• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1854-1862
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• 2024

This study aims to investigate the strain-dependent-deformation property of Gyeongju bentonite buffer material. A series of unconfined compressive tests were performed with cylindrical specimens prepared at varying dry densities (𝜌_d = 1.58 g/cm³ to 1.74 g/cm³) using cold isostatic pressing technique. It is found that as 𝜌_d increase, the unconfined compressive strength (q_u), failure strain, and elastic modulus (E) of Gyeongju compacted bentonite (GCB) increases. Normalized elastic modulus (E_sec/E_max) degradation curves of GCB specimens are fitted using Ramberg-Osgood model and the elastic threshold strain (𝜀_e,th) is determined through the fitted curves. The strain-dependency of E and Poisson's ratio (v) of GCB were observed. E and v were measured constant below 𝜀_e,th of 0.14 %. Then, E decreases while v increases after exceeding the strain threshold. The E_sec/E_max degradation curves of GCB in this study suggests wider linear range and higher linearity than those of sedimentary clay in previous study. On top of that, the influence of 𝜌_d is observed on E_sec/E_max degradation curves of GCB, showing a slight increase in 𝜀_e,th with increase in 𝜌_d. Furthermore, an empirical model of q_u with 𝜌_d and a correlation model between q_u and E are proposed for Gyeongju bentonite buffer materials.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.4
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• pp.123-128
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• 2002

This study was performed to use fiber mixed soil which has clayey soil or sandy soil with fibrillated fiber or monofilament fiber on purpose of construction materials, filling materials, and back filling materials. In addition, this study was conducted to analyze strength properties and fiber reinforcing effect with fiber mixed soil by direct-shear test. In case of fibrillated fiber mixed soil, the more quantity of fiber was in both cohesive soil and sandy soil, the larger shear stress was in respective step of normal load. The respective mixed soil at 0.5% and 0.1% mixing ratio of monofilament fiber mixed soil showed maximum shear stress. According to unconfined compression or direct-shear test, making specimen of the monofilament fiber mixed soil, it is required to be careful and stable mixing method, while it is expected that monofilament fiber mixed soil doesn't increase strength.

• Geomechanics and Engineering
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• v.16 no.5
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• pp.559-567
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• 2018

Technological innovations in sustainable materials for soil improvement have attracted considerable interest due to energy crisis and environmental concerns in recent years. This study presents results of a comprehensive investigation on utilization of nanocarbons in reinforcement of a residual soil mixed with 0, 10 and 20% bentonite. Effects of adding proportionate quantities (0, 0.05, 0.075, 0.1 and 0.2%) of carbon nanotubes and carbon nanofibers to soil samples of different plasticities were evaluated. The investigation revealed that the inclusion of nanocarbons into the soil samples significantly improved unconfined compressive strength, Young's modulus and indirect tensile strength. It was observed that carbon nanofibers showed better performance as compared to carbon nanotubes. The nanosized diameter and high aspect ratio of nanocarbons make it possible to distribute the reinforcing materials on a much smaller scale and bridge the inter-particles voids. As a result, a better 'soil-reinforcing material' interaction is achieved and desired properties of the soil are improved at nanolevel.

• Journal of the Korean Geotechnical Society
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• v.34 no.7
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• pp.5-15
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• 2018

The unconfined compressive strength (UCS) test through coring is widely used to determine the reinforcement effect of the ground with grouting. However, the UCS test through coring can disturb the ground, is expensive and takes a lot of time to prepare the specimen. In this study, the factors affecting UCS of microfine cement grouted sand are evaluated and an empirical equation of UCS of microfine grouted sand is suggested. It is observed that UCS increases linearly until 28 days, however, the increasing rate of strength decreases sharply after that 28 days. The W/C ratio is dominant factor influencing UCS and UCS increases exponentially with the decrease of water/cement (W/C) ratio. Also, UCS increases linearly with increasing the relative density ranging from 30% to 70% and with decreasing median particle size. However, in case of W/C ratio=1 and K6 ($D_{50}=0.47mm$), UCS is lower than that of K4 ($D_{50}=1.08mm$) and K5 ($D_{50}=0.80mm$) due to filtration effect. Based on the experimental results, the empirical equation of UCS of microfine cement grouted sand can be expressed as the function of median particle size ($D_{50}$), porosity (n) and W/C ratio.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.309-317
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• 2002

The mechanical characteristics of Light-Weighted Foam Soil(LWFS) are investigated in this research. LWFS is composed of the dredged soil from offshore, cement and foam to reduce the unit-weight and increase compressive strength. For this purpose, the unconfined compression tests and triaxial compression tests are carried out on the prepared specimens of LWFS with various conditions such as initial water contents, cement contents, curing conditions and confining stresses. The test results of LWFS indicated that the stress-strain relationship and the compressive strength are strongly influenced by the cement contents rather than the intial water contents of the dredged soils. On the other hand, the stress-strain relationship from triaxial compression test has shown strain-softening behavior regardless of curing conditions. The stress-strain behavior for the various confining stress exhibited remarkable change at the boundary where the confining stress approached to the unconfined compression strength of LWFS. In order to obtain the ground improvement of the compressive strength above 200kPa, the required LWFS mixing ratio is found to be 100%~160% of the initial water contents of dredged soil and 6.6% of cement contents.

