• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.107-116
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• 2020

The compaction grouting technique is widely used to improve the liquefaction resistance of loose sands that are liquefaction-prone. Particularly, the horizontal injection of compaction grout is proposed for the liquefiable ground with an overlying structure as it does not allow the vertical compaction grouting. However, there has been limited number of researches on the horizontal compaction grouting. Therefore, this study explores the grout bulb shape and expansion direction in loose sand. A series of scaled two-dimensional experiments on the horizontal compaction grouting was conducted varying the overburden stress. The results show that the grout bulb grows in an elliptical shape though its directivity of major axis changes with the overburden effective stress and relative density. The grout bulb expands faster in a horizontal direction under a low overburden stress with a small relative density. The higher overburden stress and the greater relative density cause the more circular shape with the faster expansion in a vertical direction. The presented finding is expected to contribute to accurate and efficient design of the horizontal compaction grouting method.

• Journal of the Korean Geotechnical Society
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• v.38 no.5
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• pp.47-59
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• 2022

A series of experiments were performed to investigate the design and application of a rubble-ground modification method with grout injection. A small-sized injection machine was designed, and the grouts with various mix proportions were injected into 25 mm aggregate using the designed small-sized injection machine. With the compressive strength of the grout ranging from 20 to 80 MPa, the uniaxial compressive strength of the grout-filling bodies with clean gravels was higher than 1/6th of the strength of grouts themselves. However, this fraction may reduce depending on the interface conditions. The erosion resistance of the hardened grout was evaluated, and it was determined that the grout with a strength greater than 15 MPa did not require erosion consideration. Moreover, a full-scale injection test was performed for 25 cm-sized rubbles in cages with a diameter greater than 1 m and a height of 1.2 m to evaluate the filling characteristics of the grout. Results from this test indicated that the grout flowability sensitively influenced the filling characteristics.

• Journal of the Korean earth science society
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• v.42 no.2
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• pp.164-174
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• 2021

The study examines the shearing and crushing characteristics of land-derived subaqueous granular materials in a gravel-bed river. A series of large-sized ring shear tests were performed to examine the effect of shear time and shear velocity on the shear stress characteristics of aquarium gravels with a 6-mm mean grain size. Three different shear velocities (i.e., 0.01, 0.1, and 1 mm/sec) were applied to measure the shear stress under the drained (long-term shearing) and undrained (short-term shearing) conditions. Different initial shear velocities, i.e., 0.01→0.1→1 mm/sec and 0.1→0.01→1 mm/sec, were considered in this study. The test results show that the grain crushing effect is significant regardless of drainage conditions. The shear stress of coarse-grained materials is influenced by initial shear velocities, regardless of the drainage conditions. In particular, particle breakage increases as grain size increases. The shearing time and initial shear velocity are the primary influencing factors determining the shear stress of gravels. The granular materials may be broken easily into particles through frictional resistance, such as abrasion, interlocking and fracture due to the particle-particle interaction, resulting in the high mobility of granular materials in a subaqueous environment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.1-13
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• 2022

This study aims to investigate the feasibility of the half-cell potential (HCP) measurements on the concrete surface for evaluation of corrosion rate (or corrosion levels) of reinforcing steel in concrete. A series of experimental study is performed to measure HCP (or corrosion potential, E_corr) and corrosion current density (i_corr) of reinforcing steel in concrete cube specimens, with a side length of 200 mm. Various corrosion levels in a range of 0% to 20% of the test specimens are accelerated by impressing current to the reinforcing steel in concrete immersed in 3.0 % NaCl solution. HCP is measured in accordance with ASTM C876-15, and corrosion current density is determined by using the Stern-Geary equation and measured polarization resistance measured by electrochemical impedance spectroscopy (EIS). As a result, a numerical formula that relates HCP and i_corr in the test specimen is established by a regression analysis of the measured data in this study. It is observed that HCP is linearly correlated with log(i_corr) with a R² greater than 0.87, which is less affected by the experimental variables such as concrete mixture proportion, diameter of reinforcing steel and the amount of applied current in this study. These results exhibit that HCP measurements could be effective for evaluation of corrosion rate (or corrosion levels) of reinforcing steel in concrete in the case of exposed to a certain consistent environment.

• Journal of the Korean Geotechnical Society
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• v.39 no.3
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• pp.29-40
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• 2023

In this study, we investigated the reinforcing effects of waveform micropiles in a stratigraphic setting comprising buried soil, weathered soil, and weathered rock. We conducted a series of field load tests and determined that waveform micropiles exhibited sufficient bearing capacity through frictional resistance in the soil layer and demonstrated favorable constructability in conditions with deep bedrock layers. Moreover, the vertical stiffness of waveform micropiles was approximately 2.2 times higher than that of conventional micropiles when subjected to the same design load. Pile group load tests comprising conventional and waveform micropiles showed that micropiles with higher stiffness carried a greater proportion of the load. Although there was no significant difference in the bearing capacity between conventional and waveform micropiles under the same design load, waveform micropiles with higher stiffness showed a load-carrying capacity 1.7 to 3.2 times greater than that of conventional micropiles. These findings suggest that waveform micropiles can be effectively used for foundation reinforcement and reduce the risk of foundation failure when increased loads due to modifications such as expansion remodeling are expected.

