• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.13-22
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• 2003

TSP (Tunnel Seismic Profiling) survey is a technique for imaging and characterizing geological structures ahead of a tunnel face. The seismic modeling algorithm and the synthetic data could be helpful for TSP surveys. However, there is few algorithm to describe the propagation of the elastic waves around the tunnel. In this study, existing 2-dimensional seismic modeling algorithm using finite element method was modified to make a suitable algorithm for TSP modeling. Using this algorithm, TSP modeling was practiced in some models. And the synthetic data was analyzed to examine the propagation characteristics of the elastic waves. First of all, the modeling for the homogeneous tunnel model was practiced to examine the propagation characteristics of the direct waves in the vicinity of the tunnel. And the algorithm was applied to some models having reflector which is perpendicular or parallel to the excavation direction. From these, the propagation characteristics of the reflected waves were examined. Furthermore, two source-receiver arrays were used in respective models to investigate the properties of the two arrays. These modeling algorithm and synthetic data could be helpful in interpreting TSP survey data, developing inversion algorithm and designing new source-receiver arrays.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.35-45
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• 2014

Limit equilibrium methods of slope stability analysis have been widely adopted mainly due to their simplicity and applicability. However, the conventional methods may not give reliable and convincing results for various geological conditions such as nonhomogeneous and anisotropic soils. Also, they do not take into account soil slope history nor the initial state of stress, for example excavation or fill placement. In contrast to the limit equilibrium analysis, the analysis of deformation and stress distribution by finite element method can deal with the complex loading sequence and the growth of inelastic zone with time. This paper proposes a technique to determine the critical slip surface as well as to calculate the factor of safety for shallow failure on partially saturated soil slope. Based on the effective stress field in finite element analysis, all stresses are estimated at each Gaussian point of elements. The search strategy for a noncircular critical slip surface along weak points is appropriate for rainfall-induced shallow slope failure. The change of unit weight by seepage force has an effect on the horizontal and vertical displacements on the soil slope. The Drucker-Prager failure criterion was adopted for stress-strain relation to calculate coupling hydraulic and mechanical behavior of the partially saturated soil slope.

• Korean Journal of Construction Engineering and Management
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• v.21 no.1
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• pp.78-86
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• 2020

Dozer is an expensive construction equipment and has a significant performance impact on earthwork performance. A machine guidance system has been applied to dozer equipment as a solution that can improve the performance. The system can provide earthwork-related information to equipment operators so that earthworks can be carried out with minimum support from surveyors. Construction Equipment Machine guidance has the function of supporting earthwork according to an earthwork plan by providing excavation-related information to machine operators. The objective of this study is to evaluate the performance improvement of a machine guidance system for an dozer earthwork operation, and to compare the machine guidance method with the traditional method. The performance has been evaluated in two folds: 1) productivity and 2) accuracy. The productivity shows the quantity of earthwork for a given unit time. The accuracy shows the deviation of grading level from the designed level on the construction drawing for earthwork. The machine guidance system has been applied to a testing bed in a construction site. Data comparison analysis showed that the earth earthwork had 46.59% improvement in productivity as well as 46.96% improvement in accuracy, and is expected to provide a tool for applying smart constrction to the earthwork operation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.25-36
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• 2008

When constructing subsea underground structures, the influence of high water and seepage pressure acting on the structures can not be neglected. Thus hydro-mechanical coupled analysis should be performed to estimate the behavior of the structures precisely In practice, relaxed rock load is generally used for the design of tunnel concrete lining. A method based on the distribution of local safety factor around a tunnel was proposed for the estimation of a height of relaxed rock mass ($H_{relaxed}$). In this study, the validation of the suggested method is investigated in the framework of hydro-mechanical coupled analyses. It was suggested that inducing inflow by pumping through a drainage well gave more reliable results than inducing inflow with shotcrete hydraulic characteristics in case of rock condition of Class III. In this study, therefore, inducing inflow by pumping through a drainage well are adopted in estimating $H_{relaxed}$ due to a tunnel excavation with the rock condition of Class I, III, and V. Also the estimated $H_{relaxed}$ results are compared with those of the existing suggested methods. As the result of this study, it is confirmed that estimating $H_{relaxed}$ based on the distribution of local safety factor around a tunnel can be effectively used even for the case of hydro-mechanical coupled analysis. It is also found that inducing inflow pumping through a drainage well gives more precise and consistent Hrelaxed of a subsea structure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.551-564
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• 2016

Earthworks are the fundamental steps in a construction job, and are mainly comprised of smaller tasks performed by construction machinery. The productivity of the construction job can be improved by optimizing excavation, filling, and other such operations. Earthworks involve a lot of mechanical work performed by the collaboration between various kinds of construction equipment, which in turn leads to higher fuel consumption. Actual earthworks depend mostly on the intuition and experience of the driver of the machines, thus leading to inefficiency and environmental problems caused by unnecessary emission of carbon, Recently automated and information-oriented technologies are consistently being researched towards the improvement of efficiency of earthworks in the construction industry. The present research involves the introduction and understanding of the decision-making elements of heuristics which can be applied to the earthwork planning. A method is also suggested for creating an effective work path for construction machine to perform task packages (TP) for cutting and filling processes. A simulation test is performed to verify the effectiveness of suggested methods in terms of space interference and total moving distance of construction equipment.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.5
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• pp.529-541
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• 2020

Although TBM's cutterhead requires design review for fatigue failure due to wear-induced section loss as well as heavy load during excavation, it is difficult to find a case of fatigue analysis for TBM cutterhead at present. In this study, a stress-life design review was conducted on cutter heads with a diameter of 8.2 m using S-N curves as a safety life design concept. Also, we introduced the fatigue design method of construction equipment and the method of assessing fatigue damage and explained the results of the fatigue analysis on the TBM cutter head with a diameter of 8.2 m. The S-N curve has been shown to play a key role in fatigue design and can also be used to assess how much fatigue damage a structure is suffering from at this point in time. In the future, it is necessary to find out when fatigue problems occur during using the equipment and when it is good to conduct safety inspections of the equipment.

