• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.131-139
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• 2012

The lateral reinforcements of concrete such as hoops and spiral bars are known to confine concrete to compensate the strength loss due to fire by reducing explosive spalling and improving the capacity of ductility. In this context, a study was conducted to investigate the residual mechanical properties of confined and unconfined concrete($f_{ck}$=60MPa) after a single thermal cycle at 300, 600, $800^{\circ}C$. The main parameters required to establish the stress-strain relationship are the peak stress, the elastic modulus, and the strain at peak stress. The knowledge of the residual mechanical properties of concrete is necessary whenever the thermally damaged structure is required to bear a significant share of the loads, even after a severe thermal accident. Based on the results obtained in this study, the residual stress of confined concrete under thermal damage is higher according to the level of confinement and the larger strain made it to have better ductility. The decreasing ratio of elastic modulus from the relationship of stress and strain was also smaller than that of unconfined concrete.

• International Journal of Highway Engineering
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• v.9 no.4
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• pp.171-184
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• 2007

Chemical admixture stabilization has been extensively used in both shallow and deep stabilization in order to improve inherent properties of the soil such as strength and deformation behavior. An increment in strength, a reduction in compressibility, an improvement of the swelling or squeezing characteristics and increasing the durability of soil are the main aims of the admixtures for soil stabilization. Recently, the various advanced cement stabilizer mixing technique was developed. Advanced cement stabilizer mixing technique is environmentally-friendly and has an excellent mixing property and outstanding mixing speed. In this study, to develop the rural road pavement technology using cement stabilizer, compaction and unconfined compression test were performed with various mixing ratio and two types of soil(clay and silty soil). And the freezing/thaw test and bending strength test performed to develop suitable cement stabilizer material for stabilization of rural road. Based on the test results, the liquid types of cement stabilizer material and silty soil mixture are most suitable for rural road construction and although the mixing ratio is low, cement stabilizer mixture is effective for durability of rural road surface layer.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.109-116
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• 2010

The Water glass grouting method has been applied frequently to penetration grouting in practice, but some problems, such as decrease of durability with the elapsed time and environmentally adverse effect, are raised recently. Hence, the Earth Natural Grouting method which uses micro cement and inorganic material is developed to overcomes those problems of the water glass grouting method, and is aimed for extensive ground injection bound. Volumetric strain test, syneresis test, unconfined compression test, triaxial permeability test, in-situ permeability test and heavy metal analysis were conducted to verify application of the ENG. As the result of tests, volumetric strain, syneresis and unconfined strength of the ENG were superior to those of the Water Glass SGR and ENG was proved to be impermeable. Also it is expected that the ENG would not have an effect on environmental pollution.

• Advances in Computational Design
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• v.5 no.1
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• pp.1-11
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• 2020

Soil is the fundamental element in the construction process. Soil problems affect the safety of the structures, even so the high quality of the structures and so, bad soil found the structures will affect the lifetime or even destroy the structures built on it. Therefore, the study of soil is an important step in the construction process and the investigation of the most effective characteristics of a special kind of soil (shale soil), i.e. Atterberg limits, swelling pressure, swelling potential and unconfined compression strength, are the most effective soil properties. A big projects will be constructed in new urban extension areas with expansive shale soils, like at Al-Kawamil and new Akhmim shale soils which associated with soil problems, treatment system should be used to ensure the stability of the soil under the structures foundations one of the most effective methods is by adding lime solution to the soil by specific quantities, which affect on the properties of the shale soil by decreasing the swelling and increasing the compressive strength of the treatment soils. Experimenting with the soil added to the lime, it was found that the addition of lime solution 6% improve c j the properties of the soil. The results of the tests showed the high effectiveness of using lime in the treatment of Al-Kawamil soil

• Geomechanics and Engineering
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• v.13 no.3
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• pp.459-474
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• 2017

