• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.4
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• pp.354-359
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• 2014

The objective of this study is to examine the fatigue behavior in compression of normal-weight and lightweight concrete mixtures with high volume supplementary cementitious material(SCM). The selected binder composition was 30% ordinary portland cement, 20% fly-ash, and 50% ground granulated blast-furnace slag. The targeted compressive strength of concrete was 40 MPa. For the cyclic loading, the constant maximum stress level varied to be 75%, 80%, and 90% of the static uniaxial compressive strength, whereas the constant minimum stress level was fixed at 10% of the static strength. The test results showed that fatigue life of high volume SCM lightweight concrete was lower than the companion normalweight concrete. The value of the fatigue strain at the maximum stress level intersected the descending branch of the monotonic stress-strain curve after approximately 90% of the fatigue life.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1089-1109
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• 2016

Modified two-surface model (M2SM) is one of the steel elasto-plastic hysteretic constitutive models that consider both analysis accuracy and efficiency. However, when M2SM is used for complex strain history, sometimes the results are irrational due to the limitation of stress-strain path judgment. In this paper, the defect of M2SM was re-modified by improving the judgment of stress-strain paths. The accuracy and applicability of the improved method were verified on both material and structural level. Based on this improvement, the nonlinear time-history analysis was carried out for a deck-through steel arch bridge with a 200 m-long span under the ground motions of Chi-Chi earthquake and Niigata earthquake. In the analysis, we compared the results obtained by hysteretic constitutive models of improved two-surface model (I2SM) presented in this paper, M2SM and the bilinear kinematic hardening model (BKHM). Results show that, although the analysis precision of displacement response of different steel hysteretic models differs little from each other, the stress-strain responses of the structure are affected by steel hysteretic models apparently. The difference between the stress-strain responses obtained by I2SM and M2SM cannot be neglected. In significantly damaged areas, BKHM gives smaller stress result and obviously different strain response compared with I2SM and M2SM, and tends to overestimate the effect of hysteretic energy dissipation. Moreover, at some position with severe damage, BKHM may underestimate the size of seismic damaged areas. Different steel hysteretic models also have influences on structural damage evaluation results based on deformation behavior and low cycle fatigue, and may lead to completely different judgment of failure, especially in severely damaged areas.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.5
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• pp.69-78
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• 2009

Since the blast vibration induced by explosives of the powder possibly provide damage of the nearby structures adjacent to the tunnel, the stability of the nearby structures should be estimated. In this study, the stability of the tunnel based on the allowable peak particle velocity of the structures as well as allowable stress of the structures presented in the concrete structural design standard was estimated with respect to the stress of the concrete lining and axial force of the rockbolt during the blasting operation at the ground surface of the pre-existing tunnel. The analyses were carried out by using $FLAC^{2D}$ which is one of the programs developed based on the finite difference method. The bending compressive stress and shear stress of the concrete lining and axial force of the rockbolt were rapidly increased when the blasting operation was conducted near the tunnel.

• Journal of the Korean Geosynthetics Society
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• v.14 no.1
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• pp.11-21
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• 2015

This study aims at investigating of the behavioral characteristics of foundation ground subjected to a strip load in anisotropy. Using marine clays sampled at Shihwa area, a series of laboratory tests including triaxial compressive test, plane strain compressive and expansion tests that allows horizontal deformation only and zero strain (${\varepsilon}_2$) in the direction of intermediate stress (${\sigma}_2$) are conducted. In addition, a numerical analysis using parameters obtained from the tests is carried out. In the numerical analysis, Cam-clay model that simulates the behavior of natural deposited clay properly is adopted. The analysis results show that the vertical displacements of the plane strain compressive tests are relatively larger than those of triaxial compressive tests by 18-25%. Likewise, the horizontal displacements is 13-19% larger.

• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.85-94
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• 2012

Recently, growing interests in frozen ground have stimulated us to advance fundamental theories and systematic researches on soil behavior under freezing conditions. Unlike the well-established soil mechanics theory, temperature variation and phase change of pore-water cause water migration to cold side, ground heaving, sharp increase in earth pressure, etc., which bring about serious problems in frozen geotechnical structures. Elasto-plastic mechanical constitutive model for frozen/unfrozen soil subjected to fully coupled THM phenomena is formulated based on a new stress variable that is continuous in frozen-unfrozen transitional regions. Numerical simulations are conducted to discuss numerical reliability and applicability of the developed constitutive model: one-dimensional heaving pressure, tri-axial compression test, and one-side freezing tests. The numerical results show that developed model can efficiently describe complex THM phenomena of frozen soil, and they can be utilized to analyze and design the geotechnical structures under freezing conditions, and predict their long-term behavior.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.144-159
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• 2022

