• Journal of the Korean Geotechnical Society
• /
• v.26 no.9
• /
• pp.71-74
• /
• 2010

During construction of deep foundation in soft rock under varying soil properties, it is essential to locate the rock stratum, especially when drilling with slurry. When slurry is used for drilling, the bottom of the borehole cannot be seen, thereafter soil cuttings cannot be differentiated from soft rock cuttings. A new static rock penetrometer, known as Rock Penetrometer was developed during this study. It could be a simple mechanical device that is attached to the bottom of a Kelly bar which is used to attach drilling tools such as augers and core barrels while drilling. After its calibration in the laboratory, the performance of the static rock penetrometer was verified in the several field test sites.

• Tunnel and Underground Space
• /
• v.16 no.1 s.60
• /
• pp.1-10
• /
• 2006

Rock masses in nature include various rock discontinuities such as faults, joints, bedding planes, fractures, cracks, schistosities, and cleavages. The behavior of rock structures, therefore, is mainly controlled by various rock discontinuities. In many tunnels, enormous cost and time are consumed to cope with the failing or sliding of rock blocks, which cannot be predicted because of the complexity of rock discontinuities. It is difficult to estimate the properties of rock masses before the rock excavation. The observational design and construction method of tunnels in rock masses is becoming important recently. In this paper, a new observational design and construction method for rock block evaluation of tunnels in discontinuous rock masses is proposed, and then applied to the tunnel based on actual rock discontinuity information observed in the field. It is possible to detect key blocks all along the tunnel exactly by using the numerical analysis program developed far the new observational design and construction method. This computer simulation method with user-friendly interfaces can calculate not only the stability of rock blocks but also the design of supplementary supports. The effectiveness of the proposed observational design and construction method has been verified by the confirmation of key block during the enlargement excavation.

• Tunnel and Underground Space
• /
• v.15 no.2 s.55
• /
• pp.129-136
• /
• 2005

This paper describes the implementation of rock mass rating evaluation based on genetic algorithm(GA) and conditional simulation technique to estimate RMR in the area without sufficient borehole data RMR were estimated by GA and conditional simulation technique with reflecting distribution feature and spatial correlation. And RMR determined by GA were compared with the results from kriging. Through the analysis of the results from 30 simulations, the uncertainty of estimation could be quantified.

• Tunnel and Underground Space
• /
• v.16 no.3 s.62
• /
• pp.251-258
• /
• 2006

In this paper, the applicability to the Korean rock condition of using the deformation moduli based on Rock Mass Rating (RMR) and Pressuremeter Test (PMT) is evaluated. The correlations among deformation moduli and various rock properties were also analyzed. It appears that the existing correlations using RMR overestimate the deformation moduli and wide variation was found between predicted moduli using these correlations and measured values. As for the correlations among the deformation moduli and various rock properties, Rock Quality Designation (RQD) and unconfined compressive strength (UCS) were found to correlate to deformation moduli reasonably well, but joint spacing and joint conditions appear to correlate poorly to RQD and UCS. Additionally, groundwater can not be correlated with the modulus values. While the depth has very little contribution to deformation modulus, it should be factored in the simple regression analyses with various rock mass properties, especially with the correlations made with UCS, RQD etc. With the deficiencies of these correlations, more in depth analysis techniques such as multivariate correlations may be to reliably estimate deformation modulus of rock mass.

• Computers and Concrete
• /
• v.20 no.2
• /
• pp.155-164
• /
• 2017

During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement-based concrete which is brittle in nature with low flexural and tensile strength compared to its intrinsic compressive strength. This paper presents an overview of the work carried out on the use of SF as reinforcement in cement-based concrete matrix. Reported properties in this study are fresh properties, mechanical and durability of the blended concretes.

• Geomechanics and Engineering
• /
• v.29 no.4
• /
• pp.377-390
• /
• 2022

The stability of the roof rock-coal pillar-floor rock composite structure is of great significance to coal mine safety production. The cracks existing in the composite structure seriously affect the stability of the roof rock-coal pillar-floor rock composite structure. The numerical simulation tests of rock-coal-rock composite structures with different crack characteristics were carried out to reveal the composite structures' mechanical properties and failure mechanisms. The test results show that the rock-coal-rock composite structure's peak stress and elastic modulus are directly proportional to the crack angle and inversely proportional to the crack length. The smaller the crack angle, the more branch cracks produced near the main control crack in the rock-coal-rock composite structure, and the larger the angle between the main control crack and the crack. The smaller the crack length, the larger the width of the crack zone. The impact energy index of the rock-coal-rock composite structure decreases first and then increases with the increase of crack length and increases with the increase of crack angle. The functional relationships between the different crack characteristics, peak stress, and impact energy index are determined based on the sensitivity analysis. The determination of the functional relationship can fully grasp the influence of the crack angle and the crack length on the peak stress and impact energy index of the coal-rock composite structure. The research results can provide a theoretical basis and guidance for preventing the instability and failure of the coal pillar-roof composite structure.

• Geomechanics and Engineering
• /
• v.13 no.4
• /
• pp.535-570
• /
• 2017

There are only few cases where cause and location of failure of a rock structure are limited to a single discontinuity. Usually several discontinuities of limited size interact and eventually form a combined shear plane where failure takes place. So, besides the discontinuities, the regions between adjacent discontinuities, which consist of strong rock and are called material or rock bridges, are of utmost importance for the shear strength of the compound failure plane. Shear behaviour of persistent and non-persistent joint are different from each other. Shear strength of rock mass containing non-persistent joints is highly affected by mechanical behavior and geometrical configuration of non-persistent joints located in a rock mass. Therefore investigation is essential to study the fundamental failures occurring in a rock bridge, for assessing anticipated and actual performances of the structures built on or in rock masses. The purpose of this review paper is to present techniques, progresses and the likely future development directions in experimental testing of non-persistent joint failure behaviour. Experimental results showed that the presence of rock bridges in not fully persistent natural discontinuity sets is a significant factor affecting the stability of rock structures. Compared with intact rocks, jointed rock masses are usually weaker, more deformable and highly anisotropic, depending upon the mechanical properties of each joint and the explicit joint positions. The joint spacing, joint persistency, number of rock joint, angle of rock joint, length of rock bridge, angle of rock bridge, normal load, scale effect and material mixture have important effect on the failure mechanism of a rock bridge.

• Journal of the Korean Society for Railway
• /
• v.8 no.1
• /
• pp.82-86
• /
• 2005

Numerical methods to estimate behaviors of jointed rock mass can be roughly divided into two methods : continuous and discontinuous model. Generally, distinct element method(DEM) is applied in discontinuous model, and finite element method(FDM) or finite difference method(FDM) is utilized in continuum model. To predict a behavior of discontinuous model by DEM, it is essential to understand characteristics of joints developed in rock mass through field tests. However, results of field tests can not provide full information about rock mass because field tests are conducted in limited area. In this paper, discontinuous analysis by UDEC and continuous analysis by FLAC are utilized to estimate a behavior of a tunnel in jointed rock mass. For including discontinuous analysis in continuous analysis, joints in rock mass is considered by reducing rock mass properties obtained by RMR and decreasing shear strength of rock mass. By comparing and revising two analysis results, analysis results similar with practical behavior of a tunnel can be induced and appropriate support system is decided.

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

• Geomechanics and Engineering
• /
• v.21 no.3
• /
• pp.227-236
• /
• 2020

Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.