scholarly journals Influence of Deviatoric Stress on the Deformation and Damage Evolution of Surrounding Rock under Unloading Conditions

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Gongyu Hou ◽  
Jinping Liang ◽  
Haoyong Jing ◽  
Jinxin Tan ◽  
Yongkang Zhang ◽  
...  
Keyword(s):  
Damage Evolution ◽  
Failure Process ◽  
Radial Strain ◽  
Deep Understanding ◽  
Surrounding Rock ◽  
Deviatoric Stress ◽  
Outer Diameter ◽  
Damage Development ◽  
Deformation Response ◽  
Failure Evolution

The study of the deformation and damage evolution behaviour of surrounding rock under excavation unloading conditions is of vital importance for a deep understanding of the mechanism of roadway failure. In this study, unloading testing using a partially hollow thick-walled cylinder cement mortar specimen with dimensions of 280 mm (height) × 200 mm (outer diameter) × 60 mm (inner diameter) and a solid height of 60 mm at the bottom was performed to investigate the deformation response and damage failure evolution characteristics of the surrounding rock. The experimental results showed that the higher deviatoric stress level accelerated the damage development caused by the unloading effect and improved the expansion rate of the internal cracks, which led to a higher radial strain rate, total strain, and acoustic emission hits. When deviatoric stress increased to a relatively higher level, the radial strain rates were highly unstable, and the surrounding rock near or at the opening free surface was damaged locally and regionally. During the failure process of the specimen, the generation of the deformation and damage in the unloading stage was more alive (as indicated by the growth rate). Nevertheless, the main deformation and damage to the surrounding rock were generated and accumulated in the maintaining stage after unloading.

Study on Stability and Anchoring Effect of Jointed Rock Mass of An Underground Powerhouse

2004 ◽  
Vol 261-263 ◽  
pp. 1551-1556
Author(s):  
S.C. Li ◽  
Wei Zhong Chen ◽  
Wei Shen Zhu ◽  
X.B. Qiu ◽  
Chien Hsin Yang
Keyword(s):  
Rock Mass ◽  
Damage Evolution ◽  
Evolution Equations ◽  
Progressive Failure ◽  
Failure Process ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Surrounding Rock ◽  
Underground Powerhouse ◽  
Anchoring Effect

This present paper adopts a constitutive model for elastic damage of intermittently jointed rock mass, damage-evolution equations and a supporting model of damaged rock-bolt bar(DRBB) element to simulate effect of reinforcement. The results have indicated that the above method well describes the progressive failure process of the surrounding rock mass and the anchorage effect. The theoretical achievements are of referential value to designers.

scholarly journals Towards Manufacturing of Ultrafine-Laminated Structures in Metallic Tubes by Accumulative Extrusion Bonding

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 389
Author(s):  
Matthew R. Standley ◽  
Marko Knezevic
Keyword(s):  
Solid State ◽  
Wall Thickness ◽  
Complex Geometry ◽  
Tube Wall ◽  
Film Theory ◽  
Radial Strain ◽  
Surface Preparation ◽  
Grain Structure ◽  
Outer Diameter ◽  
Laminated Structures

A severe plastic deformation process, termed accumulative extrusion bonding (AEB), is conceived to steady-state bond metals in the form of multilayered tubes. It is shown that AEB can facilitate bonding of metals in their solid-state, like the process of accumulative roll bonding (ARB). The AEB steps involve iterative extrusion, cutting, expanding, restacking, and annealing. As the process is iterated, the laminated structure layer thicknesses decrease within the tube wall, while the tube wall thickness and outer diameter remain constant. Multilayered bimetallic tubes with approximately 2 mm wall thickness and 25.25 mm outer diameter of copper-aluminum are produced at 52% radial strain per extrusion pass to contain eight layers. Furthermore, tubes of copper-copper are produced at 52% and 68% strain to contain two layers. The amount of bonding at the metal-to-metal interfaces and grain structure are measured using optical microscopy. After detailed examination, only the copper-copper bimetal deformed to 68% strain is found bonded. The yield strength of the copper-copper tube extruded at 68% improves from 83 MPa to 481 MPa; a 480% increase. Surface preparation, as described by the thin film theory, and the amount of deformation imposed per extrusion pass are identified and discussed as key contributors to enact successful metal-to-metal bonding at the interface. Unlike in ARB, bonding in AEB does not occur at ~50% strain revealing the significant role of more complex geometry of tubes relative to sheets in solid-state bonding.

