Rock Mechanics
Dariush Mohammadi; Kourosh Shahriar; Parviz Moarefvand; Ebrahim Farrokh
Abstract
The correct design of the cutterhead of a tunnel boring machine (TBM) plays a vital role in the efficient operation of the machine, as the cutterhead structure remains unchanged during the tunneling project. This paper aims to elucidate the fundamental principles in the design of the cutterhead opening ...
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The correct design of the cutterhead of a tunnel boring machine (TBM) plays a vital role in the efficient operation of the machine, as the cutterhead structure remains unchanged during the tunneling project. This paper aims to elucidate the fundamental principles in the design of the cutterhead opening in soft ground based on data obtained from TBM manufacturers. Initially, a comprehensive database of soft ground cutterheads from different TBM manufacturers across various projects and ground conditions was compiled. The most frequently used cutterhead configurations with diameters exceeding 5 meters were categorized into 36 distinct opening configurations based on a radial opening ratio curve and opening patterns per sector. Next, the performance parameters and particle flow characteristics of three Herrenknecht cutterhead designs featuring varying opening configurations in the central and circumference areas were analyzed using the Discrete Element Method (DEM) by considering material parameters for machine and soil and contact parameters between soil particles and soil particles-machine structures. Hertz–Mindlin model was assigned as the contact model for these elements. Additionally, three different cutterheads employed in Tehran metro projects in Iran were identified by monitoring the cutterhead torque and thrust force under same geotechnical conditions and operational parameters. Generally, a higher opening percentage in the central area of the cutterhead indicates good performance during excavation in cohesive soils. However, the higher opening percentage in circumferential areas is a better choice for effective excavated material removal around the cutterhead and tunnel in non-cohesive soils, weathered rocks, mixed and heterogeneous conditions.
Enayatallah Emami Meybodi; Fatemeh Taajobian
Abstract
Due to the challenge of finding identical rock samples with varying grain sizes, investigating the impact of texture on rock material has been given less attention. However, macroscopic properties such as compressive strength, tensile strength, and modulus of elasticity can indicate microscopic properties ...
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Due to the challenge of finding identical rock samples with varying grain sizes, investigating the impact of texture on rock material has been given less attention. However, macroscopic properties such as compressive strength, tensile strength, and modulus of elasticity can indicate microscopic properties like intergranular resistance properties influence rock fracture toughness. In this work, both the experimental and numerical methods are used to examine the effect of grain size on the mechanical properties of sandstone. Uniaxial compressive strength and indirect tensile tests are conducted on sandstone samples with varying grain sizes, and the particle flow code software is used to model the impact of grain dimensions on intergranular properties. Flat joint model is applied for numerical modeling in the particle flow code© software. The aim of this work is to validate the numerical model by peak strength failure and stress-strain curves to determine the effect of grain size on the mechanical behavior. The results show that increasing grain size significantly decrease compressive strength, tensile strength, and modulus of elasticity. The impact of the change in grain size is more significant on compressive strength than on the other two properties. The correlation coefficient for tensile strength and grain size is R2 = 0.57, while for modulus of elasticity and grain size, it is R2 = 0.79. The PFC software helps calibrate intergranular properties, and investigate the effect of changing grain size on these properties. Overall, this study offers valuable insights into the relationship between the grain size and the mechanical properties of sandstone, which can be useful in various engineering applications, especially in petroleum geo-mechanics.
E. Nemattolahi; A.R. Ghasemi; E. Razi; S. Banisi
Abstract
The discrete element method (DEM) has been used as a popular simulation method in order to verify the designs by visualizing how materials flow through complex equipment geometries. Although DEM simulation is a powerful design tool, finding a DEM model that includes all real material properties ...
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The discrete element method (DEM) has been used as a popular simulation method in order to verify the designs by visualizing how materials flow through complex equipment geometries. Although DEM simulation is a powerful design tool, finding a DEM model that includes all real material properties is not computationally feasible. In order to obtain more realistic results, particle energy loss due to rolling friction has been highlighted by many researchers using various models to implement a reverse torque. On account of the complexity of the problem, there is no unique model for all applications (i.e. dynamic and pseudo-static regimes). In this research work, an in-house developed DEM software (KMPCDEM©) was used to assess the robustness of three models by comparing the repose angle obtained through the draw down test. The elastic–plastic spring dashpot model was then modified based on considering the individual parameters instead of the relative parameters of two contact entities. The results showed that the modified model could produce a higher repose angle. The modified model was used for the calibration of DEM input parameters in the simulation of repose angle of iron ore pellets in a laboratory setup of the draw down test. Comparison of the calibrated DEM simulation (using 0.0007 and 0.75 for the rolling and sliding friction coefficients, respectively) with the laboratory results showed a good agreement between the predicted and measured angle of repose. The non-calibrated DEM simulations are susceptible to error, and therefore, it is strongly recommended to use the laboratory experiments to characterize the materials before using the DEM simulation as a design tool of industrial equipment.
Mineral Processing
M. Jahani Chegeni
Abstract
A deeper understanding of the milling operation of ball mills helps mineral processing engineers to control and optimize them, and therefore, reduce their consuming power. In this work, the milling operation of ball mills is investigated using two methods, i.e. DEM and combined DEM-SPH. First, a pilot ...
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A deeper understanding of the milling operation of ball mills helps mineral processing engineers to control and optimize them, and therefore, reduce their consuming power. In this work, the milling operation of ball mills is investigated using two methods, i.e. DEM and combined DEM-SPH. First, a pilot scale ball mill with no lifter is simulated by both methods. Then another pilot scale ball mill with eight rectangle lifters is simulated again by both methods. The effects of lifters on ball shoulder and toe points as well as on creation of cascading and cataracting movements for balls are studied by both methods. At the present time, there is not enough measured data available for dense slurries interacting with the coarse particulates available in the public domain that can be used adequately to validate these types of predictions. The results obtained indicated that fluid slurry in the mill lowered the charge shoulder by about 28 cm and 25 cm in the no-lifter and eight-lifter cases, respectively. However, it raised the charge toe by about 36 cm and 6 cm in the no-lifter and eight-lifter cases, respectively.
