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The performance of tunnel boring machines (TBM) highly depends on the fragmentation efficiency of the cutters. Many geological factors can influence the rock fragmentation process. In this study, a series of two dimension numerica...
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The performance of tunnel boring machines (TBM) highly depends on the fragmentation efficiency of the cutters. Many geological factors can influence the rock fragmentation process. In this study, a series of two dimension numerical modeling were performed using the discrete element method (DEM) to explore the effect of joint orientation on rock fragmentation by a TBM cutter. Results show that the joint orientation can significantly influence the crack initiation and propagation as well as the fragmentation pattern, and hence affect the penetration rate of the TBM. Such observations are also noted by laboratory and site studies. It also indicates that discontinuum-based DEM has the potential in simulating rock indentation and fragmentation by TBM cutters when rock joints are taken into consideration.
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The Ajanta caves are situated in Deccan Trap basalt and declared as one of the World Heritage Sites by UNESCO. The present study aims to investigate and understand the damage of caves and to protect the life of the visitors from t...
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The Ajanta caves are situated in Deccan Trap basalt and declared as one of the World Heritage Sites by UNESCO. The present study aims to investigate and understand the damage of caves and to protect the life of the visitors from the rockfall phenomenon at and around the caves. Information related to the detached rock mass/block was acquired by using Barton–Bandis model in Universal Distinct Element Code. Parameters for rockfall simulation were determined by rigorous field study and laboratory experiment and then calibrated some of the parameters by back analysis. RocFall 4.0 program has been used to calculate maximum bounce heights, total kinetic energies, and translational velocities of the falling blocks of different weights. The maximum bounce height varies from 14.0 to 19.0 m for the weight of the block size ranging from 500 to 2,000 kg, whereas the maximum velocity and maximum kinetic energy are 30.0 m/s and 917.66 kJ, respectively. Finally, the results of simulation have been used to find out the position of the barrier and its capacity to design the protection barrier. The barrier capacity was found to be 325 kJ for 2,000 kg of falling blocks at a height of 50.0 m.
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In this study the effects of resistivity characteristics and deformation of rock mass, specification of joints and linings on the tunnels behavior are investigated. UDEC V4 software was used for 2D analysis considering the investi...
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In this study the effects of resistivity characteristics and deformation of rock mass, specification of joints and linings on the tunnels behavior are investigated. UDEC V4 software was used for 2D analysis considering the investigated parameters. Mohr-Coulomb model was used to model the behavior. The analysis showed that increase of resistivity parameters and rock mass deformation, led to lower displacement occurred in tunnel. By decreasing the distance of the joints and also by making the joints more perpendicular to the axis of the tunnel, forces and resulting displacement would rise. Also it was observed that increase of lining thickness was not effective on the pattern and displacement size and just is important while bearing the imposed loadings.
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The rock breakage process is the interaction process between TBM and rock mass, which is affected by TBM specifications, such as thrust force, cutter tip width and profile, cutter spacing, RPM, and torque, and rock mass properties...
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The rock breakage process is the interaction process between TBM and rock mass, which is affected by TBM specifications, such as thrust force, cutter tip width and profile, cutter spacing, RPM, and torque, and rock mass properties mainly including rock material strength, rock brittleness, joint spacing and orientation. During TBM excavation, TBM cutters roll across the tunnel face and continuously crush the rock. Then, cracks are initiated from the crushed zone and propagated downwards and sideward. Chipping between two adjacent cutters does not take place until the side cracks initiated from the adjacent cuts coalesce. It is directly relevant to the cutter spacing and affects the efficiency of TBM excavation. This study assumed that the load acting on cutters is enough to chip the rock. The rock chipping process with cutter spacing of 70 mm under the action of two cuts was simulated by using a 2-D DEM code, UDEC. The chipping process was obtained. At the beginning, each cutter indents the rock independently and similarly to a single cutter indentation process. The stress field is also independent. After the formation of the crushed zone, cracks are initiated from this zone, and then the side cracks propagate along a certain direction due to the interaction of two cutters. With increasing penetration, the side cracks between two cutters propagate to each other and coalesce, and form the rock chip. The chip formation is greatly dependent on the cutter spacing and the critical cutter load.
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Although most cut slopes in Ohio consist of inter-layered, sub-horizontal units of hard and soft sedimentary rocks (sandstone, limestone, dolostone, shale, claystone, mudstone), slopes consisting of relatively thick hard rock unit...
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Although most cut slopes in Ohio consist of inter-layered, sub-horizontal units of hard and soft sedimentary rocks (sandstone, limestone, dolostone, shale, claystone, mudstone), slopes consisting of relatively thick hard rock units are not uncommon. Design of stable cut slopes in hard rock units needs to consider rock mass strength and orientation of discontinuities with respect to slope face. Results of kinematic stability analyses show that hard-rock cut slopes are less likely to have conventional plane and wedge failures, caused by unfavorable orientation of discontinuities. The main cause of failure is identified to be the undercutting-induced toppling, which is not amenable to traditional kinematic or rock mass strength-based analyses. Therefore, to recommend a suitable slope angle, numerical models, using UDEC software, were employed to study how various slope angles affect the process of undercutting-induced toppling failures. The UDEC models showed a slope angle of 45° (1H:1 V) to be the most stable angle. However, a 63° (0.5H:l V) slope angle can significantly reduce the potential for such failures and is therefore more appropriate than the widely used angle of 76°(0.25H:l V).
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Hydraulic fracturing in reservoirs with low or high fracture density could have a significant impact on the reservoirs' production rate. In the present study, having determined the fracture direction through the finite difference ...
