• Tunnel and Underground Space
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• v.30 no.6
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• pp.573-590
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• 2020

This study presents the current status of DECOVALEX-2023 project Task G and our research results so far. Task G, named 'Safety ImplicAtions of Fluid Flow, Shear, Thermal and Reaction Processes within Crystalline Rock Fracture NETworks (SAFENET)' aims at developing a numerical method to simulate the fracture creation and propagation, and the coupled thermohydro-mechanical processes in fracture in crystalline rocks. The first research step of Task G is a benchmark simulation, which is designed for research teams to make their modelling codes more robust and verify whether the models can represent an analytical solution for displacements of a single rock fracture. We reproduced the mechanical behavior of rock and embedded single fracture using a three-dimensional grain-based distinct element model for the simulations. In this method, the structure of the rock was represented by an assembly of rigid tetrahedral grains moving independently of each other, and the mechanical interactions at the grains and their contacts were calculated using 3DEC. The simulation results revealed that the stresses induced along the embedded fracture in the model were relatively low compared to those calculated by stress analysis due to stress redistribution and constrained fracture displacements. The fracture normal and shear displacements of the numerical model showed good agreement with the analytical solutions. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated using various experiments in a further study.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.47-54
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• 2013

This study investigates the crack growth behavior due to primary water stress corrosion cracking (PWSCC) in the dissimilar metal butt weld of a reactor piping using Alloy 82/182. First, detailed finite element stress analyses were performed to predict the stress distribution of the dissimilar metal butt weld in which the hydrostatic and the normal operating loads as well as the weld residual stresses were considered to evaluate the stress redistribution due to mechanical loadings. Based on the stress distributions along the wall thickness of the dissimilar metal butt weld, the crack growth behavior of the postulated axial and circumferential cracks were predicted, from which the crack growth diagram due to PWSCC was proposed. The present results can be applied to predict the crack growth rate in the dissimilar metal butt weld of reactor piping due to PWSCC.

• Composites Research
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• v.17 no.4
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• pp.7-17
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• 2004

In this study, the effect of laminate thickness on the compressive behaviour of composite materials is investigated through systematic experimental work using the stacking sequences, $[O_4]_{ns},{\;}[45/0/-45/90]_{ns}$ and $[45_n/0_n/-45_n/90_n]_s$ (n=2 to 8). Parameters such as fibre volume fraction, void content, fibre waviness and interlaminar stresses, influencing compressive strength with increasing laminate thickness are also studied experimentally and theoretically. Furthermore the stacking sequence effects on failure strength of multidirectional laminates are examined. For this purpose, two different scaling techniques are used; (1) ply-level technique $[45_n/0_n/-45_n/90_n]s$ and (2) sublaminate level technique $[45/0/-45/90]_{ns}$. An apparent thickness effect existes in the lay-up with blocked plies, i.e. unidirectional specimens ($[O_4]_{ns}) and ply-level scaled multidirectional specimens ($[45_n/0_n/-45_n/90_n]_s$). Fibre waviness and void content are found to be main parameters contributing to the thickness effect on the compressive failure strength. However, the compressive strength of the sublaminate level scaled specimens ($[45/0/-45/90]_{ns}$) is almost unaffected regardless of the specimen thickness (since ply thickness remains constant). From the investigation of the stacking sequence effect, the strength values obtained from the sublaminate level scaled specimens are slightly higher than those obtained from the ply level scaled specimens. The reason for this effect is explained by the fibre waviness, void content, free edge effect and stress redistribution in blocked $0^{\circ}$ plies and unblocked $0^{\circ}$ plies. The measured failure strengths are compared with the predicted values.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.3
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• pp.133-149
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• 2021

This study aims to report the behavioral mechanism of steel pipe reinforcement grouting, which is being actively used to ensure the stability of the excavation surface during tunnel excavation, based on measurements taken at the actual site. After using a 12 m steel pipe attached with a shape displacement meter and a strain gauge to reinforce the actual tunnel surface, behavioral characteristics were identified by analyzing the measured deformation and stress of the steel pipe. Taking into account that the steel pipes were overlapped every 6 m, the measured data up to 7 m of excavation were used. In addition, the behavioral characteristics of the steel pipe reinforcement according to the difference in strength were also examined by applying steel pipes with different allowable stresses (SGT275 and SGT550). As a result of analyzing the behavior of steel pipes for 7 hours after the first excavation for 1 m and before proceeding with the next excavation, the stress redistribution due to the arching effect caused by the excavation relaxation load was observed. As excavation proceeded by 1 m, the excavated section exhibited the greatest deformation during excavation of 4 to 6 m due to the stress distribution of the three-dimensional relaxation load, and deformation and stress were generated in the steel pipe installed in the ground ahead of the tunnel face. As a result of comparing the behavior of SGT275 steel pipe (yield strength 275 MPa) and SGT550 steel pipe (yield strength 550 MPa), the difference in the amount of deformation was up to 18 times and the stress was up to 12 times; the stronger the steel pipe, the better it was at responding to the relaxation load. In this study, the behavior mechanism of steel pipe reinforcement grouting in response to the arching effect due to the relaxation load was identified based on the measured data during the actual tunnel excavation, and the results were reported.