• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.95-102
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• 2003

Corestone rock mass has complex characters because it is made up of stronger and stiffer corestone in a weaker and softer matrix. Physical model corestone rock mass made up of stiffer corestone in weaker matrix were tested in uniaxial compression and numercal modelling analysis The result of the uniaxial compression tests showed that increasing the corestone proportion generally increased the modulus of deformation. And the strength decreased in the lower corestone proportion, but it increased in the higher proportion(45%, 65% corestone by volume). The strength and the modulus of deformation were not affected by different size coretone on the same proportion. The result of the numerical modelling analysis showed similar trend compared with the result of the result of the uniaxial compression test. But though the result of th uniaxial compression test is similar to the result of the numerical modelling analysis, it's unreasonalble to apply the results of this paper to in situ corestone rock mass. So mere laboratory tests including triaxial test and the other numerical program analyses are necessary to apply the results to in situ corestone mass

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.327-333
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• 2004

Corestone ground mass has complicated characteristics as it is made up of hard and stiff corestone in a relatively weak and soft matrix. Model corestone ground mass which is physically identical with the stiff corestone in weak matrix were tested in uniaxial compression. The tests show that the increase of the corestone proportion brought the gradual increase of the elastic modulus as well. The ground mass was weaker when the corestone proportion was low while it was stronger in higher corestone proportion. The size of the corestone had no influence on the strength and elastic modulus as long as the proportion of the corestone remains same.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.7 no.1
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• pp.68-76
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• 2004

Corestone ground mass has complicated characteristics as it is made up of hard and stiff corestone in a relatively weak and soft matrix. Model corestone ground mass whichis physically identical with the stiff corestone in weak matrix were tested in uniaxial compression. The tests showthat the increase of the corestone proportion brought the gradual increase of the elastic modulus as well. The ground mass was weaker when the corestone proportion was low while it was stronger in higher corestone proportion. The size of the corestone had no influence on the strength and elastic modulus as long as the proportion of the corestone remains same.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.551-558
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• 2000

When cut slope is excavated, corestone in cut slope exists 20∼30%. In case of soil and soft rock mixing, people lay out gradient of 1 : 0.5, because of soft rock slope. In a case, slope that exists corestone between soil happens to large landslide. So, As a study performs geological survey, Analysis of slope stability reinforcement measures, etc, A study presents example meaures and analysis on slope stability of corestone.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.89-99
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• 2007

This paper intends to introduce more objective and qualitative rock mass classification method easily applicable to the excavation of gneissic masses showing corestone weathering profiles. It is proven that corestone weathering profile could be divided with reasonable accuracy into digging, ripping and blasting layers using visual and simple mechanical techniques such as Schmidt hammer rebound test on cut slopes, taking into consideration strength and spacial distribution of corestone, workability and work efficiency of excavation. Also, seismic refraction surveys were employed for shallow investigations (down to $20{\sim}30m$ depth) in corestone weathering profile and conducted across the top of vertical exposures where the underlying geology could be directly inspected. Some discrepancies ($3{\sim}4m$ in average and 6 m occasionally) between the actual and assumed materials with respect to seismic velocities were observed. Thus it can be concluded that field geotechnical mapping and field seismic test should be used together in order to get a relatively good accuracy in assessing likely excavation conditions of corestone weather-ing profiles.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.435-443
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• 2007

This study shows the prediction of the engineering properties of weathered zone bearing corestones through the engineering geological surveys and the scale model test in the laboratory. The window survey and the observation on the borehole core were peformed on three natural slopes in corestones area in order to analyse the distribution pattern and the geometrical properties of corestones. Natural corestones were crushed and abrased for the scale model test into less than 5 mm in maximum-2mm in average by the scale reduction ratio based on the size of natural corestones and the specimen size. Scale model tests were carried out on soil and plaster model specimens with different corestone content ratio - 0%, 10%, 20%. The direct shear test on soils shows that shear strength is increased by the increase of corestone content ratio. The increase of cohesion is, however, more important factor to the shear strength of soil for 20% corestone content ratio due to interlocking of crushed corestone particles. The plaster model test shows a tendance of increase of UCS and modulus of elasticity with increase of corestone content. The variation ratio of specimen property by change of corestone content ratio in plaster model test was applied to in situ properties in order to estimate the properties of weathered zone bearing corestones. So it could be predicted that the increase of corestone content to 10% and to 20% produce about 18% and 30% UCS's increase respectively.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2007.03a
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• pp.130-139
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• 2007

