• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.137-145
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• 2004

Limestone zone in korea have been distributed to diagonal line so that it is wide from the Gangwondo to the Jeonlanamdo. The limestone cavity and fractured zone were formed by chemical weathering. Limestone cavity and fractured zone was reinforced with cemented milk(w/c=60%)by high pressure jet grouting by tripple -pipe to establish bridge foundation on the ground condition like limestone cavity. To analyze property of limestone and solid of cement milk(w/c=65%), mixed solid of cement, core NX size in the limestone cavity and fractured zone and compressive strength. Seismic tomograpy exploration was pcrforn1cd to analyze deformation modulus of limestone. The analysis suggests that deformation modulus of limestone has effect on uniaxial compressive strength, seismic velocity, seismic elasticity modulus. Average static elasticity modulus of limestone is $5.08{\times}10^5kgf/cm^2$, cement and coal mixed solid is $0.25{\times}10^5kgf/cm^2$, $0.095{\times}10^5kgf/cm^2$. Average seismic velocity of limestone is 5.240m/sec, cement and coal mixed solid is 2,211.3m/sec, 1,447.5m/sec. Average uniaxial compressive strength of limestone was $1,221.3kgf/cm^2$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $125.22kgf/cm^2$, $35kgf/cm^2$ each other. Average friction angle of limestone was $49.14^{\circ}$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $38.39^{\circ}, 25.83^{\circ}$ each other. Average cohesion of limestone was $137.7kgf/cm^2$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $23.5kgf/cm^2$, $15.5kgf/cm^2$ each other. Average deformation modulus of limestone was $2.84{\times}10^5kgf/cm^2$ and limestone specimen mixed with cement milk and solid of cement milk mixed with coal were $0.4{\times}10^5kgf/cm^2, 0.12{\times}10^5kgf/cm^2$ each other. It was analyzed that the elasticity and uniaxial compressive strength, seismic velocity of solid of cement milk mixed limestone pieces and coal had an highly interrelation regardless of existence of limestones pieces and coal but it had shown that limestones had an lower interrelation. In case of field seismic velocity and deformation of limestone, SIC solid of cement milk mixed with coal and limestone pieces had an highly interrelation.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.103-110
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• 2020

The DMM (Deep mixing method) is a construction method in which an improved pile is installed in the soft ground by excavation ground using an auger and then mixing ground stabilizer with soil. Improved pile installed in the soft ground by the DMM may have different compressive strength depending on the properties and characteristics of the soil. In the previous study, laboratory tests were performed on the ground stabilizer for the DMM developed by using the ash of the circulating fluidized bed boiler as a stimulator for alkali activation of the blast furnace slag. And the test results were analyzed to derive the correlation between the unit weight of binder (γ_B) and the uniaxial compressive strength (q_u). In this study, comparative reviews were conducted on the correlations derived from the same laboratory tests on soil material collected from the Saemangeum area and the stability of the site was evaluated by analyzing the test results performed at the site. As a result, the clay collected from the Saemangeum area satisfies the correlation between the unit weight of binder (γ_B) and the uniaxial compressive strength (q_u) derived from the previous study. And the result of the test at the field showed a higher uniaxial compressive strength than the standard strength at the field, indicating excellent stability.

• Tunnel and Underground Space
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• v.19 no.5
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• pp.450-462
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• 2009

To analyze the behavioral characteristics of rocks on indirect tests and uniaxial compressive strength, researchers have investigated 1417 pieces of rock block, which include igneous, metamorphic and sedimentary rocks in Korea. The same behavioral characteristics have been shown in every type of sedimentary rock and in the same species of rock in the case of Brazilian strength application. This suggests that correlations of rocks for geological considerations can lead to high reliability of the experimental results in case of an indirect method.

• Tunnel and Underground Space
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• v.4 no.1
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• pp.31-37
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• 1994

The effects of blasting and ground vibratons on curing concrete have not been well studied. As a results unrealistic and costly ground vibration constraints have been placed on blasting and piling when it occurs in the vicinity of curing concrete. To study the effects of ground vibrations, a shaking table was made to produce peak particle velocities in the nearly same frequency range as found in construction blasting. Concrete blocks of 33.3X27.7X16.2cm were molded and placed on the shaking table. Different sets of concrete blocks were subjected to peak vibrations of 0.25, 0.5, 1.0, 5.0 and 10cm/sec. The impulses were applied at two hour intervals for thirty seconds. Along with unvibrated concrete blocks, the vibrated concrete samples with 60.3mm in diameters were measured for elastic moduli, sonic velocity, tensile and uniaxial compressive strength. Test results showed that the vibrations in curing concrete generally have effects on the uniaxial compressive strength or physical properties of the concrete.

