• Journal of the Korean Geotechnical Society
• /
• v.28 no.3
• /
• pp.45-54
• /
• 2012

Various geosynthetics are widely applied to civil structures and waste landfill site for reinforcement and water resistance. The use of geosynthetics inevitably involves the coupled behaviors of different materials which include large displacement and strain-softening behaviors, etc. In this study, the effect of chemical element in the leachate on the interface shear strength under the cyclic loading condition was analyzed. The Multi-purpose Interface Apparatus (M-PIA) has been modified and cyclic direct shear tests have been performed. The submerging period of each specimen is 200 days. Additionally, the Field-Emission Scanning Electronic Microscopy (FIB) analysis has been also performed to induce the reason of the variation of disturbance function and verify the hypothesis on the decay-proof ability of geosynthetics. Consequently, the charateristics of chemical degradation of geosynthetic-soil interface are verified and the variation of the disturbance function is mainly caused by the different type of soil mineral decay, based on the FIB results.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.5
• /
• pp.125-139
• /
• 1999

It is difficult to evaluate the shear strength of weathered residual soils because of the difficulties of undisturbed sampling. In this study, a sampling device, direct shear box with shoe, was developed in order to get undisturbed samples easily for direct shear tests, and undisturbed samples could be successfully obtained. Through direct shear tests on undisturbed samples, the shear strength was evaluated with the variation of saturated conditions. In order to consider the effect of disturbance on the shear strength, a static compaction device was developed, and then it was found that undisturbed samples show greater shear strengths than the disturbed ones under natural water contents and similar strengths to the ones under soaked conditions. Further, the shear strength evaluated from direct shear tests was compared with the result of triaxial tests on undisturbed samples, and soaked strengths of the former were similar to the latter. As the result of stability analyses on an actual failed slope, it was found that the shear strength can be evaluated reasonably using direct shear box with shoe.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.6
• /
• pp.371-378
• /
• 2003

The compression index of clay distributed in the west and south coast of the Korean Peninsula had been studied. Compression index was obtained from the conventional consolidation test, and was conducted accordingly to obtain the field virgin compression curve by means of Schmertmann's graphical correction. To examine a correlation closely between physical properties of soils($e_o$, LL, w) and compression index(Cc), linen. and non-linear regression analysis were employed based on the data collected from tests. The conclusions are as follows. The compression index obtained by means of Schmereann's graphical correction is about 1.16 times for the value of original oedometer test curve for U/D samples. Non-liner regression curve was preferable to establish a correlation equation rather than linear regression curve. All derived equations so far achieved have been summarized and given. However, linear equation is better for practical use so that part by part simplified linear equations were also suggested alternatively together with their own non-linear regression curve.

• Journal of the Korean Geotechnical Society
• /
• v.18 no.5
• /
• pp.99-108
• /
• 2002

The nonlinear-brittle-plastic model derived from experiments as well as elastic and elasto-plastic models was applied to the analysis of the rock damaged zone around a highly stressed circular tunnel. The depths of stress redistribution and disturbed zone as well as the characteristic behaviors predicted from each numerical model were compared, As the magnitudes and stress differences of in situ stresses increased, influences of stress redistribution and stress disturbance on un(tiled region of rock mass also intensified. As a result, larger stress redistribution and disturbed zone as well as greater deviatoric stress and displacement were obtained by the nonlinear-brittle-plastic model rather than other conventional models such as elasto-plastic and elastic models. from such results, it was concluded that as the magnitudes and stress differences of in situ stresses increased, larger rock damaged zone might be predicted by the nonlinear-brittle-plastic model. Therefore, it is thought that the damage analysis may be indispensable far highly stressed tunnels.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.2
• /
• pp.45-54
• /
• 2009

The electrical characteristics of soils have been used for investigating soil properties. The purpose of this study is the development and application of the electrical resistivity cone probe (ERCP) for the evelation of the porosity in the field with high precision. The shape of the probe tip is a cone shape to minimize the disturbance during penetration. In addition, the four terminal pair configuration is adopted to minimize the electrical interference. The electrical resistances are continuously measured during penetration of the ERCP using penetration rigs with 0.33 mm/sec penetration rate at Incheon and Busan sites. With the measured resistance profile and electrical resisivity of electrolyte of undisturbed samples, soil porosity profiles are obtained by using Archie's law. The empirical coefficients for the Archie's law are obtained based on the electrolyte extracted from the undisturbed samples. The estimated porosity profiles show similar trends to those of in-situ penetration tests such as SPT, CPT, and DMT. This study suggests that the ERCP may be an effective tool for the porosity estimation in the field with minimum disturbance.

