• Geomechanics and Engineering
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• v.18 no.3
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• pp.247-258
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• 2019

Soil strength and failure surface geometry directly influence magnitudes of passive earth thrust acting on geotechnical retaining structures. Accordingly, it is expected that as long as the shape of the failure surface geometry and strength parameters of the backfill are known, magnitudes of computed passive earth thrusts should be highly accurate. Building on this premise, this study adopts conventional method of slices for calculating passive earth thrust and combines it with equations for estimating failure surface geometries based on in-situ stress state and density. Accuracy of the proposed method is checked using the results obtained from small-scale physical retaining wall model tests. In these model tests, backfill was prepared using either air pluviation or compaction and different backfill relative densities were used in each test. When the calculated passive earth thrust magnitudes were compared with the measured values, it was noticed that the results were highly compatible for the tests with pluviated backfills. On the other hand, calculated thrust magnitudes significantly underestimated the measured thrust magnitudes for those tests with compacted backfills. Based on this observation, a new approach for the calculation of passive earth pressures is developed. The proposed approach calculates the magnitude and considers the influence of locked-in stresses that are the by-products of the backfill preparation method in the computation of lateral earth forces. Finally, recommendations are given for any geotechnical application involving the compaction of granular bodies that are equally applicable to physical modelling studies and field construction problems.

• Geomechanics and Engineering
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• v.37 no.3
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• pp.213-222
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• 2024

Determination of jointed rock mass properties plays a significant role in the design and construction of underground structures such as tunneling and mining. Rock mass classification systems such as Rock Mass Rating (RMR), Rock Mass Index (RMi), Rock Mass Quality (Q), and deformation modulus (Em) are determined from the jointed rock masses. However, parameters of jointed rock masses can be affected by the tunnel depth below the surface due to the effect of the in situ stresses. In addition, the geomechanical properties of rocks change due to the effect of metamorphism. Therefore, the main objective of this study is to apply correlation analysis to investigate the relationships between rock mass properties and some parameters related to the depth of the tunnel studied. For this purpose, the field work consisted of determining rock mass parameters in a tunnel alignment (~7.1 km) at varying depths from 21 m to 431 m below ground surface. At the same excavation depths, thirty-seven rock types were also sampled and tested in the laboratory. Correlations were made between vertical stress and depth, horizontal/vertical stress ratio (k) and depth, k and Em, k and RMi, k and point load index (PLI), k and Brazilian tensile strength (BTS), Em and uniaxial compressive strength (UCS), UCS and PLI, UCS and BTS. Relationships were significant (significance level=0.000) at the confidence interval of 95% (r = 0.77-0.88) between the data pairs for the rocks taken from depths greater than 166 m where the ratio of horizontal to vertical stress is between 0.6 and 1.2. The in-situ stress parameters affected rock mass properties as well as metamorphism which affected the geomechanical properties of rock materials by affecting the behavior of minerals and textures within rocks. This study revealed that in-situ stress parameters and metamorphism should be reviewed when tunnel studies are carried out.

• Tunnel and Underground Space
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• v.32 no.1
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• pp.1-19
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• 2022

In this report, new standard, published by Japanese Geotechnical Society, on in-situ stress measurements by hydraulic fracturing was reviewed. In the standard, modification was made for the calculation of fracture re-opening pressure in consideration of fracture surface roughness and residual aperture. The standard also presents how much the system compliance influences the estimation of the fracture re-opening pressure and subsequent in-situ stresses. It is shown that the stiffer the rock mass is, the system compliance should be sufficiently small enough so as to obtain in-situ stress measurement with higher confidence.

• Korean Journal of Materials Research
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• v.25 no.12
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• pp.690-693
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• 2015

Fatigue crack growth experiments were carried out on a 304 L stainless steel compact-tension(CT) specimen under load control mode. Neutron diffraction was employed to quantitatively measure the residual strains/stresses and the evolution of stress fields in the vicinity of a propagating fatigue-crack tip. Three principal stress components (i.e. crack growth, crack opening, and through-thickness direction stresses) were examined in-situ under loading as a function of distance from the crack tip along the crack-propagation path. The stress/strain fields, measured both at the mid-thickness and near the surface of the CT specimen, were compared. The results show that much higher compressive residual stress fields developed in front of the crack tip near the surface than developed at the mid-thickness area. The change of the stresses ahead of the crack tip under loading is more significant at the mid-thickness area than it is near the surface.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.390-397
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• 1999

This paper investigates about the prediction of rail bending fatigue lifes for the purpose of the effective maintenance of surface irregularities of rail welded parts. The rail bending stresses are calculated using a track dynamic analysis program. The rail surface irregularities measured in situ are given as inputs in the analyses. On the other hand, the S-N curves are derived based on the results of bending fatigue tests. Using data found so far, rail fatigue lifes are estimated adopting a modified Miner's rule. The useful guides for maintenance of rail welded part are proposed in terms of grinding period and grinding depth of rail surface irregularities.

