• 터널과지하공간
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• 제23권3호
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• pp.212-218
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• 2013

풍화된 응회암 시험편을 모사하기 위하여 최고 예열온도를 200, 400, 600($^{\circ}C$)로 한 예열시험편을 제작하였다. 각 예열시험편에 대한 실내시험을 통해 비중, 흡수율, 탄성파속도, 일축압축강도, 압열인장강도, 탄성계수, 포아송비, 슬레이크 내구성 지수를 측정하였다. 암석에 열을 가하는 경우 물성의 열화가 발생하는 것으로 나타났으나 예외적으로 슬레이크 내구성 지수는 별로 영향을 받지 않는 것으로 평가되었다. P-파 속도와 일축압축강도, 압열인장강도, 탄성계수, 흡수율 간에는 상당한 상관성이 있는 것으로 해석되었으며, P-파 속도를 알면 일축압축강도, 압열인장강도, 탄성계수, 흡수율을 추정할 수 있는 회귀식을 도출하였다.

• 터널과지하공간
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• 제7권1호
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• pp.13-19
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• 1997

It is necessary to study on thermo-hydro-mechanical effect at rock mass performing project such as radiowaste disposal in deep rock mass. In this study, thermo-hydro-mechanical coupling analysis which is considered interaction and the variation of rock properties induced by temperature increase was performed for the circular shaft when appling temperature of 20$0^{\circ}C$ at the shaft wall. The shaft is diameter of 2 m and under hydrostatic stress of 5 MPa. In the cases, thermal expansion by temperature increase progress from the wall to outward and thermal expansion could induce tensile stress over the tensile strength of rock mass at the wall. When rock properties were given as a function of temperature, thermal expansion increased, tensile stress zone expanded. Lately, water flow is activated by increase of permeability and decrease of viscosity.

• Advances in concrete construction
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• 제7권4호
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• pp.241-247
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• 2019

In this paper the effect of bedding layer on the failure mechanism of rock in direct shear test has been investigated using particle flow code, PFC. For this purpose, firstly calibration of pfc2d was performed using Brazilian tensile strength. Secondly direct shear test consisting bedding layer was simulated numerically. Thickness of layers was 10 mm and rock bridge length was 10 mm, 40 mm and 60 mm. In each rock bridge length, bedding layer angles changes from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Totally 21 models were simulated and tested. The results show that two types of cracks develop within the model. Shear cracks and tensile cracks. Also failure pattern is affected by bridge length while shear strength is controlled by failure pattern. It's to be noted that bedding layer has not any effect on the failure pattern because the layer interface strength is too high.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 가을 학술발표회 논문집
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• pp.161-184
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• 2001

Rock masses usually contain such features as bedding planes, faults, fissures, fractures, joints and other mechanical defects which, although formed from a wide range of geological processes, posses the common characteristics of low shear strength, negligible tensile strength and high fluid conductivity compared with the surrounding rock material. In the engineering context here, the discontinuities can be the single most important factor governing the deformability, strength and permeability of the rock mass. Moreover, a particularly large and persistent discontinuity could critically affect the stability of any surface or underground excavation. For these reasons, it is necessary to develop a thorough understanding of the geometrical, mechanical and hydrological properties of discontinuities and the way in which these will affect rock mechanics and hence rock engineering.

• 터널과지하공간
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• 제5권4호
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• pp.363-375
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• 1995

Critical literature review in this study revealed that there can be a significant influence of the residual stress on the engineering properties of rock. The review also showed that few number of research works on the quantification of the influence was attributed to the limitation of the two classical measurement techniques, viz, X-ray diffraction and mechanical relaxation method. In this study, a new way of approach was sought based on the assumption that residual stress up to the failure. A series of hoop tests conducted onthe samples from the limb of Carboniferous Limestone in Clevedon, England, revealed that (i) there is no preferential orientations of microcracks and minerals which have been widely believed as the main source of the strength anisotropy of rock; (ii) the anisotropy of the tensile strength of the limestone results from the influence of the residual stress; (iii) since jointing commenced within the fold, residual stored strain energy has been released preferentially in the direction perpendicular to the major joints(o$^{\circ}$ and 90$^{\circ}$); (ⅳ) during the hoop test making it much easier to create tensile fracture in these directons, viz 45$^{\circ}$ and 135$^{\circ}$)was released during the hoop test making it much easier to create tensile fracture in these directions, viz 45$^{\circ}$and 135$^{\circ}$;(v) the direction in which the stored strain energy may be presumed to be the least, required the greatest work to cause failure.

• Geomechanics and Engineering
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• 제15권2호
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• pp.805-810
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• 2018

The abrasivity of rocks results in tool wear in rock excavation or drilling projects. It can affect significantly the cost and schedule of the projects performed in abrasive rock massess. For this reason, the understanding of the mechanism of rock abrasivity is very important for excavation projects. This study investigates the effect of strength on the LCPC abrasivity coefficient (LAC) for igneous rocks. The LCPT test, the uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS) tests were carried out on the igneous rock samples. The abrasive mineral content (AMC) was also determined for each rock type. First, the LAC was correlated to the AMC and a very good correlation was found between the two parameters. Then, the multiple regression analysis was carried out by including the AMC, UCS and BTS to the analysis in order to infer the effect of the strength on the LAC. It was seen that the correlation coefficients of multiple regression models were greater than that of the relation between the LAC and the AMC. It is concluded that the AMC is the dominant parameter determining the abrasivity of rock. On the other hand, the rock strength has also significant effect on rock abrasivity.

