• 한국농공학회논문집
• /
• 제62권6호
• /
• pp.119-129
• /
• 2020

Through 3D seepage analysis of pressure relief well installed on the embankment of agricultural reservoir, the effects of reducing pore water pressure and hydraulic gradient, and increasing piping safety, depending on diameter (0.2, 0.4, 0.6 m) and space (10, 25, 50 m) of relief well, were analyzed. The conclusions drawn through this study are as follows. i) At the location of pressure relief well, pore water pressure decreases by 25.3~62.5%, and hydraulic gradient decreases by 22.4~55.7%. ii) Between relief wells, pore water pressure decreases by 2.7~40.3%, and hydraulic gradient decreases by 2.8~47.0%, which are relatively less than at the cross section of installed location of relief well. iii) Piping safety factor by critical hydraulic gradient increases by 28.9~125.6% at the location of relief well and increases by 2.9~88.8% between relief wells. iv) Seepage analysis needs to be performed by the 3D method to make evaluation of seepage at the location of relief well and between relief wells possible. v) Additional evaluation is required for various conditions such as waterhead, engineering characteristics of embankment body and its foundation, location, diameter, spacing and depth of pressure relief well.

• Carbon letters
• /
• 제7권4호
• /
• pp.271-276
• /
• 2006

Porous carbon materials were prepared with a thermal treatment of coal tar pitch at 550 in the Ar gas. Growth, merger, and distribution of pore were characterized with scanning electron microscopy as variation ascending temperature gradient and chamber pressure. After graphitizing at the 2600 (1 hr.), walls and connecting parts between pores were investigated with X-ray diffraction patterns. Wall thickness and pore size decreases as increasing ascending temperature gradient, and pore size becomes homogeneous. Graphite quality and thermal conductivity become higher due to the enhanced orientation of walls and connecting parts between pores.

• 한국농공학회논문집
• /
• 제60권1호
• /
• pp.1-10
• /
• 2018

This study analyzed pore water pressure, seepage and leakage quantity, height of seepage and critical hydraulic gradient in order to suggest the seepage characteristics of agricultural reservoir embankment considering filter interval. The seepage characteristics of a deteriorated reservoir embankments were conducted according to the horizontal filter intervals range using three- dimensional finite element analysis. The wider the horizontal filter interval, the higher the pore water pressure increased, and the pore water pressure ratio in the center of the core has a greater effect than the base part. The seepage and leakage quantity appeared largely in the two-dimensional analysis conditions (case 1), where the filter was constructed totally in the longitudinal direction of the embankment, the wider the horizontal filter interval was gradually reduced. The reasonable filter intervals to yield efficient seepage characteristics were within 30 m for the pore water pressure of the core and the height of the seepage line. The stability of the filter installation was able to evaluate the stability of the piping by the critical hydraulic gradient method. The deteriorated reservoir with no filters or decreased functionality can significantly reduce the possibility of piping by simply installing a filter on the downstream slope. In the future, the deteriorated reservoir embankment should be checked for the reservoir remodeling because the core and filter functions have been lost or decreased significantly. In the case of a new installation, the seepage characteristic behavior due to the core and filter changes should be applied to the field after obtaining a reasonable horizontal filter interval that satisfies the safety factor by a three-dimensional analysis.

• 한국지반공학회논문집
• /
• 제22권8호
• /
• pp.55-62
• /
• 2006

샌드매트의 설계는 연약지반의 압밀침하특성과 매트의 투수성이 상호 결합된 연성압밀해석에 의해 얻어지는 간극 수압거동에 의해 검토되어야 한다. 본 연구에서는 샌드매트의 수두분포에 대하여 Terzaghi 1차원 압밀방정식을 이용한 수치해석을 실시하여 준설모래를 샌드매트 재료로 이용한 성토모형실험의 결과와 비교분석하였다. 실험결과 단계 성토가 증가하면서 간극수압은 성토중심부에서 증가되는 침하량의 영향을 받고 있다. 그리고 잔류된 간극수압 영향으로 간극수압의 상승속도가 수치해석결과보다 지연되고 있다. 따라서 최종적으로 샌드매트 시공은 성토중심부에서 증가되는 동수구배를 저감시키도록 포설되어야 한다.

• Geomechanics and Engineering
• /
• 제6권5호
• /
• pp.503-515
• /
• 2014

On the basis of Hoek-Brown failure criterion, a numerical solution for the shape of collapsing block in the rectangular cavity subjected to seepage forces is obtained by upper bound theorem of limit analysis. The seepage forces obtained from the gradient of excess pore pressure distribution are taken as external loadings in the limit analysis, and the pore pressure is easily calculated with pore pressure coefficient. Thus the seepage force is incorporated into the upper bound analysis as a work rate of external force. The upper solution of the shape of collapsing block is derived by virtue of variational calculation. In order to verify the validity of the method proposed in the paper, the result when the pore pressure coefficient equals zero, and only hydrostatic pressure is taken into consideration, is compared with that of previous work. The results show good effectiveness in calculating the collapsing block shape subjected to seepage forces. The influence of parameters on the failure mechanisms is investigated.