• Geomechanics and Engineering
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• v.30 no.1
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• pp.45-49
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• 2022

In the present study, a physical model was built for the Jintan underground gas storage cavern group according to the similarity theory. In this regard, four ellipsoid caverns were built with scaled in-situ stresses and internal pressure. Then the stability of underground caverns was analyzed. The obtained results demonstrate that loss of internal pressure adversely affects the safety of caverns and attention should be paid during the operation of gas storage.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1001-1006
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• 2000

These should be constructed partially, because many prestressed concrete box girder bridges in situ have large cross section and long span. Therefore, accurate prediction of differences, both elapse time of each construction stage and exposure of atmosphere at each position of cross section, is very important. Though it is importance, engineers are apt to overlook it. This study predicted cracks due to shrinkage and stress concentration phenomenon by each construction stage and then, ascertained reduction of tensile stresses after applying retrofit scheme.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.561-570
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• 2009

A FE analysis of a noise & vibration-free screw PHC pile constructed into an in-situ site were performed. During constructing a screw PHC pile, the component stresses, maximum stresses of pile connecting parts and relative displacements of pile were analyzed.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.78.2-79
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• 2003

Pepper defensin ( CADEFl) clone was isolated from cDNA library constructed from pepper leaves infected with avirulent strain Bv5-4a of Xanthomonu campestris pv. vesicatoria. The deduced amino acid sequence of CADEFl is 82-64％ identical to that of other plant defensins. Putative protein encoded by CADEFl gene consists of 78 amino acids and 8 conserved cysteine residues to form four structure-stabilizing disulfide bridges. Transcription of the CADEF1 gene was earlier and stronger induced by X campestris pv. vesicatoria infection in the incompatible than in the compatible interaction. CADEF1 mRNA was constitutively expressed in stem, root and green fruit of pepper. Transcripts of CADEFl gene drastically accumulated in pepper leaf tissues treated With Salicylic acid (SA), methyl jasmonate (MeJA), abscisic acid (ABA), hydrogen Peroxide (H$_2$O$_2$), benzothiadiazole (BTH) and DL-${\beta}$-amino-n-butyric acid (BABA). In situ hybridization results revealed that CADEF1 mRNA was localized in the phloem areas of vascular bundles in leaf tissues treated with exogenous SA, MeJA and ABA. Strong accumulation of CADEF1 mRNA occurred in pepper leaves in response to wounding, high salinity and drought stress. These results suggest that bacterial pathogen infection, abiotic elicitors and some environmental stresses may play a significant role in signal transduction pathway for CADEF1 gene expression.

• Geomechanics and Engineering
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• v.7 no.4
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• pp.403-430
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• 2014

Shale gas formations exhibit strong mechanical and strength anisotropies. Thus, it is necessary to study the effect of anisotropy on the hydraulic fracture initiation pressure. The calculation model for the in-situ stress of the bedding formation is improved according to the effective stress theory. An analytical model of the stresses around wellbore in shale gas reservoirs, in consideration of stratum dip direction, dip angle, and in-situ stress azimuth, has been built. Besides, this work established a calculation model for the stress around the perforation holes. In combination with the tensile failure criterion, a prediction model for the hydraulic fracture initiation pressure in the shale gas reservoirs is put forward. The error between the prediction result and the measured value for the shale gas reservoir in the southern Sichuan Province is only 3.5%. Specifically, effects of factors including elasticity modulus, Poisson's ratio, in-situ stress ratio, tensile strength, perforation angle (the angle between perforation direction and the maximum principal stress) of anisotropic formations on hydraulic fracture initiation pressure have been investigated. The perforation angle has the largest effect on the fracture initiation pressure, followed by the in-situ stress ratio, ratio of tensile strength to pore pressure, and the anisotropy ratio of elasticity moduli as the last. The effect of the anisotropy ratio of the Poisson's ratio on the fracture initiation pressure can be ignored. This study provides a reference for the hydraulic fracturing design in shale gas wells.