scholarly journals Study on Evolution Mechanism of Structure-Type Rockburst: Insights from Discrete Element Modeling

2021 ◽  
Vol 13 (14) ◽  
pp. 8036
Author(s):  
Chenxi Zhang ◽  
Diyuan Li ◽  
Shunchuan Wu ◽  
Long Chen ◽  
Jun Peng
Keyword(s):  
Shear Fracture ◽  
Pressure Coefficient ◽  
Structural Type ◽  
Structure Type ◽  
Particle Flow Code ◽  
Tensile Fracture ◽  
Discrete Element Modeling ◽  
Structural Plane ◽  
Evolution Mechanism ◽  
Radiated Energy

Taking the “11.28” rockburst occurred in the Jinping II Hydropower Station as the engineering background, the evolution mechanism of structure-type rockburst was studied in detail based on the particle flow code. The results indicate that the failure mechanism of structure-type rockburst includes a tensile fracture induced by tangential compressive stress and a shear fracture caused by shear stress due to overburdened loadings and shear slip on the structural plane. In addition, it is found that the differences between structure-type rockburst and strainburst mainly include (a) the distribution of the local concentrated stress zone after excavation, (b) the evolution mechanism, and (c) the failure locations. Finally, the influence of four factors on the structure-type rockburst are explored. The results show that (1) when the friction coefficient is greater than 0.5, the effect of structural plane is weakened, and the rock near excavation tends to be intact, the structural-type rockburst intensity decreases; (2) the dissipated and radiated energy in structural-type rockburst reduces with rockmass heterogeneity m; (3) the lateral pressure coefficient has a significant effect on the intensity of deep rock failure, specifically in the form of the rapid growth in dissipative energy; (4) and the structural-type rockburst is more pronounced at a structural plane length near 90 mm.

scholarly journals Discrete Element Modeling of Crack Initiation Stress of Marble Based on Griffith’s Strength Theory

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Suifeng Wang ◽  
Fei Tan ◽  
Minglong You ◽  
Yu-Yong Jiao ◽  
Fubin Tu
Keyword(s):  
Crack Initiation ◽  
Particle Flow Code ◽  
Biaxial Compression ◽  
Discrete Element Modeling ◽  
Compression Tests ◽  
Strength Theory ◽  
Evolution Law ◽  
Crack Initiation Stress ◽  
Damage Process ◽  
Initiation Stress

Investigating the crack initiation stress of rocks is vital for understanding the gradual damage process of rocks and the evolution law of internal cracks. In this paper, the particle flow code method is used to conduct biaxial compression tests on a marble model with an elliptical crack under different confining pressures. According to the evolution status of microcracks in the rock during compression, four characteristic stresses are defined to reflect the gradual damage process of the marble. Two different methods are used to obtain crack initiation stress of rocks, and the calculation results are compared with those based on Griffith’s strength theory to verify the accuracy of this theory under compressive stress. Based on the numerical simulation results, the evolution law for the strength parameters of marble with the degree of damage is described. According to the proportional relationship between the peak stress and crack initiation stress, a new method for predicting the initiation stress is proposed, whose effectiveness is verified. Overall, the results of this study can serve as a useful guide for solving the important problems of slab cracking and rockburst encountered in underground space engineering.

scholarly journals Neurotoxin Merging: A Strategy Deployed by the Venom of the Spider Cupiennius salei to Potentiate Toxicity on Insects

Toxins ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 250 ◽  
Author(s):  
Benjamin Clémençon ◽  
Lucia Kuhn-Nentwig ◽  
Nicolas Langenegger ◽  
Lukas Kopp ◽  
Steve Peigneur ◽  
...  
Keyword(s):  
Xenopus Laevis ◽  
Direct Interaction ◽  
Structural Type ◽  
Structure Type ◽  
Open Loop ◽  
Cytolytic Activity ◽  
Xenopus Laevis Oocytes ◽  
Cupiennius Salei

