• Geomechanics and Engineering
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• 제23권5호
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• pp.467-480
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• 2020

The failure behavior and tensile strength of sandstone materials under different strain rates are greatly different, especially under static loads and impact loads. In order to clearly investigate the failure mechanism of sandstone materials under static and impact loads, a series of Brazilian disc samples were used by employing green sandstone, red sandstone and black sandstone to carry out static and impact loading splitting tensile tests, and the failure properties subjected to two different loading conditions were analyzed and discussed. Subsequently, the failure behavior of sandstone materials also were simulated by finite element code. The good agreement between simulation results and experimental results can obtain the following significantly conclusions: (1) The relationship of the tensile strength among sandstone materials is that green sandstone < red sandstone < black sandstone, and the variation of the tensile sensitivity of sandstone materials is that green sandstone > red sandstone > black sandstone; (2) The mainly cause for the difference of dynamic tensile strength of sandstone materials is that the strength of crystal particles in sandstone material, and the tensile strength of sandstone is proportional to the fractal dimension; (3) The dynamic failure behavior of sandstone is greatly different from that of static failure behavior, and the dynamic tensile failure rate in dynamic failure behavior is about 54.92%.

• 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.

• 자원환경지질
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• 제16권4호
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• pp.257-268
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• 1983

The Cretaceous sandstone and felsite distributed in north-western border part of Taegu city were studied in the viewpoint of engineering geology with an emphasis of their discontinuities. The probability of continuity of sandstone is 0.69 and that of felsite is 0.56. The correlation coefficients of sandstone are 0.52 and 0.54. Those of felsite are 0.47 and 0.48. These values reflect that the rocks have been strongly jointed. $K_0$ value of the sandstone is close to its $K_a$ value and the test suggests that the sandstone has been in active state. On the other hand, $K_0$ value of the felsite is close to its $K_p$ value, which reflects that the felsite has been in passive state, in order to maintain the stability of the sandstone. $\delta$ value should be changed to be less than 13.2.

• 한국지구과학회지
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• 제31권1호
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• pp.18-35
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• 2010

충남 보령 지역 트라이아스기 후기 하조층은 충남분지의 최하위층으로서 하부는 주로 각력암이나 역암, 중부는 역암, 상부는 역암과 사암이 호층을 이루고 있다. 하조층은 입자지지 수평층리 역암, 입자지지 균질 각력암, 기질지지 균질 역암, 기질지지 점이층리 역암, 역질 사암, 평행 엽층리 사암, 균질 사암, 정상 점이층리 사암, 역전점이층리 사암, 판상 사층리 사암, 곡상 사층리 사암, 저경사 사층리 사암 그리고 이암의 13개의 암상으로 구성되고 이들은 4개의 상조합을 이룬다. 상조합 I은 테일러스나 상부 선상지 삼각주에서 퇴적된 것으로 보이는 입자지지 및 기질지지 균질 각력암으로 구성되어 있다. 상조합 II는 기질지지 균질 역암과 수평층리 입자지지 역암으로 구성되고 상부선상지 삼각주에서 퇴적된 것으로 보인다. 상조합 III은 기질지지 균질 역암, 평행엽층리 사암 및 균질 사암으로 구성되고 중부선상지 삼각주에서 퇴적된 것으로 보인다. 상조합 IV는 균질 역질 사암, 수평엽층리 사암과 균질 사암으로 구성되고 하부선상지 삼각주에서 퇴적된 것으로 보인다. 전체적으로 보아 하조층은 초기는 테일러스와 상부 선상지 삼각주 환경에서 퇴적되고, 중기는 상부 선상지 삼각주와 중부 선상지 삼각주가 교호한 환경에서 퇴적되었으며, 말기에는 중부 선상지 삼각주와 하부 선상지 삼각주가 교호하는 환경에서 퇴적된 것으로 해석된다.

