Applied Mechanics and Materials Vols. 170-173

Abstract: Loess soils always have lower dry densities, open structures and joint fissures, and could exhibit a significant decrease in volume due to their collapse when wetted. These soils pose potential threat on structures built on them. When a tunnel built on such soils, the bearing capacity of tunnel foundation could not always meet requirements of structural stability, and therefore need some improvements. The improvements of collapsible loess foundation include cement compaction piles and root piles.

Abstract: Tunnel construction, inevitably crosses the surrounding rock of the horizontal bedded .The construction prone to bring about the accident of the local deformation, swaping blocks even the overall collapse, in particular,before completing supporting and reinforcement. Thus, it is particularly important to finish the anchoring timely. The design and construction methods of the conventional vertical anchoring system easily leads to personnel injured, the quality of construction is difficult to guarantee, etc. In the paper, the construction technology which is we adopted is using the way to unite the bedded wall rock inclined bolt and the vertical rock layers bolt .In anchoring, we optimize the spatial arrangement and the construction time. Simultaneously, we analysis the system which is the paper adopted and the tradition technology by the mechanical theory. The results show that there is the consistent effect between the new technology and the old one. However, the new one is to reduce the construction risk and to ensure the constructors’ safe. In conclusion, the new system has the significance of guidance and reference in tunneling.

Abstract: The article studies the influence of overlying soil thickness on dynamic response of underground stuctures by adopting the method of numerical simulation analysis. It carries on numerical analyses of dynamic response to the underground structures which overlying soil thickness is 0m、1.4m、2.8m、7.0m、14m、21m、28m. The results show that with the increase of overlying soil thickness, the horizontal displacement difference of bottom and top of side walls increases gradually. When the overlying soil thickness exceeds the height of underground structures, the displacement difference basically presents the rule of linear increase, while the displacement difference of the surrounding soil in the same depth do not change with the overlying soil thickness.

Abstract: Initial structure deformation prediction based on the regression analysis is an important means to evaluate the stability of tunnel, but the commonly used regression functions, such as exponential, logarithmic and hyperbolic function, have disadvantages of low accuracy. Aiming at the drawbacks, 3 kinds of multi-parameter growth functions (Weibull growth function, Richard function and Gompertz growth function) and 3 kinds of commonly used functions (exponential, logarithmic and hyperbolic function) are used to conduct the regression analysis for a loess tunnel’s initial structure in north-west China. Comparison results show that, (1) regressions based on multi-parameter growth functions are far more precise than the commonly used functions, reflecting its superiority in initial structure deformation prediction of the loess tunnel, (2) the more coefficients the function have, the higher the regression correlation is, and (3) the similarity of iterative and error analysis algorithm in different multi-parameter growth functions lays foundations for computer programming realization of regression analysis and model selection automation.

Abstract: The self-developed finite element program is used to the simulation of true tunnel with C++ language. Applying to Line 1 of Dalian Metro, inversion parameters and true parameters are close, which indicates the superiority and good prospects of the program, and it can be used for quantitative analysis of actual tunnel.

Abstract: Aimed at the support problem of the deep large-section tunnel excavated in high-stress condition with fractured surrounding rock, the different characteristics of the stresses and displacements of the surrounding rock of the tunnel with different section supports and lateral pressure coefficients were analyzed using numerical simulation and theoretical calculation, so was the effect of the height of the double-layered I-section beam on the bearing capacity. Arched with bottom arch superimposed and fully-closed I-section beam suitable for large-section tunnel excavated in high-stress condition with fractured surrounding rock was developed. This support applies fully-closed and horse-shoe shaped structure with I-section beam overlapped and welded and its bearing capacity is 2.5 times higher than frequently-used I-section beam. Underground field testing showed that the deformation of the surrounding rock could be effectively controlled when the secondary arched with bottom arch superimposed and fully-closed I-section beam of high bearing capacity was used.

Abstract: To ensure the influence degree on the environment during constructing metro-station based on shield tunneling is very important in the subway construction. After the shield machine passed the metro-station, the field monitoring of these segments is carried on during getting rid of the segments. The connecting seam opening length of segments, the tunnel convergence and the internal force of the segments’ bolt are estimated. The results show that the opening length of segments of circular connecting seam is larger than that of longitudinal connecting seam, and all the changes of the opening length value is within 1.5 mm. Tunnel convergence change generally contains a gradually becoming smaller and a gradual recovery process, and the tunnel convergence is primarily vertical. Bolt internal force change generally involves stress increasing rapidly, and then decreasing slowly. The field monitoring study will potentially provide the knowledge and reference for similar projects

Abstract: Urban planning for vertical space use must consider underground space form and intensity. But little researches and investigations about it have been done. Planners have little knowledge about quantitative mechanism of underground space developing and evolution. Advanced countries developed experienced data of underground space distribution. Modern statistical analysis method provides an efficient tool for this kind of quantitative and empirical research of spatial correlation. This paper selected some of the major characteristic indexes of land-use transport interaction and induces spatial statistical model to analyze the correlation between intensity of underground space use and the indexes of land-use transport interaction in central four districts of Tokyo City. Results show that the intensity of underground space use has positive and stable quantitative correlations with land use function (LT), land price (LP) and floor area ratio (FAR), especially significant in commercial and mixed land-use areas. The influencing factors of land-use transport interaction could be used as external indexes for forecasting the intensity and spatial distribution of underground space in urban central areas.

Abstract: The safety control of tunnel construction of urban shallow buried adjacent existing buildings is the new problems we have met this year in tunnel construction design. The text takes the link construction of Jiaozhou Bay subsea tunnel of Qingdao into combination, established three dimensional finite element model, analysis the interaction of tunnel-stratum-existing building which is caused by the tunnel construction. Study the surface subsidence pattern, the influence length of lengthwise the tunnel excavation and the change of uneven settlement of the upper buildings. According to the situation of construction, design five construction plans to optimization the design.

Abstract: This is an important technical problem that subway tunnel excavation pass through a filled area of crushed rock soil in mountainous city,and to control the ground surface settlement and reduce the influence for existing building have great significance. The paper presents an example that tunnel excavation pass through complex geological area of metro line no.3 project in Chongqing.At first,according to the monitoring results,the big surface subsidence and structures cracking appear in the process of the tunnel excavation are discussed.And then,use the finite element method analysis and calculation. On the basis of the analysis and calculation results, many effective technical measures are proposed to ensure stability of surrounding rock and control the ground surf ace settlement. Such as small catheter grouting consolidation, CD construction method, excavation speed control and so on. The monitoring results show that the vault sinks and convergence value reduce significantly after the improved technology measures are used.At same time,the ground surface settlement is controlled effec- tively. The results show that the improved construction measures achieve the purpose to control the settlement and deformation. The study result of construction scheme can provide reference for the similar project.