• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.15-20
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• 2016

The grouting method, which can be used to effectively improve small areas within a short amount of time, may have different injection effects depending on the ground conditions and the levels of a water table. In particular, for ground with a relatively large permeability, the strength of the ground and the water proof ability can decrease over time due to the leaching process. To solve this problem, a "self-healing smart grouting (SSG) method", which was designed to maintain the initial strength of the ground by minimizing the leaching process, was developed recently. In this study, uniaxial compression tests were carried out on SSG samples to understand the strength of SSG over curing time where two different curing temperatures have been applied for comparison. The uniaxial compression strength of SSG was further compared with the samples prepared using conventional methods (LW and SGR). The test results showed that the uniaxial compression strength of SSG was higher at both high and low curing temperatures compared to that of the samples prepared using conventional methods. The initial strength of SSG was also relatively higher.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.87-98
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• 1999

Consolidation settlements on soft clay are often greatly and potentially damaging to structures. Currently, large-scale projects are in planning or progressing in Korea. These structures will be constructed on both thick and soft clay layers, and so the accurate evaluation of magnitude of settlement is required at every step in design and construction. Especially, secondary compression may play an important role in consolidation settlements of soft clay. Generally, the magnitudes of secondary compression are evaluated by laboratory and in-situ consolidation tests. The empirical $C_a/C_c$ may be economical, fast and powerful tool in estimating secondary consolidation settlement. However, the databases of the $C_a/C_c$ at construction site in Korea are insufficient. The purpose of this study is to investigate the relationship of $C_a/C_c$ on marine clay near the southern sea in Korea. A series of incremental loading consolidation tests (measuring base pore water pressure) is peformed. It was found that the $C_a/C_c$ on undisturbed marine clay is 0.0397.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.351-359
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• 2007

Multi-axial compression tests have been frequently conducted to evaluate the in situ properties of rock masses and the mechanical behaviors of rock strata through the model tests. Without the proper boundary condition for the model tests, the mechanical behavior of rock mass would deviate, as can be expected, from the in situ conditions. The boundary condition will affect the internal stress distribution of the specimens and cause some distortion on the measurement. In this study, a design process regarding the steel brush, which has been employed for multi-axial compression test to reduce the frictional restraint along the specimen/loading platen interface, is introduced. The individual brushes are regarded as a simple column and beam to calculate the cross-sectional size and length of the brushes in consideration of the buckling capacity and the allowable deflection.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.27 no.2
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• pp.27-36
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• 2021

Background : Prone hip extension (PHE) is commonly used for exercises and tests in patients with low back pain. Previous studies have shown that pelvic compression belts (PCB) and non-elastic taping (NET) contribute greatly to improvements in lumbopelvic stability. This study aimed to compare the effect of two lumbopelvic stability methods such as PCB and NET on the trunk and hip extensor muscle activities during PHE tests. Methods: Subjects who experienced low back pain (low back pain group, LBPG; n=20) and those who did not experience low back pain (non-LBPG; n=20) participated in this study. The subjects were instructed to perform PHE with and without a PCB and NET. PHE tests were performed in the condition wherein the two stabilization methods were applied, and the actions of the muscles at that time were measured using surface electromyography (EMG). EMG data were collected from the hamstring, gluteus maximus, erector spine (ES), and multifidus (MF) muscles. The data were collected three times for 5 s with a 1-min rest between each of the three sets. Results: In the LBPG, EMG of the ES muscle was significantly reduced when NET or a PCB was applied (p<.05). There was no difference in the change in the ES muscle activity when NET and a PCB were applied. The ratio of MF/ES muscleactivity showed a significant increase in the LBPG with NET (p<.05). Conclusion: Both NET and PCB applied to subjects who experienced low back pain significantly reduced the ES muscle activity during PHE exercises and helped control the balance of the superficial and deep trunk extensor muscles.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1784-1792
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• 2003

A hybrid method with supercompact multiwavelets is suggested as an efficient and practical method to compress CFD dataset. Supercompact multiwavelets provide various advantages such as compact support and orthogonality in CFD data compression. The compactness is a crucial condition for approximated representation of CFD data to avoid unnecessary interaction between remotely spaced data across various singularities such as shock and vortices. But the supercompact multiwavelet method has to fit the CFD grid size to a product of integer and power of two, m${\times}$2$^n$. To resolve this problem, the hybrid method with combination of 3, 2 and 1 dimensional version of wavelets is studied. With the hybrid method, any arbitrary size can be handled without any shrinkage or expansion of the original problem. The presented method allows high data compression ratio for fluid simulation data. Several numerical tests substantiate large data compression ratios for flow field simulation successfully.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1204-1211
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• 2008

