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ISRM International Symposium on Rock Mechanics - SINOROCK 2009
Comparative Coupled THM Modelling of Chinese HLW Disposal Concept Using Codes Rockflow And ANSYS
Kunz, Herbert (Federal Institute for Geosciences and Natural Resources) | Zhao, Hong-Gang (Beijing Research Institute of Uranium Geology) | Nowak, Thomas (Federal Institute for Geosciences and Natural Resources) | Shao, Hua (Federal Institute for Geosciences and Natural Resources) | Wang, Ju (Beijing Research Institute of Uranium Geology)
ABSTRACT Numerical simulation is essential for the understanding of the coupled thermal, hydraulic, mechanical, and chemical processes related to the disposal of radioactive high-level waste (HLW) and their effects on the long-term performance. The correct implementation of the physical-chemical processes in the numerical codes, the handling of the complicated problem, and the interpretation of the simulation results become more important due to the complexity of such systems. Within a Chinese-German co-operation program between BRIUG and BGR, a comparative coupled THM modelling exercise based on the Chinese disposal concept has been jointly performed using the numerical codes GeoSys/RockFlow and ANSYS. In the Chinese vitrified high level radioactive waste disposal concept, seven different materials (waste, carbon steel overpack, gaps filled with air and water, bentonite in the disposal hole, backfill in the tunnel, and granite rock) with in total more than 80 thermal, hydraulic, mechanical and petrophysical parameters have been considered. Three phases including excavation, emplacement of the waste package, and post closure were simulated. The coupling effects have been analysed step by step from single process modelling to coupled TM and THM modelling. The results from the two codes are comparable. The modelling results may serve as a basis for further construction design. 1 INTRODUCTION The Federal Institute for Geosciences and Natural Resources (BGR), which performs geo-scientific investigations of potential repository sites in Germany, has developed numerical codes to understand the coupled THMC processes related to the disposal of radioactive waste. One numerical fully THMC-coupled code is GeoSys/RockFlow, which has been developed jointly by BGR together with the Helmholtz Centre for Environmental Research (UFZ). This code is intensively verified within the framework of a benchmarking project and widely used in different international projects, e.g. DECOVALEX. In 2004, BGR (Germany) and Beijing Research Institute of Uranium Geology (BRIUG, China) signed a Memorandum of Understanding for the Chinese-German cooperation covering bilateral experience exchange in the field of methodological study of site characterization, study of the mechanical and hydraulic properties of the granite from Beishan site, and study of migration of radionuclide in fractured granite. During the current work phase, a comparative coupled THM modelling exercise based on the Chinese disposal concept in fractured rock has been performed. Taking the Chinese vitrified high level radioactive waste disposal concept into consideration, the BGR team simulated the evolution of temperature, humidity, and stress in the technical and geological barriers using the code GeoSys/RockFlow, while the BRIUG team used the commercial code ANSYS for the same purpose. Due to the complexity of the system and processes considered, the feasibility and handling of the codes have been analysed. The modelling results may serve as a basis for further construction design. 2 CHINESE VITRIFIED HLW CONCEPT Site characterisation for high level waste disposal is intensively being investigated by BRIUG. In Northwestern China the Beishan area in the Gansu Province has been considered as a potential area. Investigations including regional geological settings, crust stability, geological characterisation, hydrogeological and methodological studies are currently at work.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.67)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Effect of Repeated Blast Loading On Damage Extent of Penstock Tunnels In Heavily Jointed Rockmass - A Case Study
Ramulu, M. (Central Institute of Mining & Fuel Research) | Sitharam, T.G. (Department of Civil Engineering, Indian Institute of Science) | Choudhury, Pb (Central Institute of Mining & Fuel Research) | Raina, AK (Central Institute of Mining & Fuel Research) | Chakraborty, A.K. (Central Institute of Mining & Fuel Research)
ABSTRACT The detonation of explosive charges releases large quantities of energy that can produce deformations in the vicinity of blasting site. Extensive data are available on blasting in general and on the behavior of surface structures subjected to blast vibrations. However, only limited information is available on the effect of blast induced dynamic forces on underground structures like tunnels and caverns. This paper deals with the research work carried out at Koldam Hydroelectric Power Construction Project (KHEPP) on the effect of repeated blast vibrations on the jointed rock mass. Multiple rounds of blasts were conducted at the penstock tunnels and at the excavation site for powerhouse foundation. The damage caused by blast induced vibrations can be categorized into two types: i) near-field damage due to high frequency vibrations when the blast is occurring in the close proximity and ii) far-field damage due to low frequency vibrations when