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North America
Abstract: Rock support is associated with the rock mass quality as well as the in the state of situ stresses. A safety factor, defined by the strength of the support system and the load exerted on it, is usually used for rock support design. This design method is based on the principle of structure mechanics. It is appropriate to do so in a loadcontrolled situation, such as rock falls under gravity, but it is not valid to use the traditional strength-load safety factor for support design in high stress rock conditions under which instability usually involves stress-induced rock failure. In this case, the principle of rock support should be to absorb the energy released from the rock instead to equilibrate the weight of falling blocks. In this paper, the failure modes of rock under different stress conditions are first viewed. The philosophy and principles of rock support design are then presented for different rock conditions. Finally, yield support elements used so far in civil and mining engineering are briefly reviewed. Keywords: rock support, support design, pressure arch, yield rock support, steel set, rock bolt, energy-absorbing rock bolt, rock excavation. 1 INTRODUCTION Instability is always a concern in underground excavations. The stability of an underground opening, such as a tunnel, cavern or mine stope, is mainly governed by three factors: the quality of the rock mass, the in situ stress state and the size and geometry of the opening. Of these three factors, the in situ stress state is the factor that plays the crucial role in the stability of a rock mass. The type of excavation disturbance is mainly associated with the magnitudes of the in situ stresses with respect to the quality of the rock mass.
- Europe (1.00)
- North America > Canada > Quebec (0.28)
- Materials > Metals & Mining (0.67)
- Energy > Oil & Gas (0.46)
- Europe > United Kingdom > England > London Basin (0.91)
- North America > Canada (0.89)
Abstract: The present investigation is concerned with the interaction between the blast wave and a rock mass with a set of parallel joints by using a time-domain recursive method. According to the displacement field of a rock mass with a set of parallel joints, the interaction between four plane waves (two longitudinal-waves and two transverse-waves) and a joint is analyzed first. Considering the displacement discontinuity method and the time shifting function, the wave propagation equation based on the recursive method in time domain for obliquely longitudinal- (P-) or transverse- (S-) waves across a set of parallel joints is established. The joints are linearly elastic. The analytical solution by using the proposed method is compared with the existing results for some special cases, including incidence obliquely across a single joint and normal-ly across a set of parallel joints. By verification, it is found that the solutions by the new method match very well with the existing methods. Finally, a blast wave with different waveform propagating across a single or a set of parallel joints is then analyzed. The wave propagation equation derived in the present study can be straight forwardly extended for different incident waveforms to calculate the transmitted and reflected waves without mathematical methods such as the Fourier and inverse Fourier transforms. 1 INTRODUCTION The safety and stability of underground structures are often affected by blast induced waves which may come from an accidental explosion, the drill and blast excavation or weapon attacks. Since the underground structures are surrounded by jointed rock mass, the blast wave propagation in the rock mass is significantly influenced by the joints. The vastly existed joints in rock mass not only affect the mechanical properties of rock mass, but also their dynamic response (Goodman 1976). Therefore, studying the interaction between blast wave and joints has been drawing more and more attention (Berta 1994). The blast wave due to an explosion moves outward from the source rapidly and acts on the surrounding media by an effectively instantaneous rise in pressure followed by a decay of wave propagation in the rock mass (Henrych 1979). From a relative distance of the explosive centre, the blast wave is changed to an elastic wave and finally attenuated completely because of the energy dissipations both geometrically and mechanically. The interaction between a blast-induced stress wave and rock joints which relies on the impinging angle, type of the incident wave and the joint property mechanically dissipates the blast energy (Henrych 1979).
Abstract: Valley closure and valley floor upsidence occur when mining beneath valleys and other forms of irregular surface topographies. This phenomenon poses particularly risks to water flow, aquatic ecosystems and natural surface topography. Re-searchers have sought to understand and predict the non-conventional subsidence through empirical methods and various numerical approaches. The empirical predictive method has been found very site specific due to the variations from site to site. This paper provides a review of the numerical modeling methods used to evaluate the geotechnical mechanisms contributing to valley closure subsidence effects under ir-regular topographic conditions. Research has shown that mathematical modelling based on numerical methods such as FEM, FDM, BEM, DEM and the hybrid method has been studied for this purpose. These methods demonstrate the geotechnical mechanisms of rock mass strata deformation and failure that underlie the surface to-pography. In conclusion, numerical modelling has been seen to provide a fundamental and rigorous understanding of the strata displacements and the fracture of near surface structures. With better definition of the numerous factors that affect valley related movements, improvements can be achieved regarding the evaluation of the mechanisms contributing to valley closure subsidence effects. 1 INTRODUCTION Numerous longwall operations have been, or are going to be completed under signifi-cant natural features such as river valleys, creeks and cliffs which are impossible to be avoided. When mining occurs beneath or in the vicinity of these valleys and creeks, the observed vertical subsidence at the base of the valley is less than that in flat ter-rain, and the observed horizontal movement of valley sides is greater than that in flat terrain (Waddington & Kay 2002). Valley related movements were first observed in the Southern Coalfield of New South Wales in the 1970's and 1980's, when these movements were not well under-stood.
- North America > United States (1.00)
- Oceania > Australia > New South Wales (0.34)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.70)
AE Monitoring of Hydraulic Fracturing Laboratory Experi-ment With Supercritical And Liquid State CO2
Ishida, T. (Kyoto University) | Niwa, T. (Kyoto University) | Aoyagi, K. (Kyoto University) | Yamakawa, A. (Kyoto University) | Chen, Y. (Kyoto University) | Fukahori, D. (Kyoto University) | Murata, S. (Kyoto University) | Chen, Q. (3D Geoscience, Inc) | Nakayama, Y. (3D Geoscience, Inc)
Abstract: CO2 (Carbon dioxide) is often used to enhance and stimulate oil recovery in depleted petroleum reservoirs. Its behavior in rock is interesting also in projects of hot dry rock geothermal energy extraction and of carbon dioxide capture and storage. CO2 usually becomes SC (Supercritical) in underground for depth larger than 1,000m, while it becomes L (Liquid) in geological condition having low temperature. The viscosity of SC-CO2 is around 2 %, while that in L-CO2 is around 10 % of that of wa-ter. The difference in viscosity may cause difference in induced cracks and fluid flow in the cracks. As the first step to clarify the difference, we conducted hydraulic frac-turing experiments using 17 cm cubic granite blocks under the hydrostatic pressure of 1 MPa. The breakdown pressure and distribution of located AE (acoustic emission) sources with injection of SC-CO2 and L-CO2 were compared.In the experiments, SC-CO2 tended to generate thinner and wavelike cracks with more secondary branches than L-CO2. The tendency that the breakdown pressure with SC-CO2 is lower than that with L-CO2 was also observed. 1 INTRODUCTION CO2 (Carbon dioxide) is often used for miscible flooding of enhanced oil recovery in depleted petroleum reservoirs. It is considered to use CO2 as fracturing fluid for well stimulation for its advantage of elimination of formation damage and residual fractur-ing fluid (Sinal & Lancaster, 1987 and Liao et al. 2009). Also in hot dry rock geo-thermal energy extraction, a concept to use CO2 for fracturing and circulating fluid is proposed, because of reducing the circulating pumping power requirements and elimi-nating scaling in the surface piping due to its inability to dissolve mineral species (Brown, 2000). Recently, also in shale gas reservoir, enhanced gas recovery by injecting CO2 with advantage of CO2 sequestration has been examined as a feasibility (Kalantari-Dahaghi, 2010).
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource > Hot Dry Rock (0.45)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > South Viking Graben > PL 046 > Utsira Formation (0.99)