• The Journal of Engineering Geology
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• v.5 no.1
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• pp.1-20
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• 1995

A train overturn accident occurred on March 1993 in the Gupo area, northern part of Pusan, unfortunately had taken a heavy toll of lives and caused a great loss of property as well. The reasons for the subsidence of the basement under the railroads, which presumed to be the main cause of the accident, have been investigated from many different angles, including conventional geotechnical investigation methods. The deduced nuin reasons of the subsidence were: 1. blasting for tunnel excavation (NATM) at about 39 meter under the railroads, and 2. unexpected change of bedrock conditions along the direction of tunnel. But this accident was derived nrranlv from the lack of geological and geotechnical information under railroad area because it was impossible to drill beneath the railroads. This paper introduces a new geophysical survey techniqueseisrnic geotomography, and shows some results of the method applying to investigate the underground structure of the accident area. This method not only overcomes the unfavourable environment which many conventional investigation methods cannot face, but produces an image of underground structure with high resolution. Furthermore, the outputs from geotomogaphic analysis could provide very valuable in-situ basic parameters (like seismic velocities, elastic moduli, etc.) which is essential to the design and construction.

• Korean Journal of Environmental Agriculture
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• v.18 no.3
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• pp.265-271
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• 1999

The direct seeding of seeds or the pellets of three native tree species (Pinus densiflora, Parthenocissus tricuspidata and Rhus chinensis) was tried on the rock cut-slope revegetation bed established by construction of mechanical excavation or erosion break with artificially enriched soil medium. The seed $pellet(1{\sim}2\;cubic\;cm)$ made by coating seeds(treated with proper previous pregermination treatments) with the mixture of peatmoss, clay, chemical absorbant(3.5:1.0:0.2, v/v) showed about twice better percent germination than the control seeds. The percent germination and the survival rate of the germinated seedlings were higher in the spring direct seeding than the summer or the fall. The soil medium containing the compost showed extremely low percent $germination(0{\sim}3%)$ which presumably attributed to the compost inducing damping-off disease. The survival rates were affected mainly by shading of natural herbaceous vegetation invading from outside to the revegetation bed. The planting of two year old container seedlings of P. densiflora and P. tricuspidata on August 2, 1998 was successful indicating that it could be an alternative revegetation method in case the summer direct seeding is unfavorable.

• Journal of Korean Society of Forest Science
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• v.95 no.6
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• pp.636-642
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• 2006

To make a new fairy ring of Tricholoma matsutake in situ, the way of production and transplanting of ectomycorrhizal seedlings of T. matsutake using Pinus densiflora was investigated after transplanting from 2000 to 2005 as well as the method to improve their survival rate for the fungus. For the production of ectomycorrhizal pine seedlings, the seedlings planted at the edge of fairy ring of T. matsutake in November showed 97% of the survival rate, while those planted in April showed 80% of the rate. For the complete infection of the T. matsutake, it required more than two years after planting. The infection rate of mycelia for the ectomycorrhizal seedlings was 17.6% when the natural seedlings were used, whereas it was relatively low when the seedlings prepared from the nursery were used. The survival of T. matsutake mycelium reached up to 22% by the transplanting in April, while the mycelium transplanted in October and November showed less than 5% of the survival. The survival of T. matsutake on the transplanted seedlings was the highest in the seedlings having 50% of infection rate before transplanting. Excavation of the ectomycorrhizal seedling to examine the vitality of ectomycorrhizal roots of T. matsutake resulted in the perishing of them. Therefore, the method using a 'rice bag triers' to check living mycelium of T. matsutake without digging of transplanted seedlings was introduced in this study. In addition, it is recommended that the examination has to be conducted at least two years after transplanting.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.121-129
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• 2017

There have been a number of water and sewer pipe breakdown reports followed by ground subsidence. Also, the excavating works for construction due to overcrowding of city have been common. Particularly, in urban areas ground becomes unstable because of the lowered lifeline sinkage followed excavation and backfilling. In order to solve the problem, some reinforcement works for ground by rod tamping or grouting have been applied. However, it is hard to predict when the buried utilities in underground will be damaged. Also, there is a limit for the underground exploration and investigation methods. Therefore, in this study, the estimated about the water soluble polymer pouch including poor mixed admixture which is designed to eliminate the dangerous factors. The reinforcement strength of this method was confirmed by verifying three points: meltiness in a certain period, water solubility in the ground water level, and characteristics of the pouch, which can be stored in daily conditions. It is also proved that this method allows to keep the ground from getting weakened in the installation of water and sewer pipe along with back filling materials.