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Hydraulic fracturing in reservoirs with low or high fracture density could have a significant impact on the reservoirs' production rate. In the present study, having determined the fracture direction through the finite difference method according to the induced-stress distributions, this operation simulated fracturing in two reservoirs with high or low levels of natural fracturing, using the distinct-element method. The goal was to investigate the effect of hydraulic fracture length and aperture on the production rate from both reservoirs. Sensitivity analysis indicated that in a reservoir with more natural fractures, hydraulic fracture length plays a more significant role, and in a reservoir with fewer natural fractures, both hydraulic fracture length and opening are highly influential. Also, factors such as fracture coalescence and intersected fractures, which influence the production rate, were examined. Moreover, the results revealed that when the fracture length and aperture increase, the production rate fluctuates.
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The influence of joint spacing on tunnel boring machine (TBM) penetration performance has been extensively observed at TBM site. However, the mechanism of rock mass fragmentation as function of the joint spacing has been scarcely ...
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The influence of joint spacing on tunnel boring machine (TBM) penetration performance has been extensively observed at TBM site. However, the mechanism of rock mass fragmentation as function of the joint spacing has been scarcely studied. In this study, the rock indentation by a single TBM cutter is simulated by using the discrete element method (DEM), and the rock fragmentation process is highlighted. A series of two-dimensional numerical modelling with different joint spacing in a rock mass have been performed to explore the effect of joint spacing on rock fragmentation by a TBM cutter. Results show that the joint spacing can significantly influence the crack initiation and propagation, as well as the fragmentation pattern, and can hence affect the penetration rate of the TBM. Two crack initiation and propagation modes are found to fragment the rock mass due to the variation of joint spacing. The simulation results are analyzed and compared with in situ measurements.
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Waves propagating through rocks when intersected with joints gets transmitted or reflected. Joints or discontinuities in a rock affect the amplitude and velocity of the transmitted and reflected waves propagating through it. The c...
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Waves propagating through rocks when intersected with joints gets transmitted or reflected. Joints or discontinuities in a rock affect the amplitude and velocity of the transmitted and reflected waves propagating through it. The changes occurring on a transmitted wave is following the properties of the incident wave namely frequency, amplitude, wavelength and the rockmass properties namely joint angle, joint roughness, joint stiffness, number of joints. In the present work, the effect of different parameters on the wave properties is understood with the help of experimental and numerical studies. The experimental study is conducted with the help of ultrasonic pulse velocity (UPV) test on artificially simulated gypsum samples. The corresponding numerical studies and subsequent extensions are done using the Universal Distinct Element Code (UDEC). Both rock mass properties as well as wave characteristics play a significant role in the wave propagation characteristics. Empirical relationships are proposed for the estimation of wave velocity against different rock joint parameters.
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A series of simplified approaches are evaluated for their effectiveness to estimate the seismic vulnerability of historical masonry towers. First, collapse loads are evaluated on sixteen "idealized" benchmark cases with different ...
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A series of simplified approaches are evaluated for their effectiveness to estimate the seismic vulnerability of historical masonry towers. First, collapse loads are evaluated on sixteen "idealized" benchmark cases with different slenderness and shear area. Both analytical and computational approaches are used, namely the analytical procedure proposed by the Italian Guidelines on the Built Heritage and pushover analyses conducted using the commercial codes UDEC and 3Muri. The sixteen towers are representative cases which can be encountered in practice. Their geometry is idealized into parallelepiped blocks with hollow square cross-sections, thus favoring the utilization of 2D approaches, beneficial to drastically reduce the effort required for repeated computations. In addition, a Monte Carlo MC upper bound limit analysis strategy is proposed, in order to have an insight into the possible failure mechanisms for the different cases investigated. Deliberately is avoided the introduction of any form of irregularity and they are supposed isolated from the neighboring buildings, to obtain results exclusively dependent from geometric features. Among all the possible collapse mechanisms, five of them are selected according to the probability of occurrence based on past earthquake experiences. Five million cloud points of collapse accelerations are obtained by carrying the height, slenderness and shear area of the idealized towers. The approach is very fast and allows identifying different regions where single mechanisms are active. The results are confirmed repeating MC simulations with a triangular FE upper bound limit analysis discretization of the idealized towers. A series of equations are provided in order to assist engineers and practitioners to obtain a preliminary estimation of their expected collapse acceleration. For validation purposes, the results obtained previously with refined full 3D FE models of 25 towers located in the Northern Italy are reported. Satisfa
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The seismic stability of the Aknes rock slope, western Norway, was analysed by using the distinct element code UDEC (Universal Distinct Element Code). The slope poses a threat to the region as a sudden failure may cause a destruct...
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The seismic stability of the Aknes rock slope, western Norway, was analysed by using the distinct element code UDEC (Universal Distinct Element Code). The slope poses a threat to the region as a sudden failure may cause a destructive tsunami in the fjord. The dynamic input was based on earthquakes with return periods of 100 and 1000 years, and in most models the input shear wave was a harmonic function (sine wave). Models with depths of the sliding surface up to 200 m and with ground water conditions derived from site investigations were analysed, as well as models with ground water conditions assumed from possible future draining of the slope. The analyses indicate that an earthquake with a return period of 1000 years is likely to trigger sliding to great depth in the slope at the present ground water conditions and that the slope will be stable if it is drained. The analyses also indicate that sliding is not likely to be triggered by an earthquake with a return period of 100 years at the present ground water conditions.
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