• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.421-435
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• 2012

Rock excavation (removal) tests are performed with effective parameters using an abrasive waterjet. For verification of the field rock excavation capabilities, the removal performance and level of efficiency are analyzed for hard granite rock in terms of the water pressure, exposure time of the jet, and the standoff distance. In particular, experimental tests are performed with a long standoff distance required condition in the real excavation field. The rock removal performance level changes according to the rock properties. In this study, various rock specimens are used and P-wave velocities are measured in order to determine the correlation between the removal performance and the P-wave velocity. As a result of the experimental study, the effect of waterjet parameters on rock removal is analyzed.

• The Journal of Engineering Geology
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• v.5 no.1
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• pp.21-29
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• 1995

Among the index properties of granite and andesite, the relation between porosity and water content is highly correlated, but specific gravity, porosity and water content have loW relation with P wave velocity and their relationship showed dispersed zone type. With raising the temperature, Brazilian tensile strength was not changed remarkably, but decreased near $100^{\circ}C$. After the strength increased at $150^{\circ}C$, it decreased near $200^{\circ}C$ in granite. In andesite, however, the strength was increased up to $200^{\circ}C$, and then decreased. The variations of P wave velocity at each temperature zone are similar to those of tensile strength.

• The Journal of Engineering Geology
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• v.17 no.3
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• pp.329-337
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• 2007

For seven NX sized borehole models constructed from physical property data for representative geology in Korea, dispersion curves were derived and compared between models having different physical parameters. By comparing and analyzing the dispersion curves obtained from different sources (monopole and dipole) and different borehole sizes (76 mm and 150 mm), dispersion characteristics in sonic log could be understood better, particularly in the case of slim hole sonic log.

• Economic and Environmental Geology
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• v.30 no.3
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• pp.231-240
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• 1997

The behavior of rocks and microcrack development due to fatigue stresses are investigated using cyclic loading tests and ultrasonic velocity measurements. Twenty six medium-grained granite samples from the Pochon area are selected for measurements. Ultrasonic velocities are measured for samples before fatigue test to characterize the pre-existing microcracks. Then, thirteen different cycles of loadings with 70% and 80% dynamic strength are applied to the samples. The ultrasonic velocities are measured again to compare velocities after applications of fatigue stress with those before applications of fatigue stress. The results show that most microcracks are developed along the direction parallel to the axis of loading and that the amount of microcracks increases, as loading levels and numbers of cycle increase.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.4
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• pp.591-597
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• 1999

본 연구에서는 비 균질 퇴적층으로 인한 지진파의 증폭에 대한 경계/유한요소 해석을 수행하였다. 수치해석을 위해, 비 균질 퇴적층은 8절점 등 매개 변수 유한요소 사용하여 모델링하였고, 그 주위의 균질 반무한 지반은 3절점 등매개 변수 경계요소를 사용하여 모델링하였다. 경계요소와 유한요소의 접촉면에서, 표면 력의 평형조건과 변위의 적합 조건에 의해 두 개의 요소를 결합하는 알고리듬을 개발하였다. 수치해석의 영향인자로서 SH파, P파와 SV파의 입사각, 무 차원 진동수 그리고 반무한 지반과 퇴적층사이의 전단 파 속도 비와 질량밀도 비를 고려하였다.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.24-36
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• 2015

The Geochang granite widely used in construction works is one of the most popular dimension stones in Korea. In order to evaluate the physical properties of rock, a lot of laboratory tests for the Geochang granite were conducted to find unit weight, absorption ratio, P wave velocity, S wave velocity, uniaxial compressive strength, Young's modulus, Poisson's ratio, tensile strength, cohesion, friction angle and point load strength index. The uniaxial compressive strength of the Geochang granite was 19.5 times tensile strength and also 8.6 times cohesion, besides P wave velocity was 1.5 times S wave velocity. Correlation analyses were also conducted to find the correlation among 11 different physical properties, where the uniaxial compressive strength showed Pearson correlation coefficient of more than 0.8 with Poisson's ratio, point load strength index and Young's modulus, respectively. Regression analyses were finally conducted by means of both linear and multiple analysis and the brief results including coefficient of determination of more than 0.7 were presented.

