• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제19권2호
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• pp.197-215
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• 2015

Modeling water flow in variably saturated, porous media is important in many branches of science and engineering. Highly nonlinear relationships between water content and hydraulic conductivity and soil-water pressure result in very steep wetting fronts causing numerical problems. These include poor efficiency when modeling water infiltration into very dry porous media, and numerical oscillation near a steep wetting front. A one-dimensional finite element formulation is developed for the numerical simulation of variably saturated flow systems. First order backward Euler implicit and second order Crank-Nicolson time discretization schemes are adopted as a solution strategy in this formulation based on Picard and Newton iterative techniques. Five examples are used to investigate the numerical performance of two approaches and the different factors are highlighted that can affect their convergence and efficiency. The first test case deals with sharp moisture front that infiltrates into the soil column. It shows the capability of providing a mass-conservative behavior. Saturated conditions are not developed in the second test case. Involving of dry initial condition and steep wetting front are the main numerical complexity of the third test example. Fourth test case is a rapid infiltration of water from the surface, followed by a period of redistribution of the water due to the dynamic boundary condition. The last one-dimensional test case involves flow into a layered soil with variable initial conditions. The numerical results indicate that the Crank-Nicolson scheme is inefficient compared to fully implicit backward Euler scheme for the layered soil problem but offers same accuracy for the other homogeneous soil cases.

• 한국지반공학회논문집
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• 제40권1호
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• pp.39-46
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• 2024

전 지구적 기후변화에 따른 용수확보 방안으로 인공함양 기법이 활용되고 있다. 함양률을 감소시키는 클로깅 문제는 인공함양 기법의 활용에 큰 장애가 되고 있다. 이 연구는 하천수 주입 과정에서 발생할 가능성이 있는 클로깅 평가를 위한 기초자료를 확보하기 위해 인공함양 예정 지역 충적층의 토양 조직과 광물 특성을 분석하였다. 충적층 쇄설성 입자의 주요 구성 광물은 석영, 정장석, 사장석, 흑운모 등이며, 공극을 충진하는 주요 2차 광물은 일라이트, 카오린나이트, Fe-산화광물이다. 2차 광물로서 탄산염 혹은 황산염 광물의 산출이 없는 것은 인공함양 실험 전인 연구 지역 충적층에서는 지하수와 지표수 간의 반응에 의한 화학적 클로깅은 발생하지 않았음을 시사한다. 인공함양 실험과 관련된 화학적 클로깅에 대한 평가를 위해 대수층 내 공극에서 2차 광물의 생성과 성장과 같은 충적층의 토양특성에 대한 모니터링이 필요하다.

• 한국물환경학회지
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• 제23권4호
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• pp.518-526
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• 2007

There have been serious soil erosion and water pollution problems caused by highland agriculture practices at Doam-dam watershed. Especially agricultural activities, chemical and organic fertilizer and pesticide applications, soil reconditioning to maintain soil fertility are known as primary causes of soil erosion and water qaulity degradation in the receiving water bodies. Among these, soil reconditioning can accelerate soil erosion rates. To develop soil erosion prevention practices, it is necessary to estimate the soil erosion from the watershed. Thus, the Universal Soil Loss Equation (USLE) model has been developed and utilized to assess soil erosion. However, the USLE model cannot be used at watershed scale because it does not consider sediment delivery ratio (SDR) for watershed application. For this reason, the Sediment Assessment Tool for Effective Erosion Control (SA TEEC) was developed to assess the sediment yield at any point in the watershed. The USLE-based SA TEEC system can estimate the SDR using area-based SDR and slope-based SDR module. In this study, the SATEEC system was used to estimate soil erosion and sediment yield at the Doam-dam watershed using the soil properties from reconditioned agricultural fields. Based on the soil sampling and analysis, the US LE K factor was calculated and used in the SA TEEC system to analyze the possible errors of previous USLE application studies using soil properties from the digital soil map, and compared with that using soil properties obtained in this study. The estimated soil erosion at the Doam-dam watershed without using soil properties obtained in the soil sampling and analysis is 1,791,400 ton/year (123 ton/ha/year), while the soil erosion amount is 2,429,900 ton/year (166.8 ton/ha/year) with the use of soil properties from the soil sampling and analysis. There is 35 % increase in estimated soil erosion and sediment yield with the use of soil properties from soil reconditioned agricultural fields. Since significant amount of soil erosion are known to be occurring from the agricultural fields, the soil erosion and sediment yield from only agricultural fields was assessed. The soil erosion rate is 45.9 ton/ha/year without considering soil properties from soil reconditioned agricultural fields, while 105.3 ton/ha/year after considering soil properties obtained in this study, increased in 129%. This study shows that it is very important to use correct soil properties to assess soil erosion and sediment yield simulation. It is recommended that further studies are needed to develop environment friendly soil reconditioning method should be developed and implemented to decrease the speed of soil erosion rates and water quality degradation.