Damage Observation and Analysis of a Rock Brazilian Disc Using High-Speed DIC Method

2011 ◽  
Vol 70 ◽  
pp. 87-92 ◽  
Author(s):  
Shao Peng Ma ◽  
Dong Yan ◽  
Xian Wang ◽  
Yan Yan Cao
Keyword(s):  
Strain Field ◽  
Damage Evolution ◽  
High Speed ◽  
Failure Process ◽  
Tensile Load ◽  
Brazilian Test ◽  
Elastic Model ◽  
Strain Fields ◽  
Brazilian Disc ◽  
Damage And Failure

Observation of damage evolution is of great importance to the understanding of the failure process of rock materials. High-speed DIC system is constructed and used to observe the strain field evolution of the granodiorite disc in Brazilian test. The strain fields at different load levels are analyzed based on the stain abnormality indicator (SAI) which is the ratio of the strain measured in experiment to the strain from theoretical solution in an isotropy and elastic model. SAI could be used to indicate the damage in the specimen. The process of damage and failure of the specimen in Brazilian disc test is quantitatively analyzed and deeply discussed according to the strain fields and the statistics of SAI. Experimental results in this paper show that the failure process of the disc specimen in Brazilian test is not simple crack propagation under tensile load, but a complicated damage evolution procedure.

scholarly journals The Method of Determining Excavation Damaged Zone by Acoustic Test and the Application in Engineering Cases

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Qian-Cheng Sun ◽  
Hao-Sen Guo ◽  
Zhi-Hua Xu ◽  
Yue Liu ◽  
Xiao Xu
Keyword(s):  
Rock Mass ◽  
Damage Evolution ◽  
Hard Rock ◽  
Damage Zone ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Surrounding Rock ◽  
Excavation Damaged Zone ◽  
Damaged Zone ◽  
Columnar Jointed Rock Mass

It is very important to accurately determine the depth of excavation damaged zone for underground engineering excavation and surrounding rock stability evaluation, and it can be measured by acoustic test, but there is no quantitative method for analysis of the results, and it relies heavily on the experience of engineers, which leads to the low reliability of the results and also limits the application of the acoustic method. According to substantial field test data and the feedback of surrounding rock support parameters, the boundary method is proposed to determine the depth of excavation damaged zone in surrounding rock based on the relation between the ultrasonic velocity of measured point and the background wave velocity of rock mass. When the method is applied to the columnar jointed rock mass of Baihetan and the deep-buried hard rock of Jinping, the excavation damaged zone was well judged. The results in the Baihetan project show that the proposed method of determining excavation damage zone by the acoustic test can well demonstrate the anisotropy characteristics of the columnar jointed rock mass, and the damage evolution characteristics of jointed rock mass at the same position can also be obtained accurately. Moreover, the method also can accurately reveal the damage evolution process of the deep-buried hard rock under the condition of high ground stress, which proved the applicability of this method in jointed or nonjointed rock masses.

Numerical Analysis of Faults on Deep-Buried Tunnel Surrounding Rock Damaged Zones

2011 ◽  
Vol 90-93 ◽  
pp. 74-78 ◽  
Author(s):  
Jun Hu ◽  
Ling Xu ◽  
Nu Wen Xu
Keyword(s):  
Numerical Analysis ◽  
Mechanical Response ◽  
Progressive Failure ◽  
Process Analysis ◽  
Failure Process ◽  
Water Inrush ◽  
Surrounding Rock ◽  
Factors Affecting ◽  
Rock Failure Process ◽  
Tunnel Instability

