• Journal of the Korean GEO-environmental Society
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• 제10권6호
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• pp.99-103
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• 2009

This research is the result of investigating engineering characteristics of slime generated during construction of deep mixing method. Mechanical characteristics of slime have been studied through literature review and laboratory tests of unconfined compression test, permeability test and settling tests were performed. As result of field observation of slime being generated, slime started to be produced right after flight auger was penetrated into a ground and its amount was increased in progress. Unconfined compressive strength of specimen with slime obtained from in field was measured in the range of $929.7{\sim}3,509.8kN/m^2$ and the value of unconfined compressive strength was found to be changed significantly with mixing ratio of soil, cement and binder. Permeability of them was measured in the range of $4.53{\times}10^{-7}{\sim}6.62{\times}10^{-6}cm/sec$ so that the mixture was appropriate as a impervious barrier. It was also know that the value of permeability was changed with the mixing ratio of binder. As test results of solidifying slime specimen prepared in the laboratory, good quality of cement mixture with coarse soil of sand were produced, compared with fine soils of silt and clay.

• Journal of the Korean GEO-environmental Society
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• 제15권5호
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• pp.23-29
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• 2014

So far, the grouting using pressure injection has been extensively used to avoid adverse effects such as soil disturbance. Whereas, the pressure injection to the limitations of the diffusion range, so that the kinks would last injection of cement particles by introducing a frequency oscillation effect improved injection method have been recently developed. In this study, a pilot test was performed to compare injection effects of the both methods. The injections using both methods were tested on the embankment which consists of core clay and weathered soil. Subsequently, the injected volume, SPT N values, in-situ permeability and electrical resistivity were measured to compare their effects. The vibration method showed more effective permeation comparing with the pressure method. Also, it showed more homogeneously improved ground than the existing method. For SPT results, the vibration method presented increase of mean N value as much as 17.4 % comparing with the conventional method. Higher electrical resistivity was presented in case of injecting with vibration method and it indicated the injection was extensively completed. Finally, it is expected that the economic feasibility will be improved by decrease of drilling spacing, when the existing method is replaced with vibration method.

• Journal of the Korean Geotechnical Society
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• 제35권10호
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• pp.33-45
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• 2019

In this study, in order to recycle a large amount of rocks and weathered mudstones produced by civil engineering projects such as railways and highways, as materials for roadbeds or embankment materials, circumferential specimens with a diameter of 5 cm and a height of 10 cm were made. A mudstone that weathered rapidly during rainfall was collected from Pohang construction sites. The weathered mudstone passed through a 2 mm sieve. It was prepared with the cement ratio, the sand ratio, curing condition and curing days. Three specimens were prepared according to each condition and then the unconfined compressive test, durability test and SEM analysis were performed to evaluate the engineering properties of the cemented soil. In the case of 28 days cured specimen, the strength of under-water cured specimens was 32-55% and the durability index was about 15% higher than air cured specimens. In addition, when the CR increased from 8% to 16%, the unconfined compressive strength (UCS) of pure mudstone cemented soil under water increased by about 1.6 times and the durability index increased by about 1.9 times. When the SR increased from 0% to 50%, the UCS of the specimen with SR = 10% was slightly less than or equal to specimen with SR = 0%. Then, as the SR became 30-50%, the UCS increased up to 51%. Unlike the UCS, the durability index increased continuously as the SR increased. As a result of SEM analysis, when SR was 50% rather than SR = 0%, the contact between sand particles increased and they were connected to each other. Such contact between these particles resulted in the increase of strength.

• Journal of the Korean Geotechnical Society
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• 제23권7호
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• pp.57-64
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• 2007

This study proposes a method to estimate drilling torque during ground boring with an aid of electrical energy required for rotating a boring-auger. Ground boring is commonly used in geotechnical engineering such as preboring precast pile installation, soil-cement grouting, ground exploration and so forth. In order to understand the correlation between required electrical energy to rotate the boring auger and the drilling torque, a small laboratory apparatus was designed and a pilot study was performed. The apparatus rotates common drill bits of $D=5{\sim}25mm$ in CBR specimens. The velocity of a bit is 19 RPM and predefined using a reduction gear which connects a main rotation axis to a 25 Watts AC electrical motor shaft. In the middle of drilling the motor current increments and the drilling torque were measured and the correlation between the current and the torque was obtained through linear square fits. Based on the correlation the acquired motor current during drilling was applied to predict the drilling torque in consequent testing and the prediction results were compared to the measured torque. The comparison leads a conclusion that the motor current during drilling using electrical power may be a good indicator to estimate/determine strength characteristics of the ground.

• Journal of the Korean GEO-environmental Society
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• 제18권5호
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• pp.27-33
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• 2017

In this research, laboratory tests were carried out to investigate the engineering properties of Light-Weight Air Foamed Soil (LWAS) based on silty clays with the animal foaming agent and cement. LWAS has been used as an embankment material over soft ground for road and side extension of the existing road. In field, unit weight and flow value is measured right after producing in mixing plant in order to control the quality of LWAS, and laboratory tests are carried out to confirm the quality through compressive strength of LWAS as well. In this research, direct estimation of the specification requirement of strength using flow values in field is the main purpose of the study together with other characteristics. From the test results, it can be seen that flow values increase with the initial water content and unit weight increases with the depth due to material segregation. Compared to the upper specimen, lower end of 60 cm specimen shows about 2 times higher compressive strength. Relationship between flow values and normalized factor presented by Yoon & Kim (2004) was presented. With that relationship, compressive strength can be predicted from flow values in field. From the relationship, the normalized factor was calculated. Thereafter calculated compressive strengths according to the flow values were compared to measured strengths in the laboratory. The higher the initial water content of the dredged soil has, the better relationship between predicted and measured shows. Therefore it is necessary to predict the compressive strength in advance through the relationship between the flow value and the normalized factor to reflect it in the design stage.

