• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.3
• /
• pp.303-312
• /
• 2008

Multi-axial compression tests have been frequently adopted for the evaluation of material properties of rock cores and rock fracture model tests. Special care has to be applied on the boundary condition between the specimen and loading platen to draw the precise test results of the multi-axial compression tests. With the use of dry steel platen, the stress rotation will occur, due to the frictional restraint from the boundary between the specimen and loading platen. The restraint will deviate the expected test results under the conditions of the given external pressures. Various methods have been applied to reduce the side restraint along the specimen/loading platen interface. The steel brush type loading platen is one example of the attempts. In this paper, a new type of loading platen is introduced to overcome the limitation caused by the use of the brush type loading platen, which requires some internal space for the installation of the brushes. The new type of loading platen, roller supported steel piston type loading platen. is constituted of shot steel pistons which have sufficient stiffness to deliver the external pressure and the shaft type roller installed at the rear of the pistons. The pistons are designed to follow the local deformation of the specimens. In this paper, structural details of the loading platen are presented and frictional and biaxial compression tests results are shown to verify the required functions of the loading platen. Furthermore, calibration process is followed by a comparison between the test results and numerical analyses.

• Tunnel and Underground Space
• /
• v.25 no.6
• /
• pp.568-576
• /
• 2015

In this study, scenarios based on the leakage of highly compressed air and fire occurrence turned out to be high risks in an operation stage of CAES facility were constructed and estimated. By combining Bernoulli equation with momentum equation, an expression to calculate an impact force of a jet flow of compressed air was derived. An impact force was found to be proportional to the square of diameter of fracture and the pressure of compressed air. Four types of fire scenarios were composed to evaluate an effects that seasonal change and location of fire source have on the spread behavior of smoke. Smoke from the fire ignited in the vicinity of CAES opening descended more quickly below the limit line of breathing than one from the fire occurred 10 m away from CAES opening, which is expected to occur due to a propagation of wave front of smoke. It was shown that a rate of smoke spread of the winter fire is faster than one of the summer fire and smoke from the winter fire spreads farther than one of the summer fire, which are dependent on the direction of air flow into access opening. Evacuation simulation indicated that the required safe evacuation time(RSET) of the summer and winter fires are 262, 670 s each.

• Journal of the Korean Society of Groundwater Environment
• /
• v.5 no.4
• /
• pp.192-202
• /
• 1998

We investigated the geochemistry and environmental isotopes of granite-bedrock groundwater in the Yeongcheon diversion tunnel which is located about 300 m below the land surface. The hydrochemistry of groundwaters belongs to the Ca-HCO$_3$type, and is controlled by flow systems and water-rock interaction in the flow conduits (fractures). The deuterium and oxygen-18 data are clustered along the meteoric water line, indicating that the groundwater are commonly of meteoric water origin and are not affected by secondary isotope effects such as evaporation and isotope exchange. Tritium data show that the groundwaters were mostly recharged before pre-thermonuclear period and have been mixed with younger surface water flowing down rapidly into the tunnel along fractured zones. Based on the mass balance and reaction simulation approaches, using both the hydrochemistry of groundwater and the secondary mineralogy of fracture-filling materials, we have modeled the low-temperature hydrogeochemical evolution of groundwater in the area. The results of geochemical simulation show that the concentrations of Ca$\^$2＋/, Na$\^$＋/ and HCO$_3$and pH of waters increase progressively owing to the dissolution of reactive minerals in flow paths. The concentrations of Mg$\^$2＋/ and K$\^$＋/ frist increase with the dissolution, but later decrease when montmorillonite and illitic material are precipitated respectively. The continuous adding of reactive minerals, namely the progressively larger degrees of water/rock interaction, causes the formation of secondary minerals with the following sequence: first hematite, then gibbsite, then kaolinite, then montmorillonite, then illtic material, and finally microcline. During the simulation all the gibbsite is consumed, kaolinite precipitates and then the continuous reaction converts the kaolinite to montmorillonite and illitic material. The reaction simulation results agree well with the observed, water chemistry and secondary mineralogy, indicating the successful applicability of this simulation technique to delineate the complex hydrogeochemistry of bedrock groundwaters.