the blast is occurring relatively farther distances. The near-field damage was assessed by analytical damage models based on the ground vibrations. The far-field damage was assessed by measuring deformations of borehole extensometers and by borehole camera inspection surveys before and after the repeated blasting. Peak particle velocities generated by blast rounds were recorded by installing triaxial geophones near the borehole extensometers and borehole camera inspection holes. Damage assessment instrumentation was carried out at both the sides of penstock tunnel wall as another objective of the study was to compare the extent of rock mass damage with different joint orientations. The study reveals that repeated dynamic loading imparted on the jointed rock mass from subsequent blasts, in the vicinity, resulted in damage even at 23–26% of critical peak particle velocity. The far-field damage due to the repeated blast loading, after 56 rounds, was 77% of the near-field damage. It was also found that the far-field damage due to the repeated blast loading at the tunnel wall with 1500 joint orientation is 74% more than the damage at tunnel wall with 200 joint orientation. The results of the study indicate that repeated blast vibrations, even at less than critical vibration levels can cause damage problems to the structures in jointed rock mass. The paper stresses the need for consideration of the effect of repeated blast loading for comprehensive damage assessment as well as for fixing the threshold vibration limits to avoid the blast induced damage. 1. INTRODUCTION Blasting produces seismic waves similar to those produced by earthquakes, but with relatively high frequency and low amplitude and the degree of structural damage depends on the total energy of explosion, distance from the source, and the character of the medium. Blast induced damage weakens a rock mass, potentially leading to stability problems in the underground excavations. The blast damage problem is more severe and vulnerable for the jointed rock mass in underground excavations (Singh and Xavier, 2005). Unfortunately, there are no specific safety guidelines available for the blasted tunnels with regards to the threshold limits of vibrations caused by repeated blasting activity in the close proximity.
ABSTRACT The site investigations carried out by the Swedish Nuclear Fuel and Waste Management Co (SKB) at two sites along the Swedish East coast included extensive stress measurements in slim bore holes down to 800 m depth for a repository sited within 400 – 700 m depth. Both sites are composed of crystalline rocks. The objective of the stress estimation campaigns was to contribute to the geoscientific understanding of the sites, as well as to provide input for preliminary design studies carried out at both sites. Triaxial overcoring, hydraulic fracturing and hydraulic tests of pre-existing fractures were used, as well as the indirect observations such as bore hole breakouts and core disking. The purpose of this paper is to present the strategy applied for assessment of the state of stress and the experiences gained by the extensive stress characterization campaigns at the two sites. An auditing process of measurement results and indirect observations of in-situ stress orientation and magnitudes is also presented, and the outcome of measurements with the two methods in different stress regimes is discussed. 1 INTRODUCTION The in situ stress state is a design parameter required for the siting and construction of a repository for final disposal of spent nuclear fuel. This has been one of the focus areas in the recently completed site investigations of the Swedish Nuclear Fuel and Waste Management Co. (SKB). These site investigations were aimed at characterizing the suitability of the Oskarshamn and Forsmark areas, Figure 1. The distance between the two sites is roughly 500 km. A general execution program was presented prior to the start of the investigations (SKB, 2001). The goals were defined to:present the necessary data on the site for a site-adapted layout of the final repository and assessment of the repository's long-term radiological safety to be carried out, achieve fundamental geoscientific understanding, i.e. have analyzed the reliability and assessed the reasonableness of the assumptions made with respect to the current states of the site and naturally ongoing processes, and identify objects that may require special environmental considerations during construction and operation of the deep repository. With reference to the main goals of the geoscientific investigations, the rock mechanical work is mainly aimed at (SKB, 2001): 1) determine and assess the distribution of initial rock stresses within the sites, 2) determine mechanical properties of fracture zones and individual fractures, and 3) determine mechanical properties of intact rock and various rock masses. (Figure in full paper) A necessary component of the rock mechanics site descriptive model is the specification of the pre-existing state of stress in the rock mass because knowledge of the stress state is required for both analytical and numerical modelling of the stresses induced by excavation of a repository (Andersson et al., 2002). In this paper the stress measurement campaigns that were used to address objective 1 listed above, are presented and discussed. 2 STRESS DETERMINATION PROGRAM 2.1 Development Works The main scientific reference for stress measurements prior to the SKB site investigations.