• 터널과지하공간
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• 제25권5호
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• pp.417-422
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• 2015

본 논문은 TBM을 이용한 터널 굴착에서 커터의 마모 및 파손, 그에 따른 굴착속도 저하와 커터교체에 따른 공기 지연 등으로 인하여 프로젝트 전반에 심각한 영향을 미치는 전석층 지반 터널링에 관한 내용으로, 매우 조밀하고 단단한 상태의 점토지반에 강한 강도를 지니는 암석을 포함하는 싱가포르 포트캐닝 볼더베드(Fort Canning Boulder Bed, FCBB)에서의 터널링 경험을 바탕으로 볼더층을 통과하게 되는 토압식 쉴드TBM의 설계 및 시공 시 고려해야 할 주요 사항 및 볼더지반에서의 커터 마모 및 파손 특성, 점토 및 암석이 혼재된 지반에서의 쏘일 컨디셔닝 등의 내용을 기술하였으며, 향후 유사 지반에서의 터널링 프로젝트에 참고가 되길 기대한다.

• Geomechanics and Engineering
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• 제7권6호
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• pp.665-678
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• 2014

In discrete element modeling, 2D software has been widely used in order to gain further insights into the fundamental mechanisms with less computational time. The porosities used in 2D DEM studies should be determined with appropriate approaches based on 3D laboratory porosities. This paper summarizes the main approaches for converting porosities from 3D to 2D for DEM studies and theoretical evaluations show that none of the current approaches can be widely used in dealing with soil mechanical problems. Therefore, a parabolic equation and a criterion have been suggested for the determination of 2D porosities in this paper. Moreover, a case study has been used to validate that the 2D porosity obtained from the above suggestion to be rational with both the realistic contact force distribution in the specimen and the good agreement of the DEM simulation results of direct shear tests with the corresponding experimental data. Therefore, the parabolic equation and the criterion are suggested for the determination of 2D porosities in a wide range of polydisperse particle systems, especially in dealing with soil mechanical problems.

• Structural Engineering and Mechanics
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• 제4권3호
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• pp.227-242
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• 1996

An important class of problems in the field of geotechnical engineering may be analyzed with the aid of a simple integro-differential equation. Behavior of "rigid" piles(say concrete piles), "deformable" piles(say gravel piles), pile groups, pile-raft foundations, heavily reinforced earth, flow within circular silos and down drag on cylindrical structures (for example the crusher unit of a mineral processing complex) are the type of situations that can be handled by this type of equation. The equation under consideration has the form; $$\frac{{\partial}w(r,\;z)}{{\partial}z}+f(z){\int}^z_0g({\xi})(\frac{{\partial}^2w(r,\;{\xi})}{{\partial}r^2}+\frac{1}{r}\frac{{\partial}w(r,\;{\xi})}{{\partial}r})d{\xi}+h(r,\;z)=0$$ where w(r, z) is the vertical displacement of a soil particle expressed as a function of the polar cylindrical space coordinates (r, z) and the symbols f, g and h represent soil properties and the loading conditions. The merit of the analysis is its simplicity (both in concept and in application) and the ease with which it can be expressed in a computer code. In the present paper the analysis is applied to investigate the behavior of a single rigid pile to bedrock. The emphasis, however, is placed on developing the equation, the numerical techique used in its evaluation and validation of the technique, hereafter called the ID technique, against a formal program, CRISP, which uses the FEM.

