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Fernando Santos - One of the best experts on this subject based on the ideXlab platform.
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influence of Degree of Saturation in the electric resistivity hydraulic conductivity relationship
Surveys in Geophysics, 2009Co-Authors: Mohamed A Khalil, Fernando SantosAbstract:The relationship between aquifer hydraulic conductivity and aquifer resistivity, either measured on the ground surface by vertical electrical sounding (VES) or from resistivity logs, or measured in core samples have been published for different types of aquifers in different locations. Generally, these relationships are empirical and semi-empirical, and confined in few locations. This relation has a positive correlation in some studies and negative in others. So far, there is no potentially physical law controlling this relation, which is not completely understood. Electric current follows the path of least resistance, as does water. Within and around pores, the model of conduction of electricity is ionic and thus the resistivity of the medium is controlled more by porosity and water conductivity than by the resistivity of the rock matrix. Thus, at the pore level, the electrical path is similar to the hydraulic path and the resistivity should reflect hydraulic conductivity. We tried in this paper to study the effect of Degree of groundwater Saturation in the relation between hydraulic conductivity and bulk resistivity via a simple numerical analysis of Archie’s second law and a simplified Kozeny-Carmen equation. The study reached three characteristic non-linear relations between hydraulic conductivity and resistivity depending on the Degree of Saturation. These relations are: (1) An inverse power relation in fully saturated aquifers and when porosity equals water Saturation, (2) An inverse polynomial relation in unsaturated aquifers, when water Saturation is higher than 50%, higher than porosity, and (3) A direct polynomial relation in poorly saturated aquifers, when water Saturation is lower than 50%, lower than porosity. These results are supported by some field scale relationships.
Jong-sub Lee - One of the best experts on this subject based on the ideXlab platform.
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Variation in Characteristics of Elastic Waves in Frozen Soils According to Degree of Saturation
Journal of The Korean Society of Civil Engineers, 2013Co-Authors: Junghee Park, Mingu Kang, Jong-sub LeeAbstract:The strength of frozen soils is one of the significant design parameters for the construction in frozen ground. The properties of frozen soils should be investigated to understand the strength of frozen soils. The objective of this study is to figure out the characteristics of elastic waves in frozen soils, which reflect the constituent and physical structure of frozen soils in order to provide fundamental information of those according to the Degree of Saturation. Freezing cell is manufactured to freeze specimens, which are prepared with the Degree of Saturation of 10%, 40%, and 100%. Piezo disk elements are used as the compressional wave transducers and Bender elements are used as the shear wave transducers. While the temperature of specimens changes from 20℃ to -10℃, the velocities, resonant frequencies and amplitudes of the compressional and shear waves are investigated based on the elastic wave signatures. Experimental results reveal that the elastic wave velocities increase as the Degree of Saturation increases. The variation of resonant frequencies coincide with that of elastic wave velocities. A marked discrepancy in amplitudes of compressional and shear waves are observed at the temperature of 0℃. This study renders the basic information of elastic waves in frozen soils according the Degree of
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The Effect of Surface Tension on Shear Wave Velocities according to Changes of Temperature and Degree of Saturation
2012Co-Authors: Junghee Park, Mingu Kang, Sun-young Seo, Jong-sub LeeAbstract:The surface tension, which is generated in the unsaturated soils, increases the stiffness of the soils. The objective of this study is to estimate the effect of the surface tension, which varies according to the temperature, on the shear wave velocity. Nine specimens, which have the different Degree of Saturation (0%, 2.5%, 5%, 10%, 20%, 40%, 60%, 80%, 100%), are prepared by using sand-silt mixtures. Experiments are carried out in a nylon cell designed for the measurement of shear waves. A pair of bender elements, which are used for the generation and detection of shear waves, is installed as a cross-hole type. The shear waves are continuously monitored and measured as the temperature of specimens decreases from to . The results show that shear wave velocities of the fully saturated and fully dried specimens change a little bit as the temperatures of specimens decrease. However, the shear wave velocities of the specimens with the Degree of Saturations of 2.5%, 5%, 10%, 20%, 40%, 60% and 80% continuously increase as temperature decreases from to . Furthermore, a fully saturated specimen is dried at the temperature of in order to observe the shear waves according to Degree of Saturation. The shear wave velocities measured at the temperature of are generally lower than those measured at temperature of . This study demonstrates that the dependence of shear wave velocities on the temperature according to the Degree of Saturation should be taken into account in both laboratory and field tests.
Sahadat Hossain - One of the best experts on this subject based on the ideXlab platform.
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Quantification of Degree of Saturation at Shallow Depths of Earth Slopes Using Resistivity Imaging Technique
Journal of Geotechnical and Geoenvironmental Engineering, 2016Co-Authors: Golam Kibria, Sahadat HossainAbstract:AbstractEarthen slopes encountered in engineering practice typically consist of unsaturated or partially saturated soils. During rainfall, water infiltrates into the slope and causes a reduction in suction. Slope stability is affected by the increase in the Degree of Saturation as a result of the reduction in normal stress and cohesive strength along potential failure surfaces. Therefore, to determine the geohazard potential, it is important to know the Degree of Saturation within slopes at shallow depths. Resistivity imaging (RI) is one of the most convenient techniques available for geohazard studies; however, only qualitative Saturation profiles can be obtained using this method. Quantification of the Degree of Saturation has become important for using RI in the evaluation of the geohazard potential of slope failures. The objective of this study was to quantify the Degrees of Saturation at shallow depths using RI. Electrical resistivity tests were conducted in the laboratory on high plasticity clay (CH...