- Europe > Sweden (0.67)
- North America > Canada > Alberta (0.28)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics (0.48)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT The National Road RN 91 has been threatened for about twenty-five years by a huge landslide, located 25 km south-east to the town of Grenoble (France). If several million cubic meters of rock fall down, the debris will dam the valley. Then the failure of the dam by overtopping and rapid erosion might result in a catastrophic flood and dramatic consequences for human life, environment and economy throughout the valley. The paper presents the hazard assessment based on geological and hydrological surveys, including small scale hydraulic tests, as well as the risk evaluation that has been performed. The risk management relies first upon a high level monitoring and an emergency plan; various mitigation strategies have been considered. 1 INTRODUCTION In 1980, rock falls including blocks of limited size occurred on the National Road RN 91, in the valley of the Romanche river, approximately twenty kilometers southeast of Grenoble town (Figure 1). The starting point of the rocks, called "Les Ruines de Sechilienne", is located 300 m above the valley bottom, one kilometer downstream from Sechilienne village, in the French Alps. (Figure in full paper) Such rock falls are frequent in mountainous areas and nobody paid special attention to the event of 1980 as most of the slope was covered by a dense forest. But in 1985, new rock falls with large size blocks occurred and the road had to be closed during several days. An emergency monitoring was decided, during day and night. Soon afterwards a barrier of concrete blocks was set up along the road at the toe of the slope; the blocks were surmounted by detection wires connected to red lights located at both ends of the danger zone, one hundred meters long. The first geological surveys showed that the unstable area, not easily accessible and wooded, was not just a matter of one cliff generating some rock falls, but included a potential volume of a few million cubic metres. From the moment the landslide hazard was identified, the risk management was based on a monitoring system associated with an emergency plan. This system, initially composed of geodetic and extensometer manual measurements (cables stretched through fractures), was gradually developed and improved. In 1985–1986, as a first prevention measure, a diversion of the RN 91 was built in the valley floor, at the toe of the slope opposite to Les Ruines, with temporary bridges at each side of the exposed area. The heavy trucks had to keep using the old road. To avoid the potential wanderings of the river dammed by debris in case of a rockslide, a diversion channel has been dug; it is protected by an earth dyke, supposed to be able to retain 1–2 million m3 of debris. The final bridges for the road diversion were built a few years later. The main features of the hazard and risk evaluation linked to the moving rock mass are presented below.