To investigate the mechanical properties of Expanded Polystyrene (EPS) Beads Stabilized Lightweight Soil (EBSLS), Laboratory studies were conducted. Totally 20 sets of specimens according to the complete test design were prepared and tested with unconfined compressive test and consolidated drained triaxial test. Results showed that dry density of EBSLS ($0.67-1.62g/cm^3$) decreases dramatically with the increase of EPS beads volumetric content, while increase slightly with the increase of cement content. Unconfined compressive strength (10-2580 kPa) increases dramatically in parabolic relationship with the increase of cement content, while decreases with the increase of EPS beads volumetric content in hyperbolic relationship. Cohesion (31.1-257.5 kPa) increases with the increase of cement content because it is mainly caused by the bonding function of hydration products of cement. The more EPS beads volumetric content is, the less dramatically the increase is, which is a result of the cohesion between hydration products of cement and EPS beads is less than that between hydration products of cement and sand particles. Friction angle ($14.92-47.42^{\circ}$) decreases with the increase of EPS beads volumetric content, which is caused by the smoother surfaces of EPS beads than sand grains. The stress strain curves of EBSLS tend to be more softening with the increase of EPS beads content or the decrease of cement content. The shear contraction of EBSLS increases with the increase of $c_e$ or the decrease of $c_c$. The results provided quantitative relationships between physico-mechanical properties of EBSLS and material proportion, and design process for engineering application of EBSLS.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.6
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• pp.17-26
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• 2021

Greenhouses have been damaged due to the uplift pressure from strong wind, for which rebar piles are often installed near the greenhouse to resist the pressure. For the effective design of rebar piles, it is necessary to access the shear strength of soil on which the greenhouse is constructed. This study experimentally evaluates the shear strength of the soil beneath the greenhouse. Four soil samples were collected from four agricultural sites, and prepared for testing with 75, 80, 85, and 90% compaction rates. One-dimensional unconfined compression test (UC), consolidated-undrained triaxial test (CU), and resonant column test (RC) were performed for the evaluation of shear strength and shear modulus. Generally, the higher shear strength and modulus were observed with the higher compaction rates. In particular, the UC shear strength increases with the increase of #200 sieve passing rate. Resulting from the CU test, the sample with the most of coarse soil had the highest friction angle, but the variation is small among samples. Resulting from the CU and RC tests, the ratio of maximum shear modulus with the major principle stress at failure was the higher at the finer soil. The ratio was two to three times greater than the ratio from the standard sand. This indicates that the shear strength is lower for the fine soil than the coarse soil at the same shear modulus. The results of this study will be a useful resource for the estimation of the pull-out strength of the rebar pile against the uplift pressure.

• Geomechanics and Engineering
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• v.25 no.1
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• pp.41-48
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• 2021

In cold regions, the integrity of the infrastructures built on weak soils can be extensively damaged by weathering actions due to the cyclic freezing and thawing. This damage can be mitigated by exploiting soil stabilization techniques. Generally, ordinary Portland cement (OPC) is the most commonly used binding material for investigating the chemo-hydromechanical behavior. However, due to the environmental issue of OPC producing a significant amount of carbon dioxide emission, calcium sulfoaluminate (CSA) cement can be used as one of the eco-sustainable alternatives. Although recently several studies have examined the strength development of CSA treated sand, no research has been concerned about CSA cement-stabilized sand affected by cyclic freeze and thaw. This study aims to conduct a comprehensive laboratory work to assess the effect of the cyclic freeze-thaw action on strength and durability of CSA cement-treated sand. For this purpose, unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) tests were performed on the stabilized soil specimens cured for 7 and 14 days which are subjected to 0, 1, 3, 5, and 7 freeze-thaw cycles. The test results show that the strength and durability index of the samples decrease with the increase of the freeze-thaw cycles. The loss of the strength and durability considerably decreases for all soil samples subjected to the freeze-thaw cycles. Overall, the use of CSA as a stabilizer for sandy soils would be an eco-friendly option to achieve sufficient strength and durability against the freeze-thaw action in cold regions.