The venom of Cupiennius salei is composed of dozens of neurotoxins, with most of them supposed to act on ion channels. Some insecticidal monomeric neurotoxins contain an α-helical part besides their inhibitor cystine knot (ICK) motif (type 1). Other neurotoxins have, besides the ICK motif, an α-helical part of an open loop, resulting in a heterodimeric structure (type 2). Due to their low toxicity, it is difficult to understand the existence of type 2 peptides. Here, we show with the voltage clamp technique in oocytes of Xenopus laevis that a combined application of structural type 1 and type 2 neurotoxins has a much more pronounced cytolytic effect than each of the toxins alone. In biotests with Drosophila melanogaster, the combined effect of both neurotoxins was enhanced by 2 to 3 log units when compared to the components alone. Electrophysiological measurements of a type 2 peptide at 18 ion channel types, expressed in Xenopus laevis oocytes, showed no effect. Microscale thermophoresis data indicate a monomeric/heterodimeric peptide complex formation, thus a direct interaction between type 1 and type 2 peptides, leading to cell death. In conclusion, peptide mergers between both neurotoxins are the main cause for the high cytolytic activity of Cupiennius salei venom.

scholarly journals Experimental Study on the Evolution Mechanism of Landslide with Retaining Wall Locked Segment

Geofluids ◽  
2022 ◽  
Vol 2022 ◽  
pp. 1-10
Author(s):  
Han-Dong Liu ◽  
Jia-Xing Chen ◽  
Zhi-Fei Guo ◽  
Dong-Dong Li ◽  
Ya-Feng Zhang
Keyword(s):  
Shear Fracture ◽  
Retaining Wall ◽  
Stress Test ◽  
Pressure Sensors ◽  
Inertial Force ◽  
Slope Instability ◽  
Evolution Mechanism ◽  
Seismic Force ◽  
Mechanism Of Landslide ◽  
External Loads

The failure of locked segment-type slopes is often affected by rainfall, earthquake, and other external loads. Rainfall scours the slope and weakens the mechanical properties of rock-soil mass. At the same time, rainfall infiltrates into cracks of slope rock mass. Under the action of in situ stress, hydraulic fracturing leads to the development and expansion of rock cracks, which increases the risk of slope instability. Under seismic force, the slope will be subjected to large horizontal inertial force, resulting in slope instability. In this paper, a self-developed loading device was used to simulate the external loads such as rainfall and earthquake, and the model tests are carried out to study the evolution mechanism of landslide with retaining wall locked segment. Three-dimensional laser scanner, microearth pressure sensors, and high-definition camera are applied for the high-precision monitoring of slope shape, deformation, and stress. Test results show that the retaining wall locked segment has an important control effect on landslide stability. The characteristics of deformation evolution and stress response of landslide with retaining wall locked segment are analyzed and studied by changing the slope shape, earth pressure, and the displacement cloud map. The evolutionary process of landslide with retaining wall locked segment is summarized. Experimental results reveal that as the landslide with retaining wall locked segment is at failure, the upper part of the landslide thrusts and slides and the retaining wall produces a locking effect; the middle part extrudes and uplifts, which is accompanied with shallow sliding; and compression-shear fracture of the locked segment leads to the landslide failure.

scholarly journals Tensile fracture of ultrafine grained aluminum 6061 sheets by asymmetric cryorolling for microforming

2014 ◽  
Vol 23 (8) ◽  
pp. 1077-1095 ◽  
Author(s):  
Hailiang Yu ◽  
Kiet Tieu ◽  
Cheng Lu ◽  
Yanshan Lou ◽  
Xianghua Liu ◽  
...  
Keyword(s):  
Size Effect ◽  
Tensile Test ◽  
Fracture Behavior ◽  
Unsolved Problem ◽  
Shear Fracture ◽  
Tensile Fracture ◽  
The Finite Element Method ◽  
Fracture Angle ◽  
Ultrafine Grained ◽  
Number Of Passes

