Seokwon Jeon

Measurement of rock fracture toughness under modes I and II and mixed-mode conditions by using disc-type specimens

Rock fracture mechanics has been widely applied to blasting, hydraulic fracturing, mechanical fragmentation, rock slope analysis, geophysics, earthquake mechanics, hot dry rock geothermal energy extraction and many other practical problems. But a standard method to accurately determine fracture toughness of rocks, one of the most important parameters in fracture mechanics as an intrinsic property of rock, has not been yet well established. To obtain rock fracture toughness, disc-type specimens were used in this study. Rock fracture toughness under mixed-mode conditions was measured by using the straight-through crack assumption (STCA) applied to the cracked chevron-notched Brazilian disc (CCNBD) specimen and the semicircular bend (SCB) specimen. Size effects, in terms of specimen thickness, diameter and notch length on fracture toughness, were investigated. From the mixed-mode test results, fracture envelopes were obtained by applying various regression curves. The mixed-mode test results were also compared with the three well-known mixed-mode failure criteria.

Electrochemical behaviors of low-Co Mm-based alloys as MH electrodes

Abstract A series of low-Co Mm-based alloys were prepared and studied for possible application in Ni/MH batteries. Alloy phase structure and electrochemical properties of MH electrodes were investigated. For comparison, the MmNi 3.75 Co 0.62 Mn 0.36 Al 0.27 alloy, having a composition close to the commercial MmNi 3.55 Co 0.75 Mn 0.4 Al 0.3 alloy, was also examined. Electrochemical measurements show that the low-Co MmNi 3.65 Co 0.22 Mn 0.36 Al 0.27 Cr 0.2 Cu 0.2 Si 0.1 alloy exhibits satisfactory cycling stability, though the initial capacity (273 mAh/g) is lower than that of the high-Co MmNi 3.75 Co 0.62 Mn 0.36 Al 0.27 alloy (314 mAh/g). After 300 cycles at 1.0C rate, the capacity decay is 25.6% for the low-Co MmNi 3.65 Co 0.22 Mn 0.36 Al 0.27 Cr 0.2 Cu 0.2 Si 0.1 alloy and 24.4% for the high-Co MmNi 3.75 Co 0.62 Mn 0.36 Al 0.27 alloy, respectively. In addition, electrochemical impedance spectroscopy (EIS) studies have also been carried out in order to understand interfacial electrochemical reactions on MH electrodes.

MODELING THE HYDRAULIC CHARACTERISTICS OF A FRACTURED ROCK MASS WITH CORRELATED FRACTURE LENGTH AND APERTURE: APPLICATION IN THE UNDERGROUND RESEARCH TUNNEL AT KAERI

A three-dimensional discrete fracture network model was developed in order to simulate the hydraulic characteristics of a granitic rock mass at Korea Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT). The model used a three-dimensional discrete fracture network (DFN), assuming a correlation between the length and aperture of the fractures, and a trapezoid flow path in the fractures. These assumptions that previous studies have not considered could make the developed model more practical and reasonable. The geologic and hydraulic data of the fractures were obtained in the rock mass at the KURT. Then, these data were applied to the developed fracture discrete network model. The model was applied in estimating the representative elementary volume (REV), the equivalent hydraulic conductivity tensors, and the amount of groundwater inflow into the tunnel. The developed discrete fracture network model can determine the REV size for the rock mass with respect to the hydraulic behavior and estimate the groundwater flow into the tunnel at the KURT. Therefore, the assumptions that the fracture length is correlated to the fracture aperture and the flow in a fracture occurs in a trapezoid shape appear to be effective in the DFN analysis used to estimate the hydraulic behavior of the fractured rock mass.

Study on the Electrode Characteristics of Hypostoichiometric Zr‐Ti‐V‐Mn‐Ni Hydrogen Storage Alloys

The hydrogen storage performance and electrochemical properties of Zr 1-X Ti X (Mn 0.2 V 0.2 Ni 0.6 ) 1 8 (X = 0.0, 0.2, 0.4, 0.6) alloys are investigated. All of these alloys have mainly a C14-type Laves phase structure according to X-ray diffraction analysis. As the mole fraction of Ti in the alloy increases, the reversible hydrogen storage capacity decreases, while the equilibrium hydrogen pressure increases. Furthermore, the discharge capacity shows a maximum and the rate capability is increased, but the cycling durability is rapidly degraded with increasing Ti content in the alloy. The analysis of surface composition shows that the rapid degradation of Ti-substituted Zr-based alloy electrodes is due to the growth of an oxygen penetration layer. After comparing the radii of atoms and ions in the electrolyte, it is clear that the electrode surface becomes more porous, which is the source of growth of the oxygen penetration layer and causes accelerating the dissolution of alloy constituting elements with increasing Ti content. Consequently, the rapid degradation (fast growth of the oxygen-penetrated layer) with increasing Ti substitution in Zr-based alloy is ascribed to the formation of a porous surface oxide through which the oxygen atom and hydroxyl ion, with relatively large radii can easily transport into the alloy surface.

Performance Assessment of Hard Rock TBM and Rock Boreability Using Punch Penetration Test

AbstractRock indentation tests are often called punch penetration tests and are known to be related to penetration rates of drilling equipment and hard rock tunnel boring machines (TBMs). Various indices determined from analysis of the force-penetration plot generated from indentation tests have been used to represent the drillability, boreability, and brittleness of rocks. However, no standard for the punch penetration test procedure or method for calculating the related indices has been suggested or adopted in the rock mechanics community. This paper introduces new indices based on the punch test to predict the performance of hard rock TBMs. A series of punch tests was performed on rock specimens representing six rock formations in Korea with different dimensions, i.e., the core specimens had different lengths and diameters. Of the indices obtained from the punch tests, the peak load index and mean load index showed good correlations with the cutting forces measured in full-scale linear cutting machine tests on the same rock types. The indices also showed good linear correlations with the ratio of uniaxial strength to Brazilian tensile strength, which indicates the brittleness of rock. The scale effect of using core specimens was investigated, and a preferred dimension for the punch test specimens is proposed. This paper also discusses the results of the punch test and full-scale rock cutting tests using LCM. The results of this study confirm that the proposed indices from the punch tests can be used to provide a reliable prediction of the cutting forces that act on a disc cutter. The estimated cutting forces can then be used for optimization of cutter-head design and performance prediction of hard rock TBMs.

