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ABSTRACT A new commuter train tunnel under Stockholm City is currently being designed. The main portion of the tunnel is to be constructed in crystalline bedrock using drill and blast methods together with conventional support elements in the form of shotcrete and rock bolts. Standard rock reinforcement classes, which are dependent on excavation span and rock mass quality, will be used to determine the required reinforcement for the majority of the tunnel system. The rock mass was divided into four rock classes (A-D) and the tunnel into four categories for excavation span. Potential failure mechanisms were identified for the different combinations of rock mass quality and excavation span and appropriate analysis methods were selected for the various combinations. For all analyses, a range of material properties and initial stress conditions were used to account for natural variation in the input data. Preliminary standard reinforcement classes were determined by evaluating the results from all analyses and using the application of engineering judgment. Numerical analyses, including the preliminary reinforcement were then carried out for chosen combinations of rock types and tunnel sizes. 1 INTRODUCTION A new commuter train tunnel under Stockholm City, denoted the City Line, is currently being designed. The tunnel comprises a 6 km long double-track tunnel with two underground stations (Odenplan and City), service tunnel and exits to ground surface and existing subway tunnels. The main portion of the tunnel is planned to be constructed in crystalline bedrock using drill and blast methods, with conventional support elements in the form of shotcrete and rock bolts. The City Line connects to the existing rail network at Tomteboda in the north and to the existing station Stockholms Södra in the south, see Figure 1. This paper presents the methodology used to design the standard rock reinforcement classes for the City Line. The standard reinforcement classes are to be used for the majority of the planned tunnel system. Standard reinforcement classes will not be used in areas with low rock cover (less than half of the tunnel width), crossing points with existing tunnels, tunnels with a span greater than 20 m, and poor rock quality. The City Line is, with respect to civil works, divided into 5 different contracts: a) Odenplan/Vasa, including single- and double-track train tunnels, service tunnels and an underground station, b) Norrmalm, including single- and double-track train tunnels and service tunnel, c) Norrström, including single- and double-track train tunnels, service tunnels and an underground station d) Söderström, including a submerged concrete tunnel (not included in these analyses), and finally e) Södermalm, including single- and double-track train tunnels and service tunnels. The same design methodology was used for all contracts. (Figure in full paper) 2 INPUT DATA FOR ANALYSES A comprehensive geotechnical site investigation was conductedtocharacterizethegeologyalongthe plannedtunnelalignmentforeachcontract. Project guidelinesformappingandcoreloggingwere establishedearlyinthedesignphasetoensure consistencyinthedescriptionandcharacterizationof therockmass.
- Transportation > Ground > Rail (1.00)
- Transportation > Passenger (0.81)
ABSTRACT The demand for efficient new infrastructure systems is increasing and automatically leads to the underground as living space above ground is becoming more and more scarce. This also applies to the mechanical construction of tunnels, which is almost completely carried out in underground thanks to the tailor made tunnelling technology made by Herrenknecht. Mechanized tunnel excavation has entered new dimensions in terms of size, length, geological complexity and depth of underground constructions. It sets the standards regarding safety, profitability and environmental protection – in Traffic Tunnelling projects as well as in the trenchless construction of Utility Tunnels, such as sewer, water, cable tunnels and oil and gas pipelines. Different machine types and working principles have been developed to master the geological and hydrological requirements of tunnelling projects worldwide. This paper gives an overview on state-of-the-art hard rock tunnelling equipment and project possibilities but will also highlight the innovative and current design approaches to overcome the difficult specific project conditions of hard rock projects of today. Reference projects and experiences world wide show the feasibility of tunnel visions and the infrastructure importance for the respective area. 1 INTRODUCTION The tunnel projects that are realized today face more and more complex conditions. This because of the increasing need for infrastructure systems in rough terrain or in municipal areas where space above ground is limited. The project challenges in hard rock are generally high overburden, long tunnel drives, strong and abrasive rocks as currently faced with the construction of the longest railway tunnel, the Gotthard Base Tunnel in Switzerland. These complex projects demand for a safe and economical tunnelling technology, both in hard, solid rock conditions and in soft rock, which is provided by mechanized tunnelling. The cited projects focus on representative tunnelling jobs where mechanized tunnelling technology was applied. 2 MECHANIZED HARD ROCK TUNNELLING TECHNOLOGY Dependent on the rock quality different types of hard rock machines are available on the market. In general Gripper TBMs are applied to solid rock conditions whereby Shielded TBMs such as Single Shields and Double Shields, are generally used in soft rock or unstable hard rock conditions. Apart from the drilling technology, efficient and economical material transport from the tunnel face to the end of the tunnel is also a key requirement for a successful excavation process. 2.1 Gripper TBM This type of hard rock machine is typically applied to stable and massive rock conditions with low water ingress. The cutterhead is of flat face design and equipped with disc cutters to suit the rock conditions. The cuttings will be removed from the tunnel face via buckets. They are arranged at the circumference of the cutterhead and are supported by additional backscrapers on the rear side of the cutterhead. A conveyor belt along the TBM is used for the removal of excavated material from the excavation chamber to the discharge point of the material transport system in the tunnel.