- Transportation > Ground > Road (1.00)
- Automobiles & Trucks (0.88)
Correlation of Grain Size With Physicomechanical Properties of Ma On Shan Marbles
Zhou, Y.D. (Department of Civil Engineering, The University of Hong Kong) | Tham, L.G. (Department of Civil Engineering, The University of Hong Kong) | Cheuk, C. Y. (Department of Civil Engineering, The University of Hong Kong) | Chan, T.C. (Department of Civil Engineering, The University of Hong Kong)
ABSTRACT The purpose of this study is to quantify the relationships between the grain size characteristics and physicomechanical properties of selected marble rocks from Ma On Shan, Hong Kong. The rock specimens can be subdivided into white, light grey and dark grey, depending on the amount of impurities of the original limestones before metamorphism takes place. A series of laboratory tests, including the point load test, Schmidh hardness test, and uniaxial compression test, have been carried out on the same set of core samples in accordance with the procedures given by ISRM. Also microscopic observations based on the double replica method have been made to quantify the microphysical characteristics, in particular the grain size. The results are statistically analyzed and some selected physical and mechanical properties of the marble rocks are plotted against each other in order to explore possible relationships. The study in particular examines the influence of gain size characteristics on the engineering properties of the chosen marble rocks. 1 INTRODUCTION The properties of rocks are influenced by the mineral composition, texture (grain size and shape), fabric (arrangement of minerals and voids) and the weathering state (Irfan, 1996). A number of petrographic techniques have been developed to document and quantify the mineralogical and textural characteristics of various rocks using an optical microscope (e.g., Mendes et al., 1966; Onodera and Asoka Kumara, 1980), scanning electron microscope (SEM) (e.g., Clelland & Fens 1991), or other tools. Among the typical petrographic characteristics that affect the mechanical properties of rocks, grain size has long been recognized to be closely related that in general the strength of rocks is greater for finer grained rock. Hugman and Friedman (1979) suggested that the peak uniaxial compressive strength decreases linearly with the mean grain size in carbonate rocks. However, it has been more frequently found that the peak strength decrease inversely with the square root of the grain size by Olsson (1974) for marble, Brace (1961) for quartzite, Brace (1964) for dolomite and limestone, and Fredrich et al. (1990) for calcite marbleand limestone. For Yuen Long marbles in Hong Kong, Wong et al. (1996) also found experimentally similar conclusion for fine-grain and coarse-grain Yuen Long marbles. The purpose of this study is to apply correlation analysis to investigation the relationships between grain size and engineering properties of local marbles. A variety of marble rock samples from Ma On Shan area in Hong Kong were subjected to microscopic investigation. The rocks can be categorized into white, light grey and dark grey type, depending on the amount of impurities in the original limestone before metamorphism takes place. The white marble is typically coarse-grain, and the light grey and dark grey marbles have relatively smaller grain size. The same samples were then tested to determine the specific gravity, Schmidt hardness, point load strength index, uniaxial compressive strength, modulus of elasticity and the Poisson's ratio. The relationships between these properties and average grain size are described by simple regression analysis.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.84)
ABSTRACT Some serious leakage problems have occurred in the underground structures of hydroelectric projects where irregular topography had given rise to inadequate confinement of high pressure water conductor systems. The problem can be overcome through adequate rock mass testing during construction stage by checking and ensuring sufficient magnitude of in-situ stresses. Head race tunnel for Nathpa Jhakri Hydroelectric Project in the Himalayan region is a high pressure tunnel which encountered low cover reach of 9 m where steel liner of 8.5 m diameter has been provided. Location of start of steel liner had undergone considerable change in comparison to that fixed initially based on the minimum cover criteria. The locations of start and end of the steel liner in the head race tunnel were fixed finally on the basis of in-situ stress measurement using hydraulic fracturing method. Results of in-situ stress measurements at four locations for the start of steel liner and at two locations for the end of steel liner were used to reach at the final conclusions. A lot of money and time, which are always are crucial for the successful execution of a project, were saved on the basis of hydraulic fracturing in-situ stress measurement. 1 INTRODUCTION The 1500 MW Nathpa Jhakri Hydroelectric Project is located across the river Sutluj, downstream of the existing Bhaba underground power station (120MW) in Kinnaur and Shimla districts of Himachal Pradesh state in India. The Project was commissioned in the year 2003 and has been successfully operating since then. A 60.5 m high concrete gravity dam along with four underground desilting chambers (525 m long, 16.3 m wide and 27.5 m high each) are important components of the project. The project has a 10.15 m diameter and 27374 m long head race tunnel (HRT) terminating in a 21.6 m diameter and 301 m deep surge shaft; underground powerhouse with a cavern size of 222 m length, 20 width and 49 m height houses six Francis type turbine units of 250 MW each with a total installed capacity of 1500 MW for utilizing a design discharge of 405 cumecs with a rated head of 428 m; a 10.15 m diameter tail race tunnel for conveying the water back into the river Sutluj. The layout plan of the project is shown in Fig. 1. In view of the fact that the rock cover is less than the required thickness in certain reaches of the tunnel under reference, and also based on the available geological features, it was proposed to go for steel liner of 8.5 m diameter at two locations in the doubtful reaches of head race tunnel. (Figure in full paper) The Central Soil and Materials Research Station (CSMRS) conducted hydraulic fracturing tests in drill holes at different depths at six locations using Minifrac System and verified that the in-situ state of stress inside the tunnel was more than the required hydrostatic pressure of up to 3.08 MPa in these reaches so as to decide whether steel liner was required for the entire reach.
