• Geomechanics and Engineering
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• v.10 no.1
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• pp.21-35
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• 2016

Employing non-associated flow rule and Power-Law failure criterion, the failure mechanisms of tunnel roof in homogeneous and layered soils are studied in present analysis. From the viewpoint of energy, limit analysis upper bound theorem and variation principle are introduced to study the influence of dilatancy on the collapse mechanism of rectangular tunnel considering effects of supporting force and seepage force. Through calculation, the collapsing curve expressions of rectangular tunnel which are excavated in homogeneous soil and layered soils respectively are derived. The accuracy of this work is verified by comparing with the existing research results. The collapsing surface shapes with different dilatancy coefficients are draw out and the influence of dilatancy coefficient on possible collapsing range is analyzed. The results show that, in homogeneous soil, the potential collapsing range decreases with the decrease of the dilatancy coefficient. In layered soils, the total height and the width on the layered position of possible collapsing block increase and the width of the falling block on tunnel roof decrease when only the upper soil's dilatancy coefficient decrease. When only the lower soil's dilatancy coefficient decrease or both layers' dilatancy coefficients decrease, the range of the potential collapsing block reduces.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.665-672
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• 2002

In order to expand agricultural lands in the western and southern coasts of Korean Peninsula, coarse soils excavated from hillsides have been used as fill materials for reclamation. In order to tackle with the problems and to confirm availability, research on soil improvement involve mixing cement to the fine wet soils. Required undrained shear strength(c$\sub$u/) for fill material was analyzed to be 0.34∼1.2kg/$\textrm{cm}^2$. It has been known that when cement is added to high water content marine clay, its unconfined compression strength increased to 2kg/$\textrm{cm}^2$. Consolidation results show that pre-consolidation pressure increased to 1.8kg/$\textrm{cm}^2$ and 3.4kg/$\textrm{cm}^2$ with the addition of 3% and 5% of cement respectively. This result shows that low-height embankments could be constructed without significant compression. Since the effectiveness of improvement may be different site by site, the mix design for each site is necessary in order to optimize it. The process is first to determine aimed shear strength and then optimum mix ratio of cement after carrying out a series of tests.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.97-107
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• 2019

Based on the results of Han et al. (2016), in the failure zone ahead of the tunnel face it can be obviously identified that a shear failure band occurs in the lower part and a pressure arch happens at the upper part, which was often neglected in analyzing the face stability of shield tunnel. In order to better describe the collapse failure feature of the tunnel face, a new improved failure mechanism is proposed to evaluate the face stability of shield tunnel excavated in layered soils in the framework of limit analysis by using spatial discretization technique and linear interpolation method in this study. The developed failure mechanism is composed of two parts: i) the rotational failure mechanism denoting the shear failure band and ii) a uniformly distributed force denoting the pressure arch effect. Followed by the comparison between the results of critical face pressures provided by the developed model and those by the existing works, which indicates that the new developed failure mechanism provides comparatively reasonable results.

• Journal of the Korea Organic Resources Recycling Association
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• v.12 no.3
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• pp.76-85
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• 2004

Anaerobic decomposition of municipal solid waste (MSW) had potential adverse impacts such as the production of methane and long-term post closure on human health and the environment. It was demonstrated that aerobic degradation of MSW resulted in the reduction of a methane yield and the enhancement of stabilization of MSW. Excavated solid wastes were both aerobically and anaerobically treated in order to evaluate the effects of air injection on the stabilization of landfill site. The municipal solid waste (MSW) samples were excavated from a 10-year old landfill (operation period: 1991. 11~1994. 11), Jeonju, Korea. Excavated municipal solid wastes are primarily composed of soils and vinyl/plastics. For the two aerobic simulated lysimeters, the levels of $O_2$ ranged 1.6~23.1% and the levels of $CO_2$ ranged 1.5~15.1%, which confirmed the aerobic decomposition. Aeration did prevent methane formation. For the anaerobic simulated lysimeter, the $CO_2$ rose as $O_2$ was consumed and low levels of CH4 were produced. The pH levels ranged from 7.7 to 8.9 for anaerobic lysimeter and from 7.3 to 8.5 for aerobic lysimeters. As expected, aerobic treatment proved to enhance the removal of biodegradable materials in the excavated solid wastes when monitoring the concentration of BOD, COD, $NH_4-N$, and $NO_3-N$ in the leachate.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.6
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• pp.127-134
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• 2001

In order to expand agricultural lands in the western and southern coasts of Korean Peninsula, coarse soils excavated from hillsides have been used as fill materials for reclamation. In order to tackle with the problems and to confirm availability, research on soil improvement involve mixing cement to the fine wet soils. Required undrained shear strength$(C_u)$ for fill material was analysed to be 0.34~1.2 $kgf/cm^2$. It has been known that when cement is added to high water content marine clay its unconfined compression strength increased to 2 $kgf/cm^2$. Consolidation results show that pre-consolidation pressure increased to 1.8 $kgf/cm^2$and 3.4 $kgf/cm^2$ with the addition of 3% and 5% of cement respectively. This result shows that low-height embankments could be constructed without significant compression. Since the effectiveness of improvement may be different site by site, the mix design for each site is necessary in order to optimize it. The process is first to determine aimed shear strength and then optimum mix ratio of cement after carrying out a series of tests.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.139-143
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• 2008

