• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.65-76
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• 2014

For soil improvement, sand mats or sand compaction piles are often constructed on soft marine clays. In such cases, some amounts of sand and clay are inevitably mixed. Sand or gravel often exists in the weathered soils near the slope surface. This research investigates the effect of mixing sand content on consistency limits and shear strength of clays. Firstly, sand was mixed with kaolinite or bentonite at 0, 9, 17, 23, 29, 33, 50% and then liquid and plastic limits were measured. Both plastic and liquid limits decreased as a sand content increased. The water content of clay-sand mixtures with different sand content increased by 10% or 20% step by step and then their undrained shear strength was measured using a portable vane shear device called Torvane. For all cases, undrained shear strength of clay-sand mixtures decreased rapidly until reaching a certain value. Their state changed from undrained to drained state gradually as the sand content increased, which caused their undrained shear strength to decrease. On the other hand, a series of direct shear tests were also conducted on such clay-sand mixtures to investigate the effect of sand content on cohesion and angle of internal friction. It was found from clay-sand mixtures that their cohesion decreased but angle of internal friction increased as the sand content increased.

• Journal of the Korean Society for Railway
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• v.16 no.5
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• pp.386-393
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• 2013

In this study, the so-called repeated plate load bearing test (RPBT) used to get $E_{v2}$ values in order to check the degree of compaction of subgrade, and to get design parameters for determining the thickness of the trackbed foundation, is investigated. The test procedure of the RPBT method is scrutinized in detail. $E_{v2}$ values obtained from the field were verified in order to check the reliability of the test data. The $E_{v2}$ values obtained from high-speed rail construction sites were compared to converted modulus values obtained from resonant column (RC) test results. For these tests, medium-size samples composed of the same soils from the field were used after analyzing stress and strain levels existing in the soil below the repeated loading plates. Finite element analyses, using the PLAXIS and ABAQUS programs, were performed in order to investigate the impact of the strain influence coefficient. This was done by getting newly computed $I_z$ to get the precise strain level predicted on the subgrade surface in the full track structure; under wheel loading. It was verified that it is necessary to use precise loading steps to construct nonlinear load-settlement curves from RPBT in order to get correct $E_{v2}$ values at the proper strain levels.

• International Journal of Highway Engineering
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• v.10 no.2
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• pp.1-13
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• 2008

This study presents a case study of condition evaluation of various asphalt pavement sections to estimate performance lives. The pavement surface conditions including cracking and rutting are first evaluated using a automatic pavement analyzer, ARAN. HPCI(Highway Pavement Condition Index) values are estimated using the pavement surface distress data. It is observed from the pavement distress survey that the major distress type of the sections is top-down cracking. The modulus value of each pavement layer is back-calculated from the defection data obtained from a FWD(Falling Weight Deflectometer) and compared with the laboratory measured dynamic modulus values. Remaining lives of the various pavement sections are estimated based on a mechanistic-empirical approach and AAHTO 1993 design guide. The structural capacities of the all pavement sections based on the two approaches are strong enough to maintain the pavement sections for the rest of design life. Since the major distress type is top-down cracking, the remaining lives of the pavement sections are estimated based on HPCI and existing performance database of highway pavements. To evaluate the causes of premature pavement distress, various material properties, such as air void, asphalt binder content, aggregate gradation, dynamic modulus and fatigue resistance, are measured from the field cores. It is impossible to accurately estimate the binder contents of field samples using the ignition method. It is concluded from the laboratory tests that the premature top down cracking is mainly due to insufficient compaction and inadequate aggregate gradation.

• Journal of the Korean GEO-environmental Society
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• v.16 no.11
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• pp.13-19
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• 2015

Construction materials using soil which is the most common material around us have many advantages, but their long-term durability and sensation of walking as pavements have problems. Therefore, they are used after compaction or mixed with various hardening agents such as lime and cement for strength enhancement. However, studies on the behavior of pavement materials mixed with environment-friendly hardening agents or admixtures to improve walking property are still insufficient. In this study, therefore, in order to evaluate the appropriate mixing ratio and field application characteristics of pavement materials using mixed soils with environment-friendly hardening agents and natural materials such as wood chips, mechanical tests were performed to evaluate the rational mixing ratios and the ball test was performed as an elasticity test to evaluate the field applicability. The results suggest that the content of wood chips should be selected at 1.5% or lower according to the purpose of the structure, and the hardening agent at 10~15%. The evaluation results for GB/SB coefficient ratio which indicates the walking property show that the appropriate mixing ratio of the hardening agent in terms of the sensation of walking is 15% of lower, but different mixing ratios should be chosen according to the proportion of wood chips.

