Jumunjin Sand Research Articles

Experimental Investigation of Evaporation and Drainage in Wettable and Water-Repellent Sands

This study presents experimental results on evaporation and drainage in both wettable and water-repellent sands whose surface wettability was artificially modified by silanization. The 2D optical and 3D X-ray computed tomographic imaging was performed during evaporation and the water retention during cyclic drainage and infiltration was measured to assess effects of wettability and initial wetting conditions. The evaporation gradually induces its front at the early stage advance regardless of the wettability and sand types, while its rate becomes higher in water-repellent Ottawa sand than the wettable one. Jumunjin sand which has a smaller particle size and irregular particle shape than Ottawa sand exhibits a similar evaporation rate independent of wettability. Water-repellent sand can facilitate the evaporation when both wettable and water-repellent sands are naturally in contact with each other. The 3D X-ray imaging reveals that the hydraulically connected water films in wettable sands facilitate the propagation of the evaporation front into the soil such that the drying front deeply advances into the soil. For cyclic drainage-infiltration testing, the evolution of water retention is similar in both wettable and water-repellent sands when both are initially wet. However, when conditions are initially dry, water-repellent sands exhibit low residual saturation values. The experimental observations made from this study propose that the surface wettability may not be a sole factor while the degree of water-repellency, type of sands, and initial wetting condition are predominant when assessing evaporation and drainage behaviors.

Effects of temperature compensation on electrical resistivity during subsurface characterization

Electrical resistivity has been used to estimate the spatial variability of subsurface soil. The objective of this study is to evaluate the effects of temperature on electrical resistivity to create more accurate subsurface characterization using a temperature-compensated resistivity probe (TRP). The TRP consists of a two-electrode electrical resistivity module and temperature sensors, which are used to monitor temperature changes and the compensation of electrical resistivity that occurs due to temperature changes. Temperature transfer probes with diameters of 5 and 10 mm are developed to measure temperature changes during the penetration of probes into sandy soils. The temperature sensors are attached 15 mm behind the probe tips to minimize electrical interference with the electrical resistance measurement component of the TRP. Laboratory application tests are conducted in an acrylic cell containing uniform Jumunjin sand, and field application tests are conducted in loose silty clay and sand in the Kimpo area near Seoul. The test results show that the temperature changes continuously during probe penetration in both the laboratory and field tests, and electrical resistivity is over- or under-estimated when temperature compensation is not considered. This study demonstrates that temperature changes should be accounted to improve the accuracy of electrical resistivity measurement and the quality of subsurface characterization.

낮은 구속응력에 대한 주문진 표준사의 강도 및 변형 특성

매우 낮은 구속응력에서의 모래의 전단강도 및 변형특성은 상대적으로 높은 구속응력의 경우와 매우 상이한 분포를 나타낸다. 따라서 낮은 응력상태를 보이는 지반 위에 놓인 얕은 기초와 제방 등의 안정성, 토석류 혹은 얕은 파괴의 안정성 검토와 실내에서 시행하는 각종 모델시험의 경우 이에 대하여 명확히 규명할 필요가 있다. 본 연구에서는 건조된 주문진 표준사를 대상으로 구속응력을 5kPa~300kPa로 하여 배수 삼축시험을 실시하였으며, 그 결과 내부마찰각(<TEX>${\phi}$</TEX>) 및 변형계수(<TEX>$E_s$</TEX>)가 구속응력(<TEX>${\sigma}{_c}^{\prime}$</TEX>)에 따라 크게 변하는 것을 확인하였으며, 이에 따라 구속응력에 대한 조밀 및 느슨한 모래의 내부마찰각과 변형계수의 상관관계식을 제안하였다. The shear strength and deformation characteristics of granular soils at low confining stresses differ from those with high confining stresses. Thus, the clear understanding of geotechnical problems related to the low confining stress state such as the stability of shallow foundations, embankments, slope failure, debris flow characteristics and liquefaction as well as the various laboratory model tests is needed. In this study, drained triaxial compression tests with the cell pressures from 5 kPa to 300 kPa were performed on dry Jumunjin sand. The results show that the internal friction angle and deformation modulus are dependent on the confining stress. Also, the correlations between them on the dense and loose sand were established.

Using inverse analysis to estimate hydraulic properties of unsaturated sand from one-dimensional outflow experiments

A one-dimensional (1-D) vertical draining test for Jumunjin sand was carried out in one-step and multi-step outflow conditions. An inverse analysis method was conducted to determine the hydraulic properties of unsaturated soil. A non-linear optimization method combining a finite element code and inversion analysis was used to minimize the objective function, defined by the difference between observed and predicted data. Unsaturated hydraulic parameters in van Genuchten model were estimated using soil suction measurements in 10cm intervals and an outflow rate at the bottom of a sand column. The predicted hydraulic properties and the experimental results were in close agreement when the measurements were compared from the one-step and multi-step outflow experiments. The results also showed that the multi-step outflow experiment was more appropriate in determining the unsaturated hydraulic properties than the one-step outflow experiment. The comparison between predicted and measured results concluded that the inverse analysis based on the 1-D outflow experiment was reliable and useful to determine the hydraulic properties of unsaturated soils.

