• Tunnel and Underground Space
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• v.17 no.1 s.66
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• pp.9-16
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• 2007

The influence of round length on the tunnel stability and construction cost is well acknowledged by many researchers and engineers but the coherent procedure is not available for its determination. In this study, the behaviour modes of the face and unsupported span was investigated for weak rock tunnel by a small scale model test, PFC3D and FDM analyses in consideration of the round length. Total five types of behaviour modes are defined and quantitative estimation of the behaviour modes was established in terms of the safety factor for the face stability and the conditional chart. Although the proposed method has some restrictions, this method can provide useful information for the optimization of the round length and excavation, especially in design stage.

• Smart Structures and Systems
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• v.22 no.6
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• pp.663-673
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• 2018

In this study, the effect of particle size on the cracks propagation and coalescence or cracking pattern of the edge notched disc specimens are investigated. Firstly, calibration of PFC3D was performed using Brazilian experimental test output. Then micro parameters were used to build edge notched disc specimen. The horizontal wall of the assembly is let to move downward with a standard low speed of 0.016 m/s. The numerical results show that the tensile cracks are dominant failure pattern for the modeled discs. These tensile cracks initiate from the pre-existing notch tip and propagate parallel to the loading direction then interact with the upper boundary of the modeled specimen. As the size of the balls (ball diameter) decrease the number of tensile cracks increase. The tensile fracture toughness of the samples also decreases as the particle size increases. Understanding the crack propagation and crack coalescence phenomena in brittle materials such as concretes and rocks is of paramount importance in the stability analyses for engineering structures such as rock slopes, underground structures and tunneling.

• Geomechanics and Engineering
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• v.29 no.4
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• pp.463-470
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• 2022

In NATM tunnels, water inrush and tunnel collapse are often encountered in silty-fine sand with abundant water during excavation. Because of the special engineering properties of this stratum, grouting effect is difficult to achieve as expected, and it is a major problem in the field of civil engineering. Taking Beijing Metro Line 10 as a case, we applied PFC3D to simulate the process of grouting in this stratum. By analyzing the law of grout diffusing and porosity change under different grouting pressures, the study found that grouting was a process of splitting, and grouting pressure played an important role. The numerical results were verified by theoretical calculation analysis, and the grouting parameters were determined under the various grouting pressures for practice. After the excavation of this tunnel, the concretions in silty-fine sand are similar to the results of PFC3D simulation, which indicates that the grouting mechanism is confirmed by field observation further.

• Geomechanics and Engineering
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• v.35 no.5
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• pp.475-486
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• 2023

Ballast particles have an irregular shape and are discrete in nature. Due to the discrete nature of ballast, it exhibits complex mechanical behaviour under loading conditions. The discrete element method (DEM) can model the behaviour of discrete particles under a multitude of loading conditions. DEM is used in this paper to simulate a series of three-dimensional direct shear tests in order to investigate the shear behaviour of railway ballast and its interaction at the microscopic level. Particle flow code in three dimension (PFC3D) models the irregular shape of ballast particles as clump particles. To investigate the influence of particle size distribution (PSD), real PSD of Indian railway ballast specification IRS:GE:1:2004, China high-speed rail (HSR) and French rail specifications are generated. PFC3D built-in linear contact model is used to simulate the interaction of ballast particles under various normal stresses, shearing rate and shear box sizes. The results indicate how shear resistance and volumetric changes in ballast assembly are affected by normal stress, shearing rate, PSD and shear box size. In addition to macroscopic behaviour, DEM represents the microscopic behaviour of ballast particles in the form of particle displacement at different stages of the shearing process.

• Geomechanics and Engineering
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• v.37 no.1
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• pp.73-84
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• 2024

Owing to the high strength and abrasive characteristics of cobble-boulders, cutters are easily worn and damaged during shield tunneling, making construction inefficient. In the present work, the stress on the ripper and scraper on the cutterhead was analyzed by the PFC3D-FLAC3D coupling model of shield tunneling to get insight into the performance of the cutterhead for cutting underground cobble and boulders. The numerical calculation results revealed that the increase in trajectory radius leads to a rising stress on the cutters, and the stress on the front cutting surface is greater than that on the back of the cutters. Moreover, the correlation between cutter wear and stress is revealed based on field measurement data. The distribution of the cutter stress is consistent with the cutter wear and breakage characteristics in actual construction, in which more extensive cutter stress is exhibited, extreme cutter wear appears, and more cutter breakage occurs. Finally, the relationship between the cutterhead opening area's layout and cutter wear distribution was investigated, indicating that the cutter wear extent is the most severe in the region where the radial opening ratio dropped sharply.