Recently, detections of huge amount of wastes in the unsanitary landfills at a residential development sites were reported. Because the sites were the residential development sites, all landfilled wastes should be removed for the constructions. Therefore the way that the unsanitary landfills were excavated and then the wastes were sorted into three categories such as soils, noncombustibles, and combustibles was selected as the best method. Soils and noncombustibles could be recycled in the sites and combustibles could be compacted and be relandfilled in a smaller area.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.717-721
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• 2010

Soil volume conversion factors are used for estimation of an excavated the soil volume which will be removed or added in levelling the ground surface of a construction site. An accurate evaluation method will help us reduce a construction cost and time consuming. In this study, we performed the laboratory tests, including grain size measurement, water content, specific gravity, porosity, density and XRD tests, to suggest reliable soil volume conversion factors and weathering indices in field using nondestructive methods. The weathering index and soil volume conversion factor L are obtained for different types of soils. At results, the CIW index is the best method measuring the weathering index and the factor L is relative to natural porosity, void ratio, density and dry density.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.309-318
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• 1991

Analysis for landslides was studied in framework of Chungju dam right abutment, 6.5km northeast of Chungju city. $5.5{\times}10^6m^3$ landslide materials were excavated during dam construction for safety of the Chungju dam. Geology of study area is composed mainly of meta sediments such as dolomitic limestone, quartzite and schist which are dipping toward the Nam Han river. Scanline survey of discontinuities was performed for slope stability, resistivity exploration was performed for the evaluation of potential failure plane, and direct shear strength test of rocks and soils was performed for the effect on landslide. Monitoring systems of tiltmeter, tensiometer, ground water observation hole and level monument were installed during dam construction and interpreted for the evaluation of slope instability. Kinematic solution of the geological structure and evaluation using safety factor for slope may prove the failure of the slope.

• Journal of the Korean Society of Clothing and Textiles
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• v.30 no.7 s.155
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• pp.1160-1167
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• 2006

The most ideal textile conservation is to block oxygen and light from historical textiles. However it is not possible because historical textiles should be examined, cleaned, restored, and exhibited to find out its historical value. Most of excavated costumes were severely stained and soiled. They are dark yellowish brown in color. To reduce the extent and intensity of the staining and to recover the original color of gray fabrics, bleaching would be required. Conservation treatment was carried out on the 8 historical costumes which belonged to General Duk-Ryung Kim(1567-1596). Two of them do not hold the fabrics. They hold only cotton wool and a little piece of fabrics. Even though these costumes underwent the conservation treatment in 1979, they were stained and needed re-treatment. This time, they were dual-bleached using hydrogen peroxide and sodiumborohydride followed by wet cleaning to reduce the soils and stains. The treatments improved the appearance of costumes. Through the analysis of the trace of fabric, carbonized fabric fragment, and fabrics remained in other garments, we concluded the missing fabrics to be ramie or cotton. It is different result from the primary report concluded to be silk.

• Journal of the Korean Professional Engineers Association
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• v.1 no.1
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• pp.18-25
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• 1968

Higher yield in rice paddies is greatly dependent on adequately balanced and timely supply of water. A majority of rice paddy in Korea is generally irrigated by rainfall, but in many cases it has to be supplemented by artificial irrigation for optimum rice culture. Although the water requirement of rice plant is for higher Than that of athec crops, submerged condition of rice paddy is not Necessarily required. The moisture requirement of rice plant varies with its growing stages, and it is possible to increase the irrigation efficiency through reduction of water loss due to percolation in rice paddies. An experimental plots were set up by means of sandomized block design with three duplication; (a) All time submerged, (b) Economically controlled, and (c) Extremely controlled. Three different irrigation periods Were (a) Initial sage, (b) Inter-stage, and (c) Yast stage. The topsoil of the three plots were excavated to the depth of 30 cm and then compacted with clay of 6 cm thickness. There after, they were piled up with the excavated top soils, leveled and cored with clay of 6 cm thickness around footpath in order to prevent leakage. The results obtained from the experiments are as follows, 1. There is no difference among the three experiments plots in terms of physical and chemical conditions, soil properties, and other characteristics. 2. Culm length and ear length are not affected by different irrigation methods. 3. There is no difference in the mature rate and 1, 000 grain weight of rice for the three plots. 4. The control plot which was irrigated every three days shows an increased yield over the all the time submerged plot by 17.8 percent. 5. The clay lined plot whose water holding capacity was held 5 days long, needs only to be irrigated every 7 days. 6. The clay lined plot shows an increased yield over the untreated plot ; over all-the-time submerged plot by 18 percent ; extremely controlled plot by 18 percent, and economically controlled plot by 33 percent. 7. It may be saved in water requirement about one Thirds.