• Tunnel and Underground Space
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• v.31 no.6
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• pp.593-609
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• 2021

We proposed a numerical method for the thermo-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) and simulated thermally induced fracture slip. The present study is the benchmark simulation performed as part of DECOVALEX-2023 Task G, which aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as an assembly of Voronoi grains and calculated the interaction of the grains (blocks) and their interfaces (contacts) using a distinct element code, 3DEC. Based on an equivalent continuum approach, the micro-parameters of grains and contacts were determined to reproduce rock as an elastic material. Then, the behavior of the fracture embedded in the rock was characterized by the contacts with Coulomb shear strength and tensile strength. In the benchmark simulation, we quantitatively examined the effects of the boundary stress and thermal stress due to heat conduction on fracture behavior, focusing on the mechanism of thermally induced fracture slip. The simulation results showed that the developed numerical model reasonably reproduced the thermal expansion and thermal stress increment, the fracture stress and displacement and the effect of boundary condition. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.469-477
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• 2006

Models to predict the ultimate strength of simply supported or continuous deep beams with web openings are proposed. The derived equations are based on upper-bound theorem. The concrete is assumed as a perfectly plastic material obeying the modified Coulomb failure criteria with zero tension cutoff. Reinforcing bar is considered as elastic-perfectly plastic material and its stress is calculated from the limiting principal compressive strain of concrete. The governing failure mechanisms based on test results are idealized as rigid moving blocks separated by a hyperbolic yield line. The effective compressive strength of concrete is calculated from the formula proposed by Vecchio and Collins. Comparisons with existing test results are performed, and they show good agreement.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.773-783
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• 2007

A simple unbonded-type shear strengthening technique for reinforced concrete beams using wire rope units is developed. Six two-span continuous T-beams externally strengthened with wire rope units and an unstrengthened control beam were tested. The main variables investigated were the amount and prestressing force of wire rope units. All specimens had the same geometrical dimension and arrangement of internal reinforcement. Influence of the distribution of vertical stresses in beam web owing to the prestressing force of wire rope units on the diagonal shear cracking load and the ultimate shear capacity of beams tested is presented. Based on the current study, it can be concluded that the amount and initial prestress of wire rope should be limited to be above 2.5 times the minimum shear reinforcement ratio specified in ACI 318-05 and below 0.6 times its own tensile strength, respectively, to ensure the enhancement of shear capacity and ductile failure mode of the strengthened beams. A numerical analysis based on the upper-bound theorem is developed to assess the shear capacity of continuous T-beams strengthened with wire rope units. From the comparisons of measured and predicted shear capacities, a better agreement is achieved in the proposed numerical analysis than in empirical equations recommended by ACI 318-05.

• Journal of the Korean GEO-environmental Society
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• v.20 no.5
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• pp.13-21
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• 2019

There are many cuts or natural rock slopes that remain stable for a long time in the natural environment with steep slopes ($65^{\circ}$ to $85^{\circ}$). In terms of design practice, the rock mass consisting of similar rock condition and geological structures is defined as a good continuum rock slope, and during the process of decision making angle of this rock slope, it will be important to establish the geotechnical properties estimating method of the continuum rock on the process of stability analysis in the early stages of design and construction. In this study, the stability analysis of a good continuum rock slope that can be designed as a steep slope proposed a practical method of estimating the shear strength by induced from the Hoek-Brown failure criterion, and in addition, the design applicability was evaluated through the stability analysis of steep rock slope. The existing method of estimating the shear strength was inadequate for practical use in the design, as the equivalent M-C shear strength corresponding to the H-B envelope changes sensitively, even with small variations in confining stress. To compensate for this problem, it was proposed to estimate equivalent M-C shear strength by iso-angle division method. To verify the design applicability of the iso-angle division method, the results of the safety factor and the displacement according to the change in angle of the cut slope constructed at the existing working design site were reviewed. The safety factor is FS=16~59 on the 1:0.5 slope, FS=12~52 on the 1:0.3 slope, most of which show a 10~12 percent reduction. Displacement is 0.126 to 0.975 mm on the 1:0.5 slope, 0.152 to 1.158 mm on the 1:0.3 slope, and represents an increase of 10 to 15%. This is a slightly change in normal proportion and is in good condition in terms of stability. In terms practical the working design, it was confirmed that applying the shear strength estimated by Iso-angle division method derived from the H-B failure criterion as a universal shear strength for a good continuum rock mass slope was also able to produce stable and economic results. The procedure for stability analysis using LEM (Limit Equilibrium Analysis Method) and FEM (Finite Element Analysis Method) will also be practical in the rock slope where is not distributed fault. The study was conducted by selecting the slope of study area as a good rock condition, establishing a verification for which it can be applied universal to a various rock conditions will be a research subject later on.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.270-288
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• 2021