Compression index is one of the important characteristic numbers in soft soil engineering. Since 1940's, many researchers have suggested various practical solutions to define the compression index of clay using other soil properties. But, these results are only can give us an outline of soft soil behavior. In this study, the relationships between pore water pressure dissipation test results and compression index were suggested using comparison results of both tests. This relationships are based on basic concept of consolidation phenomena, essential difference between pore water pressure dissipation test and consolidation test, and disagreements between theoretical time factor and real time factor. To identify proportional factor of proposed equation, Geotechnical investigation results of Kwang-Yang(KY) site and Busan New Port(BN) site were used. The proportional factor was 0.0031 from 20 to 50% of consolidation rate where correlation parameter($R^2$) is 0.9051.

• Structural Engineering and Mechanics
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• v.55 no.5
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• pp.931-951
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• 2015

To improve the durability and service life of reinforced concrete column such as bridge piers, an advanced composite column made of Ultra High Performance Cementitious Composites (UHPCC) permanent form is proposed. Based on elasticity plasticity theory, axial compression behavior of the composite column was studied theoretically. The first circumferential cracking load and ultimate limit loading capacity are derived for the composite column. Short composite column compression tests and numerical simulations using FEM method were carried out to justify the theoretical formula. The effects of UHPCC tube thickness on the axial compression behavior were studied. Using the established theoretical model and numerical simulation, the large dimension composite columns are calculated and analyzed with different UHPCC tube thickness. These studies may provide a reference for advanced composite column design and application.

• International Journal of Concrete Structures and Materials
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• v.4 no.1
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• pp.63-68
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• 2010

With the emergence of ultra-high strength of concrete, the compression lap splice has become an important area of interest. According to ACI 318-08, a compression splice can be longer than a tension splice when high-strength concrete is used. By reevaluating the test results of compression splices and performing regression analysis, a simplified design equation for splice length in compression was developed based on the basic form of design equations for development/splice lengths of deformed bars and hooks in tension. A simple linear relation between $l_s/d_b$ and $f_{sc}\sqrt{f'_c}$ was assumed, and yields good values for the correlation coefficient and the mean and the COV (coefficient of variation) of the ratios of tests to predictions of splice strengths in compression. By including the 5% fractile coefficient of 0.83, a design equation for splice length in compression was developed. The splice length calculated using the proposed equation has a reliability that is equivalent to other provisions for reinforcing bars.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.1
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• pp.223-231
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• 2002

The pilot tests for the development of biaxial failure envelope of high strength concrete of reactor containments were performed. To apply biaxial loads to concrete, the plate specimens were used. The technical difficulties encountered on the development of a suitable biaxial test setup were discussed. To decide the optimum thickness of plate specimen, the nonlinear finite element analyses using ABAQUS were performed for a 1/8 model of cylindrical specimen(${\Phi}150{\times}300$) and four 1/4 models of plate Specimens ($200{\times}200{\times}T$(=30, 50, 60, 70)mm) under uniaxial compression. Analytical values and test data of relative strength ratio between those specimens with different geometric shapes were also compared. The various test data were obtained under uniaxial compression, uniaxial tension, and biaxial compression and then the stress-strain responses were plotted. The test data indicated that the strength of concrete under biaxial compression, $f_1/f_2=-1/-1$, is 15 percent larger than that under uniaxial compression and the poisson's ratio of concrete is 0.16. Teflon pads employed to eliminate friction between test specimen and loading platens showed an excellent effect under biaxial compression.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.6
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• pp.501-517
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• 2011

In general, the tunnel stability during excavation is assessed by comparing measured displacements at roof and sidewall to control criteria. The control criteria were established based on the past experience that considered ground conditions, size of the tunnel cross section, construction method, supports, etc. Therefore, a number of researches on the control criteria using the critical strain have been conducted. However, the critical strain obtained from uniaxial compression tests have drawbacks of not taking damage in rock mass due to increase of stress level and longitudinal arching into account. In this paper, damage-controlled tests simulating stress level and longitudinal arching during tunnel excavation were carried out in addition to uniaxial compression tests to investigate the critical strain characteristics of granite and gneiss that are most abundant rock types in Korean peninsula. Then, the critical strains obtained from damage-controlled tests were compared to those from uniaxial compression tests; the former showed less values than the latter. These results show that the critical strain obtained from uniaxial compression tests has to be reduced a little bit to take stress history during tunnel excavation into account. Moreover, the damage critical strain was proposed to be used for assessment of the brittle failure that usually occurs in deep tunnels.