• Geomechanics and Engineering
• /
• 제19권5호
• /
• pp.435-445
• /
• 2019

A series of element tests with different drainage conditions and strain rates were performed on compacted unsaturated non-plastic silt in unconfined conditions. Soil samples were compacted at water contents from dry to wet of optimum with the degree of saturation varying from 24 to 59.5% while maintaining the degree of compaction at 80%. The tests performed were shear infiltration tests in which specimens had constant net confining pressure, pore air pressure was kept drained and constant, just before the shear process pore water pressure was increased (and kept constant afterwards) to decrease matric suction and to start water infiltration. In constant water content tests, specimens had constant net confining pressure, pore air pressure was kept drained and constant whereas pore water pressure was kept undrained. As a result, the matric suction varied with increase in axial strain throughout the shearing process. In both cases, maximum shear strength was obtained for specimens prepared on dry side of optimum moisture content. Moreover, the gradient of stress path was not affected under different strain rates whereas the intercept of failure was changed due to the drainage conditions implied in this study.

• 한국농공학회논문집
• /
• 제47권4호
• /
• pp.43-52
• /
• 2005

It is known in some literatures that the B value is not equal to unity in saturated soil when effective stress is given, in which the B Value is the ratio of measured excess pore water pressure and isometric loading pressure. In this study the B value was measured on various effective stresses and on various incremental loading stresses in various grain size of specimens with saturated sand. The test results showed that the B value was affected largely by grain size of sand in specimen and the amount of effective stress. There was the semi-logarithmic relationship between B value and effective stress, and also there was the linear relationship between the gradient of the former semi-logarithmic relationship and grain size of specimen.

• 지질공학
• /
• 제34권2호
• /
• pp.217-228
• /
• 2024

피압대수층은 이를 통과하는 대심도 시추에서 암편 배출 불능, 지하수의 급격한 공내 유입, 이수 손실 등의 문제를 야기한다. 특히 자분 조건일 경우 과압 공극압이 발생하여 적절한 이수 밀도의 적용이 필수적이다. 이 논문에서는 이수창 분석을 이용하여 피압대수층을 통과하는 시추 중 적정이수밀도(SMD)의 결정방법을 제시하고 이를 사례에 적용하여 적용성을 검토하였다. 심도별 이수창의 하한인 최소이수밀도는 해당 심도의 등가이수밀도 공극압 구배 또는 이에 이송 마진을 더하여 산정되며, 피압대수층의 공극압 구배는 피압지하수위 또는 정두압의 측정으로 구할 수 있다. 시추공이 피압대수층에 도달하면 공극압 구배가 급격히 증가하고, 심도가 증가할 수 록 점차 감소한다. 킥 발생을 방지하기 위한 SMD는 굴진 중인 공저 심도와 그 상부 나공 구간의 최소이수밀도 중 최대값으로 결정할 수 있으며, 피압대수층 진입 이후 SMD는 피압대수층 최상부의 최소이수밀도로서 나공 구간 시추 중 이를 유지하여야 한다. 또한 적절한 케이싱의 설치는 SMD를 낮출 수 있어 고투수성 대수층에 대한 이수 침입 또는 이수 손실의 위험을 감소시킬 수 있다.

• 한국농공학회논문집
• /
• 제58권2호
• /
• pp.31-44
• /
• 2016

This study analyzed pore water pressure, earth pressure and settlement through field monitoring on the project site in which raising embankments are being built through backside extension, and compared the behaviors of seepage analysis, slope stability analysis and stress-strain during flood water levels and rapid drawdown under steady state and transient condition. The variation of pore water pressure showed an increase during the later period in both upstream and downstream slope, with downstream slope more largely increased than upstream slope overall. The variation of earth pressure increased according to the increase of embankment heights, while the change largely showed in the upstream slope, it was slowly increased in the downstream slope. The settlements largely increased until 23 m as embankment heights increased, and showed very little settlement overall. Under a steady state and transient conditions, the seepage quantity per day and leakage quantity per 100 m of embankment against total storage were shown to be stable for piping. The hydraulic gradient at the core before and after raising embankments was greater than the limit hydraulic gradient, showing instability for piping. The safety factor of upstream and downstream slopes were shown to be very large at a steady state, while the upstream slopes greatly decreased at a transit conditions, downstream slopes did not show any significant changes. The horizontal settlements, the maximum shear strain and stress are especially distributed at the connecting portion of the existing reservoir and the new extension of backside. Accordingly, the backside extension method should be designed and reinforced differently from the cases of other types reservoirs.

• 멤브레인
• /
• 제7권1호
• /
• pp.1-10
• /
• 1997

A review is presented for various gas transport mechanisms through microporous membranes of both polymeric and inorganic materials. Different transport modes manifest depending on the pore size and the flow regime, which is a function of pressure, temperature, and the interaction between gas molecules and the pore walls. For microporous membranes whose pores are small and the internal surface area huge, the surface diffusion becomes a significant factor. If the pores become even smaller, then the transport mechanism will be more of an activated diffusion type. When conditions are right capillary condensation will take place to create an enormous capillary pressure gradient, which will greatly enhance the permeation flux. At the same time the capillary condensate of the heavier component may block the membrane pores denying the passage of the lighter gas molecules. All of these phenomena will influence the separation of mixtures.