• 암석학회지
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• 제27권2호
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• pp.105-108
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• 2018

부산시교육청 동래교육지원청 관내 초등학교 60개, 중학교 34개, 고등학교 28개 등 모두 122개 학교를 대상으로 2017년 3월부터 2018년 6월까지 16개월 동안 학교 교재원으로서의 암석원을 현장 방문으로 조사하였다. 암석원이 조성된 학교는 122개 학교 중 29.51%인 36개였으며 초등학교는 40.0%, 중등학교(중학교, 고등학교)는 18.18%가 설치되어 있었다. 조사항목은 암석원 암석표본이 교육과정과 관련되는가? 표본 이름이 맞는가? 설명판 내용이 적합한가?로 초등학교의 경우 교육과정과의 관련성이 평균 36.7%, 표본 이름이 맞는지는 평균 55.1%, 설명판 내용이 알맞은지는 평균 55.5%로 나타났다. 중등학교는 교육과정과의 관련성이 평균 83.9%, 표본 이름이 맞는지는 평균 82.8%, 설명판의 내용이 알맞은지는 평균 84.1%로 학교급이 올라갈수록 높게 나타났다.

• 지구물리와물리탐사
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• 제18권3호
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• pp.105-114
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• 2015

상온 상습 환경에서 수포화 암석코어의 전기비저항을 장시간 모니터링 할 수 있는 장치를 구현하였다. 양쪽 금속망 전극에 덧댄 종이필터와 암석코어를 감싼 열수축튜브의 상부 중앙 외피면에 3-채널 펌프로 물을 충분히 공급하면서 전기저항을 측정하면 암석코어의 수포화 상태를 유지하면서 일주일 이상 전기비저항을 모니터링 할 수 있다. 이 장치를 이용하여 흑운모 편마암, 안산암질 응회암, 셰일의 3종류 암석코어의 수포화 전기저항을 9일간 모니터링 한 결과 다음과 같은 2가지 가설을 제시할 수 있었다. 즉, 전기비저항 온도계수의 수렴 속도는 열물성과 관련이 있을 것이라는 것과 건조 저항을 수포화 때의 평균 저항으로 나눈 건조/수포화 저항비는 유효공극률과 상관될 것이라는 것이다. 실제로, 3가지 암석의 건조/수포화 저항비는 각각 48, 705, 2로 나타났고 이때 각각의 유효공극률은 3.7%, 3.3%, 13.0%이었다.

• Geomechanics and Engineering
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• 제14권4호
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• pp.367-376
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• 2018

Samples composed of coal and rock show different mechanical properties of the pure coal or rock mass. For the same coal seam with different surrounding rocks, the frequency and intensity of rock burst can be significantly different in. First, a method of measuring the strain variation of coal in the coal-rock combined sample was proposed. Second, laboratory tests have been conducted to investigate the influences of rock lithologies, combined forms and coal-rock height ratios on the deformation and failure characteristics of the coal section using this method. Third, a new bursting liability index named combined coal-rock impact energy speed index (CRIES) was proposed. This index considers not only the time effect of energy, but also the influence of surrounding rocks. At last, a new approach considering the influences of roof and/or floor was proposed to evaluate the impact capability of coal seam. Results show that the strength and elastic modulus of coal section increase significantly with the coal-rock height ratio decreasing. In addition, the values of bursting liability indexes of the same coal seam vary greatly when using the new approach. This study not only provides a new approach to measuring the strain of the coal section in coal-rock combined sample, but also improves the evaluation system for evaluating the impact capability of coal.