• Journal of the Korean Geotechnical Society
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• v.29 no.10
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• pp.67-74
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• 2013

The objective of this study was to identify the effect of engineering properties on the resilient modulus ($M_r$) of cohesive soils as subgrade. Eight representative cohesive soils representing A-6, and A-7-6 soil types collected from road construction sites, were tested in the laboratory to determine their basic engineering properties. The laboratory tests for the engineering properties were Atterberg limits test, sieve analysis, hydrometer test, Standard Proctor compaction test, and unconfined compressive strength test. Resilient modulus test and unconfined compressive strength test were conducted on unsaturated cohesive soils at three different moisture contents (dry of optimum moisture content, optimum moisture content, and wet of optimum moisture content). The increase in moisture content considerably affected the decrease in the resilient modulus. The resilient modulus increased with an increase in maximum unconfined compressive strength, percent of clay, percent of silt and clay, liquid limit and plasticity index. The resilient modulus decreased with an increase in percent of sand.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.297-310
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• 2010

This study represents basic research into the utilization of mixed ash (fly ash and bottom ash) from the ash pond of the Taean Thermal Power Plant as a construction material. We conducted physical and mechanical experiments on the mixed ash and examined its engineering characteristics in terms of its use as a material for road landfill and structure backfill. We evaluated the physical and chemical characteristics of the ash by performing tests to determine specific gravity, maximum and minimum density, liquid limit and plastic limit, grain size distribution, composition (by X-ray diffraction), and loss on ignition. We also evaluated the mechanical characteristics by testing for permeability, compaction, CBR, and tri-axial compression. The experiments on the mixed ash yielded a specific gravity of 2.18-2.20, dry density of $9.38-13.32\;kN/m^3$, modified CBR of 16.5%-21%, permeability coefficient of 1.32 to $1.89-10^{-4}cm/sec$, and drained friction angle of $36.43^{\circ}-41.39^{\circ}$. The physical and mechanical properties of the mixed ash do not meet the quality standards stipulated for road landfill and structure backfill materials. Mixed ash with a high content of fly ash failed to meet some of the quality standards. Therefore, in order to utilize the mixed ash as a material for road landfill and structure backfill, it is necessary to improve its properties by mixing with bottom ash.

• Clinical and Experimental Reproductive Medicine
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• v.16 no.2
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• pp.139-146
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• 1989

The purpose of this study was to examine the qualitative variation of human fetal-cord sera (HCS) and to accept the sera in human lVF-ET program. One hundred and sixteenth RCS were tested with 1772 2-cell embryos of F1 (C57BL x CBA) virgin mice, Ten to sixteenth embryos were cultured in m-KRB medium with a aliquot of each serum (10%, v/v) or with bovine serum albumin(O.4%, w/v) as a control medium. Embryonic development were recorded at every 24hr for 4 days by such events as cellular compaction, cavitation, and hatching. In the control groups of eight assays, 98.1%(106/ 108) of 2-ce1l embryos developed above expanded blastocyst and the embryonic development was unified through the tests. But the developmental pattern in medium with each serum was various. Namely, the sera that supported development of 100% 2-cell embryos to above morula, early blastocyst, expanded blastocyst and hatching blastocyst was 45,7%(53/116) , 35.3%(41/116), 15.5%08/116.) and 6.9-%(8/116), respectively. And the sera that supported development of above 80% 2-cell embryos to the each embryonic stage was 92.2% (107/116), 83.6%(97/116), 63.8%(74/116) and 36.2%(42/116), respectively. Meanwhile two kinds of toxic pattern to the embryonic development were observed in some sera. The first pattern is that some sera arrested development of most embryos in pre- or post-stage of morula or blastocyst. The second pattern is that some sera promoted or arrested a part of embryos in the same dish. The ability of serum was depended on the batch of serum. Finally we could accept 69%(80/116) of the tested sera for human IVF-ET program. The base line for acceptance was the ability that supported above 80% 2-ce1l embryos to blastocyst. But some deterious sera were contained in this range. We cut off about 10% of the sera (83.6% , 97/116) that passed the baseline. This final percent of sera was similar to that of grade N of this study.

