• Title/Summary/Keyword: Rock ground

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A Comparative Study on Heat Loss in Rock Cavern Type and Above-Ground Type Thermal Energy Storages (암반공동 열에너지저장과 지상식 열에너지저장의 열손실 비교 분석)

  • Park, Jung-Wook;Ryu, Dongwoo;Park, Dohyun;Choi, Byung-Hee;Synn, Joong-Ho;Sunwoo, Choon
    • Tunnel and Underground Space
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    • v.23 no.5
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    • pp.442-453
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    • 2013
  • A large-scale high-temperature thermal energy storage(TES) was numerically modeled and the heat loss through storage tank walls was analyzed using a commercial code, FLAC3D. The operations of rock cavern type and above-ground type thermal energy storages with identical operating condition were simulated for a period of five consecutive years, in which it was assumed that the dominant heat transfer mechanism would be conduction in massive rock for the former and convection in the atmosphere for the latter. The variation of storage temperature resulting from periodic charging and discharging of thermal energy was considered in each simulation, and the effect of insulation thickness on the characteristics of heat loss was also examined. A comparison of the simulation results of different storage models presented that the heat loss rate of above-ground type TES was maintained constant over the operation period, while that of rock cavern type TES decreased rapidly in the early operation stage and tended to converge towards a certain value. The decrease in heat loss rate of rock cavern type TES can be attributed to the reduction in heat flux through storage tank walls followed by increase in surrounding rock mass temperature. The amount of cumulative heat loss from rock cavern type TES over a period of five-year operation was 72.7% of that from above-ground type TES. The heat loss rate of rock cavern type obtained in long-period operation showed less sensitive variations to insulation thickness than that of above-ground type TES.

Stability Analysis for Ground Uplift in Underground Storage Caverns for High Pressurized Gas using Hoek-Brown Strength Criterion and Geological Strength Index (GSI) (Hoek-Brown 강도기준식 및 암질강도지수를 이용한 고압 유체 지하저장 공동의 융기에 대한 안정성 평가)

  • Kim, Hyung-Mok
    • Tunnel and Underground Space
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    • v.24 no.4
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    • pp.289-296
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    • 2014
  • A simple analytical approach for stability assessment of underground storage caverns against ground uplift of overburden rock above the rock caverns for high pressurized fluid such as compressed air energy storage (CAES) and compressed natural gas (CNG) was developed. In the developed approach, we assumed that failure plane of the overburden is straight upward to ground surface, and factor of safety can be calculated from a limit equilibrium analysis in terms of this cylindrical shape failure model. The frictional resisting force on the failure plane was estimated by Hoek-Brown strength criterion which replaces with Mohr-Coulomb criterion such that both intact rock strength and rock mass conditions can be considered in the current approach. We carried out a parametric sensitivity analysis of strength parameters under various rock mass conditions and demonstrated that the factor of safety againt ground uplift was more sensitive to Mohr-Coulomb strength criterion rather than Hoek-Brown criterion.

Effect of the Earth Pressure Coefficient on the Support System in Jointed Rock Mass

  • Son, Moorak;Adedokun, Solomon;Hwang, Youngcheol
    • Journal of the Korean GEO-environmental Society
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    • v.16 no.2
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    • pp.33-43
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    • 2015
  • This paper investigated the magnitude and distribution of earth pressure on the support system in jointed rock mass by considering different earth pressure coefficients, rock types and joint inclination angles. The study mainly focused on the effect of the earth pressure coefficients on the earth pressure. Based on a physical model test (Son & Park, 2014), extended studies were conducted considering rock-structure interactions based on the discrete element method, which can consider the joints characteristics of rock mass. The results showed that the earth pressure was highly influenced by the earth pressure coefficients as well as the rock type and joint inclination angles. The effects of the earth pressure coefficients increased when the rock suffered more weathering and has no joint slide. The test results were also compared with Peck's earth pressure for soil ground, and clearly showed that the earth pressure in jointed rock mass can be greatly different from that in soil ground. This study indicated the earth pressure coefficients considering the rock types and joint inclination angles are important parameters influencing the magnitude and distribution of earth pressure, which should be considered when designing the support systems in jointed rock mass.

Control of Blast Vibration, Air Blast, and Fly Rock in Rock Excavation (암반굴착에 의한 발파진동, 소음 및 비석의 조절)

  • Ryu, Chang-Ha
    • Tunnel and Underground Space
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    • v.2 no.1
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    • pp.102-115
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    • 1992
  • Blasting operations associated with rock excavation work may have an environmental impact in nearby structures or human beings. With the increase of construction work in urban areas, vibration problems and complaints have also increased. In order to determine the optimum design parameters for safe blast, it is essential to understand blast mechanism, design variables involved in blast-induced damage, and their effects on the blasting results. This paper deals with the characteristics of ground vibrations, air blast and fly rock caused by blast, including the general method of establishing the vibration predictors, and damage criteria suggested by various investigators. The results of field measurements from open pit mine and tunnel construction work are discussed. Basic concepts of how to design blast parameters to control the generation of ground vibrations, air blast and fly rock are presented.

