• Journal of the Korean GEO-environmental Society
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• v.12 no.3
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• pp.63-67
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• 2011

Recently, the application of unsaturated-soil theory is concerned in practice. Most characteristics of unsaturated-soil is the relationship between volumetric water contents and matric suction. Usually the volume water contents is estimated by the relationship between gravity water contents and volume water contents because of the difficulty of measurement of volumetric water contents. In this case, the water exists in only void of soil, and the relationship between gravity water contents and volume water contents is calculated by only water in void, but in fact, the water exists in the particle of the soil. So the real volume water contents is different with calculated volume water contents derived by the relationship containing only void water. The object of this research is to revise the relationship between volume water contents and gravity water contents by using the absorptivity tests of the soil particle.

• The Journal of Engineering Geology
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• v.30 no.4
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• pp.485-496
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• 2020

The characteristics of volumetric water content changes in soil slopes were studied here in an effort to identify the signs of heavy rain causing shallow slope failure. Volumetric water contents in cases with and without shallow failure were measured in flume and test-bed experiments. Measurement data from 282 experiments of both types revealed that the volumetric water content gradient in shallow failure events ranged from 0.072 to 0.309. In non-failure cases, the range was 0.01~0.32. Therefore, this one specific value cannot predict shallow slope failure. However, as the volumetric water content gradient increased, there was a clear tendency to shallow failure. By using this trend, criteria for four warning levels are suggested.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.89.1-89.1
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• 2010

본 연구는 토양의 함수비를 측정하기 위하여 TDR(Time Domain Reflectometry, 시간영역 광전자파 분석기) 방식의 함수센서(CS616)에 대한 올바른 보정시험을 제안하기 위하여 피복두께, 센서간 간섭 영향, 온도의 영향 및 다짐율 변화에 대한 실내 시험을 수행하였다. 시험 결과 피복두께, 센서간 간섭 영향 및 온도의 영향은 체적함수비의 크기에 미치는 영향은 크지 않은 것으로 나타났으며, 오히려 보정시험시 정확한 체적함수비 조건을 유지하는 것이 중요할 것으로 사료된다. 또한 보정시험을 수행할 때 다짐율까지 고려한 시험을 수행하는 노력에 비하여 얻어지는 체적함수비의 정확도의 크기는 다짐율과 주기를 고려하여 얻어진 회귀식을 살펴보면 주기에 비하여 상대적으로 영향이 작은 것으로 사료된다.

• Journal of the Korean Geotechnical Society
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• v.31 no.8
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• pp.17-28
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• 2015

The purpose of this study is to measure the volumetric water content of unsaturated soils during drying and wetting process by using volumetric pressure plate extractor (VPPE) incorporated with time domain reflectometry (TDR). The VPPE consists of a pressure cell, a pressure regulator, a burette system and a TDR probe. Two samples with different initial void ratios were prepared in the pressure cell, and the air pressure at the range of 0.1 kPa - 50 kPa was applied to adjust the matric suction by the pressure regulator. The burette system was used to measure the volumetric water content change of the sample according to the matric suction. In addition, the TDR probe, installed in the cell, was used to evaluate the dielectric constant from the reflected signal of the electromagnetic wave at the probe. The volumetric water content of specimen was estimated by the empirical equation between the volumetric water content and dielectric constant, which was calibrated with the Jumunjin sand. The test results show that the volumetric water content calculated by TDR probe is strongly correlated to the measured value by burette system. The hysteresis occurs during drying and wetting process. Furthermore, the degree of hysteresis reduces in the repeated process. This study suggests that TDR may be effectively used to evaluate the water content soil for the determination of water characteristic curve of unsaturated soils.

• Journal of the Korean Geotechnical Society
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• v.31 no.2
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• pp.39-46
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• 2015

Dielectric constant depends on the variation of soil water content, and the estimation of soil water content using time domain reflectometry (TDR) has been studied by many researchers. The purpose of this study is the development and application of TDR penetrometer (TDRP) in order to evaluate the soil water content according to the penetration depth. The TDRP consists of cone, sleeve, driving rod, hammer, and guide. Three electrodes, which are used to measure the dielectric constant of soils, are mounted on the surface of sleeve and, in turn, connected with coaxial cable and time domain reflectometer. To establish the relationship between the volumetric water content and dielectric constant, several laboratory tests by using the TDRP are performed in the specimens with a variety of volumetric water content. The experimental results show that the dielectric constant is strongly correlated to volumetric water content as polynomial equations with an order of 3. In addition, the volumetric water content calculated from the dielectric constant is similar to that obtained from the sample weight. In the field, a small sampler is used to compare the volumetric water content calculated from the dielectric constant with the volumetric water content obtained from the sample. The results of field application demonstrate that the volumetric water content estimated by the TDRP shows similar trend to the gravimetric water content of sample. This study suggests that the TDRP is effectively used to evaluate the volumetric water content of unsaturated soils according to the penetration depth.

