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ABSTRACT The main aim of the present research work is to investigate the effect of joint orientation on the strength and modulus enhancement of the jointed rock due to provision of rock bolts. Laboratory tests have been carried out on the jointed rock specimens (without and with rock bolts) of size 15 cm x15 cm × 30 cm (height) under uniaxial compression. Steel bars of 6 mm diameter were used as rock bolts, which were grouted with 4 mm thick cement mortar. The joint orientation of specimens was varied from 0° to 90° with respect to loading direction. The bolts were installed normal to loading direction. The results from tests indicate that in general the strength and modulus of jointed rock increase due to rock bolts for all joint orientations. However, for critical joint orientations (θ=45° and 60°) the enhancement was quite large due to change in failure mode. Also there was reduction in extent of anisotropy of the jointed rock both in strength and deformation modulus.
ABSTRACT Mechanical characterizations of some polymer materials have been investigated as a tunnel support material. They were compared with conventional concretes. There are candidate polymers to be used as support material for tunnelling. Very thinner polymer wall can supply same support pressure instead of shotcrete. Lackings of concrete can be removed by using polymer materials. If polymer support's stiffness is very few for some tunnelling zone, fiber glass or carbon fiber can be used as an addition for increasing stiffness and strength in the same time. Polymers are preferable and economical support materials especially for swelling clay zones. Poymers allow to deform while they are supplying same or near strength because of their ductile material characteristic. And, they have much more dynamic load strength than concrete's. There is no need to membranes or other water resisting materials in sprayed-polymer application area. It can be easily sprayed with smaller air pressures by heating, or some of them are sprayed without heating, in liquid form. They reach their maximum strength quantites in very few time (like several minutes) after sprayed so polymer support materials allow to decrease advancing time. Polymer spraying application is practical and there is no rebound problem in sprayed-polymer application. Candidate polymer types were compared within.
ABSTRACT An attempt to simulate the cascading pillar collapse is made in this paper for a quick evaluation of a large number of mined-out area data that have been collected throughout China. Pillar collapse, load transfer and load redistribution are modeled by the area-apportioned method, and this methodology is general in sense and has been implemented in the expert system developed by the authors as an independent module. The proposed method can provide a quantitative criterion for determination of the failure pattern and identification of the key pillars in the stability analysis of the mined-out area formed by a pillar-room method.
ABSTRACT Pillar design is essential in mining practice, to achieve safe economic potential of an orebody. As a preliminary research on the optimized design of pillar structures, numerical analysis has been carried out to estimate pillar stability by the variation of depth and RMR grade. Also, the average pillar stress has been compared on the basis of tributary area theory and the pillar stress has been analyzed by numerical analysis. Using pillar strength calculated by three methodologies which are suggested by Salamon and Munro (1967), by Greenward (1939), and by Holland and Gaddy (1964), the safety factor of pillar has been compared with the results from numerical analysis by FLAC-3D.
ABSTRACT Difficult geo-mining conditions of a deep seated coal pillars limit the scope of conventional semi-mechanised depillaring process, mainly due to their slow rate of extraction. Application of a fully mechanized depillaring process has resulted faster rate of extraction resulting improvement in safety along with production and productivity of the depillaring faces. Out of six mechanized depillaring practices in India, the three successful ones of Anjan Hill, Jhanjra and Pinoura Mines do not belong to deep cover (<200m). While the Tandsi depillaring is practiced at nearly 260m depth of cover and achieved intermediate results. The deepest practiced mechanised depillaring panel in the county is CMP-1of VK7 at 377m of cover. This depillaring encountered massive collapse (before main fall), which adversely affected the pace of mechanisation for pillar extraction operation at higher depth in the country. Actual cause of the problem is still being investigated and is found difficult to be concluded. However, as per core analysis results, a good understanding of the nature of overlying strata might have guided the approach for a better pattern of the pillar extraction and the chance of failure might have been arrested. After realizing this fact, a depillaring operation in the neighboring panel 26 of the mine was successfully conducted. Here, the menace of dynamic loading due to competent overlying strata could successfully be encountered through management of the natural support only. The sixth mechanised depillaring face is successfully being practiced at GDK 11 Incline at around 310m of cover. Again, here application of available knowledge of the site conditions helped in successful completion of mechanised depillaring operation in couple of panels. Field investigations through underground instrumentation and monitoring showed distinct natures and amount of stress re-distribution for shallow and deep cover of the depillaring. The prominence of periodic nature of face loading at shallow cover got reduced during depillaring of a deep coal seam. Pillars around extraction line encountered, almost, continuous loading after first major fall during pillar extraction from deep seated coal seams.
- Asia > India (0.50)
- North America > United States (0.47)
ABSTRACT It has been well known that the stability of slopes in the open pit coal mines in Indonesia does not remain constant over long periods of time. This has been mainly attributed to the weathering process that intensively occurs in the tropical regions. It is therefore appropriate to carry out a research of shear strength characteristics on rock samples of the predominant coal bearing strata such as sandstone which are obtained from Tutupan coal mines in South Kalimantan, Indonesia. The research includes the shear creep test with Generalized Kelvin model rheology approach with 15 × 15 cm and 25 × 25 cm sandstone samples size respectively. The research reveals that the long term strength of that sandstone is significantly lower than their peak strengths. It is also found that the Generalized Kelvin rheology model does fit to the rheology of these rock samples.
