• Geomechanics and Engineering
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• v.12 no.3
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• pp.399-415
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• 2017

A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.205-215
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• 2018

Strain-based criteria are known as a direct method in determining the stability of the geomechanical structures. In spite of the widely use of Sakurai critical strain criterion, it is so conservative to make use of them in rocks with initial plastic deformation on account of the considerable difference between the failure and critical strains. In this study, a new criterion has been developed on the basis of the failure strain to attain more reasonable results in determining the stability status of the tunnels excavated in the rocks mostly characterized by plastic-elastic/plastic behavior. Firstly, the stress-strain curve was obtained having conducted uniaxial compression strength tests on 91 samples of eight rock types. Then, the initial plastic deformation was omitted making use of axis translation technique and the criterion was presented allowing for the modified secant modulus and by use of the failure strain. The results depicted that the use of failure strain criterion in such rocks not only decreases the conservativeness of the critical strain criterion up to 42%, but also it determines the stability status of the tunnel more accurately.

• Ocean and Polar Research
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• v.32 no.4
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• pp.489-499
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• 2010

The securing of raw material is an important requirement for economic development. Many countries, including Korea, actively seek out a stable supply of minerals such as manganese. Manganese nodules are rock concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core and include several strategic minerals necessary for economic development. In particular, the manganese nodule development project (MNDP) plays an important role in the Korean national economy. This study attempts to apply input-output (I-O) analysis in investigating the economic impacts of the MNDP in the Korean national economy. A static I-O framework was employed, focusing on four topics in its application; the production-inducing impacts, the value-added-inducing impacts, the employment-inducing impacts and R&D-inducing impacts of MNDP investments on other sectors. To this end, several versions of the demand-driven models are utilized. In addition, inter-industry linkage analysis is performed to obtain information on the forward and backward linkage effects of industries, including MNDP, to quantify the strength of causation among these industries.

• Structural Engineering and Mechanics
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• v.38 no.6
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• pp.803-823
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• 2011

In this paper, the three dimensional Parallel Realistic Failure Process Analysis ($RFPA^{3D}$-Parallel) code based on micromechanical model is employed to investigate the bonding behavior in FRP sheet bonded to concrete in single shear test. In the model, the heterogeneity of brittle disordered material at a meso-scale was taken into consideration in order to realistically demonstrate the mechanical characteristics of FRP-to-concrete. Modified Mohr-coulomb strength criterion with tension cut-off, where a stressed element can damage in shear or in tension, was adopted and a stiffness degradation approach was used to simulate the initiation, propagation and growth of microcracks in the model. In addition, a Master-Slave parallel operation control technique was adopted to implement the parallel computation of a large numerical model. Parallel computational results of debonding of FRP-concrete visually reproduce the spatial and temporal debonding failure progression of microcracks in FRP sheet bonded to concrete, which agrees well with the existing testing results in laboratory. The numerical approach in this study provides a useful tool for enhancing our understanding of cracking and debonding failure process and mechanism of FRP-concrete and our ability to predict mechanical performance and reliability of these FRP sheet bonded to concrete structures.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.745-751
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• 2009

The anchor is used extensively for a cutting slope, an earth retaining wall, an uplift resistance of sub-structures and so on at civil engineering projects and is classified by aim in use, tendon material, and ground/tension fixing type. It can be distinguished extensively into friction type, bearing type, and complex type by ground fixing type. Generally, bond length of friction type anchor has application to 3~10m depending on the friction-resistance characteristics. In this study, 'DEW(double enlargement wedge) bearing type anchor' of new concept is devised. The bond length is about 0.6~0.8m. It can be used on the ground to have the strength characteristics above it of weathered rock. There are merits which are 'period reduction' and 'cost saving' through the minimum of the boring length. In addition, it is so called environmentally friendly Methods because it can reduce the quantity of carbon dioxide through the reducing drilling machine operation time.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.171-178
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• 2020

