• Geomechanics and Engineering
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• 제33권1호
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• pp.1-9
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• 2023

The unconfined compression strength (UCS) of soils is commonly used either before or during the construction of geo-structures. In the pre-design stage, UCS as a mechanical property is obtained through a laboratory test that requires cumbersome procedures and high costs from in-situ sampling and sample preparation. As an alternative way, the empirical model established from limited testing cases is used to economically estimate the UCS. However, many parameters affecting the 1D soil compression response hinder employing the traditional statistical analysis. In this study, gene expression programming (GEP) is adopted to develop a prediction model of UCS with common affecting soil properties. A total of 79 undisturbed soil samples are collected, of which 54 samples are utilized for the generation of a predictive model and 25 samples are used to validate the proposed model. Experimental studies are conducted to measure the unconfined compression strength and basic soil index properties. A performance assessment of the prediction model is carried out using statistical checks including the correlation coefficient (R), the root mean square error (RMSE), the mean absolute error (MAE), the relatively squared error (RSE), and external criteria checks. The prediction model has achieved excellent accuracy with values of R, RMSE, MAE, and RSE of 0.98, 10.01, 7.94, and 0.03, respectively for the training data and 0.92, 19.82, 14.56, and 0.15, respectively for the testing data. From the sensitivity analysis and parametric study, the liquid limit and fine content are found to be the most sensitive parameters whereas the sand content is the least critical parameter.

• Geomechanics and Engineering
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• 제36권3호
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• pp.259-276
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• 2024

The undrained shear strength is widely acknowledged as a fundamental mechanical property of soil and is considered a critical engineering parameter. In recent years, researchers have employed various methodologies to evaluate the shear strength of soil under undrained conditions. These methods encompass both numerical analyses and empirical techniques, such as the cone penetration test (CPT), to gain insights into the properties and behavior of soil. However, several of these methods rely on correlation assumptions, which can lead to inconsistent accuracy and precision. The study involved the development of innovative methods using extreme gradient boosting (XGB) to predict the pile set-up component "A" based on two distinct data sets. The first data set includes average modified cone point bearing capacity (q_t), average wall friction (f_s), and effective vertical stress (σ_vo), while the second data set comprises plasticity index (PI), soil undrained shear cohesion (S_u), and the over consolidation ratio (OCR). These data sets were utilized to develop XGBoost-based methods for predicting the pile set-up component "A". To optimize the internal hyperparameters of the XGBoost model, four optimization algorithms were employed: Particle Swarm Optimization (PSO), Social Spider Optimization (SSO), Arithmetic Optimization Algorithm (AOA), and Sine Cosine Optimization Algorithm (SCOA). The results from the first data set indicate that the XGBoost model optimized using the Arithmetic Optimization Algorithm (XGB - AOA) achieved the highest accuracy, with R2 values of 0.9962 for the training part and 0.9807 for the testing part. The performance of the developed models was further evaluated using the RMSE, MAE, and VAF indices. The results revealed that the XGBoost model optimized using XGBoost - AOA outperformed other models in terms of accuracy, with RMSE, MAE, and VAF values of 0.0078, 0.0015, and 99.6189 for the training part and 0.0141, 0.0112, and 98.0394 for the testing part, respectively. These findings suggest that XGBoost - AOA is the most accurate model for predicting the pile set-up component.

• 한국농공학회지
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• 제26권3호
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• pp.81-89
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• 1984

To examine the moisture adsorption and permeability characteristics, weathered granite soils of different degrees of weathering, cultivated upland soils and sands of Han-river were sampled. The results are as follows: 1. In case that the mother rock was same, the pF values under same moisture content decreased according as the grain size of soil became finer by the weathering process. 2. In case that the mother rock was different, the pF value varied by the behavior of clay minerals, and the cultivated upland soils showed more sensitive reaction than sands and fresh granite soils. 3. The pF value changed by the difference of primary moisture content and also influenced by soil structure, testing method and etc. 4. The pF value and compaction curve had close relation, however under same moisture content, the pF value decreased by the increment of density. 5. The permeability depend on the available void ratio between the soil particles according to the degree of weathering, and the pF value of available void water between the soil particles which related directly to permeability was about 3.3 except the void water holded in the soil particles. 6. As the above, the pF value and permeability were differentiated by degree of weathering, primary moisture content, density and etc. Therefore it is considered unreasonable to define uniformly by soil texture.