ABSTRACT "5.12" Wenchuan Earthquake (Ms=8.0) triggered tens of thousands of geo-hazards throughout an area of about 100,000 km2. The distribution of geo-hazards is definitely affected by the such factors as geomorphology, topography, lithology and human engineering activities, but the distribution of earthquake-triggered geo-hazards is mainly controlled by the co-seismic fault, for they present zonal distribution along the co-seismic fault. Through the studies of three geo-hazard concentration areas including Doujiangyan to Wenchuan Road, Beichuan to Anxian County area, and Magong to Hongguang area, it is found that Wenchuan Earthquake-triggered geo-hazards have the following co-seismic effects:Wenchuan Earthquake is a thrust fault earthquake. The distribution of geo-hazards show marked "hanging wall and footwall effects", manifested by that the distribution concentration in the hanging wall of seismic fault is higher than that in the footwall and the former coverage is wider than the latter as well as that the scale of geo-hazards is larger than that in the footwall; the strong development zones of geo-hazards are within the range of 7 km in the hanging wall of co-seismic fault. The ranges of 7 to 11km in the hanging wall and o to 5km in the footwall can be delimited as the middle development zones. A vast majority of large-scale landslides are distributed within the range of 5km from the fault, and large-scale landslides are unlikely to occur within the range of over 10km; the transitional and staggered positions of fault are the concentration areas of geo-hazards and large-scale geo-hazards are likely to occur in these positions; the preferred direction of landslide is NW-SE, basically vertical to the spreading direction of Yingxiu-Beichuan Fault. This may be because that Longmenshan Fault Zone has always been affected by the tectonic stress field of NW-SE extrusion area since Cenozoic Time; the earthquake-triggered geo-hazards mainly occur in the zones of seismic intensity IX and higher. The concentration of geo-hazards in the seismic intensity zones XI is the same as that in seismic intensity zones X; the concentration in the seismic intensity zones IX equals to 1/3 of the abovementioned one; the concentration in the seismic intensity zones VIII is only 1/10 of the abovementioned one. 1 INTRODUCTION At 14:28 May 12, 2008(Beijing time), a great earthquake measured at 8.0 Ms according to the China Seismological Bureau struck Yingxiu Town (31.0°N, 103.4°E) of Wenchuanxian County, 70 km northwest of Chengdu, the capital of Sichuan, causing the frontal and central faults (Jingyou-Guanxian Fault and Yingxiu- Beichuan Fault) of the Longmenshan Fault Zone between the Western part of the Sichuan Basin and the eastern margin of the Qinghai-Tibet Plateau to rupture, resulting in the formation of an earthquake rupture zone of around 300km long(Huang, R.Q., et al, 2008, b; He,H.L.,et al,2008). The Wenchuan earthquake had a high magnitude and large energy release causing a strong destructive force and large area of influence. The epicenter of the strong earthquake was located in the medium to high mountain areas just West of Sichuan Basin, where the geological environment is quite weak.
