• Title/Summary/Keyword: Soft rock

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The Role of Feed Back Analysis in Observational Method (정보화 시공에서 Feed Back Analysis (터널, 암반사면, 지반굴착 등 Hard Material 사례중심으로))

  • 김학문
    • Proceedings of the Korean Geotechical Society Conference
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    • 2002.10a
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    • pp.147-179
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    • 2002
  • The important role of observational method in geotechnical engineering are emphasized together with the direction of future development, concerning successful application of the technique on the site investigation, design and feed back at various construction stages. Case histories on the application of feed back are introduced in order to achieve the most economical and reliable construction for tunnel, rock slope and deep excavations through feed back system at design and construction stages. Also the limitations and advantages of the observational method and the role of feed back system are discussed for construction of tunnel, rock slope and deep excavation in hard ground such as layered ground conditions including weathered, soft and hard rocks.

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A Case Study on Reinforcement of Cut Slope with Fault Zone (단층대가 발달한 사면의 보강대책에 관한 사례 연구)

  • Kim, Jeong-Ho;Park, Choon-Sik;Kim, Tae-Sung
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.930-937
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    • 2008
  • From the result of precise field investigation and stability analysis for the cut slope, following results were acquired. 1. The cause of the collapse of cut slope came from circle sliding collapse by fault zone which remained inner weathering zone. 2. The existing destructed soil and rock can be removed by reinforcement. And to prevent the additional destruction, it is judged that applying the method after relaxing the slope would be reasonable. 3. To make cut slope stable, soft rock layer should be done cutting 1:1.5 and 1:2.0 ~ 1:2.5 for weathered rock and soil layer. 4. Heavy water leakage section should be applied horizontal drain method so that water pressure should not act to the cut slope.

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Optimum Support Pattern Design of the Tae-Gu Subway Tunnel (대구 지하철 터널의 적정지보패턴 선정에 관한 연구)

  • 지왕률;최재진
    • Tunnel and Underground Space
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    • v.4 no.2
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    • pp.119-131
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    • 1994
  • This is a Double-Track Railway tunnel in typical Tae-Gu black and gray shale forming part of the No.1 Line of the Tae-Gu Subway. The main fault zone at tunnel is a moderately to highly weathered and closely jointed zone, 0.5 m wide with associated paralled jointing which is slickensided and fractured. After excavation by blasting, the soft rocks should need to be reinforced with optimal supporting pattern which might be better redesigned through the consideration of the results of in-situ rock measurements at the field. Performances fo the field tests included Point Load Test, Schmidt Hammer Test, and field joint measurement gave the detail data for the optimum support design and safe excavation of the No.1 Line of Tae-Gu Subway at the No.1-7 consturction site adn the safety of this redesigned supports system was analysed by the FDM program FLAC.

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Estimation of Rock Erodibility due to Energy Dissipation of Inflow Passing through the Sluice Gate of Seadike (배수갑문 유입수류의 에너지 감쇠에 따른 암석 침식 가능성 추정)

  • Jo, Jin-Hun;Park, Yeong-Jin;Park, Sang-Hyeon
    • Journal of Korea Water Resources Association
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    • v.33 no.2
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    • pp.237-245
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    • 2000
  • Sihwa seadike is originally designed to control the water level In lake Sihwa. However the sluice gate is being operated everyday to preserve the water quality of lake. Due to the frequent operation of gates the bottom of drainage canal which is composed of weathered rock and soft rock is being scoured. Recently the bottom in the front area of apron was protected by putting underwater concrete. This study is carried out to understand the hydraulic situation for protection, and to estimate the trend of scouring by comparing between energy dissipation and registance of bottom rock. Annandale(1995) introduced the erodibility index theory, and suggested a criteria to judge the erodibility of rock through the relation between the erodibility index and energy dissipation. Determenation of erodibility index of rock is based on the results of sample core analysis, and the energy dissipation of flow is calculated from the estimation of total head on the scale model. These two values are plotted on the criteria, and the erodibility of rock is determined.

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Ideal body modeling of porous rock by frost-thawing (다공질암의 동결융해 현상에 대한 이상물체 모델의 적용성 연구)

  • Han, Heui-Soo;Back, Yoog
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.12 no.5
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    • pp.399-405
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    • 2010
  • The accumulated displacements and fatigues of rock are increased by the stress-hysteresis, induced from repeated frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysteresis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, to do ideal body analysis, Kelvin model could be used to analyze the frost-thawing behavior in winter. In general, rock slope failure occurs by the deterioration of rocks, which is caused by the repetition of freezing-thawing process. In order to keep the safety of such rock mass structures the deterioration process of rock needs to be described quantitatively using some meaningful parameters. In this work, the deterioration process in freezing-thawing cycle of tuff, which is a famous soft porous rock, is investigated through laboratory tests and successfully described as a differential equation for the change of porosity. And then, the deterioration of the mechanical properties of rock, such as Young's modulus and uniaxial compressive strength, are quantitatively described as a function of the porosity.

Soil structure interaction effects on strength reduction factors

  • Eser, Muberra;Aydemir, Cem;Ekiz, Lbrahim
    • Structural Engineering and Mechanics
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    • v.41 no.3
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    • pp.365-378
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    • 2012
  • In this study, strength reduction factors are investigated for SDOF systems with period range of 0.1-3.0 s with elastoplastic behavior considering soil structure interaction for 64 different earthquake motions recorded on different site conditions such as rock, stiff soil, soft soil and very soft soil. Soil structure interacting systems are modeled and analyzed with effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. Results are compared with those calculated for fixed-base case. A new equation is proposed for strength reduction factor of interacting system as a function of structural period of system (T), ductility ratio (${\mu}$) and period lengthening ratio (T/T). It is concluded that soil structure interaction reduces the strength reduction factors for soft soils, therefore, using the fixed-base strength reduction factors for interacting systems lead to non-conservative design forces.

