Technologies一 of whole cutting through coal seam and preventing collapse in highway tunnels

华蓥山隧道在施工过程中遇到岩溶、断层、涌突水、煤层段和瓦斯等主要工程地质问题,地质情况非常复杂。总结了华蓥山隧道东口右线揭穿和通过煤层的施工技术,为隧道大断面安全揭煤提供技术参考。     

Analysis of the evolution of road tunnels equilibrium conditions with a convergence–confinement approach

Since both lining structure and rock mass exhibit delayed behaviour, tunnel equilibrium conditions evolve with time. After discussing existing work done on different aspects of long-term tunnel behaviour, the aim of this paper is to “understand” the influence of rock mass and lining degradations on the long-term stability conditions of the tunnel by means of the convergence–confinement method. In order to represent the effects of degradation on tunnel long-term conditions, specific degradation models are selected according to the disorders identified during principal inspections of road tunnels in Switzerland. By simulating the reduction of the mechanical properties of both the rock mass and the lining or by using creep models, it is possible to assess the influence of the main degradation processes on tunnel stability. The results are interpreted in terms of tunnel safety factor. The presented approach for the determination of the long-term behaviour of tunnels, although valid for simple tunnel geometry and field stress conditions, allows to roughly estimate the influence of significant degradation processes that affect the rock mass and the supporting structure. Though this approach results in some simplification, it may be generalised and adopted with more refined numerical analyses for improving the assessment of tunnel long-term conditions.     

Seepage characteristics and mechanical response of shield tunnels under localized leakage and exosmosisEI北大核心

针对有压盾构隧道中接缝水力劣化所引发的内外水力交互渗流问题,基于水力开度理论,通过数值和解析方法研究局部渗流下隧道衬砌与周围地层的渗流特性和力学响应。结果表明:基于镜像法推导的衬砌隧洞多点渗漏下渗流场解析解与数值解吻合良好,验证了给出的局部渗漏数值模型的有效性;局部外水内渗与内水外渗诱发的衬砌与地层共同作用存在较大差异,前者导致局部孔隙水压力降低引起土体挤压衬砌,衬砌轴力减小而弯矩增大从而产生衬砌外凸,后者则相反;多点局部渗漏对渗流场和衬砌响应的影响存在耦合作用,当内水压接近地层水头时可能出现外水内渗与内水外渗并存的特殊水力交互情况;地层渗透系数对局部渗漏行为的影响较大,复合地层下当局部渗漏发生于高渗透性地层时,其诱发的衬砌响应不显著,当渗漏处于下部低渗透性地层时,在地层交界面存在渗流折射现象,上部高渗透性地层起到补(排)水作用。     

Hazard-based evaluation model of water inrush disaster sources in karst tunnels and its engineering application

Water inrush is one of the typical geological hazards that may occur during tunnel construction in a karst area. In this paper, a potential model is established based on attribute mathematics, to assess the risk of water inrush. First, the CaCO₃ content of regional strong karst, thickness of the regional strong karst layer, groundwater recharge area, discharge of groundwater, average temperature characteristic, groundwater level, groundwater cycle characteristic, surface karst morphology, fault structure, fold structure, and monoclinal structure are chosen as evaluation indexes of water inrush based on the principles of scientificity, rationality, operability, and representativeness. Second, the objective weight calculation formula is used to calculate the weights of the evaluation indices, and attribute measurement functions of each evaluation index are constructed to reckon the attribute measurement of a single index and synthetic attribute measurement. Lately, the identification and classification of water and mud inrush hazard in tunnels have been performed using a confidence criterion. In this paper, hazard level is graded as one of four types. The hazard-based assessment methodology is applied to the construction site of the Jigongling Tunnel along the entire Fanba Expressway route, and the findings are compared against the site’s actual situation. The results of the engineering practice show that the evaluation result is consistent with the actual construction situation; thus, the method can provide scientific guidance for tunnel construction units.     

Wind tunnel experimental study on shed tunnels to prevent and control blowing snow on highways北大核心CSCD