Determination of Rock Abrasiveness using Cerchar Abrasiveness Test

Abstract Abrasiveness of rock plays an important role on the wear of rock cutting tools. In this study, Cerchar abrasiveness tests were carried out to assess the abrasiveness of 19 different Korean rocks. Cerchar abrasiveness test is widely used to assess the abrasiveness of rock because of its simplicity and inexpensive cost. This study examines the relationship between Cerchar Abrasiveness Index (CAI) and mechanical properties (uniaxial compressive strength, Brazilian tensile strength, Young’s modulus, Poisson’s ratio, porosity, shore hardness of rock), and the effect of quartz content, equivalent quartz content, which was obtained from XRD analysis. As a result of test, CAI was more influenced by petrographical properties than by the bonding strength of the matrix material of rock. CAI prediction model which consisted of UCS and EQC was proposed. CAI decreased linearly with the hardness of the steel pin. Numerical analysis was performed using Autodyn-3D for simulating the Cerchar abrasiveness test. In the simulations, most of pin wear occurred during the initial scratching distance, and CAI increased with the increase of normal loading.

Design of pyongtaek LPG storage terminal underneath the Lake Namyang

This paper presents the geo-engineering problems and approaches in the design of the first kind LPG storage terminal underneatha lake in the western part of Korea. The Pyongtaek LPG Terminal was proposed to be constructed underneath the Lake Namyang to facilitate the storage caverns within the limited property boundary complicated with complex geological conditions and potential interference with the neighboring storage caverns L-1 in operation. To precisely characterize the geological feature of the bed rock underneath the lake with very limited information from the outcrops, a new method of geophysical investigation was applied. And to prevent the potential hydrogeological interference with the neighboring L-1 in operation, discreet evaluation of geological data and numerical analyses were carried out. As a result, vertical and horizontal water curtain systems were constructed to prevent the detrimental draw-down of water level nearby the L-1. The depth and geometry of the new cavern were determined based on the in situ stress and operation pressure to have as large capacity as possible to overcome the spatial constraints. The continuous monitoring during the construction of the storage caverns and tunnels, any unfavorable measurement for the final tightness of the storage cavern was not taken. In May 1999, the first LPG supply in the cavern was made after the acceptance test.

A numerical study on rock cutting by a TBM disc cutter using SPH code

3 Senior researcher, Construction Equipment and Parts R&D group, Korea Institute of Industrial Technology ABSTRACT: Numerical simulation on rock cutting by a TBM disc cutter was carried out using SPH (Smoothed Particle Hydrodynamics) code. AUTODYN3D, a commercial software program based on finite element method, was used in this study. The three-dimensional geometry of a disc cutter and a rock specimen were modeled by Lagrange and SPH code respectively. The numerical simulation was carried out for Hwangdeung granite for 10 different cutting conditions. The results of the numerical simulation, i.e. the relation between cutter force and failure behavior, had a good agreement with those from LCM test. The cutter forces measured in the numerical simulation had 10% deviation from the LCM test results. Moreover, the optimum cutter spacing was almost identical with the experimental results. These results indicate that SPH code can be successfully used had applicability for simulation on rock cutting by a TBM disc cutter. However, further study on Lagrange-SPH coupled modelling would be necessary to reduce the computation time.

A Study on Punch Penetration Test for Performance Estimation of Tunnel Boring Machine

This paper discusses the methods of estimating the punch penetration indices and data analysis punch penetration test to estimate the TBM normal force and penetration rate. In punch penetration test is known as a useful test to estimate penetration rates and normal force of TBMs directly with several slope indices indicated drill-ability and brittleness of rocks. However, the standard methods and indices for punch penetration test are not suggested yet. The main purpose of punch penetration test which is prediction of normal force of TBM disc cutter when cutters excavate rock mass. In this study, the punch penetration tests were performed for 6 representative Korean rock types and variety length and diameter of rock core specimens. Among slope indices were obtained from punch penetration test, PLI and MLI which is suggested in this study show high correlation with cutter force measured by full-scale cutting test. The results show that the predicted normal force of a single disc cutter and the experimental error was 10%. Based on these results, it is concluded that punch penetration test is reliable laboratory test for estimating thrust and penetration rates of TBM.

Numerical evaluation of affecting parameters of surface subsidence in abandoned mine areas

Surface subsidence in abandoned mine areas is a keen issue since it can cause loss of lives and serious property damage. However, the hazard of surface subsidence cannot usually be predicted in advance because surface subsidence is affected by many parameters. In this study, numerical simulation was carried out to predict the probability of surface subsidence. Many factors, such as cavity size, geometry, rock mass condition, rainfall and groundwater table, are well known for their key roles. Much research has been carried out to predict the probability of surface subsidence induced by the collapse or squeezing of a mined opening. In this study, the cavity geometry (i.e. depth, width, height and angle of cavity) and rock mass condition were selected as the key parameters for subsidence. A conceptual genetic cavity model in a horizontally layered rock mass was considered in the numerical simulation. The relationship between each of the selected factors and the hazard of subsidence was obtained. The vertical displacement observed at the ground surface with varying parameters was analyzed to evaluate their influences using a statistical method.