• 한국지반공학회지:지반
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• 제7권1호
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• pp.7-14
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• 1991

시편을 통과하는 초음파의 속도를 측정 함으로써 흙의 동전단 탄성계수의 측정을 시도하였다. 초음 파의 발생 및 감지장치인 PUNDIT를 사용하였으며, 4종류의 시료에 따른 공극비 7, 포화도 7종류에 대해서 총 46개의 실험을 실시하였다. 본 연구는 시료의 공극비 및 포화도,시료의 종류등이 동전단 탄성계수에 미치는 영향에 대해서 분석하였다. 분석 결과,흙의 동전단 탄성계수는 공극비가 증가함에 따라 감소하는 경향을 보였으 며, 시료의 종류에 의 해서도 영 향을 받는다는 사실을 알 수 있었다. 또한 본 실험 장비인 PUNDIT를 사용할 경우, 시편의 길이는 5cm-8cm가 적당하였으며, 포화도의 영향은 거의 없는 것으로 판단 되었다.

• 한국토양비료학회지
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• 제41권1호
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• pp.50-54
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• 2008

근적외선스펙트로메타는 토양의 성분을 측정하는 새로운 기술로 발전하고 있다. 작물이 요구하는 토양의 인산 함량을 측정하는 데는 시간이 많이 소요되며, 침출액과 침출조건에 따라서 다르기 때문에 어려운 성분이다. 그러나 근적외선 방법을 이용하여 표준곡선을 정확하게만 만들어, 표준곡선 작성 시 Wiliams의 상관계수안내를 이용하면 상관계수의 수치에 따라서 토양의 총인산과 유효인산을 측정하는데 간편하게 이용할 수 있다. 또한 근적외 기술은 정밀도를 향상하면 포장 현지에서의 토양검정에도 쉽게 이용할 수 있는 쉬운 기술로 생각된다.

• Earthquakes and Structures
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• 제8권3호
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• pp.591-617
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• 2015

Standards for seismic assessment and retrofitting of buildings provide deformation limit states for structural members and connections. However, in order to perform fully consistent performance-based seismic analyses of soil-structure systems; deformation limit states must also be available for foundations that are vulnerable to nonlinear actions. Because such limit states have never been established in the past, a laboratory testing program was conducted to study the rotational capacity of small-scale foundation models under combined axial load and moment. Fourteen displacement-controlled monotonic and cyclic tests were performed using a cohesionless soil contained in a $2.0{\times}2.0{\times}1.2m$ container box. It was found that the foundation models exhibited a stable hysteretic behavior for imposed rotations exceeding 0.06 rad and that the measured foundation moment capacity complied well with Meyerhof's equivalent width concept. Simplified code-based soil-structure analyses of an 8-story building under an array of strong ground motions were also conducted to preliminary evaluate the implication of finite rotational capacity of vulnerable foundations. It was found that for the same soil as that of the experimental program foundations would have a deformation capacity that far exceeds the imposed rotational demands under the lateral load resisting members so yielding of the soil may constitute a reliable source of energy dissipation for the system.