• Structural Engineering and Mechanics
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• 제21권4호
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• pp.437-450
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• 2005

In this study, a complete analysis of soil-structure interaction problems is presented which includes a modelling of the near surrounding of the building (near-field) and a special description of the wave propagation process in larger distances (far-field). In order to reduce the computational effort which can be very high for time domain analysis of wave propagation problems, a special approach based on similarity transformation of the infinite domain on the near-field/far-field interface is applied for the wave radiation of the far-field. The near-field is discretised with standard Finite Elements, which also allows to introduce non-linear material behaviour. In this paper, a new approach to calculate the involved convolution integrals is presented. This approximation in time leads to a dramatically reduced computational effort for long simulation times, while the accuracy of the method is not affected. Finally, some benchmark examples are presented, which are compared to a coupled Finite Element/Boundary Element approach. The results are in excellent agreement with those of the coupled Finite Element/Boundary Element procedure, while the accuracy is not reduced. Furthermore, the presented approach is easy to incorporate in any Finite Element code, so the practical relevance is high.

• Geomechanics and Engineering
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• 제17권3호
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• pp.287-294
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• 2019

The finite element method (FEM) is widely used to evaluate the seismic performance of pile-supported buildings. However, there are problems associated with modeling the pile end resistance using the FEM, such as the dependence on the mesh size. This paper proposes a new method of modeling around the pile tip to avoid the mesh size effect in two-dimensional (2D) analyses. Specifically, we consider the area of influence around the pile tip as an artificial constraint on the behavior of the soil. We explain the problems with existing methods of modeling the pile tip. We then conduct a three-dimensional (3D) analysis of a pile in various soil conditions to evaluate the area of influence of the soil around the pile tip. The analysis results show that the normalized area of influence extends approximately 2.5 times the diameter of the pile below the pile tip. Finally, we propose a new method for modeling pile foundations with artificial constraints on the nodal points within the area of influence. The proposed model is expected to be useful in the practical seismic design of pile-supported buildings via a 2D analysis.

• 한국지하수토양환경학회지:지하수토양환경
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• 제13권2호
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• pp.70-75
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• 2008

중금속으로 오염된 폐광산지역 토양을 정화하기 위해 실규모 토양세척공정을 적용하였다. $H_2SO_4$을 이용한 토양세척시 Cd의 경우 정화목표를 달성할 수 있었지만 낮은 세척효율을 나타내었으며, Zn은 낮은 세척효율로 인해 세척 후 토양의 농도가 토양오염우려기준 미만으로 저감되지 않았다. Cd 및 Zn은 토양세척 후 농도가 저감되는데 반해 As의 경우 세척 전에 비해 세척 후 토양의 As 농도가 지속적으로 증가되는 경향을 보였다. NaOH를 사용하여 세척효율을 평가한 결과, Cd와 Zn의 농도는 저감되었으나, 세척 전에 비해 세척 후 As의 농도가 더 높게 나타나 황산으로 세척한 경우와 유사한 경향을 보였다. 이러한 세척효율을 저하시키는 원인은 처리대상 토양의 입도분포 및 실규모토양세척으로 확대 적용함에 따라 발생하는 여러 가지 문제점으로 요약할 수 있으며, 세척 후 As의 농도가 증가하는 현상은 토양 내 As의 존재형태에 기인하는 것으로 판단되었다.

• 대한토목학회논문집
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• 제40권1호
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• pp.51-58
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• 2020

달 탐사에 대한 관심이 늘어나면서 인공월면토를 포함한 달 지상 환경 모사에 대한 연구가 진행되고 있다. 인공월면토를 포함하여 진공환경을 조성할 때 발생하는 문제점 중의 하나는 토양에서 나오는 탈 가스로 인해 고진공에 도달하는 시간이 길어진다는 것이다. 이러한 탈 가스의 대부분은 수분이며, 진공챔버에 넣기 전 인공월면토의 표면에 붙어있는 수분을 제거하는 전처리 과정을 수행한다면 고진공에 도달하는 시간을 상당히 줄일 수 있다. 기존의 토양 건조 방법을 사용하여 각 방법이 인공월면토의 수분제거에 얼마나 효과적인지 확인하였다. 드라이 오븐을 이용한 방법, 마이크로웨이브 오븐을 이용한 방법, 직접가열 건조하는 방법과 진공 오븐을 이용한 방법을 이용하여 인공월면토 시료의 건조 실험을 수행하였으며, 건조 실험의 결과를 제시하였다. 실험결과 드라이 오븐에서 110℃로 건조하는 방법과 마이크로웨이브 오븐을 이용한 건조 방법은 수분제거 효과가 충분하지 않았으며, 200℃ 이상에서 진공오븐을 이용한 방법과 직접 가열하는 방법은 수분제거 효과가 좋았다.