• Tunnel and Underground Space
• /
• v.8 no.1
• /
• pp.53-66
• /
• 1998

Considering the mechanical cracking in the concrete lining of tunnels occurring in relatively short period of time after the construction, there is a need for the study on the mechanical behavior and the cracking characteristics of double lining support system(shotcrete and concrete lining). For the proposed study, downscaled lining models of Kyung-Bu High Speed Railway tunnels were tested. Most longitudinal cracks at about 93 percentage developed within 30 arch degree from the vault. Cracking load was about 30 percentage of the failure load and the deflection under the cracking load was 10 percentage of the deflection under the failure load. The overbreak around the vault contributed to the reduction of the capacity for cracking and failure by the percentage greater than the reduced effective depth. Of several rock block types considered in this research, the triangular block was the most critical, and the right triangular block under eccentric load was secondly critical for the stability of the tunnel lining system. The dimensionless support reaction curves were derived from the experimental results for single and double lining. The general equation to compute the designed flexural moment was modified.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.95-105
• /
• 2003

The existing design criteria f3r the estimation of ultimate bearing capacity of drilled shaft socketed into rock masses are mainly obtained from the ultimate pile load capacities, which are determined by inconsistent failure criteria. Therefore, these design criteria generally produce difffrent predictions even for drilled shaft in the same condition. In this paper, the accuracies of the existing design criteria are investigated to develop an optimized design process for drilled shaft socketed into rock masses. Reasonable and consistent ultimate capacities of drilled shafts socked into rock masses, necessary far the check of accuracies of predictions, are determined by applying a specific failure criterion to a total of 11 pile load test results. A comparison between the predicted and the measured load capacities shows that ultimate base load capacities calculated from Zhang and Einstein's equation and NAVFAC are close to the measured values. Rosenberg and Journeaux's equation produces satisfactory prediction f3r ultimate side load capacity.

• Geomechanics and Engineering
• /
• v.21 no.6
• /
• pp.503-511
• /
• 2020

This study evaluated the side resistance of drilled shafts socketed into rock sections. Commonly used analysis methods for side resistance of piles in rocks are examined by utilizing a large number of load test data. The analysis of the unit side resistance of pile foundations embedded into rock sections is based on an empirical coefficient (α) and the uniaxial compressive strength (q_u) or its root (${\sqrt{q_u}}$). The Davisson criterion was used to interpret the resistance capacity from the load test results to acquire the computed relationships. The α-${\sqrt{q_u}}$ relationship is proven to be reliable in the prediction of friction resistance. This study further analyzed the relationship by including the effect of rock quality designation (RQD) on the results. Analysis results showed that the analysis model of α-${\sqrt{q_u}}$-RQD provided better prediction and reliability considering the RQD classification. Based on these analyses, the side resistance of drilled shafts socked into rocks is provided with statistical data to support the analysis.

• Tunnel and Underground Space
• /
• v.17 no.2 s.67
• /
• pp.102-108
• /
• 2007

Generally, the method used most widely for rock mass classification is considering the rock strength and development of joint frequency. However, if rock bed has micro-crack and long joint, this method is not rational. Therefore, the difficulties of excavation in the rock bed with complicated geological condition are decided by combining joint frequency. indoor tests (uniaxiall compressive strength, point load test, indoor elastic wave velocity, etc.) and field seismic refraction survey, and the rock mass classification should be implemented by considering their interrelationship.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1999.03a
• /
• pp.471-477
• /
• 1999

A new stress, load and displacement controlled direct shear apparatus has recently been developed at the Hyundai Institute of Construction Technology This direct shear apparatus is capable of testing of rock joint under constant normal stiffness, constant normal stress or constant normal load boundary conditions. This paper describes this direct shear apparatus and illustrates results of shear tests at constant normal stress condition, constant normal load condition and constant normal stiffness condition with dental stones which have a same joint roughness and unconfined compressive strength.

• Tunnel and Underground Space
• /
• v.5 no.2
• /
• pp.144-154
• /
• 1995

In this paper, we make a study on comparison and evaluation of the seoul granite properties, which are unit weight, uniaxial compressive strength, Brazilian tensile strength and, point load strength. The typical result are as follow- 1. From the measured value of point load strength anisotropy index, the seoul granite is considered to be homogeneous. 2. There is a linear relationship between uniaxial compressive strength and size corrected point load strength index. 3. Brazilian tensile strength and size corrected point load strength index are closely tied together.

• Geomechanics and Engineering
• /
• v.12 no.4
• /
• pp.611-626
• /
• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• Tunnel and Underground Space
• /
• v.30 no.4
• /
• pp.404-416
• /
• 2020

An analytical procedure for calculating the failure load of a V-shaped rock notch under two-dimensional stress conditions was developed based on the slip-line plastic analysis method. The key idea utilized in the development is the fact that the α-line, one of the slip-lines, extends from the rock notch surface to the horizontal surface outside the notch when the rock around the notch is in the plastic state, and that there exists an invariant which is constant along the α-line. Since the stress boundary condition of the horizontal surface outside the rock notch is known, it is possible to calculate the normal and shear stresses acting on the rock notch surface by solving the invariant equation. The notch failure load exerted by the wedge was calculated using the calculated stress components for the notch surface. Rock notch failure analysis was performed by applying the developed analytical procedure. The analysis results show that the failure load of the rock notch increases with exponential nonlinearity as the angle of the notch and the friction of the notch surface increase. The analytical procedure developed in this study is expected to have applications to the study of fracture initiation in rocks through wedge-shaped notch formation, calculation of bearing capacity of the rock foundation, and stability analysis of rock slopes and circular tunnels.

• Tunnel and Underground Space
• /
• v.15 no.4 s.57
• /
• pp.288-295
• /
• 2005

Many mechanical defects originated from various geological causes make rock mass exhibit anisotropic characteristics. Understanding how the stress distribution occurs in anisotropic rock mass is, therefore, very important for the design of footings on rock and rock structures. In this study, the patterns of elastic stress distribution, developed by acting line load on the surface, in transversely isotropic was investigated. The influence of joint stiffness, joint spacing, and dip angle on the stress distribution was examined. By assuming the Mohr-Coulomb criterion as joint slip condition, the development of joint slip zone was also discussed.

• Geomechanics and Engineering
• /
• v.17 no.6
• /
• pp.553-564
• /
• 2019

This paper presents experimental results of rock-concrete bi-material discs under cyclically diametrical compression. It was found that both specimens under cyclical and static loading failed in three typical modes: shear crack, tensile crack and a combined mode of shear and wing crack. The failure modes transited gradually from the shear crack to the tensile one by increasing the interface angle between the interface and the loading direction. The cycle number and peak load increased by increasing the interface angle. The number of cycles and peak load increased with the interface groove depth and groove width, however, decreased with increase in interface groove spacing. The concrete strength can contribute more to the cycle number and peak load for specimens with a higher interface angle. Compared with the discs under static loading, the cyclically loaded discs had a lower peak load but a larger deformation. Finally, the effects of interface angle, interface asperity and concrete strength on the fatigue strength were also discussed.