Optimal pre-conditioning and support designs of floor heave in deep roadways

  • Wang, Chunlai;Li, Guangyong;Gao, Ansen;Shi, Feng;Lu, Zhijiang;Lu, Hui
    • Geomechanics and Engineering
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    • v.14 no.5
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    • pp.429-437
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    • 2018
  • In order to reduce deformation of roadway floor heave in deep underground soft rockmass, four support design patterns were analyzed using the Fast Lagrangian Analysis of Continua (FLAC)3D, including the traditional bolting (Design 1), the bolting with the backbreak in floor (Design 2), the full anchorage bolting with the backbreak in floor (Design 3) and the full anchorage bolting with the bolt-grouting backbreak in floor (Design 4). Results show that the design pattern 4, the full anchorage bolting with the bolt-grouting backbreak in floor, was the best one to reduce the deformation and failure of the roadway, the floor deformation was reduced at 88.38% than the design 1, and these parameters, maximum vertical stress, maximum horizontal displacement and maximum horizontal stress, were greater than 1.69%, 5.96% and 9.97%. However, it was perfectly acceptable with the floor heave results. The optimized design pattern 4 provided a meaningful and reliable support for the roadway in deep underground coal mine.

The Reinforcement Method and Stability Analysis of Cut Slopes (절토사면의 안정해석과 보강방법)

  • 지인택;이달원
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.39 no.1
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    • pp.112-121
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    • 1997
  • The aim of this study was to analyze the slope stability relating to the failure of cut slopes and the characteristics of stress-strain relations obtained by limit equilibrium method, finite element method, and stereographic projection method for the reinforced cut slopes. The following conclusions were made : 1.To use stereographic projection method led to little possibility to take the toppling and wedge failure while to use the other methods led to the failure. It was recommended to reduce the slope inclination from 1:1 to 1: 1.5~1 :1.8 and adopt coir mesh method to protect the slope surface. position with the horizontal displacement after final excavation moved to the excavation base. The maximum shear strain values concentrated at the excavation base indicated the possibility to induce the local failure. 3. It was recommended that the slope inclination for blast rock with the slope height larger than l0m was 1: 0.5, 1:1, and 1: 1~1 :1.5 for hard rocks, soft and ordinary rocks, and ripping and soils, respectively. 4. Berm width criteria for blast rock with the slope height larger than l0m were recommended as follow : 2~3m per 20m slope height for hard rocks, 1 ~2m per l0m slope height for soft and ordinary rocks, 1 ~ l.5m per 5m slope height for ripping and soils.

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Interpretation on the subsurface velocity structure by seismic refraction survey in tunnel and slope (탄성파 굴절법 탐사를 이용한 지반 속도분포 해석-터널 및 절토 사면에의 적용 사례)

  • You Youngjune;Cho Chang Soo;Park Yong Soo;Yoo In Kol
    • 한국지구물리탐사학회:학술대회논문집
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    • 1999.08a
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    • pp.48-64
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    • 1999
  • For quantitative evaluation of geotechnical engineering properties such as rippability and diggability, clear interpretation on the subsurface velocity structures should be preceded by figuring out top soil, weathered and soft rock layers, shape of basement, fracture zones, geologic boundary and etc. from the seismic refraction data. It is very important to set up suitable field parameters, which are the configuration of profile and its length, spacings of geophones and sources and topographic conditions, for increasing field data quality Geophone spacing of 3 to 5m is recommended in the land slope area for house land development and 5 to 10m in the tunnel site. In refraction tomography technique, the number of source points should be more than a half of available channel number of instrument, which can make topographic effect ignorable. Compared with core logging data, it is shown that the velocity range of the soil is less than 700m/s, weathered rock 700${\~}$1,200m/s, soft rock 1,200${\~}$1,800m/s. And the upper limit of P-wave velocity for rippability is estimated 1,200 to 1,800m/s in land slope area of gneiss. In case of tunnel site, it is recommended in tunnel design and construction to consider that tunnel is in contact with soft rock layer where three lineaments intersecting each other are recognized from the results of the other survey.

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Evaluation of Unit Side Resistance of Drilled Shafts by Revised SPT N Value (환산SPT N값을 이용한 현장타설말뚝의 단위주면마찰지지력 산정)

  • Yoon, Min-Seung;Lee, Chea-Keon;Kim, Myung-Hak
    • Journal of the Korean Geotechnical Society
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    • v.29 no.12
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    • pp.5-10
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    • 2013
  • Bearing capacity of a drilled shaft can be separated into side resistance and base resistance. But in domestic design procedure side resistance is usually underestimated compared with base resistance. Results of bi-directional test showed that measured side resistances in each different layers are larger than those evaluated from several suggested methods. In this study, measured side resistances in each different layer of drilled shafts installed in domestic sites are analyzed and compared with evaluated side resistances from the method using revised SPT N value. For weathered rock and soft rock layer, from which rock core can hardly be obtained, we suggested new evaluated methods using revised SPT N value instead of the method using uniaxial compressive strength of rock. Resuts showed that the ranges of side resistance of cohesive and non-cohesive layer are $f_s{\leq}5tf/m^2$ and $f_s{\leq}15tf/m^2$ respectively. Range of side resistance in weathered rock is $15tf/m^2$ < $f_s{\leq}50tf/m^2$ and that in soft rock $f_s{\geq}35tf/m^2$.