• The Journal of Engineering Geology
• /
• v.25 no.3
• /
• pp.357-368
• /
• 2015

Brittle failure of Mesozoic granite in the Daejeon region is predicted using empirical analysis and numerical modeling techniques. The input parameters selected for these techniques were based on the results of laboratory tests, including damage-controlled tests. Rock masses that were considered to be strong during laboratory testing were assigned to "group A" and those considered to be extremely strong were assigned to "group B". The properties of each group were then used in the analyses. In-situ stress measurements, or the ratio of horizontal to vertical stress (k), were also necessary for the analyses, but no such measurements have been made in the study area. Therefore, k values of 1, 2, and 3 were assumed. In the case of k=1, empirical analysis and numerical modeling show no indication of brittle failure from the surface to1000 m depth. When k=2, brittle failure of the rock mass occurs at depths below 800 m. For k=3, brittle failure occurs at depths below 600 m. Although both the Cohesion Weakening Friction Strengthening (CWFS) and Mohr-Coulomb models were used to predict brittle failure, only the CWFS model performed well in simulating the range and depth of the brittle failure zone.

• The Journal of Engineering Geology
• /
• v.21 no.4
• /
• pp.281-293
• /
• 2011

We investigated the causes and characteristics of a landslide at Hwangryeong Mountain, Busan, based on aerial photos, annual precipitation data, rock fracture patterns, and geomorphic features using GIS Software, and a statistical analysis of tilted trees. The analyzed slope shows evidence of a previous slope failure event and the possibility of future failures. Although the NW-SE trending slope was relatively stable until 1975, a large-scale slope failure occurred between 1975 and 1985 due to complex factors, including favorably oriented geologic structures, human activity, and heavy rain. This indicates that a detailed study of geologic structures, slope stability, and rainfall characteristics is important for slope cuttings that could be a major factor and cause of urban landsliding events. The statistic analysis of tilted trees shows a slow progressive creeping type of mass wasting with rock falls oblique to the dip of the slope, with the slope having moved towards the west since 1985. A concentration of tree tilting has developed on the northwestern part of the slope, which could reach critical levels in the future. The analysis of deformed trees is a useful tool for understanding landslides and for predicting and preventing future landslide events.

• The Journal of the Petrological Society of Korea
• /
• v.15 no.3 s.45
• /
• pp.128-138
• /
• 2006

The west stone pagoda of Gameunssji temple site (National Treasure No. 112) has been damaged mainly by fracture, exfoliation and granular disintegration. In this study, the source area of the rocks using the west stone pagoda was examined in terms of petrological feature, magnetic susceptibility, and ${\gamma}-ray$ spectrometer. The stones include abundant crystal fragments of biotite, quartz and feldspars in the fine-grained matrix; they are petrographically discriminated to vitric-crystal tuff or crystal tuff. Measured magnetic susceptibility values are of from 10 to 20 $({\times}10^{-3}\;SI\;unit)$. From the ${\gamma}-ray$ spectrometer measurement K, eU, and eTh contents of the stones are about 3%, 0 to 8ppm, and 9 to 18 ppm, respectively. These features are used as indicators to presume the source area of the stones. Comparing the petrographical and chemical characteristics between the stones of the west stone pagoda and the country rocks near the Gameunsaji temple site, it is suggested that the most similar country rock to the stones could be dacitic volcanic rocks of the Beomgokri group in the Waeup basin. The Beomgokri group is lithostratigraphically divided into Waeupri tuff, Yongdongri tuff and Beomgokri volcanic rocks. Among the three rocks, the crystal tuff of the Beomgokri volcanic rocks seems likely to have been the source rock of the stones of the west stone pagoda.

• Korean Journal of Heritage: History & Science
• /
• v.45 no.1
• /
• pp.86-101
• /
• 2012

