In underground construction projects such as tunneling, groundwater inflow during subsurface excavation affects safety and progress of construction. Methods for predicting the amount of tunnel inflow include a simple method using spreadsheet software and three-dimensional (3D) groundwater flow analysis using finite element method. For 3D groundwater flow analysis, a great deal of manpower is required for discretization and boundary condition setting according to the shape of the tunnel and the progress of the tunnel excavation. This paper proposes a 3D groundwater flow analysis method, “virtual drain model”, which can simulate the drainage effect of the excavated zones without modeling the tunnel structure. In order to verify the validity of the virtual drain model, the authors assumed homogeneous and heterogeneous structure and compared the analysis results obtained by the virtual drain model with the results obtained by the conventional modeling method. In addition, the authors modeled site with complex topography and geological structure and simulated the measured amount of the tunnel inflow using the virtual drain model. Satisfactory results were obtained in each validation case.
In this study, simulation using unsteady 3-D CFD (Computational Fluid Dynamics) analysis was conducted to understand the high dust concentration area in the tunnel and the change of dust concentration chronological change in the ventilation design phase before tunnel construction. As a result, it was found that it was possible to predict the concentration of dust in the tunnel chronological change during construction by experimental results or measuring results of field tests conducted by JNIOSH (National Institute of Occupational Safety and Health, Japan), in which tunnel ventilation was conducted using the diffusion-dilution method. Furthermore, by evaluating the dust dispersion chronological change and the arithmetic mean, we were able to confirm the changes in the mine environment due to differences in the ventilation system and ventilation parameters.
It have been worked on the development of a construction method to extend the construction span length for the purpose of rapid construction of mountain tunnel lining concrete. With this construction method, the length of one construction span is longer than usual, so there was concern that the risk of cracking due to temperature changes and drying would increase. For this reason, a joint plate was installed in the center of the center before casting, and a crack-inducing joint was formed by pulling it out to try to reduce the risk of crack occurrence. A full-scale construction experiment was conducted to confirm the applicability of this method and to confirm the crack-inducing characteristics. Furthermore, the state of crack induction was reproduced by analysis, and the applicability to actual tunnel structures was analytically verified. As a result, it was confirmed that this method can induce cracks in the joints, that the induction of cracks can be reproduced by analysis, and that the induction of cracks can be effectively induced even in an actual tunnel model.
Anisotropic in situ stress field does induce specific patterns of tunnel displacement while tunneling through hard sedimentary rocks with high overburden. Orientation of anisotropic principal stresses, along with a tunnel axis direction corresponding to these stresses, leads to the development of nonuniform stress distribution or local stress concentration in front of the tunnel face. This asymmetric stress condition with regard to a tunnel axis direction generates displacements both ahead of and behind the face, subsequently. To elucidate these mechanisms, first, in situ principal stresses were measured on the tunneling site, excavating through sedimentary rock masses that generally exhibited elastic behavior under the depth of more than 700 meters in the Akaishi Mountains region, central Japan; they were concordant with the regional anisotropic stress field: approximate east-west compressive tectonic force acting in the study area. Then, observed imbalance in displacement vectors reciprocally suggested that the asymmetric stress condition, evolving adjacent to the excavated space, might well control tunnel displacements to a certain extent. Finally, numerical analyses helped to identify that these displacements derived from anisotropic in situ stress field in conjunction with a tunnel axis direction. This paper emphasizes the importance of incorporating an impact of anisotropic in situ stress condition with the analysis or evaluation of displacement profiles for a tunnel which passes across a known regional stress field.
There is a reinforcement method using the continuous fiber sheet for reinforced concrete whose bending strength has decreased due to deterioration. However, the reinforcing effect when applied to arc-shaped members such as shield segments remains unclear. Therefore, in this study, the influence on the reinforcing effect was analyzed by a structural model that reproduced the bending test of the segment reinforced by the continuous fiber sheet. As a result, it was found that in the arc-shaped member, additional stress is generated in the tunnel radial direction on the continuous fiber sheet, and the reinforcing effect is reduced as the inner diameter is smaller and the curvature is larger. In this paper, we show the calculation method of the peel fracture strength of the continuous fiber sheet when it is affected by the curvature, and propose the reinforcement design method.
There are some cases where the deterioration of RC segments caused by chloride attack is observed in railway shield tunnels located in seaside area and under tidal rivers. This research focuses on the deterioration of segment joints and reveal the characteristics of chloride ion penetration near the segment joints by accelerated tests. Loading tests were carried out with deteriorated segment joints and revealed that rotation stiffness reduces with the corrosion of steel material near the joints. This paper also proposed the modelling method of segment joint considering the reduction of rotation stiffness caused by the corrosion of steel material for the numerical calculation of 3D finite element analysis and validated the method by simulating the loading tests.
Aging infrastructure stocks are important social issues. In this article, a mobile mapping system was utilized to realize automatic and realtime detection of delamination and peeling on tunnel concrete surfaces and potholes on road surfaces from laser 3D point cloud data. Time series analysis was applied to estimate profiles of tunnels and roads. After signal and image processing, candidate areas of damages were localized. Tunnel appendages were eliminated considering 3D features to visualize damages in 3D maps. Validity of the algorithm was demonstrated by real tunnels and roads, achieving about 80% detection rate of delamination and peeling on tunnel linings.
When designing with two-dimensional numerical analysis, the concept of stress release rate is used in order to simulate three-dimensional deformation behaviour. Generally, the stress release rate in the 2D numerical simulations is set to 40% before the support is installed and the remaining stress is released after the support is installed. However, there is no particular thing about the early closure of all sections, which has been increasingly used in recent years. Therefore, the authors derived the optimum stress release rate for the early closing of all sections by trial calculation, which is a three-stage stress release, leading displacement rate α = 40%, after installation of upper half support support β = 20%. It was also found that the semi-support + invert support = 40% could reproduce the 3D deformational behaviour more appropriately.
Shotcrete is installed in tunnels to prevent rock fall disasters. It is difficult to determine the thickness of shotcrete for each face according to the geological conditions, and it is recommended to spray 3 to 5 cm depending on the support pattern. In this study, we collected the results of quantitative evaluation of the geology of the tunnel face using image analysis technology and computer jumbo drilling data, as well as the shotcrete thickness and rock fall information of the tunnel face, and used logistic regression to determine the shotcrete thickness according to the geological conditions. As a result, it was found that the shotcrete thickness can be presented with an accuracy of about 75%. We also showed that logistic regression is a machine learning method without hidden layers, so it can clearly show the relationship between geological conditions and shotcrete thickness and rock fall.