There is a severe phenomenon of blowing snow by wind in winter in Mayitas area of Xinjiang. Road traffic interruptions and casualties caused by wind and snow disasters often occur. The existing engineering measures can alleviate the problems of low visibility and problems with accumulating snow on pavement caused by wind and snow to a certain extent, but cannot completely eliminate the impact. Aiming at the problem that the blowing snow disaster difficult to be completely cured under strong wind conditions, a shed tunnel engineering treatment scheme is proposed, and a wind tunnel simulation experiment is carried out on the shed tunnel form and snow prevention scheme at the entrance of the tunnel. The wind tunnel experimental section is 8 m long, 1. 3 m horizontally wide and 1 m high. The shed tunnel model is made by 1:60 scale 3D printing method, the snow barrier model is made of wooden strips, and the simulation medium is made of fine sand, refined salt and sawdust. Firstly, three kinds of shed structures, including fully enclosed, overhanging and ventilated, were simulated under the condition of 90° wind direction, and compared with the form of blowing snow stacking. Three parameters for similarity were used:density, particle size and stacking shape. The similarity is determined by weighted Euclidean distance between simulation medium and blowing snow, the similarity of the slump angle of the predecessors is verified, and the most suitable medium for simulating blowing snow is deduced. According to the experimental results, combined with the actual situation of wind blowing and snow disasters in Mayitas, flow field of the closed shed tunnel by a wind direction angle of 30° has been separately conducted with or without protective measures. The results show that when the wind tunnel stacking experiment is used to study the deposition state of blowing snow under non-low temperature conditions, the sawdust has good similarity with the blowing snow in the process of wind and snow movement. A large amount of medium was poured into the ventilated shed during the experiment, which proved that its anti-wind and snow performance was not ideal. By contrast, the closed shed and the overhanging shed have better wind and snow prevention effects. The snow barrier has a good blowing snow inhibition function at the entrance. From the stacking experiment, in the comparison with and without snow barrier, volume of the medium in the shed is very different, which proves that the snow barrier can effectively prevent the blowing snow from entering the shed. Among them, the difference in wind speed inside and outside the shed is obvious, which proves that snow barrier can significantly reduce the wind speed outside the shed and has the function of inhibiting the formation of weak wind areas inside the shed. The study has confirmed that the shed tunnel project with suitable snow barrier layout plan for tunnel entrance protection is an effective means to control wind and snow disasters. For highway traffic in Xinjiang, it is a feasible solution to use shed tunnel engineering to control blowing snow disasters. After dealing with the snow deposition at the entrance of shed tunnel, the shed tunnel engineering form of low-cost environment integration and the vehicle operation safety guarantee measures of long-distance shed tunnel are the problems that need to be solved in the future. © 2022 Tianjin Press of Chinese Herbal Medicines. All rights reserved.     

Damage assessment of tunnels caused by the 2004 Mid Niigata Prefecture Earthquake using Hayashi’s quantification theory type II

Mountain tunnels, being underground structures and situated deep within rock layers, are generally considered to suffer appreciably less damage from earthquakes than surface structures. However, it has been reported that many tunnels were damaged by the 1923 Great Kantou earthquake, the 1995 Great Hanshin Earthquake, the 1999 Taiwan Chi-Chi Earthquake, the 2004 Mid Niigata Prefecture Earthquake and the May 2008 Great Wenchuan Earthquake in China. In this study, the damaged tunnels resulted of the 2004 Mid Niigata Prefecture Earthquake are the study objects. The damage patterns are analyzed, and the information which is considered to be of influence, such as the distance to epicenter, the completion time, the geological conditions, etc., are collected. A database of the damaged tunnels has been created using a Geographic Information System (GIS). The influence ranking for these factors has been analyzed using Hayashi’s quantification theory II. The degree of the tunnel damage has also been assessed using GIS and Hayashi’s quantification theory II. The field investigation is in close agreement with the assessment results following Hayashi’s quantification theory II.     

Chemistry,isotope values (δD, δ18O, δ34SSO4) and temperatures of the water inflows in two Gotthard tunnels,Swiss Alps

Water inflows in the Gotthard Highway Tunnel and in the Gotthard Exploration Tunnel are meteoric waters infiltrating at different elevations, on both sides of an important orographic divide. Limited interaction of meteoric waters with gneissic rocks produces Ca–HCO₃ and Na–Ca–HCO₃ waters, whereas prolonged interaction of meteoric waters with the same rocks generates Na–HCO₃ to Na–SO₄ waters. Waters circulating in Triassic carbonate-evaporite rocks have a Ca–SO₄ composition. Calcium-Na–SO₄ waters are also present. They can be produced through interaction of either Na–HCO₃ waters with anhydrite or Ca–SO₄ waters with a local gneissic rock, as suggested by reaction path modeling. An analogous simulation indicates that Na–HCO₃ waters are generated through interaction of Ca–HCO₃ waters with a local gneissic rock. The two main SO₄-sources present in the Alps are leaching of upper Triassic sulfate minerals and oxidative dissolution of sulfide minerals of crystalline rocks. Values of δ³⁴S_SO4 < ∼+9‰ are due to oxidative dissolution of sulfide minerals, whereas δ³⁴S_SO4 >∼+9‰ are controlled either by bacterial SO₄ reduction or leaching of upper Triassic sulfate minerals. Most waters have temperatures similar to the expected values for a geothermal gradient of 22°C/km and are close to thermal equilibrium with rocks. However relatively large, descending flows of cold waters and ascending flows of warm waters are present in both tunnels and determine substantial cooling and heating, respectively, of the interacting rocks. The most import upflow zone of warm, Na-rich waters is below Guspisbach, in the Gotthard Highway Tunnel, at 6.2–9.0 km from the southern portal. These warm waters have equilibrium temperatures of 65–75°C and therefore constitute an important low-enthalpy geothermal resource.