• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.133-140
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• 1990

Th. mechanism of hydraulic fracturing in sandy soil is elucidated by investigating the relation among the hydrofracturing pressure($P{_f}^{\prime}$), the confinning pressure(${\sigma}_3^{\prime}$), the tensile strength of gelled sand(${\sigma}_t$), and the permeability of sand(k) through many injection tests on several kind of sand.

• Journal of the Korean GEO-environmental Society
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• v.6 no.4
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• pp.5-12
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• 2005

In this study, the geotechnical applicability of permeable barriers that could filter the leachate from a landfill was evaluated. Specimens were cast from sand, loess and bentonite according to the specific weight ratios of them. A series of experiments are performed to determine the unconfined compressive strength and permeability of various mixing ratio of bentonite, loess, and sand. From the laboratory test, optimum mixing ratio that satisfied the regulations of unconfined compressive strength($5kgf/cm^2$) and coefficient of permeability ($10^{-3}{\sim}10^{-4}cm/sec$) in landfill was found when the weight ratio of sand and loess was 8:2 with 2% of bentonite. Using the laboratory test data and in situ test results, the applicability of the wall will be tested for various conditions.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.497-505
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• 2019

Biocementation based on the microbially induced calcite precipitation (MICP) process is a novel soil improvement method. Biocement can improve significantly the properties of soils by binding soil particles to increase the shear strength or filling in the pores to reduce the permeability of soil. In this paper, results of triaxial consolidated undrained (CU) tests and constant shear drained (CSD) tests on biocemented Ottawa sand are presented. In the CU tests, the biocemented sand had more dilative behaviour by showing a higher stress-strain curves and faster pore pressure reducing trends as compared with their untreated counterparts. In the CSD tests, the stress ratio q/p' at which biocemented sand became unstable was higher than that for untreated sands, implying that the biocementation will improve the stability of sand to water infiltration or liquefaction.

• Geophysics and Geophysical Exploration
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• v.13 no.1
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• pp.80-87
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• 2010

This study was conducted to develop a reservoir modelling workflow to reproduce the heterogeneous distribution of effective permeability that impacts on the performance of SAGD (Steam Assisted Gravity Drainage), the in-situ bitumen recovery technique in the Athabasca Oil Sands. Lithologic facies distribution is the main cause of the heterogeneity in bitumen reservoirs in the study area. The target formation consists of sand with mudstone facies in a fluvial-to-estuary channel system, where the mudstone interrupts fluid flow and reduces effective permeability. In this study, the lithologic facies is classified into three classes having different characteristics of effective permeability, depending on the shapes of mudstones. The reservoir modelling workflow of this study consists of two main modules; facies modelling and permeability modelling. The facies modelling provides an identification of the three lithologic facies, using a stochastic approach, which mainly control the effective permeability. The permeability modelling populates mudstone volume fraction first, then transforms it into effective permeability. A series of flow simulations applied to mini-models of the lithologic facies obtains the transformation functions of the mudstone volume fraction into the effective permeability. Seismic data contribute to the facies modelling via providing prior probability of facies, which is incorporated in the facies models by geostatistical techniques. In particular, this study employs a probabilistic neural network utilising multiple seismic attributes in facies prediction that improves the prior probability of facies. The result of using the improved prior probability in facies modelling is compared to the conventional method using a single seismic attribute to demonstrate the improvement in the facies discrimination. Using P-wave velocity in combination with density in the multiple seismic attributes is the essence of the improved facies discrimination. This paper also discusses sand matrix porosity that makes P-wave velocity differ between the different facies in the study area, where the sand matrix porosity is uniquely evaluated using log-derived porosity, P-wave velocity and photographically-predicted mudstone volume.

