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ABSTRACT: Since the disposal institution of high-level radioactive waste is composed of various underground structures, a geological environment is expected to be changed by the construction of the institution. It is important to grasp the geological environment accurately during and after the construction. Micromechanics-based continuum (MBC) theory proposed by authors can reflect the effects of density, orientation and connectivity of joints as well as the property of the joints. In this article, the MBC analysis is employed to analyze the excavation of disposal tunnel and the change of the environment around the tunnel is discussed with paying attention to joints in a rock mass through the analyses. From numerical results, it is clarified that the behaviors of the rock mass axe strongly affected by the direction of initial stress, the density of joints, etc., and that the excavation of a tunnel may change the geological environment such as permeability. INTRODUCTION Japan relies on nuclear power for about one third of its total electricity production. A range of radioactive wastes is an inevitable by-product of the fuel cycle activities associated with nuclear power generation. Radioactive waste also arises through the use of radioactive materials in the fields of medicine, industry and reseaxch. It is necessaxy for all categories of radioactive waste to be managed in a safe and reliable manner and an extensive infrastructure has been developed in Japan for this purpose. Management of high-level waste (HLW) axising from nuclear power production presents a particular challenge and is an extremely important national issue in Japan (JNC (1998)). Storage techniques should be effective for defined periods of time for HLW. In Japan, it is planned to dispose of high-level waste in deep stable geological formations. The deep geological environment is not affected by climatic change and human activities at the surface. In addition, sites where there are no natural resources are to be selected, thus making the probability of future human intrusion extremely low. We should, however, consider the transport of radionuclide from the waste to the human environment with flowing ground water. The most important processes are considered to be the chemical reactions controlling the dissolution of radionuclide from the waste and the flow of ground water which is associated with the movement of radionuclide. Thus, we should consider the permeability of geomaterial during not only cavern excavation but also the storage of nuclear waste. In this stage, the disturbed area, which may be extended by the excavation, should be considered. Then, we need to construct the mechanical model, and give us the future behaviors of rock mass. In general, the rock mass usually includes a great number of joints, which makes the mechanical behaviors of the rock mass complicated. The existences and behaviors of joints in the rock mass govern not only the mechanical behaviors but also permeability of jointed rock mass. For example, in the case of cavern excavation in the jointed rock mass, the sliding and associated opening of the joints which axe initially closed by earth pressure is considered to be the governing mechanism of the mechanical behaviors of the jointed rock mass. With proceeding excavation steps, the region with the opening and sliding of joints is expanded and the loaded region moves outward. The stress redistribution caused by the joint deformation is quite important for the evaluation of cavern safety. Thus, the analytical method that can predict the behavior of the jointed rock mass accurately is indispensable. The number of joints is, however, so large that it is almost impossible to deal wit
- Water & Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
ABSTRACT: Explosives detonated in a surface construction blast produce large quantities of gases that expand rapidly to fracture the rock. The gases contain toxic fumes such as carbon monoxide. If explosives are detonated in the rock below groundwater level, gas bubbles containing toxic fumes can form in the groundwater and stay trapped in the groundwater for many days. We discuss the mechanism that forms and traps gas bubbles. Groundwater flow can transport gas bubbles laterally and allow toxic fumes to vent into the atmosphere a significant distlmce from the blast. This may cause a health risk to workers or inhabitants of buildings near a blast. The gas trapping and gas migration mechanisms are supported by measurements from a constmction case where toxic fumes migrated laterally below ground. We discuss the construction conditions and subsurface conditions that are likely to allow the formation of gas bubbles and the subsurface migration of the gas bubbles that contain toxic fumes. We recommend some simple changes to blasting and construction procedures that can reduce the risk of subsurface migration of toxic fumes. INTRODUCTION Explosives detonated in a surface construction blast produce smoke, which is usually seen immediately after the blast. Smoke is generally composed of water vapor, solid products of combustion, and other gases including toxic gases, such as carbon monoxide and nitrogen oxides. If the conditions are favorable, toxic fumes can dissipate rapidly after a surface construction blast. However, disappearance of the visible components of blast smoke is not sufficient to indicate that the toxic fumes have dissipated, because some toxic fumes such as carbon monoxide are colorless and odorless. During detonation, gas bubbles containing toxic fumes can also form below ground. Migrating gas bubbles in the groundwater can transport toxic fumes. We believe this was a previously unrecognized hazard. Toxic levels can develop in the atmosphere at the blast site or some distance from the blast site when the gas bubbles burst and the gas vents from below ground. Deep and narrow excavations that have poor air circulation will be most susceptible to build up of toxic fumes.
- Health & Medicine (1.00)
- Energy > Oil & Gas > Upstream (0.90)
- Government > Regional Government > North America Government > United States Government (0.73)
ABSTRACT : Results of analytical and numerical modeling of the stress state of rocks around tunnels designed for Pamir and Kokomeren hydropower stations are presented. New analytical method was developed to take into account geometry of both canyon and tunnel to locate the optimum site of the underground tunnel. The method was used to simulate real forms of canyon and tunnel. The method was used to evaluate the impact of the location of the Pamir tunnel on the stability of rocks in its vicinity. Results of overcoring and hydro fracture methods of stress measurements completed at the site of Kokomeren hydropower station are presented. The results of the field measurements were used to create an adequate finite-element model of the canyon. The FEM model was used to simulate the stress state of rocks before and after the erection of a soil dam. An analytical model was then used to evaluate the stress state of rocks around 2 underground tunnels before and after the construction of the dam.