ABSTRACT Investigation concerned with numerical modeling of geodynamic processes within Polish copper mines districts affected with a thick salt rock stratum presence are presented. The adequate parameters of the developed numerical model of rock mass behavior were determined using laboratory tests and back calculation procedure based on FEA. Particular attention was paid to estimating the salt-rock time-dependent behavior and its appropriate rheological parameters. Geological and geomechanical analyses permitted formulating 3d FDM based model utilizing the thick composite plate analogue, which represents sufficiently well the real geological structure and load floor and immediate roof strata with the load equal to their residual strength. The rocksalt presence above the exploited copper ore seam introduces significantly worse safety conditions as compared with salt less rock mass. This is because of the relatively low saltrock strength parameters (particularly tensile strength) as well as great thickness of salt deposit. 1 INTRODUCTION The perspective of copper ore development in the northern part of the Polkowise- Sieroszowise mine in Poland, introduces into the local mining practice the new, extremely important parameter such as time factor. This is due to thick saltrock deposit presence in the rock mass surrounding the prospective mine excavations at the depth of approximately 1,500m below the ground (Figure 1). The time factor links the mentioned upper rheological layer behavior and the stability beneath located hard rock mine workings, since:due to stress relaxation, generally considered as a positive phenomenon, this layer is able to relieve stress concentrations within its own and the adjacent rock volume, due to the associated load transfer process the layer may develop increasing rock deformations within neighboring areas; the stiff dolomitic- anhydritic rock beam which constitutes the immediate roof of mine function due to creep processes within the upper rheological deposit; assuming boundary conditions to be fixed in time domain (e.g.) face stopping), one may expect that after an ample time period, the salt deposit's entire weight should be the only load acting on the lower hard rock layer. 2 PARAMETERS OF ROCKSALT DEPOSIT The numerical analyses presented below are based on the linear Burger's model (Figure 3). Laboratory investigations and fields measurements (Pytel, 1999; Kortas, 2004) prove that saltrock, after a sufficiently lengthy period of time, behaves as a kind of liquid deforming linearly with increasing time. (Figure in full paper) Figure 1: Geotechnical diversity of overburden strata within the area of copper bearing deposit (Central Zone – Zechstein formation of stiff dolomite-anhydrite strata of 160–220 m of thickness overlaid by 200–400 m Triassic sandstone; Northern Zone – thickness of dolomite-anhydrite structure of about 32–90 m with presence of rock salt deposit and thick Triassic sandstone; Southern Zone – glacial deposits directly on Zechstein formation, no Triassic sandstone) (Monograph, 1996). Thus, such strain function characteristics permit assuming the Burger's model as a basis for numerical analysis of the loaded saltrock behavior in following parts of the paper (Figure 2). (Figure in full paper) In practice, viscosity of saltrock mass manifests itself by increasing salt mass manifests itself.
- Geology > Mineral > Native Element Mineral > Copper (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Mineral > Halide > Halite (0.93)
- (3 more...)
Advanced Natural Gas Storage Project And Verification Tests of Lined Rock Cavern In Japan
Okuno, Tetsuo (Shimizu Corporation) | Wakabayashi, Naruki (Shimizu Corporation) | Niimi, Katsuyuki (Shimizu Corporation) | Kurihara, Yuji (Obayashi Corporation) | Iwano, Masahiro (Taisei Corporation) | Komatsubara, Tohru (The Japan Gas Association)
ABSTRACT The Japan Gas Association (JGA) has been studying technologies of an underground natural gas storage system, a Lined Rock Cavern (LRC) gas storage system called ANGAS (Advanced Natural GAs Storage). The purpose of the project is to develop a suitable LRC system for Japan, and to contribute to expanding use of natural gas. It is necessary to study measures to shave off the daily peak load of natural gas through pipelines and we expect the ANGAS is one of key countermeasures for peak shaving. In the project, our goal is to ensure the design method of the LRC system under the Japanese geological conditions. One of the key technologies of the developed design method is based on plastic deformation of the steel liner considering the rock deformation appropriately. Using the developed design method and procedures, we designed and constructed a small test cavern which is located at the Kamioka mine, the midland of Japan. The test cavern is surrounded by a sedimentary rock mass which consists of mainly sandstone and mudstone. The internal design pressure of the test cavern is 20MPa. We present some results of the verification tests and confirm the validity of the LRC system for Japan in this paper. 