• Geomechanics and Engineering
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• v.22 no.1
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• pp.1-9
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• 2020

This paper presents an investigation of the ground response of a gob-side gateroad suffering mining stress induced by a 21 m-thick coal seam extraction. A field observation, including entry convergence and stress changes monitoring, was first conducted in the tailgate 8209. The observation results of entry convergence showed that, during the adjacent panel 8210 retreating period, the deformation of the gob-side gateroad experienced a continuous increase stage, subsequently, an accelerating increase stage, and finally, a slow increase stage. However, strong ground response, including roof bending deflection, rib extrusion and floor heave, occurred during the current panel 8209 retreating period, and the maximum floor heave reached 1530 mm. The stress changes within coal mass of the two ribs demonstrated that the gateroad was always located in the stress concentrated area, which responsible for the strong response of the tailgate 8209. Subsequently, a hydraulic fracture technique was proposed to pre-fracture the two hard roofs above the tailgate 8209, thus decreasing the induced disturbance on the tailgate. The validity of the above roof treatment was verified via field application. The finding of this study could be a reference for understanding the stability control of the gob-side gateroad in extra thick coal seams mining.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.2
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• pp.123-134
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• 2013

Urban underground structures at low ground elevations (i.e. shallow substructures) unlike typical tunnel structures are subjected to low overburden and high water pressures. This often causes the underground structures to become damaged. Various conventional methods for the urban underpass structures such as dead weight increasement, round anchors, and tension piles, are significantly conservative and provok concerns about the costly, time-consuming installation process. Recently, permanent drainage system becomes to widely use for supplementing the conventional method's shortcomings, but, it is applied without the considerations for ground conditions and water table. In this study, therefore, numerical analyses are performed with various parameters such as groundwater level, wall height, and ground conditions in order to establish design guidelines for induced drainage system which is a kind of the permanent drainage method constructed at the Y-area. According to the numerical results, the induced drainage system is very effective in reducing the uplift pressure that acts on the base of underpass structures.

• International Journal of Aeronautical and Space Sciences
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• v.10 no.1
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• pp.20-29
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• 2009

There are concerns about the influence of the gust wind caused by helicopters affecting the moving vehicles while hovering over the road during rescue activities. For the understanding of such complicated flow. numerical simulation of a rotor hovering above the ground has been carried out, changing the rotor/ground clearances. The rotor thrust is kept constant. and the rotor control is determined by trim adjustments incorporated into the CFD algorithm. Collective pitch angle and the required power decreases with the rotor/ground clearance which agrees with experience. Changes of the flowfield near the rotor with regard to the rotor height are investigated based on the calculated results.

• Journal of Ocean Engineering and Technology
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• v.11 no.1
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• pp.55-64
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• 1997

A wing operating in close proximity to the ground exhibits a reduction in induced drag, which increase the lift/drag ratio. The poert-augmented ram (RAR) phenomenon involves directiing the efflux from forward mounted propulsion ststem under the wings, with the efflux nearly stagnated under the wings. In the present paper, 3 dimentional PAR was numerically studied by solving the Navier-Stokes equations. Pressure distribution and velocity vectors are calculated around the wing surface and the ground. Through the numerical simulation, Cp values and lift/drag ratio are carefully reviewed by changing the height/chord; 0.05, 0.1, 0.3 and 0.8. The shape of model is NACA 0012 with a span/chord ratio of 3.0. According to the numerical results, the relationship between lift/drag and height/chord is fairly reasonable.

• Journal of the Korean Society of Safety
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• v.19 no.3 s.67
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• pp.108-117
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• 2004

Dynamic analysis method is Presented for analyzing rectangular liquid storage structures excited by horizontal and vertical ground motions. The irrotational motion of invicid and incompressible ideal fluid in rigid rectangular liquid storage structures subjected to horizontal and vertical ground motions and the motion of fluid induced by structural deformation are expressed by analytic solutions. Analysis methods are obtained by applying analytic solutions of the fluid motion to finite element equation of the structural motion. The fluid-structure interaction effect is reflected into the coupled equation as added fluid mass matrix. The free surface sloshing motion, hydrodynamic pressure acting on the wall and structural behavior due to horizontal and vertical ground motions are obtained by the presented method.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1218-1231
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• 2008