We have carried out numerical compression experiments to estimate the mechanical properties (Mohr-Coulomb and elastic) of corestone-bearing saprolites in Beolgyo area. The studied saprolite, consisting of mechanically much stronger corestone and weaker matrix, is a weathering product of the Precambrian granitic gneiss in the Youngnam massif. Since the saprolite consists of larger corestones with diameter up to 2m, it is impossible to directly measure the mechanical properties by physical experiments. We have measured the mechanical properties of corestone and matrix from naturally occurring saprolite and have used them as a reference for our numerical model. Then, we mixed each material and carried out biaxial compression tests while varying the volume percentage of corestones from 0 to 57%. We found that both cohesion and internal friction angle increase with the volume percentage of corestones while elastic modulus remains constant. We found the results from numerical experiments are in contradiction to what is known from physical experiments using artificial saprolites. This may be due to a possibility that the sharp and discrete nature of interface between corestone and matrix in physical experiments differs from the gradual interfacial nature in numerical modelling and natural saprolites.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.697-702
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• 2006

A counterplan of slope failure has to investigate about various and engineering safety factors. Especially, it is important that large cut-slope must examine rational and economic solution. In this case study, cut-slope failure caused by inflow of rainwater into alternate layers. Hereafter it is suggested that large cut-slope should consider analysis the cause for a decline of safety factor and the engineering character of corestone ground mass.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.711-716
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• 2002

When judging the ground by core-logging, depth of coring might be stopped by coming into view of the moderately weathered rock and also considered as bedrock line. However, highly weathered rock may appear again, if coring more, because there are core-stones in the residual soil and highly weathered rock by the effect of hydraulic-thermal differentiation and does the irregular rock weathering or metamorphic rock region. Therefore, there are room for misunderstanding of diagnosing the moderately weathered rock. Even though the irregular ground where the corestones were come out will show clear geotechnical differences between the ground and the gradually weathered bedrock, nowadays, the construction sites do not take into account the characteristic of core-stone region. In conclusion, to study the failure-strength characteristics of soil layers containing core-stones, we made artificial core-stones and varied percentage of corestones, and measured cohesion and friction factors to adjust them to construction sites containing corestones such as slope, tunnel, and underground.

• Economic and Environmental Geology
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• v.37 no.6 s.169
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• pp.585-601
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• 2004

A general study of domestic black sandstone and black shale quarries has not been made. For this reason it is difficult to know how the matter really stands. The objectives of this study are to achieve systematical and scientific study of the distribution, occurrences and rock quality of black sandstone and black shale resources exploited in existing quarries in the Boryeong area. The black sandstone bed survey was made from 54 mine claims on 4 sheets. In the area, 140 black sandstone and 22 black shale quarries were ascertained in 37 mine claims. The general development information data from that existing quarries were collected and synthesized. Among these black sandstone quarries for gravestones, monuments and black shale quarries for inkstone are in operation. Most of the black sandstone quarries were closed throughout the Gaewhari, Suburi, Seongjuri district in the investigated area even though these quarries had played a prominent part in the production of black sandstone. In view of commercial dimension stones, raw materials from black sandstone are classified as corestone and fresh rock body according to the characteristics of their occurrences and shape. Black sandstone beds are characteristically well-jointed and are particularly subdivided into cubic or quadrangular blocks in 3 joint sets. The colors of these black sandstones show medium dark $gray\~grayish$ black judging from the Rock Color Chart. The black sandstone beds which are intercalated in the Amisan, Jogeri, Baegunsa, Seongjuri Formations of the Daedong Supergroup are about $1\~10\;m$ in thickness.