We proposed a numerical method to simulate the hydro-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) in the paper. As a part of DECOVALEX-2023 Task G, we verified the method via benchmarks with analytical solutions. DECOVALEX-2023 Task G aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as a group of tetrahedral grains and calculated the interaction of the grains and their interfaces using 3DEC. The micro-parameters of the grains and interfaces were determined by a new methodology based on an equivalent continuum approach. In benchmark modeling, a single fracture embedded in the rock was examined for the effects of fracture inclination and roughness, the boundary stress condition and the applied pressure. The simulation results showed that the developed numerical model reasonably reproduced the fracture slip induced by boundary stress condition, the fracture opening induced by fluid injection, the stress distribution variation with fracture inclination, and the fracture roughness effect. In addition, the fracture displacements associated with the opening and slip showed good agreement with the analytical solutions. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.649-656
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• 2008

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchic void element based on the integrals of Legendre polynomials is used to characterize the fracture behaviour of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of zero stiffness element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem. It is noted that the proposed hierarchical void element can be one of alternatives to analyze the patched crack problems.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.623-630
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• 2007

Grouting materials are used for the unification of superstructural and substructural body like bridge seat (shoe) or machinery pedestal and e.t.c by filling their intercalary voids. Accordingly, grouting materials have been developed and used mainly with products of high strength because those materials are constructed specially in a part receiving large or impact load. In this situation, the structural body constructed by grouting materials with high stiffness-centered (caused by high strength) products is apt to cause brittle failure when receiving over a limit stress and to cause cracks according to cumulative fatigue by continuous and cyclic load. In addition, grouting materials are apt to cause cracks by using too much rapid hardening agents that give rise to high heat of hydration to maintain high strength at early age. In this study, to overcome these problems, cement type grouting materials including powder of waste tire and resin as elastic materials which aim to be more stable construction and to be improvement of mother-body's unification are developed and endowed with properties of high toughness and high durability add to existing properties of high flowability, non-shrinkage and high strength. Besides, this study contribute to of for green construction materials for being possible recycling industrial waste like waste tire and flyash. On the whole, seven type mixing conditions are tested and investigated to choose the best mixing condition.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.5-19
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• 2014

In this study, the structural analysis is performed on the method of shallow block and deep cement mixing pile, and then their characteristics and associated behaviors were analyzed. In the case of continuous beam analysis, the predicted settlement was very small, and shear force and bending stress are somewhat overestimated. The frame method is similar to numerical analysis in the internal force shallow block and long pile, but because the settlement of pile is underestimated, the additional calculation using the reaction of the long pile is necessary. For soil arching method and piled raft foundation method, the excessive axial force of long pile was predicted because the load sharing of pile is very large compared to the other methods. In the behavior of the shallow block and deep pile method, the settlement of shallow block and contact pressure are much in the center than the edge. In the estimating method considering the interaction between improved material and ground, the load sharing of the soil-cement pile ranges from 20% to 45%, and the stress ratio is 2.0~5.0 less than piled DCM. The maximum member forces at the boundary conditions of pile head are similar, but in fixed head the axial force and vertical displacement are different in accordance with pile arrangement.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.321-329
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• 2003

To effectively use the cross section of concrete decks, analytical and experimental studies on prestressed steel-box-girder bridges were performed in this study. The method of applying prestress was determined in the analytical study and the longitudinal behavior of the prestressed steel-box-girder bridge was considered in the experimental study. The object model for these studies was a two-span continuous bridge. The method of applying prestress determined herein was divided into two parts: one is that apply prestress to the concrete deck at its intermediate support, and the other is that apply prestress to the lower flange of the steel-box-girder bridge at its end support. The prototype bridge for the experiment was simulated based on the rule of similitude and was fabricated according to construction steps to apply prestress effectively. From the results of the experimental study, it has demonstrated that the prestressed steel-box-girder bridge provides better performance than the general steel-box-girder bridge in view of the increase of the design live load, the reduction of the tensile stress of the concrete deck at intermediate support, and the reduction of the displacement.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.45-55
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• 1999

Wave-induced response, liquefaction and stability of unsaturated seabed are studied. The unsaturated seabed is modeled as a fluid-filled polo-elastic medium. The coupled process of fluid flow and the deformation of soil skeleton is formulated in the framework of Biot's theory. The resulting governing equations are solved using a semi-analytical method to evaluate the stresses and pore water pressure of unsaturated and multi-layered seabed. The semi-analytical method can be applied to calculate a pore pressure and the stresses of in anisotropic inhomogeneous seabed. The results indicate that the degree of saturation influences mostly on the magnitudes of a pore pressure and the stresses of unsaturated and multi-layed seabed. Based on the pore pressure and stresses in seabed, the analysis on the possibilities of liquefaction and shear failure was performed. The results show that the maximum depth of shear failure occurrence is deeper than the maximum liquefaction depth.