- Asia > Indonesia > Kalimantan (0.61)
- Asia > Indonesia > South Kalimantan (0.61)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
ABSTRACT "Moshampa" is one of Iran's large dams under construction. The rock slopes facing the dam diversion tunnels failed during excavation. Site investigations and primary kinematic analyses showed that the mode of instability has been blocky toppling failure. The slope inclination was decreased and the portal was reconstructed with a new design. Since, according to the same investigations, the geological conditions of the rock mass in the portals of the power-house and diversion tunnels are similar, the slopes facing the dam power-house tunnels may also fail during excavation; so, they should be checked against blocky toppling failure. In this paper, a brief review of toppling failures of Moshampa dam has been given first. Then, the stability analyses of the portals of the diversion tunnels and their stabilization method have been checked by Goodman-Bray analytical approach under dry conditions. Finally, the stability of the slope, facing the portals of the power-house tunnels, has been checked against blocky toppling by the method and its stable inclination computed.
ABSTRACT The stability of slopes during and after excavation is always a significant issue in the field of rock mechanics. The blocky-flexural toppling failure is one of the most probable types of instabilities in rock slopes. The stability analysis of toppling failure is based on the limit equilibrium approach and the slope stability is then ascertained by determining the force necessary for equilibrium of the block at the toe of the slope. Existence some simplifications in this process affects the safety factor, indeed. In this study a stability analysis method for slopes against the blocky-flexural toppling failure is proposed. In the proposed method with the use of fracture mechanics and combination of statistical and fuzzy methods has been tried to solve these problems. Finally a software is developed by using the proposed theory and a real case study has also analyzed by that. The results of the analysis confirm that this generalization is valid an effective way of dealing with the problems in discontinuous rock mass as long as the geomechanics and geometry data are properly included in this approach.
- North America > United States (0.28)
- Asia > Middle East > Iran (0.15)
ABSTRACT We generalize our view of a bonded-particle model (BPM) to consist of a base material (of rigid grains joined by deformable and breakable cement at grain-grain contacts) to which larger-scale joints can be added and whose mechanical behavior is simulated by the distinct-element method using the two- and three-dimensional discontinuum programs PFC2D and PFC3D. The micromechanical processes that control brittle fracture and thus, should inform any micromechanical model, are summarized. The rich variety of microstructural models that can be produced by the bonded-particle modeling methodology are described and classified with respect to their microstructural and larger-scale features. These models provide a wide range of rock behaviors that encompass both compact and porous rock at both an intact and rock-mass scale, and examples are provided of how BPMs are being used to model rock at these scales. The examples include an intact anisotropic material that may swell and contract in response to changes in saturation, the behavior of two alternative BPMs that can match both the uniaxial and tensile strengths of compact rock and the embedding of an intact BPM within a larger continuum model to study fracturing around a gold-mine stope in quartzite.
- North America > United States (1.00)
- Europe (1.00)
- Asia (0.67)
- North America > Canada (0.67)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.92)
- Geology > Mineral (0.88)
Triaxial Compression Test of Artificial Sediments Containing CO2 for Enhanced Methane Hydrate Recovery
Miyazaki, Kuniyuki (National Institute of Advanced Industrial Science and Technology) | Tenma, Norio (National Institute of Advanced Industrial Science and Technology) | Sakamoto, Yasuhide (National Institute of Advanced Industrial Science and Technology) | Yamaguchi, Tsutomu (Toho University)
ABSTRACT Methane hydrate (CH4 hydrate) consists of cagelike crystal structures made up of hydrogen-bonded water molecules surrounding guest molecules of CH4. CH4 hydrate existing in marine sediments is anticipated to be a promising source of natural gas. Depressurization method is considered the most effective procedure for CH4 -hydrate production. CH4 -hydrate dissociation into CH4 gas and water takes heat energy from the neighboring strata. CO2 injection into marine sediments is thought to be a potential method to enhance CH4 -hydrate recovery, because heat energy is generated by CO2 -hydrate formation. It is essential to consider the geomechanical characteristics of CO2 -hydrate-bearing sediments to ensure sustainable CH4 -hydrate production using CO2 injection. However, the mechanical properties of CO2 -hydrate-bearing marine sediments have not been clarified, although they are essentially required to simulate the geomechanical response to CO2 injection. It has recently been revealed that gas-hydrate-bearing sediments have rocklike mechanical properties due to the cementation effect of the hydrate between soil particles. In this study, the experimental methods of drained triaxial compression test for artificial CO2 -hydrate-bearing sandy sediment were developed. The mechanical properties of CO2 -hydrate-bearing specimen were compared to those of CH4 -hydrate-bearing specimen.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Sedimentary Geology > Depositional Environment > Marine Environment (0.67)