The size effect on the mechanism of fracture in ultrafine grained sheets is an unsolved problem in microforming. This paper describes a tensile test carried out to study the fracture behavior and the shear fracture angles of both rolled and aged ultrafine grained aluminum 6061 sheets produced by asymmetric cryorolling. A scanning electron microscope was used to observe the fracture surface. The finite element method was used to simulate the tensile test using the uncoupled Cockcroft–Latham and Tresca criteria and the coupled Gurson–Tvergaard–Needleman damage criterion. It was found that the shear fracture angle decreases gradually from 90° to 64° with an increasing number of passes. The results of simulations using the Gurson–Tvergaard–Needleman criterion show trends similar to the experimental ones. The paper also presents a discussion on the fracture mechanism and the size effect during the tensile test.

Discrete Element Modeling of Soil Displacement Resulting from Hoe Openers

2019 ◽  
Vol 62 (2) ◽  
pp. 253-262
Author(s):  
Steven Murray ◽  
Ying Chen
Keyword(s):  
Performance Indicator ◽  
Discrete Element ◽  
Travel Speed ◽  
Particle Flow Code ◽  
Discrete Element Modeling ◽  
Side Band ◽  
Element Modeling ◽  
Soil Displacement ◽  
Modeling Software ◽  
Single Shoot

Abstract. Soil displacement is the most important performance indicator for seed openers, as it affects the uniformity of seeding depth. In this study, a hoe opener was modeled using Particle Flow Code in 3 Dimensions (PFC3D), a discrete element modeling software program. The objective was to simulate soil displacement in terms of soil throws. To validate the model, an air drill with hoe openers was tested in a field with clay soil at a working depth of 38 mm and travel speed of 8 km h-1. Soil throw resulting from the hoe opener was measured. To calibrate the model, a virtual soil shear test was created within PFC3D, and the output soil shear torque was compared to the torque measured in the same field. The result showed that the calibrated effective modulus, a critical micro-parameter of model particles, was 5.692 × 107 Pa. With this calibrated value, the simulated soil throws agreed well with the measured throws, with a relative error of 15%. The model was used to compare different hoe opener designs: single-shoot spread, double-shoot side-band, double-shoot paired-row, and triple-shoot openers. Among all these openers, the side-band opener resulted in the least lateral soil throw, and the paired-row opener resulted in the lowest vertical soil throw but the highest lateral throw. The developed model was effective for examining the effects of opener geometry on soil displacement. Keywords: DEM, Hoe, Opener, PFC3D, Soil displacement.

Research on the Spacing of Structural Plane Used in Rock Mass Structure Classification

2012 ◽  
Vol 446-449 ◽  
pp. 2011-2014
Author(s):  
Ai Guo Han ◽  
Min You ◽  
De Xin Nie
Keyword(s):  
Rock Mass ◽  
Large Scale ◽  
Structure Type ◽  
Engineering Properties ◽  
Rock Mass Structure ◽  
Structural Plane ◽  
Hydroelectric Project ◽  
Quality Classification ◽  
Structure Research ◽  
Made In

Great achievements have been made in rock mass structure research to evaluate engineering properties of rock mass in the engineering geology field. In fact, rock mass structure can not only indicate the quantity of structural planes (discontinuities) and size of rock blocks, but also indicate the integrity and mechanical properties of the rock mass. More and more attention has been paid to rock mass quality classification by using rock mass structure. During the past 40 years, rock mass structure research has been carried out by many scholars, and various standards of rock mass structure classification have been proposed in different industries of different countries. In these standards, the most widely used index was the spacing of structural plane. However, it is a pity that the method of determining the spacing value is not unified in different standards, therefore, the structure type of a rock mass may be different according to different standard. But which kind of method to determine the spacing value is most reasonable? It becomes an important problem to be solved. In this paper, rational method of determining the spacing of structural planes is demonstrated based on lots of statistical data in dam abutment rock mass of one large-scale hydroelectric project in Southwest China.