• Computers and Concrete
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• v.26 no.5
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• pp.377-384
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• 2020

A two-dimensional particle flow cod (PFC) is used to study the effect of missile impact on the concrete target. For this purpose firstly calibration of numerical model was performed so that tensile strength of numerical models and experimental sample were the same. Secondly, a concrete model was built. The number of concrete layers and the angle of concrete layers related to horizontal axis were changed. Their numbers were 1, 2, 3 and 4. The angles were 0°, 15°, 30°, 45°, 60°, 75° and 90°. A semi-circle missile was simulated at top of the concrete layers. Its velocity in opposite side of Y direction was 100 m/s. three measuring circles were situated at the below the missile in the model to receive the applied force. The load in the missile and measuring circles together with failure pattern were registered at the beginning of the impaction. The results show that concrete layers number and concrete layers angle have important effect on the failure load while the failure pattern was nearly constant in all of the models.

• Journal of the Korean GEO-environmental Society
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• v.12 no.7
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• pp.57-65
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• 2011

Numerical simulations by three-dimensional Particle Flow Code($PFC^{3D}$, Itasca) considering distinct element method (DEM) were carried out for prediction of triaxial compression test with sand material. The effect of scale conditions for numerical model and distinct material on final prediction results was analyzed by numerical models under various scale conditions, and following observations were made from the numerical experiments. It is very useful to model the initial material condition without any porosity conversion from 2-D to 3-D DEM. Numerical experiments have shown that in all cases considered, 3D distinct element modeling could provide good agreement on stress-strain behavior, volume change and strength properties with laboratory testing results. It was important thing to assess reasonable scale ratio of numerical model and distinct elements for saving calculation time and securing calculation efficiency under condition with accuracy and appropriateness as numerical laboratory. As results of DEM simulations under various scale conditions, most of results show that shear strength properties as cohesion and internal friction angle are similar in condition of $D_{mod}/D_{gmax}$ < 10. It shows that 3-D distinct element method could be used as efficient tool to assess strength properties by numerical laboratory technique.

• Explosives and Blasting
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• v.28 no.2
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• pp.1-16
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• 2010

This study focuses on the phenomenon that the blast damaged zone developed on rock slope surfaces can be affected by joint characteristics rather than by explosive power when the pre-splitting is applied to excavate a jointed rock slope. The characteristics of rock joints on a slope were investigated and categorized them into 4 cases. Also an image processing system has been used for comparing the distribution pattern of rock blocks. From this investigation, it was found that the rock blocks bigger than 2,000 mm occupied 42% in the case of single joint set and it showed the well efficiency of pre-splitting blast. In cases of 2~3 parallel joint sets and 2~3 intersecting joint sets are developed on rock surfaces, the rock blocks in the range of 1,000~2,000 mm occupied 43.6% and 35.8%, respectively, and it showed that the efficiency of pre-splitting was decreased. When more than 3 joint sets are randomly developed, however, the rock blocks in the range of 250~500 mm occupied 35% and there was no block bigger than 1,000 mm. This denotes that the blasting with pre-splitting was not effective. The numerical analysis using PFC2D showed that the blast damaged zone in a rock mass could be directly influenced by the pre-splitting. It is, therefore, required to investigate the discontinuity pattern on rock surfaces in advance, when the pre-splitting method is applied to excavate jointed rock slopes and to apply a flexible blating design with a consideration of the joint characteristics.

• Tunnel and Underground Space
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• v.23 no.1
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• pp.54-65
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• 2013

The LCM (Linear Cutting Machine) test is one of the most powerful and reliable methods for designing the disc cutter and for predicting the TBM (Tunnel Boring Machine) performance. It has an advantage to predict the actual load on disc cutter from the laboratory test on the real-size large rock samples, however, it also has a disadvantage to transport and/or prepare the large rock samples and to need an extra cost for experiment. In order to overcome this problem, lots of numerical studies have been performed. In this study, the PFC3D (Particle Flow Code in 3 Dimension) has been adopted for numerical analysis on optimum cutter spacing and failure aspects of Busan Tuff. The optimum cutting condition with s/p ratio of 16 and minimum specific energy of $14MJ/m^3$ was derived from numerical analyses. The cutter spacing for Busan Tuff had the good agreements with those of LCM test and numerical analysis by finite element method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.26-33
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• 2016

Recently, the use of transformer-less UPS has increased to improve the efficiency of UPS. However, transformer-less UPS is required in three-phase four-wire input IGBT PWM rectifier and the existing three-phase three-wire PFC algorithm cannot be applied in the three-phase four-wire system due to the neutral current problem of UPS input. To control the three-phase four-wire input IGBT PWM rectifier, there are two existing algorithms: 3D SVM and single phase control method. These two algorithms have advantages/disadvantages in controlling the rectifier. The single phase control method is unstable for controlling the rectifier and the 3D SVM method has a problem that must increase the L value of the input-side inductor considerably. Therefore, this paper proposes digital single phase control technology and another new algorithm considering the d-q control, to improve the characteristics of the existing control algorithm. In addition, this paper performed a simulation and experiment based on the proposed control algorithm. The simulation results showed that the proposed technology can control three-phase four-wire IGBT PWM rectifier in a stable manner and can also reduce the neutral current. The proposed algorithm is a useful tool for controlling the three-phase four-wire IGBT PWM rectifier.