• Geomechanics and Engineering
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• 제17권2호
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• pp.215-225
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• 2019

The mechanical behavior of rock is essential to estimate the capacity and long-term stability of $CO_2$ storage in deep saline aquifers. As the depth of reservoir increases, the pressure and temperature that applied on the rock increase. To answer the question of how the confining pressure and temperature influence the mechanical behavior of reservoir rock, triaxial compression experiments were carried out on brine-saturated sandstone at elevated temperature. The triaxial compressive strength of brine-saturated sandstone was observed to decrease with increasing testing temperature, and the temperature weakening effect in strength enhanced with the increase of confining pressure. Sandstone specimens showed single fracture failures under triaxial compression. Three typical regions around the main fracture were identified: fracture band, damaged zone and undamaged zone. A function was proposed to describe the evolution of acoustic emission count under loading. Finally, the mechanism of elevated temperature causing the reduction of strength of brine-saturated sandstone was discussed.

• 자원환경지질
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• 제37권6호
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• pp.585-601
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• 2004

국내의 흑색사암 및 흑색셰일 석산에 대한 전반적인 연구가 수행된 바가 없다. 따라서 이들에 대한 상황을 파악하기가 용이하지 않다. 보령지역의 기존 석산에서 채석되는 흑색사암 및 흑색셰일의 분포, 산출상태 및 암질에 대하여 조직적, 과학적으로 이 연구를 수행하는데 목적이 있다. 흑색사암 층의 조사는 4개 도폭의 54개 광구에서 실시되었다. 연구 지역에서 37개 광구내에서 140 개소의 흑색사암 석산, 22 개소의 흑색셰일 석산이 확인되었다. 이러한 기존 석산에 대한 전반적인 개발정보 자료가 수집 및 종합되었다. 이들 중에서 묘비석 및 기념비용의 흑색사암 석산, 벼루용 흑색셰일 석산에서 채석작업이 진행 중에 있다. 대부분의 흑색사암 석산은 개화리, 수부리, 성주리 지역에 밀집하며 이들 석산은 흑색사암의 생산에서 주요한 역할을 담당하고 있었다. 상업적인 석재의 관점에서 볼 때, 흑색사암 원석은 산출상태 및 형태의 특성에 따라서 핵석과 신선한 암체로 구분된다. 흑색사암층은 독특하게 절리가 잘 발달하며, 특히 3 절리조 내에서 입방체 또는 사각형으로 분리되어 있다. 이러한 흑색사암류는 암회색내지 회흑색으로 나타난다. 흑색사암층은 대동누층군의 아미산층, 조계리층, 백운사층 및 성주리층 내에 협재하며, 층후는 약 $1\~10m$ 이다.

• 자원환경지질
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• 제30권4호
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• pp.379-393
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• 1997

Geology of the Zbezkazgan copper deposit in Kazhkstan is mainly composed of Permian and Carboniferous sedimenary rocks in which copper minerals are mainly contained in grey sandstone of Carboniferous age. There are 28 layers of copper ore bodies in Zbezkazgan suite. Thickness of the ore bodies ranges from one to 35 meters, grade of the crude ore ranges from 2 to 5 wt % Cu and the extension of the orebodies is 5 to 7 km. Microscopic study on specimens from the Zbezkazgan ore deposit has exposed clues to understand the origin of this deposit. Alternatively deposited grey sandstone and red sandstone are mainly composed of quartz and feldspar grains. A big difference between the grey sandstone and the red sandstone is in grain size, the former is larger than the latter. Chalcocites as main copper minerals have cemented through grain boundary. It is assumed that quartz, feldspar and copper were derived from granitoid in which copper mineralization had taken place before exposing to weathering. The chalcocites were precipitated by a sudden change of geochemical condition (Eh, pH, temperature, etc.) of fluid which had carried quartz, feldspars, copper ions and sulphate during formation of grey sandstones. The copper ions and sulphate were stable in fluid during sedimentation of oxidation environment, however, the copper ions were no more stable at the reduced environment and changed to stable forms to precipitate copper minerals by reaction of copper ions and hydrogen sulfides. This chemical precipitation of copper minerals in the sandstone attributes to the assumption of hydrothermal origin on this sedimentary origined deposit.

• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1175-1184
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• 2022

The pore structure of uranium-bearing sandstone is one of the critical factors that affect the uranium leaching performance. In this article, uranium-bearing sandstone from the Yili Basin, Xinjiang, China, was taken as the research object. The fractal characteristics of the pore structure of the uranium-bearing sandstone were studied using mercury intrusion experiments and fractal theory, and the fractal dimension of the uranium-bearing sandstone was calculated. In addition, the effect of the fractal characteristics of the pore structure of the uranium-bearing sandstone on the uranium leaching kinetics was studied. Then, the kinetics was analyzed using a shrinking nuclear model, and it was determined that the rate of uranium leaching is mainly controlled by the diffusion reaction, and the dissolution rate constant (K) is linearly related to the pore specific surface fractal dimension (D_S) and the pore volume fractal dimension (D_V). Eventually, fractal kinetic models for predicting the in-situ leaching kinetics were established using the unreacted shrinking core model, and the linear relationship between the fractal dimension of the sample's pore structure and the dissolution rate during the leaching was fitted.

• Geomechanics and Engineering
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• 제8권4호
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• pp.541-557
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• 2015

This research aims to analyze the fracture coalescence characteristics of brittle sandstone specimen ($80{\times}160{\times}30mm$ in size) containing various flaws (a single fissure, double squares and combined flaws). Using a rock mechanics servo-controlled testing system, the strength and deformation behaviours of sandstone specimen containing various flaws are experimentally investigated. The results show that the crack initiation stress, uniaxial compressive strength and peak axial strain of specimen containing a single fissure are all higher than those containing double squares, while which are higher than those containing combined flaws. For sandstone specimen containing combined flaws, the uniaxial compressive strength of sandstone increase as fissure angle (${\alpha}$) increases from $30^{\circ}$ to $90^{\circ}$, which indicates that the specimens with steeper fissure angles can support higher axial capacity for ${\alpha}$ greater than $30^{\circ}$. In the entire deformation process of flawed sandstone specimen, crack evolution process is discussed detailed using photographic monitoring technique. For the specimen containing a single fissure, tensile wing cracks are first initiated at the upper and under tips of fissure, and anti-tensile cracks and far-field cracks are also observed in the deformation process; moreover anti-tensile cracks usually accompanies with tensile wing cracks. For the specimen containing double squares, tensile cracks are usually initiated from the top and bottom edge of two squares along the direction of axial stress, and in the process of final unstable failure, more vertical splitting failures are observed in the ligament region. When a single fissure and double squares are formed together into combined flaws, the crack coalescence between the fissure tips and double squares plays a significant role for ultimate failure of the specimen containing combined flaws.

• Geomechanics and Engineering
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• 제22권5호
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• pp.385-396
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• 2020

A uniaxial compression test was performed to analyse the mechanical properties and macroscale and mesoscale failure mechanisms of sandstone with pyrite concretions. The effect of the pyrite concretions on the evolution of macroscale cracks in the sandstone was further investigated through numerical simulations with Particle Flow Code in 2D (PFC2D). The results revealed that pyrite concretions substantially influence the mechanical properties and macroscale and mesoscale failure characteristics of sandstone. During the initial loading stage, significant stress concentrations occurred around the edges of the pyrite concretion accompanied by the preferential generation of cracks. Meanwhile, the events and cumulative energy counts of the acoustic emission (AE) signal increased rapidly because of friction sliding between the concretion and sandstone matrix. As the axial stress increased, the degree of the stress concentration remained relatively unchanged around the edges of the concretions. The cracks continued growing rapidly around the edges of the concretions and gradually expanded toward the centre of the sample. During this stage, the AE events and cumulative energy counts increased quite slowly. As the axial stress approached the peak strength of the sandstone, the cracks that developed around the edges of the concretion started to merge with cracks that propagated at the top-left and bottom-right corners of the sample. This crack evolution ultimately resulted in the shear failure of the sandstone sample around the edges of the pyrite concretions.