Fault is one of the most important factors affecting tunnel instability. As a significant and casual construction of Jinping II hydropower station, when the drain tunnel is excavated at depth of 1600 m, rockbursts and water inrush induced by several huge faults and zone of fracture have restricted the development of the whole construction. In this paper, a progressive failure progress numerical analysis code-RFPA (abbreviated from Rock Failure Process Analysis) is applied to investigate the influence of faults on tunnel instability and damaged zones. Numerical simulation is performed to analyze the stress distribution and wreck regions of the tunnel, and the results are consistent with the phenomena obtained from field observation. Moreover, the effects of fault characteristics and positions on the construction mechanical response are studied in details. Some distribution rules of surrounding rock stress of deep-buried tunnel are summarized to provide the reasonable references to TBM excavation and post-support of the drain tunnel, as well as the design and construction of similar engineering in future.

scholarly journals Evolution Mechanism of Deformation and Failure of Surrounding Rock during Excavation and Unloading of the High-Stress Rock Mass

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Wensong Xu ◽  
Guangming Zhao ◽  
Chongyan Liu ◽  
Xiangrui Meng ◽  
Ruofei Zhang ◽  
...  
Keyword(s):  
Rock Mass ◽  
High Stress ◽  
Surrounding Rock ◽  
Critical Conditions ◽  
Safety Control ◽  
Rock Samples ◽  
Failure Patterns ◽  
Failure Evolution ◽  
Splitting Failure ◽  
Confining Pressures

To deeply analyze the failure evolution of surrounding rock during excavation-induced unloading of the high-stress rock mass, a multistage failure model was established based on revealed failure patterns. The critical conditions for wing cracks were determined. The slab crack buckling analysis was carried out. The true-triaxial rockburst testing system was used for the miniature model test to study the fracturing evolution of surrounding rocks during excavation-induced unloading of the high-stress rock mass. The research results indicated that harder rock samples had higher compressive strength. Moreover, the smaller peak strains implied more obvious yield/plastic stages of harder rock samples with high confining pressures and softer rock samples with low confining pressures. V-shaped grooves appeared at the beginning of the surrounding rock’s failure while spalling and splitting occurred as the stress increased. Finally, the entire sample’s overall splitting failure was observed, and the borehole bottom bulged upward. The harder rock masses had fewer fractures and higher degrees of failure. There were obvious V-shaped grooves on both sides of the marble cave wall. The tensile failure occurred near the opening surface and shear failure at a far distance. The sandstone's overall failure was related to tensile cracking, and splitting failure occurred far away from the opening surface, which was similar to the in situ failure of surrounding rocks during excavation-induced unloading of the high-stress rock mass. The results obtained are instrumental in the construction safety control and prevention of underground engineering disasters.

scholarly journals Deformation of Stacked Metallic Sheets by Shock Wave Loading

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 679 ◽  
Author(s):  
Sandeep Patil ◽  
Rahul Murkute ◽  
Nima Shirafkan ◽  
Bernd Markert
Keyword(s):  
Shock Wave ◽  
Computational Models ◽  
Thickness Distribution ◽  
Strong Shock ◽  
Deep Understanding ◽  
Dome Height ◽  
Outer Diameter ◽  
Shock Wave Loading ◽  
Wave Loading ◽  
Metal Sheets

The focus of the present work is to develop a deep understanding of deformation of stacked metal sheets with a series of different sequences by using shock wave loading. Here, experimental and numerical investigations of deformation of a single metal sheet of 1.5-mm and the stack of three metal sheets of 0.5-mm thickness of aluminum (Al), copper (Cu) and brass (Br) material were carried out. In the shock wave experiments, helium was used as the driving gas to produce a strong shock wave. Finite elements method (FEM) simulations on 3D-computational models were performed with explicit dynamic analysis, and Johnson-Cook material model was used. The obtained results from experiments of the outer diameter, thickness distribution, and dome height were analyzed and compared with the numerical simulations, and both the results are in excellent agreement. Moreover, for the same pressure load, due to lower inter-metallic friction in the stacked sheets compared to a cohesive property of the single sheet, an excellent deformation of stacked metallic sheets was observed. The results of this work indicated that the shock wave-forming process is a feasible technique for mass production of stacked metallic sheets as well as fabricating a hierarchical composite structure, which provides higher formability and smooth thickness distribution compared to a single material.

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