• 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.

• 터널과지하공간
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• 제17권2호
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• pp.128-138
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• 2007

상대적으로 저심도에 건설되는 암반구조물의 경우 단층이나 절리 등 암반 내 존재하는 불연속면이 굴착 후 생성된 경계면과의 교차에 의해 구조적인 형태의 파괴가 지배적으로 발생하나, 고심도에 건설되는 경우 높은 현지응력과 굴착에 따른 유도응력으로 인해 공동 경계면에서 스폴링이나 슬래빙과 같은 취성파괴가 발생할 수 있다. 취성파괴는 암반구조물의 안정성을 약화시키는 주된 원인으로, 고심도 영역에서 암반구조물의 안정성을 확보하기 위하여 응력조건에 따라 발생하는 취성파괴의 개시시점, 파괴수준 및 파괴범위 등과 같은 파괴특성이 규명되어야 한다. 본 연구에서는 고심도의 암반구조물에서 발생할 수 있는 취성파괴의 파괴수준 및 개시시점과 재하응력사이의 관계를 정량적으로 평가하고자 진삼축 응력조건을 구현할 수 있는 모형실험장치를 설계, 제작하여 여러 응력조건에서 모형실험을 수행하였다. 공동주변에서 발생한 파괴수준을 육안관찰과 미소파괴음 발생양상에 의해 3단계로 구분하고, 진삼축 응력조건에 따라 제시하였다. 그 결과 파괴수준은 공동단면에 작용하는 재하응력$(S_v,\;S_{H2})$ 뿐 아니라 공동 축에 평행한 재하응력 $S_{H1}$에 영향을 받으며, $S_{H1}$와 $S_{H2}$의 크기가 증가할수록 동일한 $S_v$에서 파괴수준은 감소하였다. 파괴개시점 역시 $S_{H1}$와 $S_{H2}$의 증가에 따라 파괴개시를 위한 응력수준은 증가하였으며, 다중회귀분석을 통해 파괴개시시점과 진삼축 응력조건의 관계식을 도출하였다.

• 지질공학
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• 제32권4호
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• pp.597-610
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• 2022

중간주응력을 고려한 마찰재료의 파괴거동에 대한 확고한 이해는 대심도 보어홀 안정성 및 단층해석 등과 관련된 현장 적용의 고도화를 위한 필수적인 과정이다. 본 연구는 진삼축압축 조건을 물리적으로 구현하는 장비를 설계·제작하였으며 마찰재료로 제작된 석고 시료에 대한 진삼축압축시험을 통하여 재료의 파괴거동 특성을 논의하고 삼차원파괴함수의 적용성을 검토하였다. 진삼축압축시험을 위한 석고 재료는 52(w) × 52(l) × 104(h) mm의 직육면체 시료로 성형하였으며 다양한 조합의 𝜎₃, 𝜎₂의 조건으로 총 24회의 진삼축압축시험이 수행되었다. 또한, 삼차원 파괴기준식의 파라미터로 사용되는 석고의 강도정수 측정을 위하여 전통적인 일축압축시험 및 삼축압축시험이 수행되었다. 석고 재료의 응력-변형 특성은 중간주응력과 최소주응력의 차이가 클수록 취성거동이 더욱 강하게 나타났으며, 시료의 강도 및 변형은 중간주응력의 변화를 반영하는 것으로 평가되었다. 주응력 좌표계에서 시험 데이터에 대한 비선형 다중회귀분석을 수행한 결과 수정 Wiebols-Cook 파괴기준 및 수정 Lade 파괴기준이 석고 시료에 대한 삼차원 파괴기준으로 가장 적합하였다.

• 대한기계학회논문집A
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• 제22권3호
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• pp.595-602
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• 1998

Specimens of 304 stainless steel were tested to failure at elevated temperatures under multiaxial stress states, uniaxial tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched bar specimens. Rupture times are compared for uniaxial, biaxial, and triaxial stress states with respect to the maximum principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the principal facet stress gives the best correlation for the material investigated, and this parameter can predict creep life data under multiaxial stress states with rupture data obtained with specimens under uniaxial stresses. The results also suggest that grain boundary cavitation, coupled with localized deformation processes such as grain boudary sliding, controls the lifetimes of the specimens.

