• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.539-545
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• 2010

The field plate test has a good potential for determining since it measures both plate pressure and settlement. The deformation modulus of rock mass is differently measured for status of structures. The values of deformation modulus are obtained from laboratory test (uniaxial and triaxial test) and field test (pressuremeter test). Plate load test should be conducted by different loading plate sizes for geological structure of rock mass and scale of structures. In this paper, large plate load tests were performed to predict of structure's behavior and evaluate the ultimate bearing capacity of the foundation on soft rock. Simultaneously, deformation modulus of rock mass was estimated by back analysis of stresses measured in field test under rock mass. Finally, we verified the validation of deformation modulus of rock mass through result of large plate load test and numerical simulation.

• Geomechanics and Engineering
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• 제29권2호
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• pp.99-111
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• 2022

Instability of bolted rock mass has been a major hazard in the underground coal mining industry for decades. Developing effective support guidelines requires understanding of complex bolted rock mass failure mechanisms. In this study, the dynamic failure behavior, mechanical behavior, and energy evolution of a laboratory-scale bolted specimens is studied by conducting laboratory static-dynamic coupled loading tests. The results showed that: (1) Under static-dynamic coupled loading, the stress-strain curve of the bolted rock mass has a significant impact velocity (strain rate) correlation, and the stress-strain curve shows rebound characteristics after the peak; (2) There is a critical strain rate in a rock mass under static-dynamic coupled loading, and it decreases exponentially with increasing pre-static load level. Bolting can significantly improve the critical strain rate of a rock mass; (3) Compared with a no-bolt rock mass, the dissipation energy ratio of the bolted rock mass decreases exponentially with increasing pre-static load level, the ultimate dynamic impact energy and dissipation energy of the bolted rock mass increase significantly, and the increasing index of the ratio of dissipation energy increases linearly with the pre-static load; (4) Based on laboratory testing and on-site microseismic and stress monitoring, a design method is proposed for a roadway bolt support against dynamic load disturbance, which provides guidance for the design of deep underground roadway anchorage supports. The research results provide new ideas for explaining the failure behavior of anchorage supports and adopting reasonable design and construction practices.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.57-64
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• 2005

Since the allowable bearing capacities of piles in weathered/fractured rock are mainly governed by settlement, the load-displacement behavior of the rock socketed pile should be well known. To predict pile head settlement at the design stage, the exact understanding of the load-transfer mechanisms is essential. Therefore, in this research, the load-transfer mechanisms of drilled shaft socketed into weathered rock was investigated. For that, 5 cast-in-place concrete piles with diameters of 1,000 mm were socketed into weathered gneiss. The static axial load tests and the load-transfer measurements were performed to examine the axial resistant behavior of the piles. A comprehensive field/laboratory testing program on weathered rock at the field test sites was also performed to describe the in situ rock mass conditions quantitatively. And then, the effect of rock mass condition on the load transfer mechanism was investigated. The side shear resistance of the pile in moderately weathered rock reached to yielding point at a few millimeter displacements, and after that, the rate of resistance increment dramatically decreased. However, that in the highly /completely weathered rock did not show the obvious yielding point, and gradually increased showing the hyperbolic pattern until with the relatively high displacement (>10 mm). The end bearing-displacement curves showed linear increase at least until with the base displacement of approximately 10 mm, regardless rock mass conditions.

• 한국지반공학회논문집
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• 제21권3호
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• pp.19-25
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• 2005

숏크리트와 록볼트를 지보재로 사용한다고 해서 NATM을 채택한 것은 아니므로 RMR과 Q-system에 의해 설계된 터널은 현대식 터널로 명명하였다. 강지보재로 지보되는 재래식 터널과 숏크리트와 록볼트로 지보되는 현대식 터널은 근본적으로 차이가 있는 것으로 알려져 있다. 현대식 터널은 암반의 하중지지력을 유지하기 위하여 숏크리트 지보를 사용하여 암반의 이완과 과도한 변형을 최소화시킨다고 하나 이에 대한 증명은 명확히 이루어지지 못하고 있다. 재래식 터널과 현대식 터널의 차이점을 살펴보기 위하여 사용되는 암반분류의 지보계 특성과 암반하중을 상호비교 하였다. 재래식 터널은 Terzaghi의 암반하중분류를 대표 암반분류로 채택하고, 현대식 터널은 RMR과 Q-system을 대표 암반분류로 채택하였다. 연구결과 현대식 터널의 주지보재인 숏크리트는 재래식 터널의 주지보재인 강지보 보다 지지력이 우수하였으며 암반분류에서 제시하는 암반하중은 재래식 터널과 현대식 터널의 차이는 없는 것으로 확인되었다. 따라서, 암반분류법에 의하면 숏크리트를 사용하는 현대식 터널의 암반의 하중지지력이 재래식 터널 암반의 하중지지력 보다 크다고 볼 수는 없다.