scholarly journals Failure Mode of the Water-filled Fractures under Hydraulic Pressure in Karst Tunnels

2017 ◽  
Vol 9 (1) ◽  
Author(s):  
Xin Dong ◽  
Hao Lu ◽  
Houxu Huang ◽  
Yiqing Hao ◽  
Yuanpu Xia
Keyword(s):  
Failure Mode ◽  
Shear Failure ◽  
Lateral Pressure ◽  
Shear Fracture ◽  
Pressure Coefficient ◽  
Surrounding Rock ◽  
Hydraulic Pressure ◽  
Tensile Shear ◽  
Continuous Growth ◽  
Shear Failures

AbstractWater-filled fractures continue to grow after the excavation of karst tunnels, and the hydraulic pressure in these fractures changes along with such growth. This paper simplifies the fractures in the surrounding rock as flat ellipses and then identifies the critical hydraulic pressure values required for the occurrence of tensile-shear and compression-shear failures in water-filled fractures in the case of plane stress. The occurrence of tensile-shear fracture requires a larger critical hydraulic pressure than compression-shear failure in the same fracture. This paper examines the effects of fracture strike and lateral pressure coefficient on critical hydraulic pressure, and identifies compression-shear failure as the main failure mode of water-filled fractures. This paper also analyses the hydraulic pressure distribution in fractures with different extensions, and reveals that hydraulic pressure decreases along with the continuous growth of fractures and cannot completely fill a newly formed fracture with water. Fracture growth may be interrupted under the effect of hydraulic tensile shear.

scholarly journals Investigation into the Effect of RFSSW Parameters on Tensile Shear Fracture Load of 7075-T6 Alclad Aluminium Alloy Joints

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3397
Author(s):  
Andrzej Kubit ◽  
Tomasz Trzepieciński ◽  
Elżbieta Gadalińska ◽  
Ján Slota ◽  
Wojciech Bochnowski
Keyword(s):  
Aluminium Alloy ◽  
Shear Fracture ◽  
Load Capacity ◽  
Fracture Load ◽  
Tensile Fracture ◽  
Welding Parameters ◽  
Tensile Shear ◽  
Optimal Amount ◽  
Average Value ◽  
Type Fracture

The aim of the investigations was to determine the effect of parameters of refill friction stir spot welding (RFSSW) on the fracture load and failure mechanisms of the resulting joint. RFSSW joints were made in 7075-T6 Alclad aluminium alloy sheets using different welding parameters. The load capacity of joints was determined under tensile/shear loadings. Finite element-based numerical simulations of the joint-loading process were carried out, taking into account the variability of elasto-plastic properties of weld material through the joint cross-section. The influence of welding parameters on selected phenomena occurring during the destruction of the joint is presented. The considerations were supported by a fractographic analysis based on SEM images of fractures. It was found that there is a certain optimal amount of heat generated, which is necessary to produce the correct joint in terms of its load capacity. This value should not be exceeded, because it leads to weakening of the base material and thus to a reduction in the strength of the joint. Samples subjected to uniaxial tensile shear load showed three types of failure mode (tensile fracture, shear fracture, plug type fracture) depending on the tool rotational speed and duration of welding. Prediction of the fracture mode using FE-based numerical modelling was consistent with the experimental results. The samples that were damaged due to the tensile fracture of the lower sheet revealed a load capacity (LC) of 5.76 KN. The average value of LC for the shear fracture failure mechanism was 5.24 kN. The average value of the LC for plug-type fracture mode was 5.02 kN. It was found that there is an optimal amount of heat generated, which is necessary to produce the correct joint in terms of its LC. Excessive overheating of the joint leads to a weakening of the base metal and thus a reduction in the strength of the joint. Measurements of residual stresses along the axis specimens showed the presence of stresses with a certain constant value for the welded area on the side of the 1.6 mm thick plate.