• Geomechanics and Engineering
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• v.17 no.4
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• pp.355-365
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• 2019

It is normal to observe the presence of numerous cracks in coal body. And it has significantly effective on the mechanical characteristics and realistic failure models of coal mass. Therefore, this paper is to investigate the influence of crack parameters on coal body by comprehensive using theoretical analysis, laboratory experiments and numerical simulation through prepared briquette specimens. Different from intact coal body possessing single peak in stress-strain curve, other specimens with crack angle can be illustrated to own double peaks. Moreover, the unconfined compressive strength (UCS) of specimens decreases and follow by increasing with the increase of crack angle. It seems to like a parabolic shape with an upward opening. And it can be demonstrated that the minimum UCS is obtained in crack angle $45^{\circ}$. In terms of failure types, it is interesting to note that there is a changing trend from tensile failure to tensile-shear mixing failure with tension dominant follow by shear dominant with the increase of crack angle. However, the changing characteristics of UCS and failure forms can be explained by elastic-plastic and fracture mechanics. Lastly, the results of numerical simulations are good consistent with the experimental results. It provides experimental and theoretical foundations to reveal fracture mechanism of coal body with non-penetrating single crack further.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.31-45
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• 2019

In this study the spatial variability of soils is substantiated physically and numerically by using random field theory. Heterogeneous samples are fabricated by combining nine homogeneous soil clusters that are assumed to be elements of an adopted random field. Homogeneous soils are prepared by mixing different percentages of kaolin and bentonite at water contents equivalent to their respective liquid limits. Comprehensive characteristic laboratory tests were carried out before embarking on direct shear experiments to deduce the basic correlations and properties of nine homogeneous soil clusters that serve to reconstitute the heterogeneous samples. The tests consist of Atterberg limits, and Oedometric and unconfined compression tests. The undrained shear strength of nine soil clusters were measured by the unconfined compression test data, and then correlations were made between the water content and the strength and stiffness of soil samples with different consistency limits. The direct shear strength of heterogeneous samples of different stochastic properties was then evaluated by physical and numerical modelling using FISH code programming in finite difference software of $FLAC^{3D}$. The results of the experimental and stochastic numerical analyses were then compared. The deviation of numerical simulations from direct shear load-displacement profiles taken from different sources were discussed, potential sources of error was introduced and elaborated. This study was primarily to explain the mathematical and physical procedures of sample preparation in stochastic soil mechanics. It can be extended to different problems and applications in geotechnical engineering discipline to take in to account the variability of strength and deformation parameters.

• Geomechanics and Engineering
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• v.17 no.5
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• pp.465-473
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• 2019

Biocementation due to the microbially induced calcium carbonate precipitation (MICP) process is a potential technique that can be used for soil improvement. However, the effect of biocementation may be affected by many factors, including nutrient concentration, bacterial strains, injection strategy, temperature, pH, and soil type. This study investigates mainly the effect of chemical concentration on the formation of calcium carbonate (e.g., quantity, size, and crystalline structure) and unconfined compressive strength (UCS) using different treatment time and chemical concentration in the biotreatment. Two chemical concentrations (0.5 and 1.0 M) and three different treatment times (2, 4, and 8 cycles) were studied. The effect of chemical concentrations on the treatment was also examined by making the total amount of chemicals injected to be the same, but using different times of treatment and chemical concentrations (8 cycles for 0.50 M and 4 cycles for 1.00 M). The UCS and CCC were measured and scanning electron microscopy (SEM) analysis was carried out. The SEM images revealed that the sizes of calcium carbonate crystals increased with an increase in chemical concentrations. The UCS values resulting from the treatments using low concentration were slightly greater than those from the treatments using high concentration, given the CCC to be more or less the same. This trend can be attributed to the size of the precipitated crystals, in which the cementation efficiency increases as the crystal size decreases, for a given CCC. Furthermore, in the high concentration treatment, two mineral types of calcium carbonate were precipitated, namely, calcite and amorphous calcium carbonate (ACC). As the crystal shape and morphology of ACC differ from those of calcite, the bonding provided by ACC can be weaker than that provided by calcite. As a result, the conditions of calcium carbonate were affected by test key factors and eventually, contributed to the UCS values.