The constituting rocks of Multi-storied Round shape stone Pagoda of Unjusa Temple are lithic tuff and rhyolite tuff breaccia which show green or grey and also rock fragment with poor roundness are present in the structure. lithic tuff is composed of feldspar and quartz which are glassy texture and cryptocrystalline and also micro crystalline are scattered. phenocryst quartz and feldspar in the substrate composed of feldspar and opaque minerals are found in rhyolite tuff breaccia. dust, exfoliation, cavity, fracture and crack are observed in all the stone of the pagoda and the result of Infrared Thermography shows partial inter cavities have developed severely which may cause further exfoliation. In addition, a great deal of various grey, green, and yellow brown lichen as well as bryophyte are present at the upper part of eastern and western roof stone located above the third floor. Discolors remarkably shown at stereobate and roof stone are identified as inorganic pollutants such as manganese oxide, iron oxide and iron hydroxide. The stone of the pagoda of the Chemical Index of Alteration (CIA) and the Weathering Potential Index (WPI) are 55.69 and 1.12 respectively and this corresponds to a highly weathered stage. The measured values, average ultrasonic velocity 2,892m/s, coefficient of weathering 0.4k and compressive strength $1,096kg/cm^3$, suggest that the rock strength and durability are weakened.

• The Journal of Engineering Geology
• /
• v.22 no.1
• /
• pp.1-13
• /
• 2012

The purpose of this work is to gain a better understanding of the interrelationships between geological structures and slope failure in sedimentary rocks. In the studied slopes, construction-related slope failure could only be observed on the south-dipping slopes. This indicates that slope stability may be dependent on the angular relationships between the dip direction of bedding and the orientation of the slope. Slope failure continued, post-construction, around large fault zones in the studied outcrop; these fault damage zones are, however, not easily recognized in the field. Here we suggest a new method that uses accumulated fracture density to precisely identify fault damage zones. Multiple-faced slopes are now increasingly being exposed during large-scale construction projects in South Korea. This multiple-faced slope analysis indicates that the stability of a slope should be evaluated by identifying domains, through the analysis of possible slopes and their angular relationships with bedding and other discontinuities, prior to construction. Therefore, careful consideration of geological structures such as bedding and other discontinuities, and their angular relationships during the design of cuttings through sedimentary rocks, will increase the efficiency of construction and enable the safe construction of more stable slopes that will retain their stability after construction.

• The Journal of Engineering Geology
• /
• v.30 no.1
• /
• pp.17-30
• /
• 2020

An optical televiewer is a geophysical logging device that produces continuous high-resolution full-azimuth images of a borehole wall using a light-emitting-diode and a complementary metal-oxide semiconductor image sensor to provide valuable information on subsurface discontinuities. Recently, borehole imaging logging has been applied in many fields, including ground subsidence monitoring, rock mass integrity evaluation, stress-induced fracture detection, and glacial annual-layer measurements in polar regions. Widely used commercial borehole imaging logging systems typically have limitations depending on equipment specifications, meaning that it is necessary to clearly verify the scope of applications while maintaining appropriate quality control for various borehole conditions. However, it is difficult to directly check the accuracy, implementation, and reliability for outcomes, as images derived from an optical televiewer constitute in situ data. In this study, we designed and constructed a modular fractured borehole model having similar conditions to a borehole environment to report unprecedented results regarding reliable data acquisition and processing. We investigate sonde magnetometer accuracy, color realization, and fracture resolution, and suggest data processing methods to obtain accurate aperture measurements. The experiment involving the fractured borehole model should enhance not only measurement quality but also interpretations of high-resolution and reliable optical imaging logs.

• Journal of the Mineralogical Society of Korea
• /
• v.19 no.4 s.50
• /
• pp.239-246
• /
• 2006

KAERI Underground Research Tunnel (KURT) was recently constructed through the site investigation from the yea. of 2003 at KAERI site, Dukjin-dong, Yuseong-gu, Daejeon city. The geo-logic setting of the site has been slightly metamorphosed. There are small fractures developed in the rock and several kinds of secondary filling minerals exist in the fractures. We examined mineralogical characteristics of fracture-filling calcite, which is not only largely distributed, but also can significantly affect the radionuclides migration. The calcite is found along fractures like other secondary minerals, forming thick veins in part. Most calcite-filled fractures contain quartz, iron oxides, and dolomite as minor minerals. The calcite crystals show an characteristic appearance with an uniformly oriented growth, coated with goethite on the edge and the etch-pit sites of their surface. Some calcite crystals have been newly formed by the precipitation of elements dissolved from the tunnel shotcrete wall, and their morphology changed according to the chemistry and flow of groundwater. The calcite can modify the groundwater chemistry and significantly affect the sorption behavior of radionuclides. The characteristic crystal structure and surface morphology of the calcite examined in the KURT site will be used as important basic data for the radionuclide migration experiment in the future.