• Geomechanics and Engineering
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• 제20권1호
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• pp.1-7
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• 2020

In structures excavated in rock mass, load progressively increases to a level and remains constant during the construction. Rocks display different elastic properties such as E_i and ʋ under different loading conditions and this requires to use the true values of elastic properties for the design of safe structures in rock. Also, rocks will undergo horizontal and vertical deformations depending on the amount of load applied. However, under constant loads, values of E_i and ʋ will vary in time and induce variations in the behavior of the rock mass. In some empirical equations in which deformation modulus of the rock mass is taken into consideration, elastic parameters of intact rock become functions in the equation. Hence, the use of time dependent elastic properties determined under constant loading will yield more reliable results than when only constant elastic properties are used. As well known, rock material will play an important role in the deformation mechanism since the discontinuities will be closed due to the load. In this study, E_i and ʋ values of intact rocks were investigated under different constant loads for certain rocks with high deformation capabilities. The results indicated significant time dependent variations in elastic properties under constant loading conditions. E_i value obtained from deformability test was found to be higher than the E_i value obtained from the constant loading test. This implies that when static values of elastic properties are used, the material is defined as more elastic than the rock material itself. In fact, E_i and ʋ values embedded in empirical equations are not static. Hence, this workattempts to emerge a new understanding in designing of safer structures in rock mass by numerical methods. The use of time-dependent values of E_i and ʋ under different constant loads will yield more accurate results in numerical modeling analysis.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.603-610
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• 2005

The end bearing behavior of piles socketed in weathered/soft rock is generally dependent upon the mass conditions of rock with fractures rather than the strength of intact rock. However, there are few available data and little guidance in the prediction of the end bearing capacity of drilled shafts socketed in weathered/soft rock, considering rock mass weathering. Therefore, a database of 13 load tests was constructed first, and new empirical relationships between the base reaction modulus of piles in rock and rock mass properties were developed. No correlation was found between the compressive strengths of intact rock and the base reaction modulus of weathered/soft rock. The ground investigation data regarding the rock mass conditions(e.g. Em, Eur, RMR, RQD) was found to be highly correlated with the base reaction modulus, showing the coefficients of correlation greather than 0.7 in most cases. Additionally, the applicability of existing methods for the end bearing capacity of piles in rock was verified by comparison with the field test data.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.611-618
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• 2005

In this research, the effect of rock mass weathering on the side shear resistance of drilled shaft socketed into weathered rock was investigated. For that, a database of 23 cast-in-place concrete piles with diameters varying from 400mm to 1,500mm were socketed into weathered igneous/meta-igneous rock at four different sites. The static axial load tests were performed to examine the resistant behavior of the piles, and a comprehensive field/laboratory testing program at the field test site was also performed to describe the in situ rock mass conditions quantitatively. No correlation was found between the compressive strengths of intact rock and the side shear resistance of weathered/soft rock. The ground investigation data regarding the rock mass conditions (e.g. $E_m,\;E_{ur},\;_{plm}$, RMR, RQD, j) was found to be highly correlated with the side shear resistance, showing the coefficients of correlation greater than 0.7 in most cases. Additionally, the applicability of existing methods for the side shear resistance of piles in rock was verified by comparison with the field test data. The existing empirical relations between the compressive strength of intact rock and the side shear resistance(Horvath (1982), Rowe & Armitage(1987) etc.) appeared to overestimated the side shear resistance of all piles tested in this research unless additional consideration on the effect of rock mass weathering or fracturing was applied. The existing methods which consider the effect of rock mass condition were modified and/or extended for weathered rock mass where mass factor j is lower than 0.1, and RQD is below 50%.

• 한국지반공학회논문집
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• 제25권8호
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• pp.77-93
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• 2009

본 연구에서는 3차원 유한차분해석을 통하여 말뚝직경, 암반물성, 불연속면의 간격 및 방향 등 주요 인자가 암반근입 현장타설말뚝의 선단거동에 미치는 영향에 대한 분석을 수행하였으며, 이를 토대로 초기기울기 및 극한 단위선단지지력을 변수로 하는 쌍곡선형태의 선단하중전이(q-w)함수를 제안하였다. 제안식의 국내 암반지반에의 적용을 위하여 국내에서 수행된 14개 현장 23본의 시험말뚝의 재하시험자료를 토대로 제안식의 경험계수를 산정하였으며, 더불어 기존 초기기울기 및 극한단위선단지지력 산정식의 타당성 검토도 수행하였다. 현장재하시험 사례와의 비교분석 결과, 본 연구에서 제안된 산정식은 국내 암반지반에 근임된 현장타설말뚝의 선단거동을 비교적 잘 예측 가능하고, 말뚝지지력 및 침하량 예측값이 실측값에 가까움을 알 수 있었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.455-465
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• 2008

In this study, the load distribution and deformation of rock-socketed drilled shafts subjected to axial load are investigated based on small scale model tests. In order to analyze the effects of major influencing factors of end bearing capacity, Hoek-cell triaxial tests were performed. From the test results, it was found that the initial slope of end bearing load transfer (q-w) curve was highly dependent on rock mass modulus and pile diameter, while the ultimate unit toe resistance ($q_{max}$) was influenced by rock mass modulus and the spacing of discontinuities. End bearing load transfer function of drilled shafts socketed in rock was proposed based on the Hoek-cell triaxial test results and the field loading tests which were performed on granite and gneiss in South Korea. Through the comparison with pile load tests, it is found that the load-transfer curve by the present study is in good agreement with the general trend observed by field loading tests, and thus represents a significant improvement in the prediction of load transfer of drilled shaft.

• 터널과지하공간
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• 제17권2호
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• pp.102-108
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• 2007

일반적으로 암판정을 수행하기 인해 가장 널리 사용되는 방법은 암석의 강도와 절리의 발달빈도를 고려하는 것이다. 하지만 미세균열과 연장성이 긴 절리들이 암반에 존재하고 있는 경우에는 이러한 방법이 합리적이지 않다. 그러므로 복잡한 지질조건을 가지고 있는 암반에서의 굴착난이도 결정은 절리빈도와 실내시험(일축압축강도, 점하중강도, 실내탄성파속도 등)과 현장탄성파속도와의 상관관계를 종합하여 암판정을 수행하는 것이 더욱 더 합리적이라고 판단된다.