• Geomechanics and Engineering
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• 제23권1호
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• pp.61-69
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• 2020

The uniaxial compressive strength (UCS) of rock is a basic parameter in underground engineering design. The disadvantages of this commonly employed laboratory testing method are untimely testing, difficulty in performing core testing of broken rock mass and long and complicated onsite testing processes. Therefore, the development of a fast and simple in situ rock UCS testing method for field use is urgent. In this study, a multi-function digital rock drilling and testing system and a digital core bit dedicated to the system are independently developed and employed in digital drilling tests on rock specimens with different strengths. The energy analysis is performed during rock cutting to estimate the energy consumed by the drill bit to remove a unit volume of rock. Two quantitative relationship models of energy analysis-based core drilling parameters (ECD) and rock UCS (ECD-UCS models) are established in this manuscript by the methods of regression analysis and support vector machine (SVM). The predictive abilities of the two models are comparatively analysed. The results show that the mean value of relative difference between the predicted rock UCS values and the UCS values measured by the laboratory uniaxial compression test in the prediction set are 3.76 MPa and 4.30 MPa, respectively, and the standard deviations are 2.08 MPa and 4.14 MPa, respectively. The regression analysis-based ECD-UCS model has a more stable predictive ability. The energy analysis-based rock drilling method for the prediction of UCS is proposed. This method realized the quick and convenient in situ test of rock UCS.

• Geomechanics and Engineering
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• 제32권5호
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• pp.495-502
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• 2023

In this study, stress relaxation tests were carried out by keeping silt type soil specimens under different strain levels. Decreases in the stress values with time data was collected to better understand the effect of the strain level on the relaxation properties of soil specimens. In addition, the stress relaxation effect on the uniaxial compressive strength (UCS) values of the specimens was investigated with a series of tests. According to the results obtained from this study, the UCS values of the silt specimens significantly vary as a result of the stress relaxation effect. The UCS values were determined to increase with an increase of relaxation strain level to a threshold value. On the other hand, the UCS values were found to be affected adversely in case of high stress levels at the initiation of the relaxation, which are close to the peak level.

• Geomechanics and Engineering
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• 제23권2호
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• pp.115-125
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• 2020

This study aims to explore practical and useful equations for rapid evaluation of uniaxial compressive strength of concrete (UCS-C) during the preliminary design stage of aggregate selection. For this purpose, aggregates which were produced from eight different intact rocks were used in the production of concretes. Laboratory experiments involved the tests for uniaxial compressive strength (UCS-R), point load index (PLI-R), P wave velocity (UPV-R), apparent porosity (n-R), unit weight (UW-R) and aggregate impact value (AIV-R) of the rock samples. UCS-C, point load index (PLI-C) and P wave velocity (UPV-C) of concrete samples were also determined. Relationships between UCS-R-rock parameters and UCS-C-concrete parameters were developed by regression analyses. In the simple regression analyses, PLI-C, UPV-C, UCS-R, PLI-R, and UPV-R were found to be statistically significant independent variables to estimate the UCS-C. However, higher coefficients of determination (R²=0.97-1.0) were obtained by multiple regression analyses. The results of simple regression analysis were also compared to the limited number of previous studies. The strength conversion factor (k) values were found to be 14.3 and 14.7 for concrete and rock samples, respectively. It is concluded that the UCS-C can roughly be estimated from derived equations only for the specified rock types.

• 지질공학
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• 제21권4호
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• pp.361-367
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• 2011

일축압축강도는 깎기비탈면이나 지하구조물 등의 설계 및 시공에서 중요하게 취급되는 인자로 인식되고 있으나 실무에서는 일축압축강도를 시험하기 위해 많은 시간과 비용이 소요되는 것이 현실이다. 따라서 일축압축강도에 비해 상대적으로 시험방법이 간단하며 시료성형 시간 및 비용이 적게 소요되는 점재하강도 시험결과를 바탕으로 통계적인 방법의 하나인 선형회귀분석법을 이용하여 일축압축강도를 산정 할 수 있는 모델을 제안하였다. 이를 위해 통계 프로그램의 상관분석을 통해 일축압축강도와 밀접한 인자를 선별하고 이렇게 선별된 인자들과 일축압축강도의 상관관계를 선형회귀분석으로 공식화하였다. 추가로 모델과 실제 일축압축강도시험으로 구한 결과값을 비교 분석함으로써 제안된 모델의 적합성을 검증하였다. 점재하강도 시험시 얻어지는 인자들과 일축압축강도의 상관관계를 분석한 결과 일축압축강도에 가장 크게 영향을 미치는 인자는 점재하강도 및 시료의 형상인 것으로 나타났으며 모델에 의해 산정된 일축압축강도는 일축압축강도시험으로 구한 일축압축강도와 거의 유사한 결과를 보여 주었다. 따라서 본 연구에서 개발된 일축압축강도 산정모델은 연구지역과 같은 화강암질 암반 조건에서 일축압축강도의 산정을 위한 예측모델로서 활용이 가능할 것으로 사료된다.