• 터널과지하공간
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• 제11권3호
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• pp.237-247
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• 2001

이 연구에서는 수압파쇄시험 결과의 해석에 대한 파괴역학모델의 적용성을 검토하기 위해 시험결과의 해석에 주로 이용되고 있는 탄성모델과 함게 파괴역학모델을 이론적으로 고찰하였으며, 국내에서 실시된 4개 현장의 측정결과를 이용하여 각 모델의 해석 결과를 비교·검토하였다. 파괴역학모델로부터 얻어진 해석 결과는 탄성모델에 의한 계산 값과 차이를 보였으며, 이러한 차이는 기존 균열의 길이가 작을수록 크게 나타났다. 파괴역학모델은 균열 길이의 판단이 가능한 경우와 같이 특수한 조건에 대해서만 적용이 가능할 것으로 판단된다. 암석의 인장강도는 파괴역학모델에 의한 값이 가장 크게 나타났으며, 압열인장시험, 탄성모델에 의한 값의 순서로 크게 나타났다. 이러한 현상은 시험규모에 따른 크기효과 때문이며, 따라서 수압파쇄시험의 탄성모델로부터 얻어진 암석의 인장강도는 현지암반의 인장강도를 추정할 때 이용될 수 있을 것으로 보인다.

• Advances in concrete construction
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• 제4권4호
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• pp.243-261
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• 2016

This research study focuses on utilizing sandstone which is overburden waste rock in coal mines to use in concrete as a replacement of fine aggregate. Physical properties of sandstone like water absorption, moisture content, fineness modulus etc., were found to be similar to conventional fine aggregate. Scanning Electron Microscope (SEM) analysis was carried out for analysing elemental composition of sandstone. There was no sulphur content in sandstone which is a good sign to carry the replacement. Fine aggregate was replaced with sandstone at 25%, 50%, 75% and 100% by volume and moulds of concrete cubes and cylinders were prepared. Compressive strength of concrete cubes was tested after 3, 7 and 28 days and split tensile & flexural strength was determined after 28 days. The strength was found to be increasing marginally with increase in sandstone content. Fine aggregate that was replaced by 100% sandstone gave highest strength among all the replacements for the compressive, split tensile and flexural strengths. Though increase in strength was marginal, still sandstone can be an effective replacement for sand in order to save the natural resource and utilize the waste sandstone.

• 한국터널지하공간학회 논문집
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• 제5권2호
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• pp.189-198
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• 2003

터널의 대단면화에 따라 각 암반 지보의 역할과 그 보강효과를 확인하고 보다 합리적인 지보구조로의 변화가 요구되고 있다. 특히, 굴착직후 숏크리트에 의한 지보효과가 효과적이지 못한 터널에서는 지보 매커니즘에 대한 추가적인 검토가 필요하다. 강도가 발생하지 않는 터널이 가장 불안한 상태에 있을 때의 지보구조는 충분한 검토가 필요하다. 본 논문에서는 약재령 (若材令)시 록볼트에 의한 보강효과를 볼트 그라우트재의 경화를 고려하여 모의암반에 의한 실험 및 수치해석을 실시하여 시간의존에 따른 그라우트재의 압축강도와 재령, 부착강도와 재령, 부착강성과 재령과의 관계를 명확하게 하는 것으로 굴착직후의 록볼트의 암반보강 효과를 검토하고, 약재령시 록볼트의 모델화 및 물리정수를 산정하였다. 또 그라우트재의 효과를 가지지 않고도 해결되는 수압팽창형 프리쿠션볼트에 의한 굴착직후의 암반보강효과에 대해서도 검토하였다.

• 터널과지하공간
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• 제23권5호
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• pp.362-371
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• 2013

수압파쇄법으로 최대수평주응력 크기 규명에 필요한 요소 중 하나인 암반의 인장강도를 측정하는 방법에 대해 연구하였다. 석모도 시추공에서 회수한 화강암 시료에 대해 두 가지 실내시험(중공원통 인장시험 및 압열인장시험)으로 인장강도를 측정하고 두 결과가 차이를 보이는지 비교하였다. 중공원통 인장시험에서는 높은 수압증가율 상태에서 더 높은 인장강도를 보여, 현장의 수압파쇄시험에서 보인 수압 증가율 상태에서 측정된 인장강도나 그 증가율로 보정된 인장강도를 이용해야한다는 점을 보였다. 인장강도에 대한 수압 증가율 효과와 크기효과를 보정하면 중공원통 인장시험 결과는 압열인장시험 결과와 유사하게 나타났으며 이는 수압파쇄 인장강도를 위해 압열인장강도를 이용할 수도 있다는 점을 시사한다.