• Geomechanics and Engineering
• /
• v.35 no.4
• /
• pp.333-366
• /
• 2023

Rock as a mass generally exhibits discontinuities, commonly witnessed in rock slopes and underground structures like tunnels, rock pillars etc. When these discontinuities experiences loading, a new crack emerges from them which later propagates to a macro scale level of failure. The failure pattern is often influenced by the nature of discontinuity, geometry and loading conditions. The study of crack growth in rocks, namely its initiation and propagation, plays an important role in defining the true strength of rock and corresponding failure patterns. Many researchers have considered the length of the discontinuity to be fully persistent on rock or rock-like specimens by both experimental and numerical methods. However, only during recent decades, there has been a substantial growth in research interest with non-persistent discontinuities where the crack growth and its propagation phenomenon were found to be much more complex than persistent ones. The non-persistence fractures surface is generally considered to be open and closed. Compared to open flaws, there is a difference in crack growth behaviour in closed or narrow flaws due to the effect of surface closure between them. The present paper reviews the literature that has contributed towards studying the crack growth behaviour and its failure characteristics on both open and narrow flaws subjected to uniaxial and biaxial compression loading conditions.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.6
• /
• pp.143-154
• /
• 1999

In this study, the load transfer mechanism of tendon-grout interface of rock anchors has been examined through a series of static pull-out tests conducted on the model rock anchors constructed in the natural and artificial rock masses of granite and concrete, respectively. Several rock masses with horizontal discontinuities have been prepared to study the effects of weak planes on the shear stress distribution in tendon-grout interface. As a result, for the rock anchors constructed in the rock mass without discontinuities, stress concentration occurs on the upper part of the tendon-grout interface. On the contrary, as the frequency or the number of discontinuities increases, the shear stress distribution along the depth tends to be uniform. Also, an experimental equation about shear stress distribution between tendon-grout interface can be made by the regression of test results. The shear stresses computed from the experimental results between the rock surface and the depth of 2~3 times the tendon diameter are smaller than those from theory. Below the depth, the reverse can be observed.

• Journal of Industrial Technology
• /
• v.23 no.A
• /
• pp.69-81
• /
• 2003

Numerical analysis is important for the design, construction and maintenance of large caverns. The rock mass contains generally discontinuities such as faults, joints and fissures. The mechanical behavior and geometric characteristics of these discontinuities would have a significant impact on the stability of the caverns. In this research the Distinct Element Method(DEM) was used to analyze the structural stability of the large cavern. The Barton-Bandis Joint Model (B-B J.M) was used as a constitutive model for the joint. In addition, two different cases 1) analysis with a support system and 2) analysis with no support system, were analyzed to optimize a support system and to investigate reinforcing effects of a support system. The most significant parameters of in-situ stress, JRC of in-situ natural joints, and spatial distribution characteristics of discontinuities were acquired through field investigation. Displacement (horizontal, joint shear), maximum joint opening, maximum and minimum principal stresses, range of relaxed zone, rockbolt axial forces and shotcrete stresses were calculated at each excavation stage. As a result of analysis the calculated values proved to be under the allowable value Rockbolts also proved to be an efficient support measure to control joint shear displacement which had significant effects on extending the relaxed zone. As a consequence, the structural stability of the cavern was assured with an appropriate support system.

• Geomechanics and Engineering
• /
• v.16 no.1
• /
• pp.21-34
• /
• 2018

Discontinuities considerably affect the mechanical and hydraulic properties of rock mass. These properties of the rock mass are influenced by the geometry of the discontinuities to a great extent. This paper aims to render an account of the geometrical parameters of several discontinuity sets related to the surrounding rock mass of Rudbar Lorestan Pumped Storage Power Plant powerhouse cavern making use of the linear and areal (circular and rectangular) sampling methods. Taking into consideration quite a large quantity of scanline and the window samplings used in this research, it was realized that the areal sampling methods are more time consuming and cost-effective than the linear methods. Having corrected the biases of the geometrical properties of the discontinuities, density (areal and volumetric) as well as the linear, areal and volumetric intensity accompanied by the other properties related to four sets of discontinuities were computed. There is an acceptable difference among the mean trace lengths measured using two linear and areal methods for the two joint sets. A 3D discrete fracture network generation code (3DFAM) has been developed to model the fracture network based on the mapped data. The code has been validated on the basis of numerous geometrical characteristics computed by use of the linear, areal sampling methods and volumetric method. Results of the linear sampling method have significant variations. So, the areal and volumetric methods are more efficient than the linear method and they are more appropriate for validation of 3D DFN (Discrete Fracture Network) codes.