• Geomechanics and Engineering
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• 제36권5호
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• pp.465-474
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• 2024

Uniaxial compressive strength (UCS) is a critical geomechanical parameter that plays a significant role in the evaluation of rocks. The practice of indirectly estimating said characteristics is widespread due to the challenges associated with obtaining high-quality core samples. The primary aim of this study is to investigate the feasibility of utilizing the gene expression programming (GEP) technique for the purpose of forecasting the UCS for various rock categories, including Schist, Granite, Claystone, Travertine, Sandstone, Slate, Limestone, Marl, and Dolomite, which were sourced from a wide range of quarry sites. The present study utilized a total of 170 datasets, comprising Schmidt hammer (SH), porosity (n), point load index (Is(50)), and P-wave velocity (Vp), as the effective parameters in the model to determine their impact on the UCS. The UCS parameter was computed through the utilization of the GEP model, resulting in the generation of an equation. Subsequently, the efficacy of the GEP model and the resultant equation were assessed using various statistical evaluation metrics to determine their predictive capabilities. The outcomes indicate the prospective capacity of the GEP model and the resultant equation in forecasting the unconfined compressive strength (UCS). The significance of this study lies in its ability to enable geotechnical engineers to make estimations of the UCS of rocks, without the requirement of conducting expensive and time-consuming experimental tests. In particular, a user-friendly program was developed based on the GEP model to enable rapid and very accurate calculation of rock's UCS, doing away with the necessity for costly and time-consuming laboratory experiments.

• 터널과지하공간
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• 제21권1호
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• pp.41-49
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• 2011

본 연구는 침관입시험을 이용하여 연약암반에 대한 일축압축강도를 추정하기 위한 연구결과를 나타낸 것이다. 침관입시험을 위한 인공암반의 배합비는 시멘트(C):벤토나이트(B):물(W) = 1.3:0.7:2.3 또는 1.5:0.5:2.0이 적절한 것으로 나타났다. 침관입시험에 의해 측정된 침관입저항력(NPR)과 이로부터 추정된 일축압축강도(UCS) 관계에서 NPR과 UCS는 양생기간이 길어짐에 따라 증가하는 경향을 보였다. 또한 침관입시험에 의해 측정된 NPR과 실제 시험에서 얻어진 UCS 관계에서는 NPR-UCS가 배합비와 상관없이 양생기간이 3일~14일까지는 선형적으로 증가하다가 14일~28일에서는 NPR-UCS가 작은 차이를 보이지만 거의 일정한 관계로 나타났다. 결론적으로 전체적인 NPR-UCS의 관계는 대체적으로 선형적인 관계를 보이며, 이것은 연약암반의 경우 침관입 시험에 의한 NPR로부터 일축압축강도를 추정하는 것이 가능함을 의미한다.

• 터널과지하공간
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• 제31권6호
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• pp.440-459
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• 2021

최근 대형 로드헤더가 국내 터널현장에 도입되면서 해외 제조사의 굴진율 예측모델에 대한 관심이 증가하고 있다. 현재 주로 사용되는 해외모델은 압축강도로부터 굴진율을 예측하고 있는데, 암석 시험편의 직경 대 길이의 비율이 1.0인 시편을 일축압축시험으로 사용하고 있다. 일반적으로 시편의 형상과 치수는 강도에 영향을 미치는 것으로 알려져 있다. 본 기술보고에서는 직경 대 길이 비율에 따른 암석강도의 변화에 대한 기존 연구사례를 조사하였다. 그 형상효과에 대한 원인을 이론적으로 고찰하였다. 이를 토대로 국내 예정된 암종에 대해서 길이 비율에 따른 강도의 변화 양상을 예측하고 굴진율 수정모델을 제시하였다.