Modified Cyclic Shear Test for Evaluating Disturbance Function and Numerical Formulation of Geosynthetic–Soil Interface Considering Chemical Effect

Abstract Geosynthetics have been broadly used in waste landfill sites for filtration, drainage, and separation. Geosynthetics contact soil directly, creating a geosynthetic–soil interface corresponding to the external forces and conditions. The differences in the intrinsic material characteristics at the interface induce complicated stress–strain behaviors and strain-softening processes. Recent studies have presented the behaviors of geosynthetic–soil systems as depending on the interface shear strength degradation, which is affected by ambient factors such as the water content, chemical condition, etc. In this study, the disturbed state concept (DSC) and a disturbance function are introduced to explain the cyclic shear stress behavior of the interface. The degree of interface damage can be expressed by the disturbance function, and the shape of the disturbance function curve represents the intrinsic characteristics of the material. Massive sets of cyclic shear tests have been performed to investigate the effects of the pH values of leachates on the shear behavior of the geosynthetic–soil interface. Both geosynthetics and Jumunjin sand have been submerged in acid, neutral, and basic solutions for 200 days. A multi-purpose interface apparatus that can simulate the cyclic shear conditions of a geosynthetic–soil interface has been newly manufactured and modified for better performance. Test results display remarkable distinction in chemical degradation trends according to the pH values. New disturbance function parameters that determine the characteristics of the shear strength of the interface were estimated according to the chemical conditions as well. Furthermore, it was discovered via focused ion beam electronic microscopy that the different patterns of damage on the surface of soil particles with different pH values induce variation in the disturbance phase at the geosynthetic–soil interface. For the numerical formulation of the disturbance function, the constitutive equations of the DSC were modified using the Mohr–Coulomb model. Based on the modified DSC equations, verification and numerical implementation shall be performed for further study.

평균 모세관압과 네트워크 모델을 이용한 불포화토의 유효 열전도도 산정에 관한 연구

Thermal conduction of the particulate composites or granular materials can be widely used in porous materials and geotechnical engineering. And it has continued to develop thermal of medium by modeling energy relationship among particles in medium. This study focuses on the development of the effective thermal conductivity at the unsaturated conditions of soils using the modified network model approach assisted by synthetic 3D random packed systems (DEM method, Discrete Element Method) at the particle scale. To verify the network model, three kinds of glass beads and the Jumunjin sand are used to obtain experimental values at various unsaturated conditions. The PPE (Pressure Plate Extractor) test is then performed to obtain SWCC (Soil-Water Characteristic Curve) of soil samples. In the modified network model, SWCC is used to adjust the equivalent radius of thermal cylinder at contact area between particles. And cutoff range parameter to define the effective zone is also adjusted according to the SWCC at given conditions. From a series of laboratory tests and the proposed network model, the modified network model which adopts a SWCC shows a good agreement in modeling thermal conductivity of granular soils at given conditions. And an empirical correlation between the fraction of the mean radius () and thermal conductivity at given saturated condition is provided, which can be used to expect thermal conductivity of the granular soils, to estimate thermal conductivity of granular soils.

동결 온도와 재하속도에 따른 동결토의 일축압축 및 쪼갬인장 강도특성

Recently the world has been suffering from difficulties related to the demand and supply of energy due to the democratic movements sweeping across the Middle East. Consequently, many have turned their attention to never-developed extreme regions such as the polar lands or deep sea, which contain many underground resources. This research investigated the strength and initial elastic modulus values of eternally frozen ground through a uniaxial compression test and indirect tensile test using frozen artificial soil specimens. To ensure accurate test results, a sandymud mixture of standard Jumunjin sand and kaolinite (20% in weight) was used for the specimens in these laboratory tests. Specimen were prepared by varying the water content ratio (7%, 15%, and 20%). Then, the variation in the strength value, depending on the water content, was observed. This research also established three kinds of environments under freezing temperatures of <TEX>$-5^{\circ}C$</TEX>, <TEX>$-10^{\circ}C$</TEX>, and <TEX>$-15^{\circ}C$</TEX>. Then, the variation in the strength value was observed, depending on the freezing environment. In addition, the tests divided the loading rate into 6 phases and observed the variation in the stress-strain ratio, depending on the loading rate. The test data showed that a lower freezing temperature resulted in a larger strength value. An increase in the ice content in the specimen with the increase in the water content ratio influenced the strength value of the specimen. A faster load rate had a greater influence on the uniaxial compression and indirect tensile strengths of a frozen specimen and produced a different strength engineering property through the initial tangential modulus of elasticity. Finally, the long-term strength under a constant water content ratio and freezing temperature was checked by producing stress-strain ratio curves depending on the loading rate.

