• Geomechanics and Engineering
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• 제37권3호
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• pp.213-222
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• 2024

Determination of jointed rock mass properties plays a significant role in the design and construction of underground structures such as tunneling and mining. Rock mass classification systems such as Rock Mass Rating (RMR), Rock Mass Index (RMi), Rock Mass Quality (Q), and deformation modulus (Em) are determined from the jointed rock masses. However, parameters of jointed rock masses can be affected by the tunnel depth below the surface due to the effect of the in situ stresses. In addition, the geomechanical properties of rocks change due to the effect of metamorphism. Therefore, the main objective of this study is to apply correlation analysis to investigate the relationships between rock mass properties and some parameters related to the depth of the tunnel studied. For this purpose, the field work consisted of determining rock mass parameters in a tunnel alignment (~7.1 km) at varying depths from 21 m to 431 m below ground surface. At the same excavation depths, thirty-seven rock types were also sampled and tested in the laboratory. Correlations were made between vertical stress and depth, horizontal/vertical stress ratio (k) and depth, k and Em, k and RMi, k and point load index (PLI), k and Brazilian tensile strength (BTS), Em and uniaxial compressive strength (UCS), UCS and PLI, UCS and BTS. Relationships were significant (significance level=0.000) at the confidence interval of 95% (r = 0.77-0.88) between the data pairs for the rocks taken from depths greater than 166 m where the ratio of horizontal to vertical stress is between 0.6 and 1.2. The in-situ stress parameters affected rock mass properties as well as metamorphism which affected the geomechanical properties of rock materials by affecting the behavior of minerals and textures within rocks. This study revealed that in-situ stress parameters and metamorphism should be reviewed when tunnel studies are carried out.

• 한국지반공학회논문집
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• 제34권2호
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• pp.5-17
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• 2018

본 연구에서는 연약지반에서의 재하/제하에 대한 안정해석과 응력-변형 해석시 전단 파라미터(UU; Unconsolidated Undrained, CU; Consolidated Undrained(전응력), ${\bar{CU}}$ ; Consolidated Undrained(유효응력))에 따른 초기 지중응력, 강도, 응력-변형 특성을 평가하였다. 시공단계를 고려한 유한요소 해석시 입력하는 전단 파라미터에 따라 초기 지중응력과 이후 해석 결과가 달라질 수 있음을 확인하였다. 특히, Mohr-Coulomb 모델의 입력 파라미터인 내부마찰각(Phi)을 0으로 입력하여 초기 지중응력과 이후 응력-변형 거동을 해석할 경우 잘못된 결과를 도출 할 수 있다는 것을 확인하였다. 전응력 파라미터, CU를 초기 및 전단시 일괄 적용한 해석과 유효응력 파라미터, CU에서 전응력 파라미터, CU로 변경한 해석 결과가 큰 차이를 보이지 않았다. 따라서, 연약지반에 대한 수치해석시 CU 파라미터를 적용하여도 초기 지중응력과 이후 응력-변형 거동에 큰 차이 없이 예측할 수 있음을 알 수 있었다. 또한, 실무에서 적용하기 편한 방법으로 실제 흙의 거동과 동일한 강도를 갖는 Mohr-Coulomb 모델의 전단 파라미터를 산정하는 방법을 제안하였다.

• Computers and Concrete
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• 제34권4호
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• pp.477-487
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• 2024

The in-situ stresses of concrete are an essential index for assessing the safety performance of concrete structures. Conventional methods for pore pressure release often face challenges in selecting drilling ring parameters, uncontrollable stress release, and unstable detection accuracy. In this paper, the parameters affecting the results of the concrete ring hole stress release method are cross-combined, and finite elements are used to simulate the combined parameters and extract the stress release values to establish a training set. The GridSearchCV function is utilized to determine the optimal hyperparameters. The mean absolute error (MAE), root mean square error (RMSE), and coefficient of determination (R²) are used as evaluation indexes to train the gradient boosting decision tree (GBDT) algorithm, and the other three common algorithms are compared. The RMSE of the GBDT algorithm for the test set is 4.499, and the R² of the GBDT algorithm for the test set is 0.962, which is 9.66% higher than the R² of the best-performing comparison algorithm. The model generated by the GBDT algorithm can accurately calculate the concrete in-situ stresses based on the drilling ring parameters and the corresponding stress release values and has a high accuracy and generalization ability.

