• 한국농공학회논문집
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• 제48권7호
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• pp.35-43
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• 2006

This study was carried out to investigate the liquefaction behaviour and predict deviator stress with matric suction, of unsaturated silty sand. The unsaturated soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. The axis translation technique was used to create the desired matric suctions in the specimen. Undrained triaxial compression tests were carried out at matric suction of 0, 2, 5, 10 and 25 kPa. The specimens were sheared to axial strains of about 20% to obtain steady state conditions. The results showed that liquefaction of silty sand only occurs at matric suction of 0 kPa and 2 kPa. The results also show that at matric suctions of 5, 10 and 25 kPa, the resistance to liquefaction increases. As the suction increases, the undrained effective stress path approached the drained stress path. Also, the predicted and measured maximum deviator stress for unsaturated soils using the effective stress concept showed good agreement as matric suction increases. The deviator stress increase is nonlinear as matric suction increases.

• 대한토목학회논문집
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• 제32권1C호
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• pp.7-16
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• 2012

본 논문에서는 낙동강 불포화 실트질 모래의 매우 중요한 기본특성인 불포화 투수계수를 산정하기 위하여 Huang(1998)이 제안한 삼축셀을 이용하여 정적 측정 방법으로 불포화 투수계수를 구할 수 있도록 수정하여 불포화 투수 실험을 실시하였다. 이 시험 장치는 모관흡인력(matric suction)의 증가에 따른 투수계수의 변화를 측정할 수 있도록 설계되었다. 시험 장치를 사용하여 얻은 투수계수 값과 경험적 투수함수식으로부터 계산된 투수계수 값을 비교 분석하였다. 그 결과 불포화투수계수 값이 상대밀도, 실트함유율, 모관흡인력의 증가에 따라 감소하는 경향을 보였는데, 이러한 경향은 함수비와 간극비의 변화에 아주 밀접한 관련이 있다는 것을 알 수 있었다. 또한 Fredlund & Xing(1995)에 의하여 제시된 경험적 투수 함수식이 낙동강 실트질 모래의 불포화투수계수를 표현하는데 제일 적합한 모델이라는 판단을 내리게 되었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.836-841
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• 2008

CFRD (Concrete Faced Rockfill Dam) has been world-widely constructed due to a lot of advantages compared with rockfill dam and recently, sand/gravel materials, instead of crushed rock materials, are also utilized as a main rockfill material to overcome geological and environmental problems. In this paper, the process of water infiltration into the originally unsaturated sand/gravel-fill dam is studied using two-dimensional saturated-unsaturated seepage theory. According to the results of seepage analysis, if the effective drainage zone is installed in the dam, the reservoir water infiltrate into the dam along a downward flow path towards the lower drainage area. The main body constructed with sand/gravel materials, therefore, remains unsaturated.

• Geomechanics and Engineering
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• 제5권4호
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• pp.343-362
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• 2013

Simple relationships are proposed in this paper by modifying the Schmertmann's equation for settlement estimations of footings (i.e., $B/L{\approx}1$) carrying vertical loads in saturated and unsaturated sandy soils. The modified method is developed using model plate load tests (PLTs) and cone penetration tests (CPTs) results conducted in saturated and unsaturated sand in a controlled laboratory environment. Seven in-situ large-scale footings tested under both saturated and unsaturated conditions in sands were used to validate the proposed technique. The results of the study are encouraging as they provide reliable estimates of the settlement of shallow footings in both saturated and unsaturated sands using the conventional CPT results.

• Geomechanics and Engineering
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• 제23권5호
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• pp.419-429
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• 2020

To investigate the effect of spatial variability on hydraulic properties of unsaturated soils, a numerical model is set up which can simulate seepage process in an unsaturated heterogeneous soil. The unsaturated heterogeneous soil is composed of matrix sand embedded with a small proportion of clay for simulating the heterogeneity. Soil-water characteristic curve and unsaturated hydraulic conductivity curve of the unsaturated soil are expressed by Van Genuchten model. Hydraulic parameters of the matrix sand are considered as random fields. Different autocorrelation lengths (ACLs) of hydraulic parameter of the matrix sand and different proportions of clay are assumed to investigate the influence of spatial variability on the equivalent hydraulic properties of the heterogeneous soil. Four model sizes are used in the numerical experiments to investigate the influence of scale effects and to determine the sizes of representative volume element (RVE) in the numerical simulations. Through a number of Monte Carlo simulations of unsaturated seepage analysis, the means and the coefficients of variations (COVs) of the equivalent hydraulic parameters of the heterogeneous soil are calculated. Simulations show that the ACL and model size has little influence on the means of the equivalent hydraulic parameters, but they have a large influence on the COVs of the equivalent hydraulic parameters. The size of an RVE is mainly affected by the ACL and the proportion of heterogeneity. The influence of spatial variability on the hydraulic parameters of the heterogeneous unsaturated soil can be used as a guidance for geotechnical reliability analysis and design related to unsaturated soils.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.129-134
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• 2001