1 INTRODUCTION 1.1 ANGAS project The ANGAS project was performed over 4 years, from 2004 to 2007. The purpose of the project is to develop a suitable LRC gas storage system for Japan, and to contribute to the expanding use of natural gas. For example, it is necessary to study measures to shave off the daily peak load of natural gas through pipelines because, as a special characteristic in Japan, there is a large daily fluctuation in gas supply and we expect ANGAS to be a key countermeasure in peak shaving. Furthermore, there is a possibility that LRC could be a novel storage system in inland areas. In this project, our goal is to develop a design method for commercial LRC systems, under Japanese geological conditions of the limited hard rock distribution, referring to the results of the verification tests on the test cavern. The concepts of LRC are as follows: Gas pressure is transmitted to the surrounding rock mass through the backfilled concrete behind the steel liner and resisted by the rock mass; Gas-tightness is ensured with a steel liner; Groundwater around the storage cavern can be drained with a drainage system (composed of drainage pipes and other elements) while the storage cavern is being constructed or the inner gas pressure is released. The objective is to prevent extremely high external water pressure from acting on the steel liner. (Figure in full paper) 1.2 Key technologies In order to ensure the concepts of LRC under the above design conditions, the LRC system needs evaluation technologies for the surrounding rock mass and design technologies for the storage cavern, as key technologies. In particular, design technologies for the storage cavern have been developed in the project.
ABSTRACT The space structure and scale of mined-out area are dynamical variable using high-sublevel fullymechanized coal caving in steep and thick coal seam. Due to segment pre-blasting, the degree of coal damage and cracks would be increased, and the complexity of the physical-geometric structure and time-space relationship of the mined-out-area would be enhanced. Firstly, the comprehensive analysis of complexity of the B1+2 workings environment and the mining technology character at Weihuliang coal mine, and the blasting parameter optimization, dynamite quantity and blasting effect were also optimized. Then, the pre-blasting was applied successfully in 52m sublevel caving and effective deteriorate coal-seam. Finally, the effect had been detected and verified by RSM-SY5-broken-zone device and YS(B)-optic-borehole-camera. It was obviously indicated that the average-forces of the front and behind support were raising based on field monitoring results. All of these could be used as referencing for the subsequent safe mining to the 102m and 18m sublevel-top-coal caving. 1 INTRODUCTION During the top-coal caving, the weakening and the accessibility of the top coal directly determine its fully-breaking and its release safety and efficiency (Xie et al. 1999, Shi et al. 2006, Kang et al. 2004, Chen et al. 2002) The mined-out area caused by using high-sublevel fully-mechanized coal caving in steep and thick coal seam is a spatial structure of varying sizes (or dimensions). Due to the segment pre-blasting, the development of coal damage and cracks, the complexity of the physical-geometric structure, and the time-space relationship of the mined-out all increased (Gao et al. 2001, Wang 2007, Shao et al. 2007). Weihuliang coal mine is a mine of low gas. The +579E2EB1+2 steep seam (from 64° to 69°) is a high level top coal caving workface, which is along the strike direction of the B1+2 coal seam, and there are some coal pillars with different heights, respectively 52m, 102m and 18m. During the mining of the 52m coal pillar, several times of large-scaled dynamic collapse occurred, which led to people hurts caused by some harmful gases which were squeezed into the workface. To ensure fast and safe caving, segment pre-blasting of the 52m coal pillar must be carried out. Analyzed from some aspects like the complexity of the workface, the optimization of the blasting parameters and the techniques, the amount of explosives, and the blasting effects, the segment pre-blasting was finally successfully implemented at the position where it is 100m ahead of the workface. And this can provide some references of the mining of the follow-up process, which will be done to the 102m coal pillar and the 18m coal pillar. 2 EMBEDDING CONDITION AND CHARACTERISTICS OF MINING TECHNIQUES 2.1 Geological conditions and characteristics of in-situ stress The joints in the B1+2 coal seam are fully developed. The structure of the coal seam is complex, and its roof and floor and loose. The strike direction of the seam is 55°, its dip direction is 325°, its dip angle is from 64° to 69°, and its f-factor is 3.