Recently the energy dependence of LNG resource is being increased. So the enlargement of LNG storage is constructed in the coastal area. Most of LNG tanks are constructed below the ground level, and thus the hydraulic uplift pressure could be a problem against the weight of tank structure. Specifically, the settlement of foundation soil in the LNG tank is also important in the aspect of safety. The low temperature around LNG tank is induced the ground freezing and hence increasing the soil volume and earth pressure. The additional lateral earth pressure due to ground freezing could be applied to the LNG tank. In this study, the stability of LNG storage tank was evaluated with consideration of freezing earth pressure by using computer program TEMP-W.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.736-737
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• 2007

The single point bonding in underground transmission system can induce high voltage on the sheath when ground fault, lightning serge and switching serge occurs, at that time underground cable systems cannot offer a return path of fault current. Accordingly if fault current, which cannot return to ground, flows at the single point bonding, high voltage can be induced in SVL and that voltage can cause aging and breakdown of SVL. Therefore this paper study on the effect of parallel ground conductor at the single point bonding when ground fault and lightning serge occurs by using ATPDraw.

• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.377-390
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• 2019

A method for estimating the floor response spectra (FRS) of elastic structures under earthquake excitations is proposed. The method is established based on a previously proposed direct estimation method for single degree of freedom systems, which generally overestimates the FRS of a structure, particularly in the resonance period range. A modification factor is introduced to modify the original method; the modification factor is expressed as a function of the period ratio and is determined through regression analysis on time history analysis results. Both real and artificial ground motions are considered in the analysis, and it is found that the modification factors obtained from the real and artificial ground motions are significantly different. This suggests that the effect of ground motion should be considered in the estimation of FRS. The modified FRS estimation method is further applied to a 10-story building structure, and it is verified that the proposed method can lead to a good estimation of FRS of multi-story buildings.

• Journal of the Society of Disaster Information
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• v.4 no.2
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• pp.10-27
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• 2008

When the ground is excavated adjacent to the existing tunnel, which is loaded by the surcharge on the ground surface, the tunnel stability would be very sensitive to the deformation of the ground induced by the horizontal displacement of braced wall. The stability of the existing surcharged tunnel could be controlled by pre-loading on the braced wall. In this paper, it was investigated, if it would be possible to keep the existing surcharged tunnel stable by preventing the horizontal displacement of a braced wall by imposing the pre-loading during the ground excavation. For this purpose, large scale model tests were performed in a scale 1/10 at the test pit which was 2.0m in width and 6.0m in height and 4.0m in length. Isotropic test ground was constructed homogeneously by wet sand. Model tunnel was constructed in the test ground. Surcharge was loaded on the ground surface above the tunnel. During the tests, the behavior of model tunnel and model braced wall was measured. Numerical analyses were also performed in the same condition as the tests. And their results were compared to that of the model tests. Consequently, the effect of a surcharge could be compensated by imposing the pre-loading on the braced wall. The existing tunnel and the braced wall could be kept stable by preventing the horizontal displacement of the braced wall through pre-loading, although the tunnel is surcharged.

• Geomechanics and Engineering
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• v.30 no.6
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• pp.551-564
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• 2022

Fragmenting the rock mass is considered as the most important work in open-pit mines. Ground vibration is the most hazardous issue of blasting which can cause critical damage to the surrounding structures. This paper focuses on developing an explicit model to predict the ground vibration through an multi objective evolutionary polynomial regression (MOGA-EPR). To this end, a database including 79 sets of data related to a quarry site in Malaysia were used. In addition, a gene expression programming (GEP) model and several empirical equations were employed to predict ground vibration, and their performances were then compared with the MOGA-EPR model using the mean absolute error (MAE), root mean square error (RMSE), mean (𝜇), standard deviation of the mean (𝜎), coefficient of determination (R²) and a20-index. Comparing the results, it was found that the MOGA-EPR model predicted the ground vibration more precisely than the GEP model and the empirical equations, where the MOGA-EPR scored lower MAE and RMSE, 𝜇 and 𝜎 closer to the optimum value, and higher R² and a20-index. Accordingly, the proposed MOGA-EPR model can be introduced as a useful method to predict ground vibration and has the capacity to be generalized to predict other blasting effects.