• Journal of Soil and Groundwater Environment
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• v.8 no.1
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• pp.48-56
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• 2003

A geophysical conductivity logging technique has been adopted to determine hydraulic constants using a simplified physical model that depicts the borehole condition. An experiment has been made by monitoring the conductivity change within the model hole using borehole environment water and incoming-outgoing water of different salinity, under the state of constant flow rate by maintaining balance between inflow and outflow. Conductivity variation features were observed that depended on flow rate, salinity contrasts between fluid within the hole and incoming-outgoing fluid, and density contrasts between fluid conductivity within the hole and incoming fluid. The results of the experiment show the uniform change of fluid conductivity within the hole with time, a fairly good correlation between the flow rate and the conductivity change rate. The geophysical conductivity logging technique can be an efficient tool for determining hydraulic constants if the model equation is verified by henceforward experiments.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.4
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• pp.479-490
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• 2018

The granite melting concept, which was suggested by Gibb's group for the closing of a deep borehole, was experimentally checked for KURT granite. The granite melting experiments were performed in two pressure conditions of atmospheric melting with certain inorganic additives and high pressure melting formed by water vaporization. The results of atmospheric tests showed that KURT granite started to melt at a lower temperature of $1,000^{\circ}C$ with NaOH addition and that needle shaped crystals were formed around partially melted crystals. In high pressure tests, vapor pressure was increased by adding water with maximum pressure of about 400 bars. KURT granite was partially melted at $1,000^{\circ}C$ when vapor pressure was low. However, it was not melted at vapor pressures higher than 200 bars. Therefore, it was determined that high pressure with a small amount of water vapor more effectively decreased the melting point of granite. Meanwhile, high temperature and high pressure vapor caused severe corrosion of the reactor wall.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.429-438
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• 2017

Monte Carlo N-Particle (MCNP) modeling algorithm based on the Monte Carlo method was used to perform the simulation of neutron logging in order to increase the reliability and utilization of neutron logs applied in geological and resource engineering fields. To perform the simulation using MCNP, we used a realistic three-dimensional configuration of neutron sonde and formation. Validation of the modeling was confirmed by comparing the calibration curves of sonde manufacture with those calculated by MCNP modeling. After the validation, lithology effects, pore fluid effects, borehole diameter change, casing effect, and effects of borehole water level were investigated through modeling experiments. Numerical tests indicate that changes in neutron count ratio according to the lithology were quantitatively understood. In case of a borehole with a diameter of 3 inches, ratio of counting rates was higher than expected to be interpreted as borehole fluid has small effects on neutron logging. Effect of casing was also small in general, particular when porosity increases. Since modeling results above the groundwater level showed a tendency opposite to those below the groundwater level, neutron logs can be used to detect groundwater level. The modeling results simulated in this study for various borehole environments are expected to be used for data processing and interpretation of neutron log.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.1-11
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• 2017

In order to improve the accuracy of microseismic epicenter location through the inversion techniques using P and S wave first arrivals, field experiments of microseismic monitoring were performed using borehole 3-component geophones. The direction of epicenter was estimated from the hodograms of P-wave first arrivals through the weight drop experiments in which the $\times$ component of 3-component geophone was aligned to the magnetic north. The picking of S wave first arrival was possible in the polarization filtered data even if S waves are difficult to be identified in raw data. The inversion technique using only P wave first arrival times can often converge to the local minimum when the initial values for epicenter are largely apart from the true epicenter, so that the correct solution can not be found. To solve this problem, the epicenter determination method using differences between P and S wave arrival times was used to estimate proper initial values of epicenter. The inversion result using only P-wave first arrival times which started from the estimated initial values showed the improved accuracy of the epicenter location.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.69-76
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• 2007

High-frequency electromagnetic (EM) wave propagation associated with borehole ground-penetrating radar (GPR) is a complicated phenomenon. To improve the understanding of the governing physical processes, we employ a finite-difference time-domain solution of Maxwell's equations in cylindrical coordinates. This approach allows us to model the full EM wavefield associated with crosshole GPR surveys. Furthermore, the use of cylindrical coordinates is computationally efficient, correctly emulates the three-dimensional geometrical spreading characteristics of the wavefield, and is an effective way to discretise explicitly small-diameter boreholes. Numerical experiments show that the existence of a water-filled borehole can give rise to a strong waveguide effect which affects the transmitted waveform, and that excitation of this waveguide effect depends on the diameter of the borehole and the length of the antenna.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.491-498
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• 2004