• Steel and Composite Structures
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• 제49권6호
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• pp.645-666
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• 2023

Due to the steadily declining supply of natural coarse aggregates, the concrete industry has shifted to substituting coarse aggregates generated from byproducts and industrial waste. Oil palm shell is a substantial waste product created during the production of palm oil (OPS). When considering the usage of OPSC, building engineers must consider its uniaxial compressive strength (UCS). Obtaining UCS is expensive and time-consuming, machine learning may help. This research established five innovative hybrid AI algorithms to predict UCS. Aquila optimizer (AO) is used with methods to discover optimum model parameters. Considered models are artificial neural network (AO - ANN), adaptive neuro-fuzzy inference system (AO - ANFIS), support vector regression (AO - SVR), random forest (AO - RF), and extreme gradient boosting (AO - XGB). To achieve this goal, a dataset of OPS-produced concrete specimens was compiled. The outputs depict that all five developed models have justifiable accuracy in UCS estimation process, showing the remarkable correlation between measured and estimated UCS and models' usefulness. All in all, findings depict that the proposed AO - XGB model performed more suitable than others in predicting UCS of OPSC (with R², RMSE, MAE, VAF and A_15-index at 0.9678, 1.4595, 1.1527, 97.6469, and 0.9077). The proposed model could be utilized in construction engineering to ensure enough mechanical workability of lightweight concrete and permit its safe usage for construction aims.

• 터널과지하공간
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• 제22권5호
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• pp.330-338
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• 2012

일축압축강도(UCS)는 암석의 주요 물성 중 하나이다. 그러나 항상 UCS 실험을 위한 시료를 취득할 수는 없다. 이러한 경우 점하중시험과 같은 간접시험법이 유용한 대안이 될 수 있다. 본 연구에서는 임계지역에 분포하는 석회암을 대상으로 일축압축강도와 점하중강도지수 사이의 상관관계를 분석하였으며 선형 회귀식이 제안되었다. 또한 석회암을 대상으로 수행된 이전 연구결과와 이번 연구 결과를 비교하였다. 동일한 암종이라도 국내에서 분포하는 지역에 따라 변환계수가 다를 수 있으며, 분석의 정확성을 높이기 위해서는 더 많은 자료가 필요할 것으로 판단된다.

• 한국도로학회논문집
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• 제20권4호
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• pp.21-26
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• 2018

PURPOSES : The objective of this study is to evaluate the application of soil stabilization method for soft shoulder construction in the iRoad Project of Sri Lanka. METHODS : Firstly, the quantitative analysis of soil strength improvement due to soil stabilization was done for soil samples collected from iRoad construction sites. Two types of soils were selected from iRoad Project sites and prepared for soil stabilization testing by the Road Development Authority. Secondly, the appropriate stabilizer was selected at given soil type based on test results. Two different stabilizers, ST-1 and ST-2, produced in Korea were used for estimating soil strength improvements. Finally, the optimum stabilizer content was determined for improving shoulder performance. The uniaxial compressive strength (UCS) test was conducted to evaluate the strength of stabilized soil samples in accordance with ASTM D 1633. The use of bottom ash as a stabilizer produced from power plant in Sri Lanka was also reviewed in this task. RESULTS : It is found from the UCS testing that a 3% use of soil stabilizer can improve the strength up to 2~5 times in stabilized soft shoulder soils with respect to unstabilized soils. It is also observed from UCS testing that the ST-1 shows high strength improvement in 3% of stabilizer content but the strength improvement rate with increase of stabilizer content is relatively low compared with ST-2. The ST-2 shows a low UCS value at 3% of content but the UCS values increase significantly with increase of stabilizer content. When using the ST-2 as stabilizing agent, the 5% is recommended as minimum content based on UCS testing results. Based on the testing results for bottom ash replacement, the stabilized sample with bottom ash shows the low strength value. CONCLUSIONS : This paper is intended to check the feasibility for use the soil stabilization technique for shoulder construction in Sri Lanka. The use of soil stabilizer enables to improve the durability and strength in soft shoulder materials. When applying the bottom ash as a soil stabilizer, various testings should be conducted to satisfy the specification criteria.