• Tunnel and Underground Space
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• v.19 no.6
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• pp.567-582
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• 2009

The world's largest nucleon decay experiment facility is constructed at a depth of approximately 1,000meters, in the Kamioka mine, Japan. Because of the character as a large cavern in deep underground, in-situ stress measurements were conducted to provide basic information for design of the cavern. Three overcoring methods were used: 8-element embedding gauges developed by Japanese Central Research Institute of Electric Power Industry, hemispherical ended borehole technique with eight strain cross-gauges, and Hollow Inclusion Cell with 12 strain gauges. The principle stresses were not perfectly similar in each measurement. The average values of the 6 stress element were used to provide the direction and the magnitude of three principle stress.

• Tunnel and Underground Space
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• v.31 no.3
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• pp.145-166
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• 2021

Korea Stress Map database is built by integrating actual data of 1,400 in-situ stress measurements using hydraulic fracturing and overcoring method in South Korea. Korea Stress Map 2020 is presented based on the guideline proposed by World Stress Map Project. As detailed data, stress ratio and maximum horizontal stress direction distribution for each region are also presented. The dominant maximum horizontal stress direction in the Korean Peninsula is from northeast to southeast, and the magnitude of the in-situ stress is relatively distributed. There is some stress heterogeneity caused by local characteristics such as topographical and geological properties. We investigated case studies in which the in-situ stress was affected by mountainous topography, difference in rock quality of fracture zone, presence of mine or underground cavities, and geological structure of fault zone.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.237-247
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• 2002

A total of 18 stress measurements were performed in the rock and rock-like blocks in the laboratory to estimate the influence of anisotropy in rock. Full scale overcoring equipment, which consists of a coring machine and a biaxial loading system by flat jacks, was developed to simulate the in-situ rock stress condition in the laboratory By comparing the isotropic analysis with the anisotropic analysis in measuring the stress, conclusions have been drawn as to the influence of anisotropy. The maximum difference between the isotropic and the anisotropic analysis was 34% and it was shown that the stress measurement considering the anisotropy was needed. To confirm the validity of the observed data, a diagnostic analysis of stress relief curve by overcoring was conducted using the three dimensional finite difference program, FLAC 3D.

• Tunnel and Underground Space
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• v.8 no.1
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• pp.67-73
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• 1998

This paper presents the results of deformation measurement and numerical analysis carried out to study the behaviour of the rock mass around large underground oil storage caverns. Displacements during excavation have been monitored using borehole extensometers which had been installed before the excavation of caverns proceeded. Numerical analysis has been carried out to examine the three-dimensional behaviour of rock and the face advance effect. The input parameters for this analysis were determined from the results of laboratory and field tests. The deformation modulus of the rock mass was determined from plate loading test at the site and in-situ stresses were measured from the overcoring method with USBM deformation gauge. The results from this study gave a clear picture for three-dimensional behaviour of the rock mass, hence would be used for the optimum design.

• Tunnel and Underground Space
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• v.1 no.2
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• pp.218-228
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• 1991

Natural stress measurements have been made at two sites at the depth of 280m from surface by means of stress relief overcoring methods using three directonal deformation gage. Attempts have been made to determine the state of natural stress in the rock and provide useful basic data to investigate the stress distribution and the determination of yield zone around powerhouse cavern. The magnitude and the direction of the miximum principal stress obstained from in-situ stress measurements is -96.1kgf/$\textrm{cm}^2$ and N38$^{\circ}$W, N35$^{\circ}$W respectively. Vertical stresses are in approximately agreement with the theoretical value. The ratio of measured to theoretical stresses are 85% at two sites. The ratio of average horizontal to vertical stresses(k=($\sigma$h)ave/$\sigma$v is 1.07.

• The Journal of Engineering Geology
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• v.26 no.2
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• pp.169-175
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• 2016

Estimations of regional stress are demonstrated in this paper. Firstly, regional stress is defined and the characteristics of regional stress are then discussed based on the local stresses measured by the Compact Conical-ended Borehole Overcoring (CCBO) technique and the results from the earthquake focal mechanism. Secondly, the regional stresses are estimated by a back analysis of three-dimensional finite element models, using the local stresses measured by the CCBO and hydraulic fracturing.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1-6
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• 2008

When a saturated clay is sampled in an undisturbed manner from a bore hole, the sample extends vertically and shrinks horizontally under undrained conditions due to stress release. The conventional consolidation test specimen is trimmed from the expanded sample so that its diameter is equal to the inner diameter of the consolidation test ring, this test procedure does not reproduce the actual consolidation behavior. The measurement of sample extension was conducted by means of overcoring method found that the extension strains were 1 to 2%. To simulate the in-situ consolidation behavior, the consolidation test method that uses a specimen with a slightly smaller diameter than the inside diameter of consolidometer so that the specimen expands laterally to the inside of the ring.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.1125-1132
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• 2009

The theory and a probe of the pilot hole wall deformation method, which is a 3-dimensional stress measurement method based on the stress relief principle, were developed. A pilot hole is drilled from the bottom of a borehole and the stress measurement probe is inserted into the pilot hole. The borehole is advanced as the overcoring and the changes in the radius of the pilot hole in three directions and in the axial lengths between the borehole bottom and the pilot hole wall along four axial lines are measured by cantilever type-displacement sensors. The differences between the displacements by the elastic stress analysis and those measured by using the probe were within 3% in the uniaxial compression test of an acrylic resin plate having a hole.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.248-258
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• 2002

The sixth underground pumped powerhouse cavern is now under construction in Korea. For the stability analysis for the caverns of the five underground powerhouses, finite element method was used. For the analysis, in-situ rock stress were measured by overcoring method. The stress measurement showed that initial horizontal to vertical stress ratio was 1.07-1.32 in low powerhouse sites. Rock mass strength and elasticity were assumed from rock core properties through engineering processes. So the ratio of input elasticity fur the analysis were about 0.16-0.55 to rock core elasticity. In most of the analysis, elasto-plastic condition with Mohr-Coulomb failure criteria were applied. But in one case, viscoelastic condition was applied, too. The input cohesion and internal friction angle were approximately 0.12-0.22, 0.6-0.87 to rock core strength parameters, respectively.

• Journal of the Korean Geotechnical Society
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• v.18 no.2
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• pp.65-74
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• 2002

The measurement of in-situ stress is essential to estimate the ground displacement and the stress distribution of a tunnel and an underground structure. In this study, the in-situ stress distribution of the Southern Korean peninsula was re-evaluated by the new 380 in-situ data which were determined by overcoring and hydrofracturing methods, and the three-din erosional numerical analysis of tunnelling was performed. The results of in-situ stress distribution show that the distribution of horizontal stress tends to be more irregular in metamorphosed(gneiss) and granite areas than in sedimentary and volcanic areas. The ratio of horizontal to vertical stresses(K-value) in volcanic area is less than 1 below the depth of 150m. The direction and magnitude of three dimensional in-situ stresses were shown simultaneously in a figure for the first time in Korea. The three-dimensional numerical analysis of tunnelling indicates that the orientation and magnitude of displacement around a tunnel are controlled mainly by the difference between the maximum and minimum horizontal stresses.