• Journal of the Korean Geotechnical Society
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• v.32 no.5
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• pp.5-13
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• 2016

A calcium source is necessary for calcite precipitation within soil particles by microbial decomposition of urea and a calcium chloride is usually used. The harmful environmental impact of calcium chloride on road, ground and plants is severe. In this study, an eggshell with vinegar is investigated for an environmental-friendly calcium source. Urea-decomposing microorganism and eggshell or calcium chloride as a calcium source are mixed with Ottawa sand to precipitate calcite. Then, the cemented sand with calcite is tested for calcite precipitation, permeability and unconfined compressive strength. A specimen is prepared by loose Ottawa sand in a size of 5 cm in diameter and 10 cm in height. A urea solution with Sporosarcina pasteurii and two different calcium sources is injected into the specimen once a day for 30 days. Calcite precipitated at average of 7.2% on the specimen with eggshell as a calcium source, which was 1.2 times more than that with calcium chloride. The permeability of a specimen with eggshell was at average of 3.82E-5 cm/s, which was 7.7 times lower than that with calcium chloride. Unconfined compressive strength of a specimen with eggshell was at average of 387 kPa, which was 1.2 times higher than that with calcium chloride. As more calcite precipitated, the strength increased while the permeability decreased, regardless of calcium sources.

• Geomechanics and Engineering
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• v.36 no.4
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• pp.317-328
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• 2024

Adopting a rational engineering methodology for building structures on sandy-clay soil layers has become increasingly important since it is crucial when structures erected on them often face seismic and cyclic wave loads. Such loads can cause a reduction in the stiffness, strength, and stability of the structure, particularly under un-drained conditions. Hence, this study aims to investigate how the dynamic properties of sand-clay mixtures are affected by loading frequency and clay content. Cyclic triaxial tests were performed on a total of 36 samples, comprising pure sand with a relative density of 60% and sand with varying percentages of clay. The tests were conducted under confining pressures of 50 and 100 kPa, and the samples' dynamic behavior was analyzed at loading frequencies of 0.1, 1, and 4 Hz. The findings indicate that an increase in confining pressure leads to greater inter-particle interaction and a reduced void ratio, which results in an increase in the soil's shear modulus. An increase in the shear strength and confinement of the samples led to a decrease in energy dissipation and damping ratio. Changes in loading frequency showed that as the frequency increased, the damping ratio decreased, and the strength of the samples increased. Increasing the loading frequency not only reflects changes in frequency but also reduces the relative permeability and enhances the resistance of samples. An analysis of the dynamic properties of sand and sand-clay mixtures indicates that the introduction of clay to a sand sample reduces the shear modulus and permeability properties.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.852-857
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• 2009

Recently the centrifuge test has been used increasingly to clarify a problem of seepage in dam. However, one of the most difficult challenges in the testing is to conform permeability properties of model ground to the prototype. In order to resolve the problem, a few solutions, such as an increase of pore water viscosity and a regulation of water permeability, are suggested. Although the use of prototype materials is principles if a model test is carried out, the materials of similarity gradation is used in the centrifuge model test because of the nature of the model test for dam. Therefore, we choose the latter method for model ground materials. In this study, the permeability properties of soil-bentonite mixtures are studied through the permeation test using triaxial compaction test apparatus.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.109-119
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• 2017

In this research, it was investigated that whether the upper sand deposited in Nakdong River Estuary Delta region has the role of horizontal drains like sand mat. The results from tests for particle size distribution and permeability of the upper sand deposit did not meet completely the criteria for the horizontal drain material. Thus, numerical analysis has been conducted additionally. Numerical analyses of consolidation of soft soils with upper layer of sand deposit are conducted in both the sand mat with a thickness of 1m and the upper sand deposit with 1, 2, 3, and 4 m of thickness and their results are compared. As the results of numerical analysis, the upper sand deposit with a thickness of 2m or more may play the role of horizontal drains similar to a sand mat. If a PVD is installed, the ability of upper sand deposit as horizontal drains is increased. Form this study, it was concluded that the upper sand deposited in Nakdong River Estuary Delta has the role of horizontal drain.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.261-273
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• 1993

In order to study hydraulic properties and mechanical properties on unsaturated region, soil-water retention curve was obtained for suction plate method and pressure plate method, respectively. To investigate permeability of unsaturated soil and soil-water retention curve at the same time, unsaturated permeability tests using an improved Richard's method were performed on Joomoonjin Sand. These experimental results were compared with those by empirical equations. The relationship between air entry value and saturated permeability of filter was obtained for selecting a proper filter in unsaturated soil tests.

• Geomechanics and Engineering
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• v.17 no.3
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• pp.307-316
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• 2019

Dam deformation should be strictly controlled for the construction of 300 m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.