• Geomechanics and Engineering
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• 제14권2호
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• pp.203-209
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• 2018

Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

• 터널과지하공간
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• 제32권6호
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• pp.530-548
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• 2022

고준위방사성폐기물 심층처분 부지선정과정은 단계별로 진행될 예정이며, 부지선정과 관련된 평가인자는 103개로 제안된 바 있다. 이 중 암반공학분야에서 무결암, 절리나 암반에 대한 평가인자는 33개가 있으며, 기본조사와 상세조사 단계에서 적용된다. 본 보고에서는 일축압축강도와 원위치 응력, 절리분포, 암반등급을 주요 평가인자로 선정하고, 이 중 일축압축강도와 원위치 응력을 핵심 평가인자로 선정하였다. 선정한 핵심 평가인자에 대한 분포범위를 평가하기 위해 원주와 춘천지역의 화강암을 대상으로 통계적 기법 또는 회귀분석을 수행하였다. 사후분포를 통해 추정된 원주지역의 일축압축강도의 평균은 약 171 MPa, 춘천지역은 약 123 MPa이다. 원주지역에 작용하는 최대 원위치 응력은 30 MPa 이하이며 춘천지역은 40 MPa 이하였다. 회귀분석에 의해 산정된 최대수평응력의 방향은 원주의 경우 101°이며 춘천의 경우는 95°였다.

• 한국표면공학회지
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• 제47권6호
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• pp.303-310
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• 2014

In this study, the average in-situ stress in metallic thin film was measured during deposition of the Cu thin films on the Si(111) wafer and then the phenomenon of stress shift by the interruption of deposition was measured using Cu thin films. We have observed the stress shift in accordance with changing amount of atom's movement between the surface and grain boundary through altering the grain size of the Cu thin film with variety of parameters. The grain size is known to be affected on the deposition rate, film thickness and deposition temperature. As a experimental results, the these parameters was not adequate to explain stress shift because these parameters affect directly on the amount of atom's movement between the surface and grain boundary as well as the grain size. Thus, we have observed the stress shift toward tensile side in accordance with the grain size changing through the interlayer deposition. From an experiment with inserting interlayer before deposit Cu, in thin film which has big grain size with high roughness, amount of stress movement is higher along direction of tensile stress after deposition that means, after deposition process, driving force of atoms moving in grain boundary and on the surface of the film is relatively higher than before.

• 한국지반공학회논문집
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• 제20권9호
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• pp.33-45
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• 2004

모래를 사용해서 매립하는 경우 일반적으로 한 가지 이상의 포설방법으로 매립이 수행된다. 따라서 모래매립지반은 그 특성이 층별로 다양하게 형성되며, 이러한 지반특성을 파악하기 위해서 일반적으로 콘관입시험이 널리 이용되고 있다. 콘저항값은 임의의 깊이에서 현장의 응력수준, 즉 상재하중의 크기에 따라 영향을 많이 받기 때문에 콘저항값을 현장의 응력수준으로 정규화할 필요가 있다. 그러므로 현장응력수준으로 정규화된 콘저항값을 이용하여 신뢰할 수 있는 지반정수와의 상관관계식을 도출하는 것이 바람직하다. 본 연구에서는 응력에 대해 최적으로 정규화된 콘저항값을 이용하여 더욱 합리적인 지반정수를 도출하고자, 싱가폴 창이 동부 매립현장에 위치한 l0m 높이의 여성토를 약 2 m씩 단계적으로 제거하며, 각 단계마다 콘관입시험을 실시하였다. 여기서 측정된 콘저항값을 다양한 방법으로 응력정규화하여 그 값들을 비교함으로써 최적의 정규화 방법을 제안하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 연약지반처리위원회 학술세미나
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• pp.71-78
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• 2000

