• Structural Engineering and Mechanics
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• v.74 no.2
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• pp.283-296
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• 2020

The coupled hydro-mechanical loading conditions commonly occur in the geothermal and petroleum engineering projects, which is significantly important influence on the stability of rock masses. In this article, the influence of flaw inclination angle of fracture behaviors in rock-like materials subjected to both mechanical loads and internal hydraulic pressures is experimentally studied using the 3-D X-ray computed tomography combined with 3-D reconstruction techniques. Triaxial compression experiments under confining pressure of 8.0 MPa are first conducted for intact rock-like specimens using a rock mechanics testing system. Four pre-flawed rock-like specimens containing a single open flaw with different inclination angle under the coupled hydro-mechanical loading conditions are carried out. Then, the broken pre-flawed rock-like specimens are analyzed using a 3-D X-ray computed tomography (CT) scanning system. Subsequently, the internal damage behaviors of failed pre-flawed rock-like specimens are evaluated by the 3-D reconstruction techniques, according to the horizontal and vertical cross-sectional CT images. The present experimental does not only focus on the mechanical responses, but also pays attentions to the internal fracture characteristics of rock-like materials under the coupled hydro-mechanical loading conditions. The conclusion remarks are significant for predicting the rock instability in geothermal and unconventional petroleum engineering.

• Geomechanics and Engineering
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• v.21 no.4
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• pp.391-399
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• 2020

Brittleness is one of the most important properties of rock which has a major impact not only on the failure process of intact rock but also on the response of rock mass to tunneling and mining projects. Due to the lack of a universally accepted definition of rock brittleness, a wide range of methods, including direct and indirect methods, have been developed for its measurement. Measuring rock brittleness by direct methods requires special equipment which may lead to financial inconveniences and is usually unavailable in most of rock mechanic laboratories. Accordingly, this study aimed to develop a new strength-based index for predicting rock brittleness based on the obtained base form. To this end, an innovative algorithm was developed in Matlab environment. The utilized algorithm finds the optimal index based on the open access dataset including the results of punch penetration test (PPT), uniaxial compressive and Brazilian tensile strength. Validation of proposed index was checked by the coefficient of determination (R²), the root mean square error (RMSE), and also the variance for account (VAF). The results indicated that among the different brittleness indices, the suggested equation is the most accurate one, since it has the optimal R², RMSE and VAF as 0.912, 3.47 and 89.8%, respectively. It could finally be concluded that, using the proposed brittleness index, rock brittleness can be reliably predicted with a high level of accuracy.

• Tunnel and Underground Space
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• v.1 no.2
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• pp.181-203
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• 1991

The effects of geologic structures such as rock joins and bedding planes on the thermal conductivity of a discontinuous rock mass are studied. The expressions for the equivalent thermal conductivities of jointed rock masses are derived and found to be anisotropic. The degree of anisotropy depends primarily on the thermal properties contrast between the joint phase and surrounding intact rock, the joint density expressed as volume fraction and the inclination angle of the joint. Within the context of 2-dimensional finite element heat transfer scheme, the isotherms around a circular hole are analyzed for both the isotropic and anisotropic rock masses in 3 different thermal boundary conditions. i.e. temperature, heat flux and convection boundary conditions. The temperature in the stratified anisotripic rock mass is greatly influenced by the thermal properties of the rock formation in contact with the heat source. Using the excavation-temperature coupled elastic plastic finite element method, analyzed is the thermo-mechanical stability of a circular opening subjected to 10$0^{\circ}C$ at a depth of 527m. It is found that the thermal stress concentration was enough to deteriorate the stability and form a plastic yield zone around the opening, in contrast to the safety factor greater than 2 resulted form the excavation-only analysis.

• Computers and Concrete
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• v.22 no.2
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• pp.239-248
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• 2018

TBM penetration rate is a function of intact rock properties, rock mass conditions and TBM operational parameters. Machine rate of penetrationcan be predicted by knowledge of the ground conditions and its effects on machine performance. The variation of TBM operational parameters such as penetration rate and thrust plays an important role in its performance. This study presents the results of the analysis on the TBM penetration rates in schistose rock types present along the alignment of Golab tunnel based on the analysis of a TBM performance database established for every stroke through different schistose rock types. The results of the analysis are compared to the results of some empirical and theoretical predictive models such as NTH and QTBM. Additional analysis was performed to find the optimum thrust and revolution per minute values for different schistose rock types.