• Geomechanics and Engineering
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• 제30권4호
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• pp.345-352
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• 2022

When rock burst occurs, the damaged coal, rock and other fragments can be ejected to the roadway at a speed of up to 10 m/s. It is extremely harmful to personnel and mining equipment, and seriously affects the mining activities. In order to study the energy evolution characteristics, especially kinetic energy, in the process of rock mass failure, this paper first analyzes the energy changes of the rock in different stages under uniaxial compression. The formula of the kinetic energy of rock sample considering the energy from the indenter of the testing machine is obtained. Then, the uniaxial compression tests with different stiffness ratios of the indenter and rock sample are simulated by numerical simulation. The kinetic energy U_d, elastic strain energy U_e, friction energy U_f, total input energy U and surface energy U_θ of crack cracking are analyzed. The results show that: The stiffness ratio has influence on the peak strength, peak strain, U_d, U_e, U_θ, U_f and U of rock samples. The variation trends of strength, strain and energy with stiffness are different. And when the stiffness ratio increases to a certain value, if the stiffness of the indenter continues to increase, it will have no longer effect on the rock sample.

• Geomechanics and Engineering
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• 제19권1호
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• pp.49-60
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• 2019

Crack instability propagation during coal and rock mass failure is the main reason for electromagnetic radiation (EMR) generation. However, original cracks on coal and rock mass are hard to study, making it complex to reveal EMR laws and mechanisms. In this paper, we prefabricated cracks of different inclinations in coal and rock samples as the analogues of the native cracks, carried out uniaxial compression experiments using these coal and rock samples, explored, the effects of the prefabricated cracks on EMR laws, and verified these laws by measuring the surface potential signals. The results show that prefabricated cracks are the main factor leading to the failure of coal and rock samples. When the inclination between the prefabricated crack and axial stress is smaller, the wing cracks occur first from the two tips of the prefabricated crack and expand to shear cracks or coplanar secondary cracks whose advance directions are coplanar or nearly coplanar with the prefabricated crack's direction. The sample failure is mainly due to the composited tensile and shear destructions of the wing cracks. When the inclination becomes bigger, the wing cracks appear at the early stage, extend to the direction of the maximum principal stress, and eventually run through both ends of the sample, resulting in the sample's tensile failure. The effect of prefabricated cracks of different inclinations on electromagnetic (EM) signals is different. For samples with prefabricated cracks of smaller inclination, EMR is mainly generated due to the variable motion of free charges generated due to crushing, friction, and slippage between the crack walls. For samples with larger inclination, EMR is generated due to friction and slippage in between the crack walls as well as the charge separation caused by tensile extension at the cracks' tips before sample failure. These conclusions are further verified by the surface potential distribution during the loading process.

• Geomechanics and Engineering
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• 제9권6호
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• pp.815-827
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• 2015

The mechanical behavior of soil and soil-rock mixture is investigated via the discrete element method. A non-overlapping combination method of spheres is used to model convex polyhedron rock blocks of soil-rock mixture in the DEM simulations. The meso-mechanical parameters of soil and soil-rock interface in DEM simulations are obtained from the in-situ tests. Based on the Voronoi cell, a method representing volumtric strain of the sample at the particle scale is proposed. The numerical results indicate that the particle rotation, occlusion, dilatation and self-organizing force chains are a remarkable phenomena of the localization band for the soil and soil-rock mixture samples. The localization band in a soil-rock mixture is wider than that in the soil sample. The current research shows that the 3D discrete element method can effectively simulate the mechanical behavior of soil and soil-rock mixture.

• Geomechanics and Engineering
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• 제27권6호
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• pp.615-626
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• 2021

The main objective of this study is to present a fast and reliable approach to predict the swelling potential of clay-bearing rocks. Investigations showed that there is a good correlation between the swelling potential of a rock and its desire to absorb water due to its clay content which could be measured using the "Contact Angle" test as one of the most common ways to determine the wettability. In this test, the angle between a water drop and the flat rock surface on which it rests is measured. The present method is very fast and returns repeatable results and requires minimal sample preparation. Only having a saw-cut surface of a sample with any shape is all one needs to perform this test. The logic behind this approach is that the swelling potential of a rock is a function of its mineral content and molecular structure, which are not only distributed in the bulk of the sample but also reflected on its surface. Therefore, to evaluate swelling behavior, it is not necessary to wait for a sample to get wet all the way to its "internal structure" (which, due to the low permeability of clay-bearing rocks, is very slow and time-consuming). Instead, one can have a good sense of swelling potential by studying its surface. Parametric studies on the effect of moisture content, porosity, and surface roughness on the contact angle measurements showed that using a saw-cut oven-dried sample is a convenient way to evaluate the swelling potential by this method.