• Journal of the Korean Geotechnical Society
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• v.23 no.2
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• pp.71-83
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• 2007

Liquefaction resistance depends strongly upon the degree of saturation, which is expressed in terms of the pore pressure coefficient, B. The B-value has been widely used to quantify the state of saturation of laboratory samples. However, it is practically impossible to determine in situ state of saturation by using the B-value. So, P-wave velocity can be alternatively used as a convenient index for evaluating the in situ state of saturation. In this paper, the Stokoe type torsional shear (TS) testing system was modified to saturate the specimen, with which it is also possible to measure P ($V_p$), S-wave velocity ($V_s$) and the excess pore water pressure buildup In order to examine the effect of B-value for nearly saturated sands. A series of the tests were carried out at 3 relative densities (40%, 50% and 75%) and various B-values using Toyoura sand. Based on the test results, the variations of $V_p\;and\;V_s$ with B-value were analyzed and compared with a existing theoretically derived formula. The normalized pore water pressure, $du/{\sigma}{_0}'$ and cyclic threshold shear strain, ${\gamma}^c_{th}$ with B-value were also analyzed. Additionally the test results related to pore water pressure were analyzed by $V_p$ to apply to the field seismic analysis.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.65-73
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• 2008

In the current practice for slope stability problem in Japan, the shear strength, $\tau$, mobilized along the failure surface is usually estimated based on an empirical approximation in which the cohesion, c, is assumed to be equal to the soil thickness above the supposed slip surface, d(m). This approximation is advantageous in that the result of stability analysis is not influenced by the designers in charge. However, since the methodology has little theoretical background, the cohesion may often be grossly overestimated, and conversely the angle of shear resistance, $\phi$, is significantly underestimated, when the soil thickness above the supposed slip surface is quite large. In this paper, a case record of natural slope failure that took place in Hyogo Prefecture in 2007, is described in detail for the case in which the shear strength along the collapsed surface was carefully examined in a series of direct shear box (DSB) tests by considering the effects of in-situ shear stress along the slip surface. It is demonstrated that the factor of safety agrees with that of in-situ conditions when the shear strength from this kind of DSB test was employed for the back-analysis of the slope failure.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.27-38
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• 2009

In this study, a series of 1 g shaking table model pile tests were carried out in saturated dense and loose sand to evaluate dynamic p-y curves for various conditions of flexural stiffness of a pile shaft, acceleration frequency and acceleration amplitude for input loads. Dynamic p-y backbone curve which can be applied to pseudo static analysis for saturated dense sand was proposed as a hyperbolic function by connecting the peak points of the experimental p-y curves, which corresponded to maximum soil resistances. In order to represent the backbone curve numerically, empirical equations were developed for the initial stiffness ($k_{ini}$) and the ultimate capacity ($p_u$) of soils as a function of a friction angle and a confining stress. The applicability of a p-y backbone curve was evaluated based on the centrifuge test results of other researchers cited in literature, and this suggested backbone curve was also compared with the currently available p-y curves. And also, the scaling factor ($S_F$) to account for the degradation of soil resistance according to the excess pore pressure was developed from the results of saturated loose sand.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.647-657
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• 2006

Probabilistic Risk Assessment considering statistically random variables is performed for the preliminary design of a Cable Stayed Bridge, which is Prestressed Concrete Bridge consisted of cable and plate girders, based on the method of Working Stress Design and Strength Design. Component reliabilities of cables and girders have been evaluated using the response surface of the design variables at the selected critical sections based on the maximum shear, positive and negative moment locations. Response Surface Method (RSM) is successfully applied for reliability analyses for this relatively small probability of failure of the complex structure, which is hard to obtain through Monte-Carlo Simulations. or through First Order Second Moment Method that can not easily calculate the derivative terms of implicit limit state functions. For the analysis of system reliability, parallel resistance system consisting of cables and plate girder is changed into series connection system and the result of system reliability of total structure is presented. As a system reliability, the upper and lower probabilities of failure for the structural system have been evaluated and compared with the suggested prediction method for the combination of failure modes. The suggested prediction method for the combination of failure modes reveals the unexpected combinations of element failures in significantly reduced time and efforts compared with the previous permutation method or system reliability analysis method, which calculates upper and lower bound failure probabilities.

• Asia Marketing Journal
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• v.10 no.2
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• pp.31-69
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• 2008

The purpose of this study is to identify the organizational characteristics that enhance CRM performances of a company. Based on a review of diverse definitions of CRM performance, this study examines the relationships among CRM performance measures and organizational characteristics. A questionnaire survey of 123 CRM managers of Korean companies was conducted to test the proposed research model, and a series of structural equation modeling identified the strong effects of organizational characteristics on CRM performance. It was found that top management commitment to CRM and a firm's strategic readiness lead to high levels of CRM investment, which, in turn, enhance directly task-related performance and indirectly customer-related performance. This study also confirmed that customer orientation is significantly related to task-related CRM performance and that the variables of CRM commitment and organizational culture may enhance customerrelated performance indirectly through their effects on the task-related performance. However, organizational members' resistance to change was found to have no effects on CRM performance. Overall our research broadly supports the role of organizational characteristics revealed in the CRM literature.