- Asia (0.29)
- North America > United States (0.29)
- Geology > Geological Subdiscipline > Geomechanics (0.49)
- Geology > Structural Geology > Tectonics (0.49)
ABSTRACT: This project involved the design and construction sequencing of a 50-foot high by 75-foot wide wine cave in Napa, California. The cave was constructed as a dome in lahar that consisted of fresh andesite boulders in a matrix of highly weathered rhyolite. Cover over the dome is sloping and relatively shallow, with an average cover of approximately 30 feet. The design included construction sequencing and ground support details using the New Austrian Tunneling Method (NATM), also known as the Sequential Excavation Method (SEM). Final dome geometry was a multi-radius section, which was designed taking into account both architectural concept drawings and previously excavated tunnel geometry. An 8-foot wide walkway circles the inner edge of the mushroom-shaped dome and is elevated 18-feet above the invelt. Ground support for the dome consisted of 16-foot long, I-inch diameter steel threadbar rock dowels and a shotcrete lining reinforced with welded wire fabric. I INTRODUCTION Most of the wine making industry in northern California is located in Napa Valley and in adjacent Sonoma Valley. This region has seen tremendous agricultural growth in the last 40 years, which has put a premium on land available for growing wine grapes. The wine making process also requires significant space for fermentation and storage of wine in barrels until the wines mature and can be bottled.
ABSTRACT: The Washington National Cathedral is one of the largest masonry structures in the USA, and like many of its European Gothic counterparts, it required nearly a century to construct. The design was altered during this period, resulting in greater loadings than were originally anticipated on the soil beneath the foundation. When signs of continuing differential settlement were observed in the early 1990''s, the Cathedral approached the US Bureau of Mines (now the National Institute for Occupational Safety and Health (NIOSHยป for assistance in monitoring the movements of the massive towers and walls. An array of dual-axis tiltmeters was installed about 40m above ground level to measure wall and tower inclination, with the data sent over a dedicated phone line to the NIOSH Pittsburgh Research Laboratory for processing. Mechanical gages and string-potentiometers are also being used to measure motion across cracks and joints, and differential pier settlement is being monitored with optical-level surveying. Data have now been collected for almost 7 years, and they show a long-term settlement trend masked by dramatic diurnal and seasonal thermal movements. The paper discusses the major findings of the study, implications for the future of the Cathedral, and conclusions regarding the use of geotechnical monitoring at major national monuments.
- Health, Safety, Environment & Sustainability > Safety (1.00)
- Health, Safety, Environment & Sustainability > Health (0.75)
- Management > Professionalism, Training, and Education > Communities of practice (0.40)
- Data Science & Engineering Analytics > Information Management and Systems > Knowledge management (0.40)
ABSTRACT : A spillway stilling basin was originally excavated downstream of several buttresses at Pueblo Dam. Geologic information indicated the presence of weak shale seams in the foundation that daylight in the stilling basin excavation. The reservoir had not filled completely since original construction, and therefore the foundation was not fully tested. Analyses indicated the foundation could have a very slim margin of safety if the reservoir filled to normal levels. Due to the large population at risk downstream from the dam, there was strong justification to reduce the risk, and modifications were undertaken to improve foundation stability. The modifications consisted of buttressing the foundation with roller-compacted concrete (RCC) and rock bolts. Additional drainage was also installed. Although the design was completed using limit equilibrium techniques, unique aspects of the geometry were investigated using UDEC and DDA analyses. Both confirmed the design provided adequate resistance. This paper focuses on the design and analysis of the foundation treatment system. 1 INTRODUCTION Pueblo Dam is a composite earthfill and concrete massive head buttress dam (see figure 1) on the Arkansas River just upstream of Pueblo, Colorado. The dam, completed in 1975, is about 53.3 m high. A spillway stilling basin, 168 m long and 13.7 m deep was originally excavated at the downstream toe of Buttresses 8 through 14, which form the uncontrolled overflow spillway for the dam.
- Geology > Geological Subdiscipline (0.50)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.38)
ABSTRACT: This paper describes a case study involving 23.5 km of water supply tunnel in carbonate rocks. The process of excavations and the water flow become extremely problematic due to the existence ofkarstic regions along the tunnel route and also because of big springs in the area. INTRODUCTION Along with population growth and technological developments, there has been an increasing demand on the construction and use of tunnels. Long tunnels such as Seikan (Matsuo. 1986) and British Channel (Howcraft. 1990), among others, are examples of such demand. In designing a tunnel, the shape, dimensions, and depth of the tunnel can be considered as important factors besides rock mass (Sinha. 1989). But in the case of long tunnels, such as Seikan and British Channel, which are constructed under the sea, the consideration of te1''l''ain conditions can also be of vital importance. Experience gained in the construction of these two tunnels is very valuable and can, therefore, be used in long-tunnel constructions presently under way. There has always been the question of whether the diameter of a tunnel should be given the first consideration or its length. As far as stress is concerned, the diameter can be given the first priority, but when we come to problems such as ventilation and operational difficulties, we can not underestimate the importance of the length factor.