• International Journal of Oral Biology
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• v.46 no.2
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• pp.81-84
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• 2021

Salivary glands are exocrine glands that secrete saliva into the oral cavity, and secreted saliva plays essential roles in oral health. Therefore, maintaining the salivary glands in an intact state is required for proper production and secretion of saliva. To investigate a specific signaling pathway that might affect the maintenance of mouse submandibular gland (SMGs), RNA sequencing was performed. In SMGs, downregulated expression patterns of Rho-associated protein kinase (ROCK) signaling pathway-related genes, including Rhoa, Rhob, Rhoc, Rock1, and Rock2, were observed. Gene expression profiling analyses of these genes indicate that the ROCK signaling pathway is a potential signal for SMG maintenance.

• Tunnel and Underground Space
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• v.7 no.2
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• pp.108-115
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• 1997

Uniaxial and biaxial compressive tests were conducted on limestone specimens containing artificial joints and a circular hole to investigate the influence of inclination and number of joints on compressive strength and deformation behavior of rock with a circular hole. Under uniaxial and biaxial compressive condition, the inclination of joints showing the maximum and minimum strength were 0$^{\circ}$ and 30$^{\circ}$ respectively, which was independent of the number of joints. Under uniaxial compressive condition, relative maximum strength of rock with n=1 and 3 to intact rock with a circular hole were 12.5%~82.8% and 11.4~62.5% respectively, and under biaxial compressive condition, 18.2~91.0% and 17.0~87.5% respectively. The influence of the number of joints on the decrease of compressive strength was greater under uniaxial than under biaxial compressive condition. Under uniaxial and biaxial compressive condition, axial and lateral deformations of rock showed the least values where $\alpha$=30$^{\circ}$. Under uniaxial compressive condition, axial and lateral deformation at maximum strength of rock have the increasing tendency with increase the number of joints. But they have the decreasing tendency under biaxial compressive condition. Under uniaxial and biaxial compressive conditions, axial deformation of circular hole was greater than lateral deformation without respect to the number of joints and the inclination of joints.

• Economic and Environmental Geology
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• v.17 no.1
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• pp.57-78
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• 1984

The object of this study is to offer the standarized data for the design and calculating engineering cost of the rock excavation an the construction of the 3rd and 4th Seoul Subway lines From Jnauary to March in 1983, this study was carried out by the both methods of the field and laboratary studies. In the field, the geological survey in the entire area of Seoul City and sites on the subway lines were carried out and also a site measure of uniaxial compressional strength of rock masses by using Schmidt hammer was done. The labartory studies were carsied out by a study of preuions surveyes, microscopic studies of the mineral composition and degree of weathering of rocks, and measure of uniaxial compressional strengths Finally an engineering classification of each rock masses of South Africa council for Scientific and Industrial Research, CSIR, after Bieniawski, 1974. was done. In this method of classification 6 parameters such as strength of intact rock material, rock quality designation, spacing of fractures, condition of fractures, groundwater conditions, and the effect of fracture strike and dip orientation in tunnelling were used to evaluate rating of each rock mass.

• Proceedings of the KSEG Conference
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• 2002.04a
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• pp.109-114
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• 2002

Development of a three-dimensional mine visualization model for a section of the mine is addressed first. Discontinuity orientation and location information was taken from this visualization model for use in slope stability analyses. Estimated shear strength properties of discontinuities and mechanical properties of intact rock from the rock mass samples obtained from the mine are discussed next. The third part of the paper is focused on the results obtained for maximum safe slope angles for the section considered of the mine based on block theory analysis conducted under only the gravitational forces using the mapped discontinuities at the mine. Finally, the effects of water that exist in the rock mass, a tension crack, slope face inclination, overall wedge height and double benching on factor of safety of wedge stability are illustrated through limit equilibrium slope stability analyses conducted on a single tetrahedral wedge belonging to potential key block category that exist in the investigated area of the mine.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.41-49
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• 2000

Rock Mass Rating has been widely applied to the underground tunnel excavation and many other practical problems in rock engineering. However, Rock Mass Rating is hard, even by the experts of tunnel assessment owing to lack of investigation system. In this study, using multivariate analysis we presented rock mass rating system that is objective and easy to use. The constituents of RMR are decided to RQD, condition of discontinuities, groundwater conditions, intact rock strength, orientation of discontinuities, spacing of discontinuities in important order. In each step, we proposed the best multiple regression model for RMR system.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.328-338
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• 2009

Schmidt hammer test as an indirect method has so far been widely applied for determining the physical properties of intact rock, and many researchers have developed procedures for its use on rock cores, blocks and in field. Though many methods have developed upto date for indirect using, the almost were single blow which has many errors. The purpose of this study was to evaluate the established as for ASTM, ISRM, BSI, Poole & Farmer and Hucka method and to suggest a new optimum test method and statistical analysis on rocks. The finding has indicated that succeeding blow has served as an optimal to predict physical properties of rocks. To conduct the experiment, researchers have examined 150 rock blocks, which include igneous, metamorphic and sedimentary rocks in Korea nation wide.