The present study developed a sequential approach-based numerical simulator for modeling coupled thermal-hydrological-mechanical (THM) processes in the ground and investigated the computational performance of the coupling analysis algorithm. The present sequential approach linked the two different solvers: an open-source numerical code, OpenGeoSys for solving the thermal and hydrological processes in porous media and a commercial code, FLAC3D for solving the geomechanical response of the ground. A benchmark test of the developed simulator was carried out using a THM problem where an analytical solution is given. The benchmark problem involves the coupled behavior (variations in temperature, pore pressure, stress, and deformation with time) of a fully saturated porous medium which is subject to a point heat source. The results of the analytical solution and numerical simulation were compared and the validity of the numerical simulator was investigated.

• Structural Engineering and Mechanics
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• v.72 no.2
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• pp.141-153
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• 2019

The effect of galleries on the earthquake behavior of dams should be investigated to obtain more realistic results. Therefore, a roller compacted concrete (RCC) dam with and without galleries are examined under ground motion effects. For this purpose, Cine RCC dam constructed in Aydın, Turkey, is selected in applications. The optimal mesh around galleries is investigated to obtain the most realistic results. Two-dimensional finite element models of Cine RCC dam with and without galleries are prepared by using ANSYS software. Empty and full reservoir conditions were taken into account in the time-history analyses. Hydrodynamic effect of the reservoir water was taken into account considering two-dimensional fluid finite elements based on the Lagrangian approach. It is examined that how principle stresses and displacements change by height and during earthquake. The dam-foundation-reservoir interaction was taken into consideration with contact-target element pairs. The displacements and principle stress components obtained from the linear analyses are compared each other for various cases of reservoir water and galleries. According to numerical analyses, the effect of galleries is clear on the response of RCC dam. Besides, hydrodynamic water effect obviously increases the principle stress components and horizontal displacements of the dam.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.57-64
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• 2007

Since matric suction of unsaturated soil was related to soil and ground water contaminations, it is very important to analyze its mechanism that was represented by shear characteristics. In three phases of soil, a little air makes the condition of unsaturated soil on contract or shrinkage surface between water and air. Capillarity and suction in pore of unsaturated soil cause surface tension and surface force so it makes negative pore water pressure and increases effective stress as a result. Therefore, negative pore water pressure in partially saturated soil affects the soil structure and degree of saturation and it is important to evaluate accurately unsaturate flow and behavior. In this study, the shear strength characteristics of the seven sandy soils were investigated using consolidated drained triaxial tests with special emphasis on the effects of the negative pore pressure and the matric suction. These tests involved shearing under either a constant net confining pressure and varying matric suction or under a constant matric suction and varying net normal stress.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.151-161
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• 2007

EPS provides a superb self-sufficient stability. Studies on the process of EPS construction method focus on the inchoate phase of general construction, which is increasingly applied to construction sites throughout the world. Unfortunately, there has been little study on the durability and long-term soil behavior involving EPS materials. In this study, the boring, in-site and laboratory tests were conducted to examine the long-term soil behavior in the back-filling of alternating behind the side to which EPS was applied. And results of finite element analysis considering various test results and the soil behavior data measured during the construction show that EPS construction method is a superb process that relieves the load and consequently reduces the settlement, alleviates the stress on the abutment, and prevents lateral flow.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.245-259
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• 2003

Refering to the articles "Squeezing rocks in tunnels(Barla, 1995)" and "Tunnelling under squeezing rock conditions(Barla 2002)" this article deals with technologies for design, stability analysis and construction of the tunnel being driven in the squeezing rock mass. The definition of this type of behavior was proposed by ISRM(1994). The identification and quantification of squeezing is given according to both the empirical and semi-empirical methods available to anticipate the potential of squeezing problems in tunnelling. Based on the experiences and lessons learned in recent years, the state of the art in modem construction methods was reported, when dealing with squeezing rock masses by either conventional or mechanical excavation methods. The closed-form solutions available for the analysis of the rock mass response during tunnel excavation are described in terms of the ground characteristic line and with reference to some elasto-plastic models for the given rock mass. Finally numerical methods were used for the simulation of different models and for design analysis of complex excavation and support systems, including three-dimensional conditions in order to quantify the influence of the advancing tunnel face to the deformation behavior of the tunnel.