel with the cavern. Effect of the dip angle of beddings and that of in-situ major stress vector on deformation and failure of rock mass around the cavern was investigated. The mechanism underneath the image of deformation and failure was also discussed. It is found that the dip angle of beddings has less influence than the in-situ stress on deformation while the dip angle of bedding and the direction of in-situ major stress vector are equally important to the failure of surrounding rock mass.

Abstract: With the development of transportation construction, soft rock tunnel with high geostress construction has become a key problem to overcome of traffic engineering construction. In order to explore the deformation mechanism and control technology of soft rock tunnel with high geostress, Xiakou tunnel engineering as an example, the geological characteristics and deformation characteristics of the tunnel were analyzed, to obtain the deformation mechanism of soft rock tunnels with high geostress, and to develop deformation control technology, the results provide a basis and reference for the domestic and foreign the similar engineering construction.

Abstract: As the excavation of tunnels, there are new channels of the groundwater drainage. The original supply of the circulatory system has been destroyed. The effects of groundwater to rock mass of surrounding rock are aggravated. In this paper, combined with a new highway tunnel project, the model is built according to the design parameters and the site engineering geological conditions of the tunnel. The fluid-structure interaction module of the finite difference software FLAC3D is used for the research on tunnel excavation. The distribution of seepage field, the stability of surrounding rock and rock deformation under saturated conditions during the tunnel excavation have been analyzed. The simulation results have certain guiding meaning on fracture development, the stability design of tunnels in water-rich stratum and the design and construction of anti-drainage.

Abstract: According to the geological characteristics of Xi'an, analyze the accidents may occur in metro construction. A metro construction safety risk assessment system should be built on the basis of the cause of the accident. Combined with the data of survey and design of Xi'an No.4 subway construction, using the fuzzy AHP to reach the parameters of risk assessment and build a CIM model. CIM model is applied to the risk assessment of Xi'an No.4 subway construction. The total metro construction safety risk can be gained through analyzing. In addition, risk events that may occur based on specific risk factors to determine the risk level. Lastly, control measures are put forward.

Abstract: It is rather complicated to predict the characteristics of strata response to mining operation in thick seams. However, a comprehensive evaluation of ground behavior is a prerequisite for maintaining efficient production, especially when the top-coal-caving method behind the face is applied. An analysis of the conditions of top coal has revealed that a 1.8m thick layer of coal just above the shield supports is well fractured. However, a 4.2m thick layer of coal above the fractured part is either not fractured or is fractured in the form of large blocks leading to obstruction of windows of shields during coal drawing. It is concluded that, in order to decrease dilution and increase extraction ratio and efficiency of operation, top coal should be as uniformly fractured as possible. Hence, an efficient and continuous coal flowing behind the face can be maintained.

Abstract: Based on the traditional safety coefficient method,Continuum Model and single track railway tunnel lining structure, the paper does numerical simulation calculates and compares effects of actions on tunnel lining structure, analyses and get the effect of actions in different section of tunnel lining.According to the tunnel lining element’s safety coefficient and standard requirements, reasonable lining structure thickness is gave by comparison and optimization of lining structure thickness,and this provides the theory support for the structure design of track railway tunnel .

Abstract: Due to the brittle rock deformation is not obvious, and the destruction process has the features of sudden and concealment, it is often neglected in the field during construction. In this paper, Brittle rock was selected as the research object. Using the vault subsidence as monitoring parameters, the excavation process was simulated in single line tunnel by the finite element analysis tool of ANSYS, we obtain the maximum displacement of brittle rock and stress variation with time. Then the subsidence effect of different buried were analyzed, to determine the stability period of III Brittle surrounding rock. The research results can be used to guide the development of the monitoring standard, in underground engineering construction of the brittle rock.

Abstract: Site observations were conducted to investigate the reasons for the poor current rock-mass conditions being experienced in essential crosscuts, to provide recommendations for remedial support measures. Conceptual analyses of mining induced stresses within abutment pillars were undertaken using elastic analytical and mathematical modelling. The results showed that damage to the crosscuts is due to high mining-induced stresses, with the major stress probably acting vertically, the protection pillar for the 480 Level crosscut should be at least 100 m wide. The research demonstrated that only 2.4 m grouted rock-bolts and timber sets is not enough in these conditions, so the 480 Level and 580 Level central haulage should be re-supported with a combination of 4.0 m pre-tensioned cable-bolts, a 75 mm layer of steel mesh (or fibre) reinforced shotcrete, and even steel arch sets with lots of log.

Abstract: Determining control empty size can be used as a standard of deciding whether contact grouting in the empty area is needed, in order to reduce the construction difficulty and enhance running safety of underground penstock. In this paper, underground penstock operation process has been simulated by means of the well-known FEA software-ANSYS. The empty conditions and joint bearing of steel lining and surrounding rock have been simulated by setting contact element. In this way, control empty width of different radius steel pipe and different initial gap has been calculated. The result provides reference to decide whether contact grouting between steel lining and back filled concrete needed.