scholarly journals Analysis of Rock β-Dynamic Parameters and the Stability of Earthquake Dangerous Rocks Based on PFC

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Yun Tian ◽  
Lin-feng Wang ◽  
Biao Zeng ◽  
Hong-hua Jin
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Failure Mode ◽  
Confining Pressure ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Triaxial Tests ◽  
Tensile Fracture ◽  
Rock Materials ◽  
Synthetic Rock

Mesoparameters of rock materials are the main factors affecting the macromechanical properties of dangerous rock slopes. Based on the principle of particle flow and synthetic rock mass technology (SRM), the influence of mesoparameters on macromechanical properties is investigated by calibrating mesoparameters of rock materials at depth for a rock sequence in Beichuan Qiang Autonomous County, Sichuan Province, China. By combining these parameters with conventional and dynamic cycle triaxial tests, sensitivity analysis of rock β-parameters was completed. As a result, the reliability of mesoparameters in the simulation of dangerous rocks is strengthened, providing a basis to examine the failure mechanism of earthquake dangerous rocks in this region. Results indicate that, in the triaxial test, sandstone failed in tension, and brittleness gradually weakened as confining pressure increased. Mudstone recorded shear failure, and the characteristic value of brittle attenuation showed a V-shaped change with increasing confining pressure. Under cyclic loading, cracks had a degrading effect on the damping ration (β) and the damping coefficient (C) of sandstone. Mudstone recorded relatively low β and low brittleness whilst sandstone had high β and high brittleness. In rock materials, β n is more sensitive than β s in mechanical properties. When the value of the β n -parameter was between 0.2 and 0.3 and the value of the β s -parameter was between 0.2 and 0.6, rock brittleness was more stable, and the reflected macroscopic mechanical properties were the most authentic. By using a deepened mesoparameter trial adjustment method, the failure mode of the Particle Flow Code (PFC) dangerous rock model near provincial highway 205, simulated under conditions for the Wenchuan earthquake, indicated a tensile fracture-horizontal slip failure. The simulated failure mode was consistent with that of real dangerous rocks, with the failure trend being concentrated between the first and the third layer of the rock mass.

Discrete Element Modeling of Railway Ballast for Studying Railroad Tamping Operation

2020 ◽  
Author(s):  
Nilesh Dama ◽  
Mehdi Ahmadian
Keyword(s):  
Simulation Model ◽  
Element Model ◽  
Discrete Element ◽  
Performance Comparison ◽  
Particle Flow Code ◽  
Computer Simulation Model ◽  
Discrete Element Modeling ◽  
Railway Ballast ◽  
Insertion Force ◽  
Elliptical Motion

Abstract The dynamic behavior of ballast particles during track tamping is studied by developing a computer simulation model using the Discrete Element Model (DEM) method. The simulation model is developed in a commercially available DEM software called PFC3D (Particle Flow Code 3D). The study primarily evaluates a complete tamping cycle as defined by insertion, squeeze, hold, and withdrawal. Using a Taguchi approach, the effect of Tine motion’s frequency and amplitude, insertion velocity, and squeeze velocity are evaluated on tamping effectiveness. The compactness of the ballast particles, as defined by the average number of contacts per particle (referred to “Coordination Number”) is used as a measure of the effectiveness of tamping. Setting up the DEM model and important elements such as selection and calibration of particle shapes, ballast mechanical properties, contact model, and parameters governing the contact force models are described in detail. The tamping process is evaluated using a half-track layout with a highly modular code that enables a high degree of adjustability to allow control of all parameters for improved simulation flexibility. A parametric study is performed to find the best values of tine motion parameters for improving tamping efficiency. A performance comparison is made between linear and elliptical tamping. The results indicate that smaller squeeze and release velocities of the tines yield better compaction. Of course, reducing the velocities would result in increased tamping time. Additionally, the results indicate that the linear motion of the tines potentially result in better compaction than elliptical motion, although the latter may require less insertion force (power) and cause less ballast damage.

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