• 한국지반공학회논문집
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• 제18권6호
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• pp.17-24
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• 2002

본 연구에서는 초음파실험을 통하여 카올린 점토 시료의 초음파 전파 속도와 감쇠특성을 조사하였다. 슬러리 압밀 방법을 이용하여 이산구조와 면모구조를 갖는 두 종류의 카올린 점토를 인공적으로 제작하였다. 초음파를 이용하여 각 구조를 가진 점토의 압축파 속도 및 감쇠 거동을 측정하였다. 측정시 가진 주파수, 시료 길이, 측정 방향 등을 변화시키며 그에 대한 영향을 조사하였다. 실험 결과 전파속도는 같은 압축 응력 조건에서 제작된 본 시료의 경우 미세구조의 영향이 크지 않았으나 감쇠 특성은 미세구조의 영향이 큰 것으로 나타났다.

• Geomechanics and Engineering
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• 제17권3호
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• pp.247-252
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• 2019

Modulus of deformation of soil is an essential parameter used for design analysis of foundations, despite its importance; little attention is paid to developing empirical models for predicting the sensitivity of deformation moduli to other parameters that obtained from the pressuremeter tests. Various methods of analysis used to predict the horizontal at rest pressure from pressuremeter testing ($P_o$), these values showed distinctive variations, five methods used to evaluate the values of horizontal at rest pressure, these values been used to evaluate the modulus of elasticity using three methods of analysis. The values of modulus showed distinctive increase when the values of horizontal at rest pressure increase for the same pressuremeter test, these increases may reach to 65%. This sensitivity of the moduli to values of horizontal lead the author to propose some reliable methods of analysis for both the horizontal at rest pressure and the modulus of deformation from pressuremeter testing.

• 한국토양비료학회지
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• 제42권6호
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• pp.467-471
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• 2009

고랭지농업 환경에 적합한 당근재배지의 토양검정 시비기준을 설정하고자 표고 850m의 사양질 밭토양에서 N, P 및 K 비료의 시비수준을 달리하여 포장시험을 수행하였다. 고랭지 당근에 대한 안정 수량을 생산하기 위한 NP-K의 적정 시비배율은 현행 평난지 토양검정 기준량 대비 각각 0.75-0.50-0.50배이었다. 산출된 적정 시비배율을 현행 시비추천식에 적용하여 고랭지 여름작물인 당근에 알맞은 시비추천식으로 도출해 낼 수 있었다. 도출한 시비추천 방법에 의한 고랭지 당근의 NPK 시비량과 당근의 재배면적을 적용하여 산출한 화학비료의 총 절감량은 질소-인산-칼리의 경우 8.1-5.0-9.9톤으로 총합계는 23.0톤이었다. 이는 현행 평난비 시비량의 25~50%를 절감할 수 있는 양으로 고랭지에 본 연구결과의 시비추천식을 적용하면 고랭지 당근의 생산성도 유지하면서 고랭지 농업환경 오염을 경감할 수 있다.

• 한국토양비료학회지
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• 제42권3호
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• pp.167-171
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• 2009

고랭지 농업환경에 적용할 수 있는 토양검정에 의한 시비기준을 설정하고자 고랭지 무에 대하여 2004년에 표고 850m의 사양질 밭토양에서 N, P 및 K 비료의 시비수준을 달리하여 포장시험을 수행하였다. 고랭지 무에 대한 안정 목표수량을 생산하기 위한 NPK의 적정 시비배율은 현행 평난지 토양검정 기준량 대비 각각 0.90, 0.77 및 0.50배이었다. 산출된 적정 시비배율을 조정된 시비추천식에 적용하여 고랭지 여름작물인 무에 알맞은 시비추천식을 설정할 수 있었다. 설정된 시비추천 방법에 의한 무의 N, P 및 K 시비량에 작물의 재배면적을 적용하여 산출한 고랭지 무 재배시 화학비료의 절감량은 질소, 인산 및 칼리의 경우 각각 71.3, 0 및 173.1톤으로 총합계 244.4톤이나 되었다. 따라서 평난지의 토양검정시비량보다 10~50%를 절감할 수 있는 새로운 시비추천식을 적용하면 고랭지 무의 생산성도 유지하면서 고랭지 농업환경 오염을 경감할 수 있을 것이다.