- Europe > Sweden (0.29)
- Europe > Switzerland (0.25)
- Geology > Rock Type > Metamorphic Rock (0.49)
- Geology > Rock Type > Igneous Rock (0.48)
Two extra-long tunnels, with two tubes each, were excavated in a corridor of about 200 m in Qinling Mountain in the central part of China, for railway and road lines from Xi'an to Ankang, respectively. During tunnel excavations, severe rockbursts have occurred in several gneiss sections. The rockburst features indicate the pronounced effect of the fabric of the schistous structure of gneiss on the strength and deformation characteristics of intact rocks. The analysis on the geological conditions in terms of initial geostatic stress, rock strength and the occurrence of the gneiss foliation planes indicates that the schistous structure of gneiss is in favor to the severe rockburst in the section of magmatic gneiss with large overburden. The influence of anisotropic feature of the gneiss on the rockburst becomes significant on the condition that a large initial principal stress is nearly parallel to the foliation planes and the foliation structure composed mainly of biotite and quartz provides a weak plane to brittle failure.
- Geology > Rock Type > Metamorphic Rock > Gneiss (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT Collapses are serious or even disastrous accidents during tunnel construction, which of frequent occurrence. This paper describes a method for assessing the risk associated with collapses in tunnels. The focus is put on collapses which occur in the tunnel constructed by drill and blast method. And the preference is attached to studying their causes and mechanisms and assessing their risk during tunnel construction. On the basis of an extensive literature search, causes and mechanisms analysis of collapse is carried out. All the potential risk factors related to tunnel collapse are identified. The statistical analysis and the accident tree analysis are carried out to analyze the contribution of each risk factor to tunnel collapse. The importance ranking of risk factors is given. It can be confirmed that precise geological investigation and appropriate construction process are the most effective controllable factors for preventing the occurrence of tunnel collapse. Accident tree analysis is also employed to estimate the probability of collapse occurrence. And the analytic hierarchy process is employed to evaluate the potential loss of collapse. At last a whole approach for tunnel collapse risk assessment is presented. 1 INTRODUCTION Collapses are a major hazard in tunnels for highways and railways in mountainous terrain, especially in tunnels constructed by drill and blast method. Apart from the damage such as high cost and downtime, the most vital feature of collapse is bringing about fatalities and serious injuries. According to the statistics, there are over 60 collapses during the construction of Guanjiao tunnel in Qingzang railway (Yang et al. 2003); 19 large-scale collapses in the construction of Dayaoshan tunnel (Sun et al. 2006). one collapse occurred every 86m on average in a zone of Dafengyakou tunnel. The statistic data of Japan shows that collapses account for 33% in tunnel accidents (Xian 1998). In brief the impacts of collapses should be taken into account very carefully. Therefore, causes of collapses have to be recognized, and procedure for collapses assessment must be established. The collapse of tunnel has been discussed in many papers and textbooks. The Health and Safety Executive (HSE) carried out an investigation after the collapse of Heathrow Express Rail Link Station tunnels, and reported the causes of the collapses as unpredicted geological causes, planning and specification mistakes, calculation or numerical mistakes, construction mistakes and management and control mistakes (Dimitrios K. 2008); Seidenfuß (2006)provides a comprehensive categories for tunnel collapses and analyzes the different causes of collapses as well as their mechanisms on the basis of an extensive literature search; Feng w.x. et al.(2001) presents the causes, the treatment and the treatment effect of collapses through a lot of cases analysis. All the researches show that the uncertainty factors, such as inadequacy of geotechnical information, wrong choice of construction methodology, as well as improper organization of the works, initiate collapses. How can we lower down these uncertainties to avoid or at least reduce collapses in tunnels in future? One effective way to do so is to understand and control these uncertainties.