• Journal of the Korean Geosynthetics Society
• /
• v.4 no.3
• /
• pp.45-52
• /
• 2005

Most marine structures are constructed on very soft soil, soil improvements are needed for the area of road, buildings. In this paper, some considerations of several case studies on soil placement method after geotextile placement, known as surface treatment, are done. Considerations of strength applicability on the advanced construction method of sand and soil placement are proposed in this paper. Typical tensile strength of geotextile used in the surface soil stabilization method is 15t/m, and thickness of sand and soil placement between 1.6m and 3.1m. Undrained shear strength of soft clay layer ranges $0.2{\sim}1.2t/m^2$. In order to minimize the difficulties which include soil disturbance, soft soil gush and overturn of vertical drain installation rig more studies are needed.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.15 no.2
• /
• pp.127-137
• /
• 2003

The researches on the construction of artificial coastal wetlands have been progressed in order to cope with the situation that the area of Korean tidal flat has been reduced due to several coastal developments This study, as a part of the project on construction of the artificial tidal flats, deals with the comparison of the geotechnical characteristics between natural tidal flat and artificial tidal flat, and is also focused on the stability analysis of tidal flats. Various laboratory tests were performed using disturbed and undisturbed samples, which were obtained from a sandy tidal flat in Korea. The stability of the sandy soils accumulated on the tidal flat was investigated by comparing the shear strength of soil evaluated from laboratory test with induced shear stress due to both current and wave action.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2003.03a
• /
• pp.77-84
• /
• 2003

Deep excavations in the urban areas have been frequently going on in large scale. Soil-nailing and Earth-anchor supporting methods are generally used in deep excavation. These construction methods cause ground disturbances during drilling process, and damages of adjacent structures and ground due to the differential settlement throughout construction period, and unexpected behaviors of supporting system according to the characteristics of drilling machine and ground condition. This article introduces two actual examples of adjacent deep excavation for the construction of university buildings in granitic Seoul area. The important results of construction and measurements obtained using Crawler drilling machine for Soil-nailing and Earth-anchor supporting methods are summarized. And some suggestions are given to improve and develop the technique of design and construction in the deep excavation projects having similar ground condition and supporting method.

• Geotechnical Engineering
• /
• v.10 no.3
• /
• pp.33-40
• /
• 1994

The effects of smear and well resistance should be taken into account for the design of sand drains. Practically, simple design, which employs the method using 112 reduced diameter of drains or assuming the coefficient of consolidation in horizontal direction equals to that in vertical direction, based on the theory neglecting these effects, has been used. In this study, the reliability of existing simple design methods as well as the influences of smear and well resistance was investigated with the equations proposed by Hansbo and Onoue. It is shown that the consolidation time is chiefly governed by the effect of smear for drains with highly permeable sands. For general soil condition and placing type of sand drain, consolidation time is underestimated for simple design wi어. 1/2 reduced diameter of drains, and it is overestimated for that with the assumption that the coefficient of consolidation in horizontal direction equals to that in vertical direction. Through the investigations on different reduced diameter, it was shown that simple design with 1/4 reduced diameter of drains yielded the reliable results with errors less than 6%.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.42 no.4
• /
• pp.115-123
• /
• 2000

This study compared the degree of consolidation by hyperbolic, curve fitting , Asaoka's and methods using values measured with a theoretical curve in consideration of smear effect and well resistance. The degree of consolidation by the Hyperboilc method was underestimated than the degree of consolidation by Curve fitting. Asaoka's , and Monden's methods. The typical range of the coefficient of horizontal consolidation was Ch=(2-3)Cv in the case considering smear effect and well resistance, and Ch =(0.5-2.1) Cv in the case disregarding smear effect and well resistance. The degree of consolidation obtained by ground settlement monitoring was nearly the same value when the coefficient of smear zone permeability by back analysis was shown to be half that of in-situ and the diameter of the smear zone was shown to be double that of mandrel. By increasing the diameter reduction ratio of the drain, the time of consolidation was delayed. The effect of well resistance showed that the case of a small coefficient of permeability was much more than in the case of a large coefficient of permeability . It was recommended that when designing diameter reduction of a drain, well resistance should be considered.