SHANSEP method involves the consolidation to stresses in excess of the preconsolidation pressure in order to overcome sample disturbance effect. The concept of SHANSEP is based on an approach to laboratory test which attempts to reproduce the in-situ conditions more closely than is possible in routine tests and evaluates normalized strength parameters for the soil as a function of OCR. But SHANSEP method can be applied only to fairly uniform clay deposits, and is unsuitable for a random deposit. In this study, CK/sub o/U triaxial compression test and incremental loading consolidation test were performed for the application of SHANSEP method on Yangsan clay. During the K/sub o/-consolidation, triaxial specimens were consolidated to stress equal to two times the in-situ vertical effective stress. And for overconsolidated condition, the specimens were swelled to a known vertical effective stress in order to have the desired OCR. With the results of CK/sub o/U triaxial compression test using the block samples, the relationship between c/sub u//σ/sub vc/' and OCR on Yangsan clay was established. For evaluating the undrained shear strength of Yangsan clay with depth, CK/sub o/U triaxial compression test was performed using the piston samples taken from Yangsan site. And also undrained shear strength was analyzed from the in-situ test such as Cone Penetration Test(CPT), Dilatometer Test(DMT), and Field Vane Test(FVT) and was compared with that of CK/sub o/U triaxial compression test.

• 한국지반환경공학회 논문집
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• 제19권12호
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• pp.25-32
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• 2018

본 논문은 암반에 형성되어 있는 불연속면이 지진 또는 발파에 의해 유발되어 암반을 통해 전달되는 동적 전단응력파에 미치는 영향에 대해서 수치해석적 매개변수 연구를 통해 조사하고 그 결과를 제시하는 것이다. 수치해석적 매개변수 연구를 수행하기 위해서 먼저 이론적 해를 얻을 수 있는 조건에 대해서 타당성해석을 수행하고 그 결과를 이론해와 비교한 후 암반조건 및 불연속면 조건을 달리한 경우에 대해서 매개변수해석을 수행하였다. 암반조건으로는 암반 초기 현장응력 상태가 고려되었으며 불연속면조건으로서는 불연속면의 전단강도 정수인 마찰각과 점착력이 고려되었다. 또한 불연속면의 경사각 또한 매개변수로서 고려되었다. 이와 같은 다양한 조건의 매개변수연구를 통해 전단응력파의 변화를 파악한 결과, 매질을 통해 전달되는 동적 전단응력파는 암반의 초기 현장응력조건 뿐만 아니라 불연속면의 전단강도 및 경사각 조건에 크게 영향을 받는 것으로 나타났다. 이를 통해 지진 또는 발파유발 동적하중이 절리형성 암반지층이나 서로 다른 지층으로 이루어진 토사지층을 통과할 때, 지층의 초기응력 상태와 더불어 불연속면 또는 지층경계면의 특성 등을 반드시 고려하여 주변시설물 및 구조물에 대한 동적영향을 파악해야 할 것으로 판단된다.

• Coupled systems mechanics
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• 제12권5호
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• pp.429-444
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• 2023

The comprehension and structural modeling of masonry constructions is fundamental to safeguard the integrity of built cultural assets and intervene through adequate actions, especially in earthquake-prone regions. Despite the availability of several modeling strategies and modern computing power, modeling masonry remains a great challenge because of still demanding computational efforts, constraints in performing destructive or semi-destructive in-situ tests, and material uncertainties. This paper investigates the shear behavior of masonry walls by applying a plane-stress FE continuum model with the Modified Masonry-like Material (MMLM). Epistemic uncertainty affecting input parameters of the MMLM is considered in a probabilistic framework. After appointing a suitable probability density function to input quantities according to prior engineering knowledge, uncertainties are propagated to outputs relying on gPCE-based surrogate models to considerably speed up the forward problem-solving. The sensitivity of the response to input parameters is evaluated through the computation of Sobol' indices pointing out the parameters more worthy to be further investigated, when dealing with the seismic assessment of masonry buildings. Finally, masonry mechanical properties are calibrated in a probabilistic setting with the Bayesian approach to the inverse problem based on the available measurements obtained from the experimental load-displacement curves provided by shear compression in-situ tests.