• Tunnel and Underground Space
• /
• v.6 no.2
• /
• pp.166-174
• /
• 1996

Stability of rock slope is greatly affected by the geometry and strength of discontinuities developed in the rock mass. In this study an analytical method which is capable of analyzing the effect of relative orientation between the discontinuities and the slope face on the safety of slope by assessing their vector components was used to evaluate the stability and the maximum cut-angle for the proposed slope design. The results of computerized vector analysis revealed that slope area under investigation might be divided into 3 sections of different face directions. The safety factors for benches in each 3 sections were calculated using the limit-equilibrium theory. Then, by utilizing the concept of probabilistic risk analysis, the susceptibility of entire slope failure was estimated. Based on the distribution of safety factor in each bench, the maximum cut angle of each section could be selected differently ot achieve the permanent stability of the entire slope.

• 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.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.11
• /
• pp.43-53
• /
• 2008

The rock mass classification systems used in Korea are not standardized. And also the criteria values differ between agencies. So different opinions for rock mass classification can occur among engineers who participate in each design process. In this research, a new rock mass classification system was suggested to correct these problems. For this purpose, the criteria used in the Korean agencies were compared with the criteria used in foreign agencies and standard criteria were selected. Thereafter rational and objective criteria values were suggested quantitatively for the new classification system.

• Proceedings of the KSR Conference
• /
• 2004.06a
• /
• pp.967-973
• /
• 2004

Rock socketed drilled shafts transfer significant portion of structural loads at the socketed part. Therefore, a proper design of side and base resistances of a shaft at the socket is a major concern for the geotechnical engineers. In this study, we modified the Hoek-Brown criterion to estimate side resistance of rock socketed drilled shafts. Earlier method to compute side resistance of a shaft is linear or power functions of intact rock masses. However, side resistance is mobilized like shearing which influenced by the mechanical properties of concrete and rock masses, adhesion of rock/concrete interface, roughness of rock socket. Therefore, a single coefficient or power of uniaxial compressive strength of intact rock cannot provide accurate values of side resistance in a wide range of the uniaxial compressive strength. A new approach proposed in this study can consider in situ rock mass condition (frequency or discontinuities, weathering condition), and rock types thus, it has a wider applicability than the earlier models.

• Tunnel and Underground Space
• /
• v.16 no.5 s.64
• /
• pp.394-404
• /
• 2006

Dynamic behavior of rock structures depends largely on the dynamic characteristics of ground and input earthquake wave. For blocky rocks with intense discontinuities, the mechanical characteristics of blocks and structural and mechanical characteristics of discontinuities affect overall behavior. In this study, UDEC was adopted to evaluate the dynamic behavior of rocks with various structural characteristics. Obtained results were compared to those of $FLAC^{2D}$, a continuum analysis, and the validity of the method was examined for dynamic analysis of discontinuous rocks for earthquake. Analysis considering the discontinuity showed significant changes in structural shape by the influence of joint behavior, and the behavior by continuum analysis was overestimated.

• Tunnel and Underground Space
• /
• v.30 no.1
• /
• pp.63-75
• /
• 2020

When tunnel is excavated via drilling and blasting, the excessive overbreak is the primary cause of personal or equipment safety hazards and increasing the cost of the tunnel operation owing to additional ground supports such as shotcrete. The practical management of overbreak is extremely difficult due to the complex causative mechanism of it. The study examines the relationship between rock mass characteristics (unsupported face condition, uniaxial compressive strength, face weathering and alteration, discontinuities- frequency, condition and angle between discontinuities and tunnel contour) and the depth of overbreak through using feed-forward artificial neuron networks. Then, Overbreak Resistance Factor (ORF) has been developed based on the weights of rock mass parameters to the overbreak phenomenon. Also, a new concept of tunnel overbreak management system using ORF has been suggested.