• Journal of the Korean Geotechnical Society
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• v.30 no.11
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• pp.39-49
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• 2014

Volcanic rocks in Jeju island show vesicular structure caused by various environmental factors, and indicate the differences in geological and mechanical characteristics from region to region. Previous studies on the volcanic rocks in Jeju island have been actively conducted on geological and chemical properties in terms of geophysics and geology and on physical and mechanical properties in terms of engineering. But comprehensive comparative analysis on physical and mechanical properties of volcanic rocks in Jeju island is not conducted. In this study, the physical and mechanical properties of volcanic rocks in Jeju island were compared and analyzed comprehensively through the existing research papers and reports about volcanic rocks in Jeju island. As a result, it was found that the relationship between absorption (porosity) and apparent specific gravity is commonly linear and could be represented as two different linear approximations. In addition, it was found that the relationship between P-wave velocity and S-wave velocity and the relationship between absorption (porosity) and uniaxial compressive strength could be classified more clearly, considering two different linear relationships in absorption (porosity) and apparent specific gravity.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.53-60
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• 2009

Construction of a tunnel induces rock masses damage around the tunnel. The degree of damage produced on rock masses will affect on the mechanical and hydraulic behaviors of the rock masses. In this paper, P wave velocity measured by cross-hole test was used to assess rock masses damage around the test tunnel. Initiation of source signal was carried out using mechanical impact at the source installed borehole. In consequence, the generated P wave signal was low noise and apparent wave form, which allows accurate pick-up of first arrival time. From the test, the region where rock damage is expected shows relatively low P wave velocity. In addition, with multiple points of P wave velocity measurement along each cross-hole, two dimensional P wave tomography was obtained. The tomography provides apparent view of the rock damage behind the tunnel. The measured P wave velocity was correlated with features of rock masses, porosity and Q value.

• Geophysics and Geophysical Exploration
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• v.16 no.3
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• pp.109-118
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• 2013

On and near the 23-m high earthen Cheongcheon dam in Boryeong City, Korea, short seismic refraction and surface-wave profiles were conducted using a 5-kg sledgehammer. From vertical and horizontal components of the seismic waves, near-surface P-wave velocities (${\nu}_p$) and S-wave velocities (${\nu}_s$) were derived by inverting first-arrival refraction times and dispersion curves of Rayleigh waves. Average ${\nu}_p$ and ${\nu}_s$ for the Jurassic sedimentary basement were determined to be 1650 and 950 m/s at a depth of 30 m directly beneath the dam and 1650 m/s and 940 m/s at a depth of 10 m at the toe of the dam, respectively. The dynamic Poisson's ratio for these strata were therefore in the range of 0.24 to 0.25, which is consistent with ratios for consolidated sedimentary strata. Near a 45-m borehole 152 m downstream from the dam crest, an SH tomogram indicates a refraction boundary with an average ${\nu}_s$ of 870 m/s at depths of 10 ~ 12 m. At this site, the overburden comprises the upper layer with relatively constant ${\nu}_p$ and ${\nu}_s$ around 500 and 200 m/s, respectively, and the lower layer in which both ${\nu}_p$ and ${\nu}_s$ increase with depth almost linearly. The dynamic Poisson's ratios for the overburden were in the range of 0.30 to 0.43.

• Economic and Environmental Geology
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• v.35 no.5
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• pp.445-454
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• 2002

3-D P-wave velocity model in the southern Korean Peninsula is investigated by using the earthquake tomography method. This velocity model would be used to locate the exact hypocenter position, and also useful for our understanding of the crustal structure. The simultaneous inversion is used to get the minimum 1-D model and hypo-center relocation, which are used as an initial 3-D velocity model. The velocities in the minimum 1-D model are 6.04 km/s, 6.45 km/s, and 7.78 km/s between the depth of 0-19 km, 19-32 km, and 32-55 km respectively. In the 3-D P-wave velocity model, Layer 1 (0~3 km) has high velocities in Kyongsang basin, Yonglam massif, and Okchon folded belt, and low velocities in Kyonggi massif. In layer 2 (3~19 km) high velocities are predominent around Kyonsang basin and Yongnam massif except Yonil basin, but low velocities exist around Kyonggi massif and Okchon folded belt. In Laye. 3 (19~32 km) high velocities prevail throughout the southern part of Korean Peninsula, but low velocity does throughout the middle except SNU, YIN station in Konggi massif. In Layer 4 (32 km), the maximum velocity is showed in the middle and southwestern part, while the minimum velocity in the southeastern and coastal area. The depth of the velocity boundary corresponds to the crustal structure of the southern Korean Peninsula which is calculated by gravity data.