• Steel and Composite Structures
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• v.10 no.6
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• pp.501-516
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• 2010

This paper is aiming to study the performances of reinforced high-strength concrete (HSC) short columns confined with aramid fibre-reinforced polymer (AFRP) sheets. An experimental program, which involved 45 confined columns and nine unconfined columns, was carried out in this study. All the columns were circular in cross section and tested under axial compressive load. The considered parameters included the concrete strength, amount of AFRP layers, and ratio of hoop reinforcements. Based on the experimental results, a prediction model for the axial stress-strain curves of the confined columns was proposed. It was observed from the experiment that there was a great increment in the compressive strength of the columns when the amount of AFRP layers increases, similar as the ultimate strain. However, these increments were reduced as the concrete strength increasing. Comparisons with other existing prediction models present that the proposed model can provide more accurate predictions.

• Magazine of the Korean Society of Agricultural Engineers
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• v.22 no.3
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• pp.46-59
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• 1980

This study was conducted to obtain the most effective distribution of grain size and the optimum lime content for lime-soil stabilization. To achieve the aim, the change of consistency, the characteristics of compaction and unconfined compressive strength were tested by adding of 0, 4, 6, 8, 10 and 12 percent lime by weight for all soils adjusted by given ratios of sand to clay. The results obtained were as follows; 1. There was a tendency that the plasticity index of lime-soil mixture was decreased by increasing the amount of lime, whereas the liquid limit was varied irregularly and the plastic limit was increased. 2. With the addition of more lime, the optimum moisture content of lime-soil mixture was increased, and the maximum dry density was decreased. 3. The optimum lime content of lime-soil mixture was varied from soil to soil, and the less amount of small grain size, the less value of optimum lime content. 4. The optimum distribution of grain size for lime-soil mixture was in the soil, having the ratio of about 60 percent of cohesive clay and about 40 percent of sand by weight. 5. In the soil having fine grain size, the effect of curing appeared for long periods of time, whereas the increasing rate of unconfined compressive strength was great on the soil of coarse grain size in the earlier stage of curing period.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.02a
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• pp.84-95
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• 1999

Laboratory experiments were performed to evaluate the strength characteristics of solidified sandy soils by portland cement with mixing conditions. Factors considered in the experiments were the fine content(<#200, %), cement content(%) and water-cement ratio and unconfined compressive strength tests were performed on samples at 7 and 28 cured day. Results of tests showed that for a low cement content(7%∼10%) the fine content was very important while for a high cement content the water-cement ratio was very important. For 7%∼10% cement content, the optimum fine content which gained maximum strength was about 30%. But for 13% cement content, low fine content and water-cement ratio were more useful than others. In the multi regression analysis, significant equation was gained.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.303-311
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• 2009

In this study, weakly cemented sand was cured at air dry condition with different periods (3, 7, 14, 21, 28 days) and its unconfined compressive strength was evaluated. As a result, the strength of specimens with low cement ratios such as 4 and 8% increases until 7 days curing but, after 7 days, their strength continuously decreases. The strength of specimens with relatively high cement ratios such as 12 and 16% increases up to 7 days curing and then stays almost constant until 21 days. After 21 days curing, their strength suddenly dropped down, which is much lower than the strength of 3 days curing specimen. A cemented sand and gravel called CSG, which is highly permeable, could be exposed to repetitive drying and wetting conditions due to rainfall or groundwater table change during curing. In this study, the weakly cemented sand is exposed to repetitive drying and wetting and then its unconfined compressive strength was evaluated. As a result, the strength of a specimen with 27 days drying condition following 1 day wetting was at maximum 35% lower than the one cured under 28 days drying. The strength degradation due to wetting decreases as a cement ratio increases. However, the strength of a specimen with repetitive drying and wetting increases as the number of wetting increases until 3 cycles. After 3 cycles of drying and wetting, the rate of strength increase decreases due to an insufficient water for hydration or stays constant. If the sufficient water supply is provided to cemented sand during curing, the target or design strength increase can be achieved. Otherwise, the strength degradation due to wetting should be considered at the design stage.

• Journal of the Korean Geosynthetics Society
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• v.22 no.4
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• pp.35-42
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• 2023

This paper described the strength variation characteristics to evaluate the applicability of a reactive material that can absorb organic pollutants as an underground barrier. The Strength was evaluated by unconfined compression test. The test results showed that the strength of the reactive material according to the absorption of each pollutant was in the order of water > TCE > TPH. However, the strength of the reactive material absorbing TPH was greater than that of the case absorbing TCE, when the composition ratio of polynorbornene was 12% or less. The strength of the reaction material in contact with water continued to decrease as the polynorbornene composition ratio decreased. The strength of the reaction material in contact with TCE and TPH increased as the polynorbornene composition ratio decreased from 30% to 21%, and then decreased. In other words, the optimal composition ratio of the reactive material should be applied considering the strength due to contact with pollutants according to the stress conditions occurring in the ground.