In recent years, as an effort to grasp the leading position in the field of maritime trading, new ports and container terminals arc now under construction. Old ports are extended. At the beginning, stones were thrown down to form stone embankments, that is stone-dams, in the outer and inner boundaries of the planned reclamation-land. S.C.P(Sand Compaction Pile) works are often needed to improve the stability of stone-dams, where marine sediments arc relatively thick. Here, interests are centered on the shape of stone body. In this, drilling work won't provide a sufficient resolution. In addition, the result corresponds to only one borehole point information. Thus, the aim of this paper is to introduce an affordable technology, that is, a combined geophysical method(seismic tomography + Televiewer) enables to get the whole information about stone-dam section. The measuring and evaluating procedure is described in detail with an emphasis on dealing with the use of seismic detonator, proper borehole deployment and integrated data analysis. Examples of field experiments at Busan new port are illustrated, which will prove the benefit of combined geophysical method.

• Geomechanics and Engineering
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• v.22 no.2
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• pp.133-142
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• 2020

The evolution of the mining-induced fracture network formed during longwall top coal caving (LTCC) has a great influence on the gas drainage, roof control, top coal recovery ratio and engineering safety of aquifers. To reveal the evolution of the mining-induced stress and fracture network formed during LTCC, the fracture network in front of the working face was observed by borehole video experiments. A discrete element model was established by the universal discrete element code (UDEC) to explore the local stress distribution. The regression relationship between the fractal dimension of the fracture network and mining stress was established. The results revealed the following: (1) The mining disturbance had the most severe impact on the borehole depth range between approximately 10 m and 25 m. (2) The distribution of fractures was related to the lithology and its integrity. The coal seam was mainly microfractures, which formed a complex fracture network. The hard rock stratum was mainly included longitudinal cracks and separated fissures. (3) Through a numerical simulation, the stress distribution in front of the mining face and the development of the fracturing of the overlying rock were obtained. There was a quadratic relationship between the fractal dimension of the fractures and the mining stress. The results obtained herein will provide a reference for engineering projects under similar geological conditions.

• Journal of the Korean GEO-environmental Society
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• v.10 no.2
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• pp.61-68
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• 2009

This paper presents the numerical investigation for the hydraulic behavior of a fractured rock mass with a hydromechanical interaction which may be considered during the in-situ hydraulic injection test. These experiments consist in a series of flow meter injection tests for fractures existing along an open hole section installed in a borehole, and experimental results are applied for testing a numerical model developed to the analysis and prediction of such hydromechanical interactions. Field experimental results show that conductive fractures form a dynamic and interdependent network, that individual fractures cannot be adequately modeled as independent systems, that new fluid intaking zones generate when pore pressure exceeds the minimum principal stress magnitude in that borehole, and that pore pressures much larger than this minimum stress can be further supported by the circulated fractures. In this study, these characteristics are investigated numerically how to influence the morphology of the natural fracture network in a rock mass by using a discrete fracture ntework model.

• The Journal of Engineering Geology
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• v.21 no.2
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• pp.147-156
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• 2011

We conducted laboratory experiments to determine the physical and mechanical properties, and the failure behaviors, of cements for use as grouting material in a $CO_2$-injection borehole. Samples with lour different ratios of water to cement mass (0.4, 1, 2, and 3) were tested. The analyzed properties (porosity, sonic velocity, modulus, and compressive and tensile strengths) varied systematically as a function of the ratio of water to cement (w/c), showing a sharp change between w/c ratios of 0.4 and 1. Triaxial compression tests revealed a clear boundary between brittle and ductile failure depending on the w/c ratio and confining pressure. The present results can be utilized as input parameters for numerical models to understand the initial deformation and failure behavior of grouting cements in a $CO_2$-injection borehole.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.87-92
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• 2014

The Ground anchor is reinforcement to resist pull-out through ground that is used supports structure. The pull-out resistance of anchor is constructed by skin friction resistance from compression borehole wall in expanded wings and bearing pressure from the ground. Especially, underreamed ground anchor is reinforcement that adopts active reinforcement to prevent deformation of ground using bearing resistance generated reaming anchorage. This study is conducted to calculate bearing resistance of underreamed ground anchor. Realistic model tests were fulfilled to determine bearing resistance of anchor, and correlate results of tests to Uniaxial Compressive Strengths (UCS) of ground models that assumed weathered rock condition in 8 case. In a comprehensive series of the tests, the bearing resistances were measured by pull-out tests. The bearing resistances derived from tests have a linear correlation with UCS. We also suggest empirical equation between bearing resistance and UCS of rocks by single linear regression analyses. In test results of this study, the bearing resistances were evaluated approximately 13 times higher than UCS of the grounds, and it is qualitatively similar to numerical values of pull-out force derived from theory.