- Transportation > Ground > Rail (0.75)
- Transportation > Infrastructure & Services (0.54)
Damage Analysis of Tunnels Caused By Earthquake Using GIS And Quantification Theory II
Zhu, Zheming (Department of Engineering Mechanics, Sichuan University) | Jin, Xinxing (Department of Engineering Mechanics, Sichuan University) | Tang, Hao (Department of Engineering Mechanics, Sichuan University) | Xie, Heping (Department of Engineering Mechanics, Sichuan University)
ABSTRACT Rock materials contain cracks, and under certain conditions, these cracks will extend, branch and coalesce, which have received the most attention recently. In this paper, an attempt is made to set up a fracture criterion for the special case as cracks are situated along a straight line. Under compression, cracks close and the crack surface friction can resist crack surface sliding. A set of complex stress functions and the solution of stress intensity factors have been presented in the author's previous publication and will be applied in this paper. A fracture criterion for the case of collinear cracks under compression is developed, which is expressed in terms of principal stresses. For the case of materials without pre-existing cracks, this new fracture criterion becomes the well known Coulomb-Mohr failure criterion. 1. Introduction Fracture or Failure criterion describes the limiting loading conditions that materials can sustain. Because such a limiting state has become so important in the usual design methods for engineering rock mechanics, a great deal of effort, both from the theoretical and experimental point of view, has been devoted to studying the behaviour of rock materials loaded to failure, and many fracture or failure criteria have been developed (Bieniawski, 1974; Hoek and Brown, 1980; Johnston, 1985; Gates, 1988; Li, 1990; Fuenkajorn and Daemen, 1992; Zhu, 1999). Most brittle materials in nature contain preexisting cracks or flaws, such as underground rock mass and concrete, and they usually are subjected to compressive loads. Therefore, in the study of rock material fracture criterion, the following three aspects have to be considered: the interaction between cracks, because cracks affect each other, and under certain conditions, they extend, branch and coalesce, which have received the most attention (Nemat-Nasser and Horii, 1982; Steif, 1984; Ashby and Hallam, 1986; Li and Nordlund, 1993; Germanovich et al., 1994; Baud et al. 1996; Rice et al., 2001; Sih, 2002). However, no exactly analytical solution is available today for multiple cracks under compression; crack surface friction, because under compression, cracks close and friction exists between the crack surfaces. The friction can resist crack surface sliding and thus it significantly affects crack tip stress intensity factor (Zhu et al. 2006; Zhu 2009); and confining stress, because material strength increases as confining stress increases (Zhu et al. 1996; 1997; 2006; 2008; Zhu, 1999; 2009). The general fracture criteria for mode II crack can be written as KII KIIC. However, such fracture criterion is difficult to apply because KIIC is difficult to measure, and the measurement results are usually scattered in a large range. In order to avoid such difficulties in measuring rock fracture toughness, the general fracture criterion will be transformed into a new form expressed in terms of principal stresses, without KII and KIIC involved. In this paper, a new fracture criterion is developed for specimens containing two collinear cracks under compression, and also for specimens containing a single crack, the corresponding fracture criterion is obtained which is the same as the criterion of two collinear cracks.