• Journal of Mechanical Science and Technology
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• 제19권7호
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• pp.1432-1440
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• 2005

High-temperature rupture behavior of 5083-Al alloy was tested for failure at 548K under multiaxial stress conditions: uniaxial tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched bar specimens. Rupture times were compared for uniaxial, biaxial, and triaxial stress conditions with respect to the maximum principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the von Mises effective and principal facet stresses give good correlation for the material investigated, and these parameters can predict creep life data under the multiaxial stress states with the rupture data obtained from specimens under the uniaxial stress. The results suggest that the creep rupture of this alloy under the testing condition is controlled by cavitation coupled with highly localized deformation process, such as grain boundary sliding. It is also conceivable that strain softening controls the highly localized deformation modes which result in cavitation damage in controlling rupture time of this alloy.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.139-146
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• 2001

Undrained triaxial tests were peformed for a weathered soil, which includes local measurement using LVDT The behavior from small In large strain conditions could be evaluated consistently through a triaxial test, The stress-strain relationship of undisturbed samples were compared with the disturbed and the shear moduli in the small strain level had the almost same values. Especially the shear moduli were mostly affected by the initial condition of water contents. An anisotropic hardening model based on the total stress concept could predict the stress-strain relationship accurately, which makes it possible to analyze the geotechnical problem reasonably for the weathered soil.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1997년도 Lecture Notes by Two Distinguished Scholars
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• pp.1.2-22
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• 1997

Anisotropic behaviour in soils and soft rocks may be either fabric of stress related ultra in practice is invariably a combination of both. Theoretical studies in the paper include tile iMluence oil untrained strength of assuming both the critical state and Mo21r-Coulomb concepts to hold, and the influence of elastic anisotropy oil predicted undrained effective stress paths. The predictions stemming from these theoretical concepts are examined in the light of evidence from triaxial compression and extension tests oil laboratory prepared, compacted and natural clays and from triaxial compression tests on clay shales. The experimental studies also show the Buence of sample orientation on untrained snear strength, as wen as the iIBluence of anisotropy old the effective stress angle cishearing resistance and of stress patn on measured stiffness.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 가을 학술발표회 논문집
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• pp.295-302
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• 2000

Earthquakes not only produce additional load on the structures and underlying soil, but also change the strength characteristics of the soil. Therefore, in order to analyze soil structures for stability, the behaviour after earthquake must be considered. In this paper, a series of cyclic triaxial tests and monotonic triaxial tests were carried out to investigate the undrained shear strength and liquefaction strength characteristics of Nak-Dong River sand soils which were subjected to cyclic loading. The sample was consolidated in the first stage and then subjected to stress controlled cyclic loading with 0.1Hz. After the cyclic loading, the cyclic-induced excess pore water pressure was dissipated by opening the drainage valve and the sample was reconsolidated to the initial effective mean principal stress(p/sub c/'). After reconsolidation, the monotonic loading or cyclic loading were applied to the specimen. In the results, the undrained shear strength and liquefaction strength characteristics depended on the pore pressure ratio(Ur=U/p/sub c/'). The volume change following reconsolidation can be a function of cyclic-induced excess pore water pressure and the maximum double amplitude of axial strain.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 3차
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• pp.55-60
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• 2010

Rockfill zones in CFRD consist typically of large granular materials, usually the maximum particle size up to several meters, which makes laboratory testing to determine the mechanical properties of rockfill difficult. Commonly, the design strength of the rockfills is obtained by scaling down the original rockfill materials and performing laboratory strength tests for the reduced size materials. The objective of the present study is to investigate the effect of particle size on the shear behavior and the strength for granular materials. A series of large-scale triaxial tests was conducted on large granular materials with the maximum particle size varying from 20 to 50mm. The test results showed that overall shear behaviors were similar between the samples with different particle sizes while there were slight differences in the magnitudes of the peak shear stress between the samples. In addition, a simulation of the granular material with the max. particle size of 20mm was performed using DEM code, $PFC^{2D}$, and compared with the test results. The deviatoric stress versus strain behaviors of experimental and numerical tests were found to be matched well up to the peak stress state.

• Geomechanics and Engineering
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• 제24권2호
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• pp.105-113
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• 2021

Deformations in soils induced by dynamic loads cause damage to the structures above the soil layers. It is important for geotechnical engineering practice that how the soil behaves due to repeated loads and the necessary precautions to be taken accordingly. Turkey is one of the most important seismic regions in Europe and earthquake studies to be conducted in this area are intended to reduce the damage as a result of taking the necessary measures. To determine the properties of soils under dynamic loads, stress-controlled dynamic triaxial and resonant column tests can be performed. In this study, these experiments were implemented in the laboratory on the clayey sand soil samples obtained from Bilecik Söğüt. To evaluate the effects of the confining pressure and rate of loading on the dynamic behavior of soils, samples were dynamically loaded by different rates at varying confining pressures. As a result, the changes in stress-strain properties of soils under dynamic loads were investigated. The alteration in behavior in terms of modulus reduction and damping ratios was obtained to vary a lot with the change of the lateral pressure on soil along with the frequency of the load.