• Journal of Appropriate Technology
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• 제6권2호
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• pp.115-125
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• 2020

Housing issues such as mushrooming slums remain as chronic in most developing countries. Due to the state's restrained capacity, the housing-vulnerable's self-help approaches have been increasingly inevitable and vital for addressing the housing issues. However, there are still two challenges: securing good quality with economic efficiency, and climate change mitigation and adaptation. This study aims at doing an architectural experiment by developing and educating the production of eco-friendly interlocking stabilized soil bricks (ISSB) by employing vernacular materials and technologies for housing-vulnerable communities in Indonesia. In collaboration with a local architectural NGO, the study features a co-creation workshop in which 40 evicted households participate in the whole process. Soil analysis, mixed design, compression tests, and economic analysis are carried out. This paper illustrates that ISSB also has a high potential as an alternative to a burned brick or a cement block. The application of ISSB to self-help housing is expected to have socioeconomic and environmental effects, thereby facilitating the housing-vulnerable's self-help approaches and contributing to addressing the housing challenges in Indonesia.

• Journal of the Korean GEO-environmental Society
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• 제18권2호
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• pp.39-45
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• 2017

This paper is to grasp the applicability of a cumulative rebound angle measured from the rebound action generated after impacting an object for the assessment of compressive strength of construction materials nondestructively and to propose the test results. For this study, an impact device was devised and used for impacting an object by an initial rotating free falling impact and following repetitive impacts from the rebound action which eventually disappears. Five types of construction materials, which are soil cement, cement paste, wood (pine tree), and two types of rock (shale and granite), were tested and both peak rebound angle and cumulative rebound angle were measured for each material by using a high-speed camera. The measured angles were compared with the directly measured compressive strength for each material. The comparison showed that for materials such as cement and rock the cumulative rebound angle, which reflects energy dissipation, rather than the peak rebound angle is more appropriate indicator for assessing the compressive strength of a material, but for a construction material such as wood which has a high toughness the magnitude of rebound is not an indicator to assess the compressive strength of a material.

• Journal of the Korean Society for Railway
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• 제17권4호
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• pp.251-259
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• 2014

The transition zone between an earthwork and a bridge effect to the vehicle's running stability because support stiffness of the roadbed is suddenly changed. The design criteria for the transition structure on ballast track were not particular in the past. However with the introduction of concrete track is introduced, it requires there is a higher performance level required because of maintenance and running stability. In this present paper, a transition structure reinforced with geosynthetics is suggested to improve the performance of existing bridge-earthwork transition structures. The suggested transition structure, in which there is reinforcing of the approach block using high-tension geosynthetics, has a structure similar to that of earth reinforced abutments. The utilized backfill materials are cement treated soil and gravel. These materials are used to reduce water intrusion into the approach block and to increase the recycling of surplus earth materials. An experiment was performed under the same conditions in order to allow a comparison of this new structure with the existing transition structure. Evaluation items are elastic displacement, cumulative settlement, and earth pressure. As for the results of the real-scale accelerated testing, the suggested transition structure has excellent performance for the reduction of earth pressure and settlement. Above all, it has high resistance the variation of the water content.

• Journal of the Korean Geotechnical Society
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• 제24권1호
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• pp.37-49
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• 2008

A geothermal heat pump system is a preferable alternative energy system in Korea because it uses the heat energy of the earth, which is environmentally friendly and inexhaustible. In order to characterize the thermal conductivity and viscosity of grout materials used for backfilling ground heat exchangers, nine bentonite grouts, one marine clay from Boryung, and cement grouts adapted in the United State have been considered in this study. The bentonite grouts indicate that the thermal conductivity and viscosity increase with the content of bentonite or filler (silica sand). In addition, material segregation can be observed when the viscosity of grout is relatively low. The marine clay turns out to be unsuitable for backfilling the ground heat exchanger due to its insufficient swelling potential. The saturated cement grouts appear to possess much higher thermal conductivity than the saturated bentonite grouts, and the reduction of thermal conductivity in the cement grouts after drying specimens is less than that in the case of the bentonite grouts. Maintaining the moisture content of grouts is a crucial factor in enhancing the efficiency of ground heat exchangers.

• Journal of Soil and Groundwater Environment
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• 제18권1호
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• pp.102-111
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• 2013

A novel MgO-based binder was developed and applied to treat the anoxic sediment that was collected from Seonakdong river, Korea and was contaminated with heavy metals. The treated sediment was evaluated by measuring compressive strength, expansion, leaching of heavy metals and storage characteristics for $CO_2$. Initially, an optimal blending ratio of lime (L)/fly ash (FA)/blast furnace slag (BFS) that was to be mixed with MgO was screened to be $L_{0.3}-FA_{0.1}-BFS_{0.6}$. Long-term strengths of the sediments that were treated by various mixtures of MgO and $L_{0.3}-FA_{0.1}-BFS_{0.6}$ were then evaluated and the blending ratios between 4 : 6 and 6 : 4 were found optimal, which yielded a compressive strength of 4.09 MPa. On this basis, the optimal MgO-based binder was selected to be a 5 : 5 mixture of MgO and $L_{0.3}-FA_{0.1}-BFS_{0.6}$. The good performance of the MgO-based binder was believed to be due to the formation of Mg $(OH)_2$, which filled the micropores and also increased the density of the solidified matrices. The MgO-based binder exhibited an average stabilizing capacities for heavy metals of 92.9%, which was similar to or higher than that of Portland cement. It was found that 69.1 kg of carbon dioxide could be sequestrated after 365 days of curing when treating a ton of anoxic sediments.