불포화토에서 흙의 구조가 흙-함수특성에 미치는 영향

본 연구에서는 토립자의 입경과 입도분포가 불포화토의 흙-수분특성에 미치는 영향을 검토하고자 하였다. 이를 위해 축이동기법이 적용된 시험장치를 이용하여 현장에서 채취한 새만금실트에 대해 함수특성시험을 실시하였다. 비교를 위해 주문진 표준사에 대해서도 시험을 실시하였다. 시험으로부터 측정된 모관흡수력과 체적함수비를 토대로 van Genuchten 모델에 대한 흙-함수특성곡선을 추정하였다. 추정된 함수특성곡선의 비교분석결과 포화체적함수비, 잔류체적함수비 그리고 공기함입치 모두 모래보다 실트에서 더 높게 나타났으며, van Genuchten 모델의 계수 <TEX>${\alpha}$</TEX>, <TEX>$n$</TEX>, <TEX>$m$</TEX> 모두 실트보다 모래에서 더 크게 나타났다. 이는 불포화토의 흙-함수특성곡선은 흙의 구조적 특성(간극크기, 형태, 분포)과 밀접한 관계를 가지며 상대적으로 입경이 크고 입도분포가 불량한(다시 말해, 간극크기가 크고 간극분포가 균등한) 조립토일수록 포화체적함수비, 잔류체적함수비, 그리고 공기함입치가 작고, 모관흡수력 변화에 따른 체적함수비의 변화율이 크며, 따라서 전이 영역의 범위가 좁게 나타나는 경향이 있다는 것을 보여준다. The purpose of this study is to determine the effect of soil grain size and its distribution on soil-water characteristic. To do this, soil-water characteristic tests were conducted on Saemangeum silt using the axis translation technique. For comparison, the test was also conducted on Jumunjin sand. Using the test results, the soil-water characteristic curves (SWCCs) of Saemangeum silt and Jumunjin sand were predicted by Van Genuchten model. By comparison and analysis between two SWCCs, the silt shows higher values of matric suction, water content, and air entry value than the sand. On the other hand, the sand has higher values of Van Genuchten model parameters of <TEX>${\alpha}$</TEX>, <TEX>$n$</TEX>, <TEX>$m$</TEX> than the silt. It indicates that the SWCC is significantly dependent on the structure of soils. In other words, if a soil has relatively high grain size and poor grain size distribution curve, the values of saturated volumetric water content, residual volumetric water content, and air entry value are small, and the variation of volumetric water content is high in accordance with the matric suction variation, and consequently it shows a narrow range of funicular region.

Partitioning tracer method for quantifying the residual saturation of refined petroleum products in saturated soil

The effective site assessment is crucial to the successful remediation of the subsurface contaminated with light nonaqueous phase liquids (LNAPLs). Recent studies showed that large spatial volumes of the subsurface contaminated with LNAPLs could be investigated with the partitioning tracer method. This study investigated the applicability of the partitioning tracer method for detecting and quantifying refined petroleum products in a saturated aquifer containing alluvial soil or weathered granite soil. In the batch-partitioning experiments, the partition coefficients of alcohol tracers between the petroleum mixture and water were measured, and they were found to be increased in proportion to the boiling points of the alcohol tracers when the molecular weights of the alcohol tracers were similar. The sorption isotherm experiments indicated that a considerable amount of 4-methyl-2-pentanol was sorbed into Jumunjin sand (JS) or weathered granite soil (WGS). In the column experiments, it was confirmed that the partitioning tracer method could be used as a method for detecting the presence of the petroleum mixture in saturated soil, and the residual saturation of the petroleum mixture in the soil column prepared by firstly contaminating with the petroleum mixture and secondly saturating with water was measured higher than that in the soil column prepared by firstly saturating and secondly contaminating. The highest accuracy of estimation using the partitioning tracer method was found for 2-ethyl-1-butanol and the lowest accuracy was found for 4-methyl-2-pentanol.

Shear Strength of Jumunjin Sand according to Relative Density

The properties of sands pertaining to shear strength have been studied extensively by plane strain and triaxial tests for relative densities above 40%. Unfortunately, properties of sand have not been comprehensively studied for relative density below 40%. An experimental investigation of the shear strength of Jumunjin sand was carried out using a plane strain, triaxial and direct shear apparatus according to relative density ranges from 0 to 100%. Because of the complexity of the shear tests on coarse materials, correlations were developed that would be useful for practical purposes. This article presents a comparison of strength properties' results and their correlation with relative density.