• Geomechanics and Engineering
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• v.13 no.2
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• pp.195-215
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• 2017

This paper proposes gob-side entry retaining by roof break and filling in thick-layer soft rock conditions based on the thick-layer soft rock roof strata migration law and the demand for non-pillar gob-side entry retaining projects. The functional expressions of main roof subsidence are derived for three break roof direction conditions: lateral deflection toward the roadway, lateral deflection toward the gob and vertically to the roof. These are derived according to the load-bearing boundary conditions of the main roadway roof stratum. It is concluded that the break roof angle is an important factor influencing the stability of gob-side entry retaining surrounding rock. This paper studies the stress distribution characteristics and plastic damage scope of gob-side entry retaining integrated coal seams, as well as the roof strata migration law and the supporting stability of caving structure filled on the break roof layer at the break roof angles of $-5^{\circ}$, $0^{\circ}$, $5^{\circ}$, $10^{\circ}$ and $15^{\circ}$ are studied. The simulation results of numerical analysis indicate that, the stress concentration and plastic damage scope to the sides of gob-side entry retaining integrated coal at the break roof angle of $5^{\circ}$ are reduced and shearing stress concentration of the caving filling body has been eliminated. The disturbance of coal mining to the roadway roof and loss of carrying capacity are mitigated. Field tests have been carried out on air-return roadway 5203 with the break roof angle of $5^{\circ}$. The monitoring indicates that the break roof filling section and compaction section are located at 0-45 m and 45-75 m behind the working face, respectively. The section from 75-100 m tends to be stable.

• Journal of the Korean GEO-environmental Society
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• v.10 no.2
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• pp.5-12
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• 2009

Soil samples from the King Sejong Station in Antarctic and Vladivostok were tested in the laboratory and specific gravity, compaction curve, grain size distribution were determined. The effect of temperature change on the thermal conductivity, unfrozen water content, compressive strength were investigated. In addition, the change of tensile strength with temperature of the soil from Vladivostok was measured. Samples for the compressive strength test and tensional strength test were prepared in a mould with a fixed volume to prevent swelling. Also the effects of temperature and water content change on those strength were compared. Results from the thermal conductivity test showed that thermal conductivity values for both soils was larger at temperatures below freezing than those above freezing. The unfrozen water content dropped rapidly within a temperature range of $0{\sim}-5^{\circ}C$ and then gradually decreased further $-20^{\circ}C$. Compressive strength test results showed various stress/deformation curves with a change in water content. Sandy soil of the King Sejong Station had a much larger strength than ice at an identical temperature, while clayey soil of Vladivostok had a smaller strength than ice in the initial stage, but showed a larger strength at temperatures belows $-15^{\circ}C$. Tensile strength tests revealed an increase in the strength with a decreasing temperature.

• Journal of Korean Society of Forest Science
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• v.84 no.2
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• pp.166-177
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• 1995

This study was carried out to discuss how soils in the area planned for a forest road construction can be mechanically tested and practically applied. For this, 16 soil test samples from 8 plots(2 samples per plot) were used. The major tests are focused on unit weight before and after cut, water content, liquid and plastic limits, sieve and hydrometer analysis etc. The total unit weight(${\rho}_t$) before and after cut are $1.69g/cm^3$ and $1.19g/cm^3$, respectively. Their water contents are 21.0% and 20.5%. The coefficient of uniformity U and coefficient of curvature C obtained from sieve and hydrometer analysis are 125 and 0.42, which mean generally not well graded. On the soil classification by USCS, SM(silty sand or silt-sand mixed soil)is a Key soil, but it seems to be not good for fill material. From the standard proctor test are resulted $1.40{\pm}0.065g/cm^3$ for the unit weight(${\rho}$) in the nature and $1.88{\pm}0.049g/cm^3$ for the optimum proctor unit weight(${\rho}pr$) each. With this to say, it is necessary more powerful compaction work at earth filling, with which this soil reachs enough the ${\rho}pr$, and more earth.