• 터널과지하공간
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• 제2권2호
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• pp.251-264
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• 1992

In this study, the size effect in measuring the fracture toughness of rock was investigated using the ISRM Suggested Method for Fracture toughness using Chevron Bend Specimens. Total 58 specimens were prepared with 4 different diameters, 29, 42, 54, 68mm and center cut-chevron notch. In addition to this, to evaluated the effect of anisotropy of Jecheon granite, which is the sample for this study, core drilling direction was adjusted perpendicular(short transverse) and parallel(arrester) to the rift plane in the sample and the measured fracture toughness for each direction were compared. Important results obtained from this study are as follows. Level ll test condition is more adequate than l, because of low data scattering and precision and corrected fracture toughness of Jechoen granite measured and 2.2MPa{{{{ SQRT { m} }}}} for arrester direction with minimum initial crack length 0.7cm. From the relationship between core diameter and initial crack length presented in the ISRM testing method, the specimen diameter should be bigger than 47mm. The fracture toughnesses measured for arrester and short transverse directon show 10% difference. This is to the anisotropy of Jecheon granite possessing rift plane.

• Geomechanics and Engineering
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• 제25권3호
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• pp.253-266
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• 2021

In this paper, we discuss a mathematical method for determining the return energy of the wave from the sample and comparing it with the mechanical energy consumed to change the dimension of the sample in the triaxial test of the rock. We represent a method to determine the mechanical energy and then we provide how to calculate the return energy of the wave. However, the static energy and pulse return energy will show higher amounts with axial pressure increase. Three types of clastic sedimentary rocks including sandstone, pyroclastic rock, and argillitic tuff were selected. The sandstone showed the highest strength, Young's modulus and ultrasonic P and S waves' velocities versus others in the triaxial test. Also, from the received P wavelet, the calculated pulse wave returning energy indicated the best correlation between axial stress compared to wave velocities in all specimens. The fact that the return energy decreases or increases is related to increasing lateral stress and depends on the geological characteristics of the rock. This method can be used to determine the stresses on the rock as well as its in-situ modulus in projects that are located at high depths of the earth.

• Geomechanics and Engineering
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• 제14권2호
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• pp.151-159
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• 2018

Annually, the global production of construction aggregates reaches over 40 billion tons, making aggregates the largest mining sector by volume and value. Currently, the aggregate industry is shifting from sand to hard rock as a result of legislation limiting the extraction of natural sands and gravels. A major implication of this change in the aggregate industry is the need for understanding rock fragmentation and energy absorption to produce more cost-effective aggregates. In this paper, we focused on incorporating dynamic rock and soil mechanics to understand the effects of loading rate and water saturation on the rock fragmentation and energy absorption of three different sandstones (Red, Berea and Buff) with different pore sizes. Rock core samples were prepared in accordance to the ASTM standards for compressive strength testing. Saturated and dry samples were subsequently prepared and fragmented via fast and dynamic compressive strength tests. The particle size distributions of the resulting fragments were subsequently analyzed using mechanical gradation tests. Our results indicate that the rock fragment size generally decreased with increasing loading rate and water content. In addition, the fragment sizes in the larger pore size sample (Buff sandstone) were relatively smaller those in the smaller pore size sample (Red sandstone). Notably, energy absorption decreased with increased loading rate, water content and rock pore size. These results support the conclusion that rock fragment size is positively correlated with the energy absorption of rocks. In addition, the rock fragment size increases as the energy absorption increases. Thus, our data provide insightful information for improving cost-effective aggregate production methods.