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Blast Design of Hilly Rock Excavation Adjacent to Structures and Facilities (구조물 및 시설물 인접 구릉지의 암반굴착 발파설계)

  • 류창하;선우춘;신희순;정소걸;최병희
    • Tunnel and Underground Space
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    • v.4 no.1
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    • pp.38-46
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    • 1994
  • This paper concerns the design of blasts adjacent to structures and facilities. In order to investigate the site characteristics, measurements of in-situ wave propagation and laboratory tests of rock cores taken from the boreholes were carried out. Effects of rock media and delay intervals on ground vibration levels were identified from over sixty measurements of three times of test blasts. For practical use in the field, an empirical propagation equation was derived so as to reflect the characteristics of rock media and delay effects. Safe limits of vibration level for structures were conservatively established based on various suggested criteria. Safe limits for facilities were adopted so that vibration levels induced by blasting should not exceed the allowable limits specified in the manufacturer's installation condition. Suggested were blast pattern and operation to enhance the rock fracturing and to reduce the ground vibration levels under the restricted conditions.

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Probabilistic Q-system for rock classification considering shear wave propagation in jointed rock mass

  • Kim, Ji-Won;Chong, Song-Hun;Cho, Gye-Chun
    • Geomechanics and Engineering
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    • v.30 no.5
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    • pp.449-460
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    • 2022
  • Safe underground construction in a rock mass requires adequate ground investigation and effective determination of rock conditions. The estimation of rock mass behavior is difficult, because rock masses are innately anisotropic and heterogeneous at different scales and are affected by various environmental factors. Quantitative rock mass classification systems, such as the Q-system and rock mass rating, are widely used for characterization and engineering design. The measurement of rock classification parameters is subjective and can vary among observers, resulting in questionable accuracy. Geophysical investigation methods, such as seismic surveys, have also been used for ground characterization. Torsional shear wave propagation characteristics in cylindrical rods are equal to that in an infinite media. A probabilistic quantitative relationship between the Q-value and shear wave velocity is thus investigated considering long-wavelength wave propagation in equivalent continuum jointed rock masses. Individual Q-system parameters are correlated with stress-dependent shear wave velocities in jointed rocks using experimental and numerical methods. The relationship between the Q-value and the shear wave velocity is normalized using a defined reference condition. This relationship is further improved using probabilistic analysis to remove unrealistic data and to suggest a range of Q-values for a given wave velocity. The proposed probabilistic Q-value estimation is then compared with field measurements and cross-hole seismic test data to verify its applicability.

Support Characteristics of Rock Bolt and Spiral Bolt (록 볼트 및 스파이럴 볼트의 지보특성)

  • Cho, Young-Dong;Song, Myung-Kyu;Lee, Chung-Shin;Kang, Choo-Won;Ko, Jin-Seok;Kang, Seong-Seung
    • Tunnel and Underground Space
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    • v.19 no.3
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    • pp.181-189
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    • 2009
  • This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

The Case Studies on Application of Mat Foundation System to Building Structure Founded on Weathered Ground (풍화대지반에 지지된 건축구조물의 전면기초 적용에 관한 사례 연구)

  • Choi, Yongkyu;Kim, Sungho;Lee, Minhee
    • Journal of the Korean GEO-environmental Society
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    • v.10 no.6
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    • pp.5-18
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    • 2009
  • In construction of buildings in Korea, the buildings are frequently founded on the weathered ground (weathered soil/rock, fractured rock). In this case, to make a full use of a bearing capacity of a weathered ground for economic design, the shallow mat foundation system could be used. In this study, we have researched three cases of mat foundations on the weathered ground in Korea, and analyzed and considered the design procedures and the reinforcing methods. That is, we have considered the detail design, analysis proceedings, the ground settlement evaluation proceedings, the rock face mapping evaluations after excavation and reinforcing methods of the mat foundation on the weathered ground. And large scale plate load tests on the weathered ground supporting the mat foundation were performed and also load bearing capacity and settlement of actual mat foundation, considering the scale effect, were evaluated.

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A study on the change of strength parameters reinforced rock bolt in the ground around tunnel (록볼트로 보강된 터널주변지반의 강도정수 변화에 대한 연구)

  • Kim, Sang-Hwan;Bang, Gyu-Min
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.7 no.1
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    • pp.51-61
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    • 2005
  • In general the strength parameter of the ground will be changed by reinforcing the ground around tunnel. In this case, the concept of tunnel design, such as supporting system, excavation, lining and so on, should be modified based on the failure criteria or the ground changed by the reinforcement. This paper presents the variation mechanism of strength parameters and new failure criteria of the reinforced ground. In order to perform this research, theoretical and experimental works were carried out. It was clearly founded that the cohesion of strength parameters is only increased by reinforcement of ground, especially by rock bolting.

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Ground Investigation and Characterization for Deep Tunnel Design (대심도 암반의 터널 설계를 위한 지반 조사와 특성화)

  • Yoon, Woon-Sang;Choi, Jae-Won;Park, Jeong-Hoon;Song, Kook-Hwan;Kim, Young-Keun
    • Proceedings of the Korean Geotechical Society Conference
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    • 2009.09a
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    • pp.584-590
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    • 2009
  • One of the critical design problems involved in deep tunnelling in brittle rock, is the creation of surface spalling damage and breakouts. If weak fault zone is developed in deep tunnel, squeezing problem is added to the problems. According to the results of ground investigation in the study area, hard granitic rockmass and distinguished high angle fault zone are distributed on the tunnel level over 400m depth. To analyse the probability of brittle failure and squeezing, ground characterization with special lab. and field test were carried out. By the results, probability of brittle failures like spalling and rock burst is very low. But squeezing may be probable, if weak fault zone observed surface and drill core is extended to designed tunnel level.

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