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Investigation of Degree of Saturation in landfill liners using electrical resistivity imaging.
Waste Management, 2015Co-Authors: Golam Kibria, Sahadat HossainAbstract:Abstract During construction of compacted clay liners and evapotranspiration (ET) covers, quality control involves laboratory and field tests in individual lifts. However, the available methods may be inadequate to determine non-uniform compaction conditions, poor bonding of lifts, and/or variable soil composition. Moreover, the applicability of the available methods is restricted, in many instances, when spatial variability of the subsurface is expected. Resistivity Imaging (RI) is a geophysical method employed to investigate a large area in a rapid and non-destructive way. High resistivity of clay liner soil is an indication of a low Degree of Saturation, high air-filled voids, and poor lift bonding. To utilize RI as a quality control tool in a landfill liner, it is important to determine the Saturation condition of the compacted soils because compaction and permeability of liner soil are functions of Degrees of Saturation. The objective of the present study is to evaluate the Degree of Saturation of a municipal solid waste (MSW) landfill liner, using RI. Electrical resistivity tests were performed in the laboratory, at varied moisture contents and dry unit weights, on four types of soil samples, i.e., highly plastic clay (CH), low plastic clay (CL), Ca-bentonite, and kaolinite. According to the experimental results, electrical resistivity of the specimens decreased as much as 15.3 times of initial value with increase in the Degrees of Saturation from 23% to 100%. In addition, cation exchange capacity (CEC) substantially affected resistivity. A multiple linear regression (MLR) model was developed to correlate electrical resistivity with Degree of Saturation and CEC using experimental results. Additionally, RI tests were conducted on compacted clay liners to determine the Degrees of Saturation, and predicted Degrees of Saturation were compared with the in-situ density tests. The study results indicated that the developed model can be utilized for liner soils having CEC, resistivity and Degrees of Saturation between 13.3 and 79 cmol +/kg, and 2.6 and 504.3 Ohm m, and 21.8% to 100%; respectively.
Tomoyuki Ikariya - One of the best experts on this subject based on the ideXlab platform.
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a new model for unsaturated soil using skeleton stress and Degree of Saturation as state variables
Soils and Foundations, 2011Co-Authors: Feng Zhang, Tomoyuki IkariyaAbstract:In this paper, based on experimental results a new constitutive model, using skeleton stress and Degree of Saturation as independent state variables, is proposed for unsaturated soil, in which the influence of the Degree of Saturation can be properly described. In the model, a very simple moisture characteristics curve considering moisture hysteresis of unsaturated soil is also proposed. The moisture characteristics curve can not only be applied to secondary drying process but also primary drying process originated from slurry soil. The constitutive model is able to describe not only the behavior of unsaturated soil but also saturated soil because the skeleton stress can smoothly shift to effective stress if Saturation changes from unsaturated condition to saturated condition. Meanwhile the overconsolidation, one of the main features of soils that are discussed in the models for saturated soils, is also considered together with the Degree of Saturation. Other mechanical features such as structure of soil and stress-induced anisotropy can be easily incorporated into the proposed model within the framework of the present research. It is known from the simulation that the main features of unsaturated soil in isotropic consolidation test and triaxial compression test under drained and exhausted condition with different confining stress and suction can be qualitatively described.
Tomoyoshi Nishimura - One of the best experts on this subject based on the ideXlab platform.
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influences of Degree of Saturation and strain rate on strength characteristics of unsaturated granular subbase course material
Transportation geotechnics, 2014Co-Authors: Yuan Zhang, Tatsuya Ishikawa, Tetsuya Tokoro, Tomoyoshi NishimuraAbstract:The aim of this study is to clarify strength characteristics of a subbase course material changed due to the Degree of Saturation and the strain rate. A series of monotonic triaxial compression tests was carried out under desired unsaturated and strain rate conditions using a medium-size triaxial compression apparatus. The test results indicate that the Degree of Saturation can significantly affect shear behaviors of the subbase course material in terms of the shear strength and deformability. On the other hand, the triaxial compression tests with the strain rate of 0.5%/min were conducted as well as those with 0.05%/min, which has been usually employed. The experimental results show that the mechanical behavior of the subbase course material is susceptible to the strain rate, and such relations can vary depending on the Degree of Saturation in shear. Furthermore, change in the strength parameters such as the total internal friction angle and the total cohesion resulting from the Degree of Saturation and the strain rate effects will be discussed. The calculation results show that the effects of Degree of Saturation and strain rate on the total internal friction angle appear to be negligible, while the total cohesion can be affected by the Degree of Saturation and the strain rate. More specifically, the failure envelope for the subbase course material is nonlinear under the low suction ranges. Therefore, the failure surface drawn through the failure envelope with respect to the matric suction is curved surface. The failure surface for unsaturated specimens with higher strain rate is located above that with lower strain rate.