• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.3
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• pp.323-345
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• 2019

It is essential to predict ground conditions ahead of a tunnel face in order to successfully excavate tunnels using a shield TBM. This study proposes a forward prediction method for a mixed soil ground and/or a ground containing core stones by using electrical resistivity and induced polarization exploration. Soil conditioning in EPB shield TBM is dependent upon the composition of mixed soils; a special care need to be taken when excavating the core-stoned soil ground using TBM. The resistivity and chargeability are assumed to be measured with four electrodes at the tunnel face, whenever the excavation is stopped to assemble one ring of a segment lining. Firstly, the mixed ground consisting of weathered granite soil, sand, and clay was modeled in laboratory-scale experiments. Experimental results show that the measured electrical resistivity considerably coincides with the analytical solution. On the other hand, the induced polarization has either same or opposite trend with the measured resistivity depending on the mixed ground conditions. Based on these experimental results, a method to predict the mixed soil ground that can be used during TBM tunnel driving is suggested. Secondly, tunnel excavation from a homogeneous ground to a ground containing core stones was modeled in laboratory scale; the irregularity of the core stones contained in the soil layer was modeled through random number generation scheme. Experimental results show that as the TBM approaches the ground that contains core stones, the electrical resistivity increases and the induced polarization fluctuates.

• 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 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 KSEEG Conference
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• 2007.04a
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• pp.643-645
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• 2007

• 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.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2002.03a
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• pp.97-102
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• 2002

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2007.03a
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• pp.125-129
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• 2007

• 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.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.227-233
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• 2006

Bedrock is inhomogeneous for its genetically diverse origins and geological conditions when it forms, and especially, conglomerates and core-stones are one of these typical composite geo-materials composed of weak matrixes and strong pebbles. Mechanical properties of these composite bedrocks, like a conglomerate, generally vary depending on the mechanical properties and distributions of pebbles and the matrix. Therefore, regarding the consequence of understanding mechanical property of bedrocks in the designing slopes, tunnels, and other engineering facilities, empirical rock classification methods generally applied in the mechanical property modeling may not be suitable and rather, we may need some other classification methods, or tests more specific for these inhomogeneous composite bedrocks. This study includes a series of analyses to see elastic behaviors and modulus of composite geo-materials using homogenization theory. Forty nine case models were made for the elastic analysis with considering 5 factors such as gravel content, gravel size, strength of matrix, sorting and dip angle. The results analyzed are applicable to calculate elastic modulus of composite geo-materials as conglomerates and core-stones.