• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.888-895
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• 2009

Compaction is a process of increasing soil density using physical energy. It is intended to improve the strength and stiffness of soil. In embankment, degree of compaction affects the construction time, money, also method of soil improvement. In large scale embankment project, difficulties of embankment should change due to uncertainty of settlement. So it is very important to predict the final settlement and factor of safety induced by embankment. In many construction site, there are primarily design of high embankment using in-situ soil. Therefore numerical analyses are necessary for valid evaluation of the settlement prediction. But due to the construction cost and schedule, there were lacking in properties of soil and also limited number of in-situ test were performed. So we proposed the method that can easily estimate the proper soil parameters and suggest the proper method of numerical analysis. From this, two-dimensional finite-difference numerical analysis was conducted to investigate the settlement and factor of safety induced by embankment with various case of compaction rate and embankment height.

• Geomechanics and Engineering
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• v.10 no.3
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• pp.325-334
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• 2016

Rock salt is a near-perfect material for gas storage repositories due to its excellent ductility and low permeability. Gas storage in rock salt layers during gas injection and gas production causes the stress redistribution surrounding the cavity. The triaxial cyclic loading and unloading tests for rock salt were performed in this paper. The elastic-plastic deformation behaviour of rock salt under cyclic loading was observed. Rock salt experienced strain hardening during the initial loading, and the irreversible deformation was large under low stress station, meanwhile the residual stress became larger along with the increase of deviatoric stress. Confining pressure had a significant effect on the unloading modulus for the variation of mechanical parameters. Based on the theory of elastic-plastic damage mechanics, the evolution of damage during cyclic loading and unloading under various confining pressure was described.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.63-70
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• 2002

In tunnel construction, the information on the rock quality and the location of fault or fracture are crucial for economical design of support pattern and for safe construction of the tunnel. The grade of rock is commonly estimated through the observation with the naked eye of recovered cores in drilling or from physical parameters obtained by their laboratory test. Since drilling cost is quite expensive and terrains of planned sites for tunnel construction are rough in many cases, however, only limited information could be provided by core drilling Electrical resistivity and EM surveys may be a clue to get over this difficulty. Thus we have investigated electrical resistivity and EM field data providing regional Information of the rock Quality and delineating fault and fracture over a rough terrain. In this paper, we present some case histories using electrical resistivity and EM survey for the site investigation of tunnel construction. Through electrical resistivity and EM survey, the range and depth of coal seam was clearly estimated, cavities were detected in limestone area, and weak zones such as joint, fault and fracture have been delineated.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.381-388
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• 2002

A series of centrifuge model tests were performed to investigate the behavior of piled bridge abutment subjected to lateral soil movements induced by the construction of approach embankment. In these tests, both the depth of soft clay and the rate of embankment construction are chosen as key parameters to examine the effects on lateral soil movements. The depth of soft clay layer varies from 5.2 m to 11.6 m, and the rate of embankment construction has two types of staged construction(1m/30days, 1m/15days) and instant construction. It is shown that, the distribution of lateral flow induced by stage embankment construction has a trapezoidal distribution. And practical guidelines to check the possibility of some lateral movement of piled abutment were investigated. The validity of the proposed guidelines by centrifuge test was compared with the observed performance by lateral movement index, F(Japan Highway Public Corporation) and modified I index(Korea Highway Corporation). Based on the results obtained, the critical values of F and modified I, as a practical guidelines, are proposed to 0.03 and 2.0, respectively.

• Geomechanics and Engineering
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• v.13 no.3
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• pp.505-515
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• 2017

Based on the collapse characteristics of a shallow rectangular cavity, a three-dimensional failure mechanism which can be used to study the collapsing region of the rock mass above a shallow cavity roof is constructed. Considering the effects of surcharge pressure and surface bolt on the collapsing block, the external rate of works produced by surcharge pressure and surface bolt are included in the energy dissipation calculation. Using variational approach, an analytic expression of surface equation for the collapsing block, which can be used to study the collapsing region of the rock mass above a shallow cavity roof, is derived in the framework of upper bound theorem. Based on the analytic expression of surface equation, the shape of the collapsing block for shallow cavity is drawn. Moreover, the changing law of the collapsing region for different parameters indicates that the collapsing region of rock mass decreases with the increase of the density of surface bolt. This conclusion can provide reference for practicing geotechnical engineers to achieve an optimal design of supporting structure for a shallow cavity.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.19-42
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• 1999

In urban area, there are several major factors to be considered in tunnel design and construction. The first is to predict the magnitude and distribution of ground movements for particular ground conditions and construction procedures. The second is to assess the potential damage to nearby structures in response to the predicted ground movements. The third is to select the measures to be taken if a potential damage is foreseen. This study is concerned primarily with the first and second stages of the problem. Particularly, this paper is focused on the second stage to assess the potential damage to the nearby building with any type of geometries and locations above ground surface. In order to solve this problem, we introduced damage parameters(angular distortion, deflection ratio, maximum building settlements, maximum differential settlements, horizontal strain, etc.), and extended these parameters into 3-dimensional safety assessment. Also, to assess the safety of any walls existing in the building, we developed a 3-dimensional analysis program, and various parametric studies for the nearby building with any type of geometries and locations were presented. In addition to these parametric studies, we compared the results of the proposed techniques with some abroad case records for particular tunnels and adjacent buildings.