• Geomechanics and Engineering
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• v.23 no.1
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• pp.61-69
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• 2020

The uniaxial compressive strength (UCS) of rock is a basic parameter in underground engineering design. The disadvantages of this commonly employed laboratory testing method are untimely testing, difficulty in performing core testing of broken rock mass and long and complicated onsite testing processes. Therefore, the development of a fast and simple in situ rock UCS testing method for field use is urgent. In this study, a multi-function digital rock drilling and testing system and a digital core bit dedicated to the system are independently developed and employed in digital drilling tests on rock specimens with different strengths. The energy analysis is performed during rock cutting to estimate the energy consumed by the drill bit to remove a unit volume of rock. Two quantitative relationship models of energy analysis-based core drilling parameters (ECD) and rock UCS (ECD-UCS models) are established in this manuscript by the methods of regression analysis and support vector machine (SVM). The predictive abilities of the two models are comparatively analysed. The results show that the mean value of relative difference between the predicted rock UCS values and the UCS values measured by the laboratory uniaxial compression test in the prediction set are 3.76 MPa and 4.30 MPa, respectively, and the standard deviations are 2.08 MPa and 4.14 MPa, respectively. The regression analysis-based ECD-UCS model has a more stable predictive ability. The energy analysis-based rock drilling method for the prediction of UCS is proposed. This method realized the quick and convenient in situ test of rock UCS.

• Geomechanics and Engineering
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• v.17 no.1
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• pp.47-56
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• 2019

Crossing (X-type) flaws are commonly encountered in rock mass. However, the crack coalescence and failure mechanisms of rock mass with X-type flaws remain unclear. In this study, we investigate the compressive failure process of rock-like specimens containing two X-type flaws aligned in the loading direction. For comparison purposes, compressive failure behavior of specimens containing two aligned single flaws is also studied. By examining the crack coalescence behavior, two characteristics for the aligned X-type flaws under uniaxial compression are revealed. The flaws tend to coalesce by cracks emanating from flaw tips along a potential path that is parallel to the maximum compressive stress direction. The flaws are more likely to coalesce along the coalescence path linked by flaw tips with greater maximum circumferential stress if there are several potential coalescence paths almost parallel to the maximum compressive stress direction. In addition, we find that some of the specimens containing two aligned X-type flaws exhibit higher strengths than that of the specimens containing two single parallel flaws. The two underlying reasons that may influence the strengths of specimens containing two aligned X-type flaws are the values of flaw tips maximum circumferential stresses and maximum shear stresses, as well as the shear crack propagation tendencies of some secondary flaws. The research reported here provides increased understanding of the fundamental nature of rock/rock-like material failure in uniaxial compression.

• Journal of the Korean GEO-environmental Society
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• v.11 no.9
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• pp.47-53
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• 2010

This study was made on the fact that the compressive strength characteristic of the recently developed alkali silica-sol chemical grout material was examined, whose grout material used for this study was designed to understand its strength property through the uniaxial compressive strength test(homo-gel, sand-gel), permeability test, deflection strength test, etc. In order to compare with the engineering characteristics regarding alkali silica-sol grout material and sodium silicate grout material. The uniaxial compressive strength of silica-sol grout material was identified to be increased more than 3~5 times than sodium silicate grout material at the early stage(within 72 hours). When comparing with the uniaxial compressive strengths of Sand-gel and Homo-gel at the material age of 28 days in case of silica-sol grouting material the strength of Sand-gel was measured to be about 1.3 times higher than Homo-gel. In case of silica-sol, it is assumed to have the property to exert high strength when it is actually grouted into the ground. As a result of permeability test it is judged that it is possible to apply the silica-sol to the site in the place requiring the water cut-off as the silica-sol. As a result of testing the strength at the material age of 28 days of grouting-use silica-sol showed more than 3 times' difference than the sodium silicate grouting material.

• Steel and Composite Structures
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• v.11 no.3
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• pp.183-205
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• 2011

This paper presents the results of an investigation into the post-buckling behaviour and ultimate strength of imperfect corroded steel plates used in ship and other marine-related structures. A series of elastic-plastic large deflection finite element analyses is performed on randomly corroded steel plates. The effects of general corrosion on both sides of the plates are introduced into the finite element models using a random thickness surface model. The effects on plate compressive strength as a result of parametric variation of the corroded surface geometry are evaluated. A proposal on the effective thickness is concluded in order to estimate the ultimate strength and explore the post-buckling behaviour of randomly corroded steel plates under uniaxial compression.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.330-338
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• 2012

Though the uniaxial compressive strength (UCS) of rock material is one of the key properties for rockmass characterization purposes, core samples for the test cannot always be obtained from the field. Indirect tests such as the point load test (PLT) can be a useful alternative. In this study, correlation between the UCS and the point load strength index of limestone of Imgye area was analyzed, and the linear regression equation obtained from regression analysis of two variables was suggested. The results of this study were also compared with previous studies on limestone. It was suggested that conversion factors for the same rock type from diverse areas in Korea may have different values, and more data should be obtained to increase the accuracy of regression analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.821-832
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• 2008

The hazard warning levels are necessary for the rational design and safety construction of underground space, as mountain and urban tunnel. Sakurai provided the hazard warning levels for assessing the stability of tunnels using the critical strain of rock mass, which is defined as a ratio between uni-axial compressive strength and the Young's modulus. The concept of critical strain guidelines is introduced in this study for the assessment of tunnel safety during excavation. Moreover, in this paper, the critical strain properties of sedimentary rock in Korea has investigated and analysed in detail by Lab. test, as the uniaxial and triaxial compression tests. Finally, critical strain properties of sedimentary rock on uniaxial and triaxial stress condition is discussed the relationship of failure strain values, uniaxial and triaxial compression strengths, confining pressure and Young's modulus.