Mountainous areas cover more than 70% of Korea. With the rapid increase in tunnel construction, tunnel-collapse incidents and excessive deformation are occurring more frequently. In addition, longer tunnel structures are being constructed, and geologically weaker ground conditions are increasingly being encountered during the construction process. Tunnels constructed under weak ground conditions exhibit long-term deformation behavior that leads to tunnel instability. This study analyzes the behavior of the bottom region of tunnels under geological conditions of long-term deformation. Long-term deformation causes various types of damage, such as cracks and ridges in the packing part of tunnels, as well as cracks and upheavals in the pavement of tunnels. We observed rapid tunnel over-displacement due to the squeezing of a fault rupture zone after the inflow of a large amount of groundwater. Excessive increments in the support member strength resulted in damage to the support and tunnel bottom. In addition, upward infiltration pressure on the tunnel road was found to cause severe pavement damage. Furthermore, smectite (a highly expandable mineral), chlorite, illite, and hematite, were also observed. Soil samples and rock samples containing clay minerals were found to have greater expansibility than general soil samples. Considering these findings, countermeasures against the deformation of tunnel bottoms are required.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.119-126
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• 2002

Fractures, especially faults have most significant influence on the difficulties encountered in various engineering and mining works, because they can give rise to inevitable reductions in shear strength as well as large increase in permeability. Thus, before underground access is possible, it is desirable to estimate the distribution and geometry of fractures in advance, if reliable structural data from e.g. Televiewer tool are available. To this end, fracture face mapping is just the evaluation method used to form a fracture image determined by intersecting of each fracture plane with a selected plane section of a rock mass, assuming that all fractures be planar with fixed-aperture. Although many fractures are geometrically complex and others are altered chemically, according to the abundant experiments in recent years, it would seem that the technique could be applied to benefit the design of numerous engineering works such as slope stability, tunnel excavations, dam foundation and diverse environmental works. This paper presents at first an evaluation algorithm for fracture face mapping and then concludes with various representative examples of applications.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.695-702
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• 2002

Groundwater flow is primarily influenced by the presence of fractures, functioning as conduits. To block the flow, grouting operation is commonly used. Thereby the fractures are then expected to be sealed, which will add to enhance the shear strength in rock. This far, regarding the assessment of grouting efficiency, however, there's been a considerable uncertainty That is, several geophysical methods of high resolution such as tomography, S-wave logging have produced a significant amount of measurable response caused by grouting, but they can inevitably be used only for the qualitative assessment. Thus, this paper deals with an accurate quantitative assessment about the grouting result. In this, a new strategy is introduced, based mainly on evaluating the opening of fractures. For fracture-opening investigation purposes, borehole Televiewer has already proven to be an excellent logging technique that produces both amplitude image and traveltime image. As well known, the traveltime image can be converted to a high precision 3D caliper log with max. 288 arms, which allows to observe the opening of fractures. To evaluate the fracture opening from the traveltime image, an algorithm of practical use was developed, in which image correction due to the borehole deviation, feature discrimination of wall roughness from fractures, automatic evaluation procedure etc. were considered. Field examples are shown to confirm the efficiency of the suggested method.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.715-718
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• 1998

In this work, bisphenol type vinyl ester was impregnated into the three-dimensional glass fabrics fabricated from different thickness changes. Their mechanical properties of the specimens have been investigated by three-point bending and flatwise compression tests. Also, interlaminar shear strength (ILSS) has been determined through short-beam test for the evaluation of interfacial adhesion at interfaces between fibers and matrix of the composites. The effect of thickness changes in three-dimensional glass fabric-reinforced composites have been described in this work.

• Geomechanics and Engineering
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• v.9 no.6
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• pp.793-813
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• 2015

Characterization of discontinuous media is an endeavor that poses great challenge to engineers in practice. Since the inherent defects in cracked domains can substantially influence material resistance and govern its behavior, a lot of work is dedicated to efficiently model such effects. In order to overcome difficulties of material instability problems, one needs to comprehensively represent the geometry of cracks along with their impact on the mechanical properties of the intact material. In the present study, stress-strain results from laboratory experiments on Inada granite was used to derive crack tensor as a tool for the evaluation of fractured domain stability. It was found that the formulations proposed earlier could satisfactorily be employed to attain crack tensor via the invariants of which judgment on cracks population and induced anisotropy is possible. The earlier criteria based on crack tensor analyses were reviewed and compared to the results of the current study. It is concluded that the geometrical parameters calculated using mechanical properties could confidently be used to judge the anisotropy as well as strength of the cracked domain.