• The Journal of Engineering Geology
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• v.24 no.2
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• pp.247-260
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• 2014

Rock masses at the site for the $2^{nd}$ step construction of the KAERI Underground Research Tunnel (KURT) are divided into six units to establish a rock mechanics model that is dependent on the geological characteristics and degree of joint development. The site primarily consists of three granitic units (G1, G2, and G3), two dykes (D1 and D3), and a fault zone of poor rock mass quality (F3). The F3 unit crosses the tunnel at the beginning of the site of $2^{nd}$ step construction. The rock masses of each unit are classified by RMR (Rock Mass Rating), Q-system, and RMi (Rock Mass Index), all based on borehole logging data. The deformation modulus, rock mass strength, cohesion, and friction angle for each unit are calculated using established empirical relationships. The representative rock mass classification and geotechnical parameters for the rock mass units are established, and a rock mechanics model for the site is proposed, which will be useful in the design and stability analysis of the $2^{nd}$ step construction of KURT.

• Journal of the Korean Geotechnical Society
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• v.22 no.1
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• pp.35-44
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• 2006

In general typically granular soils contain a certain amount of fines. It is also widely recognized that foundation soils under working loads show highly non-linear behavior from very early stages of loading. In the present study, a series of laboratory tests with sands of different silt contents are conducted and methods to assess strength and stiffiness characteristics are proposed. Modified hyperbolic stress-strain model is used to analyze non-linearity of silty sands in terms of non-linear Degradation parameters f and g as a function of silt contents and Relative density Dr. Stress-strain curves were obtained from a series of triaxial tests on sands containing different amounts of silt. Initial shear modulus, which is used to normalize Degradation modulus of silty sands, was determined from resonant column test results. From the laboratory test results, it was observed that, as the Relative density increases, values of f decrease and those of g increase. In addition, it was found that values of f and g increase and decrease respectively as a Skeleton void ratio $(e_{sk})$ increases.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.813-824
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• 2010

Thermal conductivity of soils is one of the most important parameters to design horizontal ground heat exchangers. It is well known that the thermal conductivity of soil is strongly influenced by its density and water content because of soil's particulate structure. This paper reviewed and evaluated some of the commonly used prediction models for thermal conductivity of soils with the experimental data available in the literature. Semi-theoretical models for two-component materials were found inappropriate to estimate the thermal conductivity of dry state sands. It came out that the model developed by Cote and Konrad gave the best overall prediction for unsaturated sands available in the literature. Also, a parametric analysis is conducted to investigate the effect of thermal conductivity and water content, soil type on the horizontal ground heat exchanger design. The analysis shows that a required pipe length for the horizontal ground heat exchanger is reduced with the increase of soil thermal conductivity and water content. The calculation results also show that the dimension of the horizontal ground heat exchanger can be reduced to a certain extent by using backfilling material with a higher thermal conductivity of solid particles.

• Geomechanics and Engineering
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• v.31 no.3
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• pp.237-248
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• 2022

Nowadays, more and more subway tunnels were planed and constructed underneath the ground of urban cities to relieve the congested traffic. Potential damage may occur in existing tunnel if the new tunnel is constructed too close. So far, previous studies mainly focused on the tunnel-tunnel interactions with circular shape. The difference between circular and horseshoe shaped tunnel in terms of deformation mechanism is not fully investigated. In this study, three-dimensional numerical parametric studies were carried out to explore the effect of different tunnel shapes on the complicated tunnel-tunnel interaction problem. Parameters considered include volume loss, tunnel stiffness and relative density. It is found that the value of volume loss play the most important role in the multi-tunnel interactions. For a typical condition in this study, the maximum invert settlement and gradient along longitudinal direction of horseshoe shaped tunnel was 50% and 96% larger than those in circular case, respectively. This is because of the larger vertical soil displacement underneath existing tunnel. Due to the discontinuous hoop axial stress in horseshoe shaped tunnel, significant shear stress was mobilized around the axillary angles. This resulted in substantial bending moment at the bottom plate and side walls of horseshoe shaped tunnel. Consequently, vertical elongation and horizontal compression in circular existing tunnel were 45% and 33% smaller than those in horseshoe case (at monitored section X/D = 0), which in latter case was mainly attributed to the bending induced deflection. The radial deformation stiffness of circular tunnel is more sensitive to the Young's modulus compared with horseshoe shaped tunnel. This is because of that circular tunnel resisted the radial deformation mainly by its hoop axial stress while horseshoe shaped tunnel do so mainly by its flexural rigidity. In addition, the reduction of soil stiffness beneath the circular tunnel was larger than that in horseshoe shaped tunnel at each level of relative density, indicating that large portion of tunneling effect were undertaken by the ground itself in circular tunnel case.