The purpose of this study is to investigate properties of unsaturated polyester mortar using the shale as find aggregates. To evaluate properties of unsaturated polyester mortar using crushed sand from Black shale, Red shale, Gray shale, we peformed the experiment according the F/B ratio of 25, 30, 35% and the volume of fine aggregate of 50, 53, 56%. The Result of this study is as follows. the strength of unsaturated polyester mortar is higher than those of river sand. The F/B ratio is higher and the volume of find aggregate is lower, the strength of unsaturated polyester mortar is higher

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.761-768
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• 2008

This paper presents the results of a laboratory study on the thermal conductivity of sand(silica, quartzite, limestone, sandstone, granite and masonry sand)-water mixtures used in ground heat exchanger backfilling materials. Nearly 260 tests were performed in a thermal conductivity measuring system to characterize the relationships between the thermal conductivity of mixtures and the water content. The experimental results show that the thermal conductivity of mixtures increases with increasing dry density and with increasing water content. The most widely used empirical prediction models for thermal conductivity of soils were found inappropriate to estimate the thermal conductivity of unsaturated sand-water mixtures. An improved model using a exponential relationship to compute the thermal conductivity of dry sands and empirical relationship to assess the normalized thermal conductivity of unsaturated sand-water mixtures is presented.

• 대한토목학회논문집
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• 제33권6호
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• pp.2369-2379
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• 2013

불포화 조건에서 흙의 초기 밀도에 따라 흙-함수특성곡선이 변화시키게 되며, 이로 인하여 불포화 조건에서 투수특성도 변화하게 된다. 이에 대한 영향을 고찰하기 위하여 상대밀도 40%, 60% 및 75%의 주문진 표준사에 대한 건조 및 습윤과정에서의 흙-함수특성곡선(SWCC)과 불포화 투수계수함수를 산정하였다. van Genuchten (1980)의 방법을 이용하여 흙-함수특성곡선(SWCC)을 산정한 결과 공기유입값과 관계된 계수 ${\alpha}$는 습윤과정에서 더 큰 값을 가지며, 변곡점의 경사에 관계된 계수 n과 잔류함수비에 관계된 계수 m은 건조과정에서 더 큰 값을 갖는다. 그리고 상대밀도가 증가할수록 공기함입치는 증가하지만 수분함입치는 감소하며, 동일한 상대밀도에서 공기함입치는 수분함입치보다 크게 발생된다. 한편, 계수추정방법 가운데 하나인 van Genuchten (1980)의 방법을 적용하여 불포화 투수계수함수를 산정한 결과 불포화 투수계수는 포화시 투수계수로 일정하게 유지되다가 공기함입치 혹은 수분함입치 직전에 급격하게 감소하는 것으로 나타났다. 건조과정에서의 포화투수계수는 습윤과정에서의 포화투수계수보다 크게 나타나며, 상대밀도가 증가함에 따라 건조 및 습윤과정에서의 포화투수계수는 감소한다. 실험결과에 의하면 주문진 표준사의 초기 간극비에 따라 흙-함수특성곡선(SWCC)에서의 공기함입치(AEV)는 감소하고 포화투수계수는 증가하므로, 흙-함수특성곡선(SWCC)과 불포화 투수계수함수(HCF)는 초기 간극비에 영향을 받는 것으로 나타났다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제16권6호
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• pp.27-33
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• 2011

Infiltration plays an important role in the urban water cycle. Infiltration has a potential to contribute to groundwater recharge in addition to runoff reduction. However, infiltration in urban areas has been considered only as a means of runoff reduction. Conventional design methods for infiltration facilities assume soils to be fully-saturated for the sake of simplicity. The amount of groundwater recharge can not be estimated properly with this scheme. Hence, the characteristics of the unsaturated soil condition need to be considered. The finite element model using SEEP/W to estimate infiltration under the unsaturated condition is presented. Infiltration tests for Joomonjin sand are performed and the infiltration behavior of Joomoonjin sand under the unsaturated condition is measured experimentally to verify the validity of the finite element model. The results from comparing infiltrated volume between the saturated and the unsaturated conditions under the same soil and rainfall conditions show that the infiltrated volume in the unsaturated condition is two times bigger than that in the saturated condition.

• 지질공학
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• 제14권2호
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• pp.169-177
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• 2004

포화 및 불포화 상태로 이루어진 지반 내에서 지하수의 함량 및 오염물질의 침투 이동은 지반을 구성하고 있는 다공질 매질의 공극률과 유효공극률에 매우 큰 영향을 받는다. 본 연구는 불포화 매질에 대한 유효공극률을 측정하기 위해서 Frequency domain reflectometry(FDR) system 및 측정센서를 개발하여 실내실험을 수행하였다. 또한 측정된 유전율상수의 관계로부터 유효공극률을 산정할 수 있는 유전을 믹싱모델(dielectric mixing model)을 제안하였다. 실험결과에서 불포화 흙 시료인 표준사(standard sand)와 강모래(river sand)의 유효공극률의 범위는 공극률과 비교해 약 65∼85% 내외에서 측정되었다. 특히, 측정된 유효공극률과 공극률의 관계에서 공극률이 증가할수록 유효공극률은 다소 감소하는 경향을 보이는 것으로 측정되었다. 이는 흙 입자사이의 공극 내에 존재하는 미량의 공기에 의한 것으로써 불포화 상태의 흙 칼럼이 충분히 포화 상태에 도달하지 못하였기 때문이다.