• The Journal of Engineering Geology
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• v.15 no.2 s.42
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• pp.123-132
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• 2005

This study presents the results of a laboratory investigation performed to study physical properties of soil-bentonite mixtures through the vertical permeation test and dielectric measurement test using Frequency Domain Reflectometry system for the liner of waste landfill. For the laboratory experiments, geotechnical testing was conducted on pre-mixed soil-bentonite which is consisted of standard sand, weathered granite soil and bentonite for estimating physical parameters such as a volumetric water content, void ratio and dielectric constant. In experiment results, initial soil-bentonite mixing rate has an effect of change of volumetric water content. Also change of volumetric water content of a soil-bentonite mixture is clearly detected to measure a response of dielectric constant. In order to estimate an unsaturated permeable property of soil-bentonite mixtures, equations between volumetric water content and dielectric constant were derived from this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.737-746
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• 2019

Most landslides in the country are shallow failures triggered by intense rainfall. Many researchers have revealed the possibility of predicting shallow failure through the volumetric water content (VWC). This study examined how to determine shallow failure using the gradient characteristics of the volumetric water content. For this, flume experiments were conducted using weathered granite soil. To confirm the saturation state of the surface layer under a rainfall intensity of 30 and 50mm/hr, VWC sensors were installed at depths of 10 and 20 cm on the upper, middle and lower slope. The test results showed that a shallow failure determination using VWC could be applied limitedly according to the slope degree. In addition, the effective cumulative rainfall due to the rainfall infiltration velocity is considered the main factor for the failure time. The failure prediction using the gradient of the VWC depends on the installation location and depth of the sensor. According to the experimental data, the measured value at 20 cm below the slope was most effective. Therefore, an analysis method of VWC and the method of selecting the installation location confirmed through this study can provide important data for presenting the measurement criteria using VWC in the future.

• The Journal of Engineering Geology
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• v.15 no.4 s.42
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• pp.487-494
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• 2005

In order to estimated a reason of soil slope failure new measurement technology is demanded to measure a variation of volumetric water content which is a key physical parameter for understanding the slope failure in the field. In this study a laboratory soil tank test were conducted to use RDB and ADR measurement probes for measuring the variation of volumetric water content. These experiments were compared with two physical parameters as volumetric water content and pressure water head which are estimated to the compacted weathered granite soil under the artificial rainfall, 7.5mm/hour, in the whole of two stages. From the results the variation of volumetric water content and pressure water head is represented to nearly similar travel time.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1395-1399
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• 2008

국내 토층 사면을 대상으로 강우에 의해 발생되는 침투수 거동 특성을 분석함으로써 지속적인 토층의 물성 변화 계측을 통해 산사태 예 경보시스템을 구축이 가능하다. 본 연구에서는 산사태 예 경보시스템 구축의 사전 단계로써, 국내 대표적인 지질 매질인 화강암 풍화토, 편마암 풍화토와 주문진 표준사에 대해 공극률과 체적함수비 등의 토질 물성 변화를 고려한 실내 보정실험을 수행하였다. 실험조건은 공극률, 체적함수비 변화에 대한 측정센서의 측정 정밀도 향상과 이를 통해 국내 현장토에 대한 고유 보정기법을 제시하기 위함이다. 측정센서는 각 실험 조건별 물성 변화에 따라 전압을 측정함으로써 현장토에 대한 물성치와 상호 분석이 가능하도록 하였다. 주문진 표준사 뿐만 아니라 국내 현장토인 화강암 풍화토와 편마암 풍화토에 대한 체적함수비에 대한 보정식도 함께 제시하였다.

• Geotechnical Engineering
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• v.28 no.1
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• pp.39-44
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• 2011

TDR 함수량계는 전자기파를 이용하여 흙의 밀도와 함수비를 비파괴적으로 신속하게 평가하는 유망한 기술이다. TDR 시험법은 10~20cm 길이의 2~3개의 탐침을 지중에 관입시킨 후 전자기파의 이동시간을 측정하여 유전상수($K_a$)를 산정한다. 제안식을 이용하여 유전상수로부터 체적함수비(${\theta}$)의 산정이 가능하므로, 이 시험법은 흙의 함수비를 측정할 수 있는 비파괴시험 장치로 개발되어 활용되고 있다. 또한, 흙의 종류에 따른 보정상수가 파악되어 있는 경우에는 현장 밀도와 현장 함수비를 동시에 평가할 수 있으므로, TDR 함수량계를 이용하여 성토지만비나 노상토에 대한 신속하고 간편한 다짐관리가 기능하다.