Applied Mechanics and Materials Vols. 353-356

Abstract: In this paper, the mechanical behavior of excavation and support construction of Weishe tunnel, which is a section of the Yangwu expressway, is studied quantitatively using 3D finite difference numerical simulation method. A sequential excavation method is used and the results show that the vault settlement occurs mainly on the phase of upper bench excavation. The convergences of upper and lower sidewalls occur mainly on the phase of lower bench excavation. During the construction, the surrounding rock pressure in the vault and sidewall of the tunnel decrease. Axial force of anchor reaches the maximum value after the finish of second lining. However, the surrounding rock pressure and internal force of steel arch reach the maximum value after completing the upper bench excavation, and then become as smaller as half of the peak value during the lower bench excavation.

Abstract: In order to reduce the negative impact of the environment by shallow tunnel construction, ground movement and deformation must be estimated correctly, through simulating the entire process of the shallow tunnel construction, the methods of monitor numbers analysis and numerical simulation have been used to validate the surrounding rock stress and strain in different situation, then the rules of stress changing and the trend of ground surface movement have been in-depth studied. On the basis, non-linear regression method considered time factor has been used to research the space-time deformation law of ground surface, the work provides a new way of estimating the effect on ground surface about shallow tunnel construction.

Abstract: Based on the fractal geometry theory, the bending form of crack expansion on concrete lining of hydraulic tunnel is described, according to the model of fractal fracture, stress intensity factor of concrete lining crack of hydraulic tunnel is established. Combined with the fracture mechanics theory, the relationship of stress intensity factor on l concrete lining crack is obtained under the hypothesis of crack linear expansion and crack irregular expansion, while the stress intensity factor of latter is less than the former, which is more close to the actual circumstance and more reasonable, whose fractal dimension is obviously larger than the former. The conclusion can provide reference for the engineering design.

Abstract: Reasonable evaluation for weak surrounding rock of shallow tunnel under unsymmetrical pressure is very important for the design and construction of tunnel project. The evolvement rule and space distribution characteristic of surrounding rock under different thickness of side covering soil were gained, which include the stress field and plastic zone by adopting rock mass deterioration model, to reveal the instability and failure mechanisms of surrounding rock. And then through analyzing and calculating the measured data in site, the stress characteristics of surrounding rock and supporting structure were gained. The conclusion can be a reference for the design and construction of Hongshigou Tunnel and other similar engineering projects.

Abstract: For Xuefengshan tunnel, supporting stability in the course of tunneling is analysed by use of changed parameters of construction and design, which is based on construction simulation of left tunnel in the fault. It was shown that tunnel structure can keep stability after advanced little pipe injection grouting is used and supporting parameters and excavation model are changed. It can provide scientific evidence for directing construction and ameliorating supporting parameters, and it can reduce loss which is resulted by heavy collapse because of incorrect support.

Abstract: Taking Xian Bell Tower and metro line 6 as research background, at first, according to the theory of Euler-Bernoulli beam in Winkler foundation, the analysis model of train-track-foundation system was established, and then, time-history curve of metro-induced loading acts on tunnel structure is obtained by using Matlab software. Two-dimensional finite element model of the structure-soil-tunnel interaction model was established using software Ansys,. Taken loading time delay into consideration for the first time, dynamic response law of the bell tower under the metro-vibration loading is obtained. Finally, the impact of metro line 6 on Xian Bell Tower was evaluated according to the Technical specification for protection of historic buildings against man-made vibration. Xi'an Bell Tower timber structure is safe when two trains running of the line 6.

Abstract: During the excavation by TBM of the Aicha Exploratory Tunnel along the Brenner Base Tunnel in Italy, in hard brittle granitic rocks, an instability phenomenon occurred at chainage 6+151. The left-hand sidewall lining partially collapsed for a length of approximately 60m. This led to a stoppage of the TBM lasting about 4 months. With the reconstruction of the geological model, a sub-vertical fault, not forecast at the design stage, was identified parallel to the direction of the excavation. In this paper, a three-dimensional (3D) model, which simulates the complex interaction between the rock mass, the TBM and its system components, and the tunnel support, is presented. The model accounts for the main machine components: shields, cutterhead, grippers, pea gravel and lining. The brittle failure of a thin granite diaphragm between the fault zone and the tunnel wall is reproduced and the results are discussed in terms of failure zone and horizontal displacements.

Abstract: The effects of metro line 2 and line 6 on Xi'an Bell Tower was studied by numerical analysis in this paper. At first, according to the theory of Euler-Bernoulli beam in Winkler foundation, the analysis model of train-track-foundation system was established, and then, time-history curve of metro-induced loading acts on tunnel structure is obtained by using Matlab produce platform. Secondly, two-dimensional finite element model of the structure-soil-tunnel interaction model was established using ANSYS. Finally, the impact of metro line 2 and 6 and ground transportation on Xi’an Bell Tower was evaluated according to the Technical specification for protection of historic buildings against man-made vibration. The construction of Metro Line 2 and Line 6 will affect the safety of Xi'an Bell Tower.

Abstract: According to the existence of uncertainty in the subway risk identification, introduced rule-based expert system technology, integrated expertise into the knowledge base, automatically identified construction parameters based on CAD drawings, discussed and designed automatic subway security risk identification expert system based on confidence factor theory. And taken underflow sand pit in subway station construction as an example, elaborated the key issues in the knowledge base construction in details, such as risk mechanism analysis, fact base structuring and rule base structuring. And proposed to combine the contribution (C(eij)) with fact credibility ( F(eij)) to confirm the evidence credibility CF(eij) =C(eij) × F(eij), solving the credibility assignment conflict when the fact of certainty and uncertainty existed simultaneously; Selected the threshold of risk conclusions credibility in representative conditions as the sub-boundary for risk potential classification, avoiding the risk omission problem. In this way, the application of expert intelligent decision technology was broadened in subway construction.

Abstract: Bolt design has an important role to give full play to the effect of bolt support and ensure the roadway safety. Based on numerical simulation by ANSYS software, stress - strain is no longer as the analysis object in the study, but creating the paths mapped equivalent plastic strain to observe the changes in the plastic zone. This paper studies the influence of bolt direction on the surrounding rock, and proposes a reasonable range of support direction to provide a reference for the actual bolt. The result has shown that the large oblique bolt results in the equivalent plastic strain increasing and it is not conducive to control the deformation of the surrounding rock. The best supporting direction is from-30 ° to 30 °.