• Geomechanics and Engineering
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• v.12 no.4
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• pp.611-626
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• 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
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• v.29 no.6
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• pp.523-531
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• 2019

In the applications of rock mechanics or rock engineering including drill and blast, drilling and mechanical excavation, the fracture toughness is an important factor. Several methods have been proposed to measure the fracture toughness of rocks. In this study, wedge splitting test specimen which is prepared with ease and tested under compression loading was used to obtain mode I fracture toughness of rocks. The equation of stress intensity factor through numerical analysis is proposed from the stress state of crack tip considering both vertical and horizontal loads due to the vertical load acting on the wedge. The validity of the wedge splitting test method was confirmed by comparing the mode I fracture toughness values obtained by the GD and SENB test specimens.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.23-35
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• 2006

Shear load transfer characteristics of rock-socketed drilled shafts were analyzed. The constant normal stiffness (CNS) direct shear tests were performed to identify the major influencing factors of shaft resistance, i.e., unconfined compressive strength, borehole roughness, normal stiffness, initial confining stress, and material properties. Based on the CNS tests, shear load transfer function of drilled shafts in rocks is proposed using borehole roughness and the geological strength index (GSI), which indicates discontinuity and surface condition of rock mass in Hoek-Brown criterion (1997). The proposed load-transfer function was verified by the load test results of seven rock-socketed drilled test shafts subjected to axial loads. Through comparisons of the results of load tests, it is found that the load-transfer function by the present study is in good agreement with the general trend observed by in situ measurements, and thus represents a significant improvement in the prediction of load transfer of drilled shafts.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.33-40
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• 2008

The load distribution and deformation of rock-socketed drilled shafts subjected to axial loads are evaluated by a load-transfer method. The emphasis is on quantifying the effect of coupled soil resistance in rock-socketed drilled shafts using the 2D elasto-plastic finite element analysis. Slippage and shear load transfer behavior at the pile-soil interface are investigated by using a user-subroutine interface model (FRlC). It is shown that the coupled soil resistance provides the influence of pile toe settlement as the shaft resistance is increased to an ultimate limit state. The results show that the coupling effect is closely related to the value of pile diameter over rock mass modulus (D/$E_{mass}$) and the ratio of total shaft resistance against total applied load ($R_s$/Q). Through comparisons with field case studies, the 2D numerical analysis reseanably presented load transfer of pile and coupling effect due to the transfer of shaft shear loading, and thus represents a significant improvement in the prediction of load deflections of drilled shafts.

• Journal of Drive and Control
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• v.16 no.2
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• pp.1-7
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• 2019

Jaw crusher is a device that breaks rock collected from mines or quarries to produce aggregates of the size desired by user. A representative method for measuring load is to measure them by attaching force sensors directly to the part where the load is generated. However, the direct method has many limitations such as high-impact loads generation in equipment or space constraints, sensor capacities and costs. Therefore, Transfer Path Analysis (TPA) was used to indirectly measure impact loads by attaching acceleration sensors. In this study, both direct and TPA methods were used to measure the impact load of Jaw crusher. This study finally quantifies the impact of the load generated by the Jaw crusher using direct method and TPA method, and comparing the impact load measured calculated the derive the error rate.

• Journal of the Korean Geotechnical Society
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• v.20 no.4
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• pp.89-102
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• 2004

The generated blasting pressure wave initiated under decoupled-charge condition is a function of peak blasting pressure, rise time, and wave-shape function. The peak blasting pressure and the rise time are also the function of explosive and rock properties. The probabilistic distributions of explosive and rock properties are derived from the results of their property tests. Since the probabilistic distributions of explosive and rock properties displayed a normal distribution, the peak blasting pressure and the rise time can also be regarded as a normal distribution. Parameter analysis and uncertainty analysis were performed to identify the most influential parameter that affects the peak blasting pressure and the rise time. Even though the explosive properties were found to be the most influential parameters on the peak blasting pressure and the rise time from the parameter analyses, the result of uncertainty analysis showed that rock properties constituted major uncertainties in estimating the peak blasting pressure and the rise time rather than explosive properties. Damage and overbreak of the remaining rock around the excavation line induced by blasting were evaluated by dynamic numerical analysis. A user-subroutine to estimate the rock damage was coded based on the continuum damage mechanics. This subroutine was linked to a commercial program called 'ABAQUS/Explicit'. The results of dynamic numerical analysis showed that the rock damages generated by the initiation of stopping hole were larger than those from the initiation of contour hole. Several methods to minimize those damages were proposed such as relocation of stopping hole, detailed subdivision of rock classification, and so on. It was found that fracture probability criteria and fractured zones could be distinctively identified by applying fuzzy-random probability.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.97-100
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• 2006

This study performed numerical analysis for obtaining optimal frequency and damping ratio of tuned mass damper (TMD) using 20 seismic loads measured at rock site. The structures of $1{\sim}2$ second natural period were considered, and optimal frequency and damping ratio were estimated for different mass ratio in terms of displacement and absolute acceleration response control. Numerical results showed that the values of the optimal parameters were different those from previous study by Hartog.

• Earthquakes and Structures
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• v.3 no.3_4
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• pp.457-471
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• 2012

Current code procedures for stress and stability analysis of new and existing concrete-gravity dams are primarily based on conventional methods of analysis. Such methods can be applied in a straightforward manner but there has been evidence that they may be inaccurate or, possibly, not conservative. This paper presents finite element modeling and analysis procedures and makes recommendations for local failure criteria at the dam-rock interface aimed at predicting more accurately the behavior of dams under hydraulic and anchoring loads.

• The Journal of Engineering Geology
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• v.31 no.3
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• pp.295-306
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• 2021

This study used numerical modeling to investigate the stability of railway roadbed in areas with various underground cavities and rock conditions associated with mining activities. It compared combined loads from both passenger and freight trains with loads from only passenger trains. Stability was assessed with reference to the Korean government standards for railway subsidence allowance and railway warping repair. Sufficient stability regarding the railway subsidence allowance standard was not achieved when cavities were at depths of <5 m. The criteria for requiring railway warping repair were met when cavities were at depths of <15 m, depending on the rock fracture condition. This study provides the first report on systematic analysis land subsidence related to cavity size and rock fracture conditions associated with mining activities. We expect that this study could serve as an important reference for railway construction in mining areas.

• Journal of the Korean Geotechnical Society
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• v.28 no.1
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• pp.29-39
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• 2012

The maximum unit point resistance ($q_{max}$) of rock socketed drilled shafts subjected to axial loads was investigated by a numerical analysis. A 3D Finite Difference Method (FDM) analysis and a Distinct Element Method (DEM) analysis were performed with varying rock elastic modulus (E), discontinuity spacing ($S_j$), discontinuity dip angle ($i_j$), and pile diameter (D). Based on the results of obtained, it was found that the ultimate point resistance ($q_{max}$) increased as rock elastic modulus (E) and rock discontinuity spacing ($S_j$) increased. But, it was found that $q_{max}$ decreased as pile diameter (D) increased. As for the influence of the dip angle of rock discontinuity ($i_j$), it was shown that $q_{max}$ decreased up to 50% of maximum value within the range of $0^{\circ}$ < $i_j$ < $60^{\circ}$ due to the shear failure at rock discontinuities. Furthermore, it was found that if $20^{\circ}{\leq}i_j{\leq}40^{\circ}$, influence of $i_j$ should be taken into account because $q_{max}$ tended to approach a minimum value as $i_j$ approached a value near the friction angle of the discontinuity (${\phi}_j$).