scholarly journals Energy Characteristics of Acoustic Emission at the Volume-Expansion Point of a Rock Bridge: A New Insight into the Evolutionary Mechanism of Coastal Cliff Collapse

2021 ◽  
Vol 9 (12) ◽  
pp. 1338
Author(s):  
Hongran Chen ◽  
Mengyang Zhai ◽  
Lei Xue
Keyword(s):  
Acoustic Emission ◽  
Energy Level ◽  
Volume Expansion ◽  
Evolutionary Mechanism ◽  
Rock Bridge ◽  
Rock Bridges ◽  
Coastal Cliff ◽  
Coastal Cliffs ◽  
The Stability ◽  
Expansion Point

The recession of a coast can destabilize coastal cliffs. The stability of a cliff is controlled by a rock bridge. Identifying the volume-expansion point of rock bridges is crucial to assess cliff stability, but currently there are few identifying methods. Using a numerical analytical tool, we investigate the acoustic emission characteristics during shear tests on rock bridges. Acoustic emission events with a high energy level, i.e., characteristic events which occur at the volume-expansion point of rock bridges, can indicate this point. The characteristic events, the mainshock (the maximum event corresponding to rock-bridge rupture), and the smaller events between them constitute a special activity pattern, as the micro-seismicity during the evolutionary process of a coastal cliff collapse in Mesnil-Val, NW France showed. This pattern arises in rock bridges with different mechanical properties and geometry, or under different loading conditions. Although the energy level of characteristic events and mainshocks changes with the variation of the conditions, the difference of their energy level is approximately constant. The spatial distribution of characteristic events and mainshocks can indicate the location of rock bridges. These findings help to better understand the evolutionary mechanism of collapses and provide guidelines for monitoring the stability of coastal cliffs.

scholarly journals Investigating the Effect of Rock Bridge on the Stability of Locked Section Slopes by the Direct Shear Test and Acoustic Emission Technique

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 638 ◽  
Author(s):  
Qifeng Guo ◽  
Jiliang Pan ◽  
Meifeng Cai ◽  
Ying Zhang
Keyword(s):  
Acoustic Emission ◽  
Shear Strength ◽  
Normal Stress ◽  
Direct Shear Test ◽  
Shear Test ◽  
Rock Slope ◽  
Direct Shear ◽  
Acoustic Emission Technique ◽  
Rock Bridge ◽  
The Stability

As a portion of intact rock separating joint surfaces, rock bridge plays a significant role in the stability of rock slopes. This paper aims to investigate the effect of different rock bridges on the mechanical properties and failure mode of rock slope by means of the direct shear test and acoustic emission technique. Field conditions were simulated in direct shear tests which were carried out on specimens with rock bridges at different continuity rates, normal stress, arrangements, and joint angles. Experimental results indicate that the strength of specimens is controlled by the rock bridge and the structural plane. The rock bridge contributes to the strength of the specimen, while the through plane weakens the strength of the specimen. The increase of normal stress can weaken the stress concentration near the tip of the rock bridge and improve the shear resistance of the specimen. The different arrangement of rock bridge has little effect on the normal displacement of the specimen, and has a great influence on the shear strength. The shear capacity of the specimen is related to the angle of the crack, and the angle of the crack is approximately proportional to the peak shear strength. For the specimens with different joint occurrence, the mode of crack propagation at the initial stage is basically the same, and the specimen is finally damaged due to the generation of through cracks in the core area of rock bridge. The instantaneous release of the huge energy generated during the experiment along the shear direction is the root cause of the sudden failure of the rock bridge. The formation, aggregation, and transfixion process of rock bridge is of concern and has been experimentally investigated in this paper for the prevention and control of the locked section rock slope with sudden disasters.

Analysis of removability and stability of rock blocks by considering the rock bridge effect

2016 ◽  
Vol 53 (3) ◽  
pp. 384-395 ◽  
Author(s):  
Yinhe Zheng ◽  
Lu Xia ◽  
Qingchun Yu
Keyword(s):  
Safety Factor ◽  
Optimization Problem ◽  
Normal Force ◽  
Rock Bridge ◽  
Rock Bridges ◽  
Sliding Direction ◽  
The Stability ◽  
Minimum Safety Factor ◽  
Boundary Surfaces ◽  
Unified Method

In traditional block theory, the removability and stability of rock blocks are analyzed independently; that is, the stability of a removable block is analyzed in detail, and nonremovable blocks are regarded as stable. However, in practical situations, nonremovable blocks may pose more danger than removable blocks. This paper presents a unified method for analyzing the removability and stability of rock blocks. In this method, the cracking of rock bridges is considered and nonremovable blocks are not assumed to be stable. First, possible cracking rock bridges are identified by extending finite-sized fractures and comparing the boundary surfaces of the resulting blocks with those of the original blocks. Then, the sliding direction associated with each possible moving block is determined by solving an optimization problem. The normal force acting on each sliding surface is determined, and the resisting force on each rock bridge is calculated and integrated into the total resisting force when calculating the safety factor of a possible moving block. Procedures to determine all possible moving blocks are introduced, and the possible moving block with the minimum safety factor is regarded as the actual moving block. The corresponding minimum safety factor is defined as the actual safety factor of the block. The proposed method is verified by considering a few examples. The results show that nonremovable blocks may be unstable if the cracking of rock bridges is considered.

scholarly journals Numerical Simulation of Fluid-Solid Coupling in Surrounding Rock for River Stope Mining

2020 ◽  
Vol 2020 ◽  
pp. 1-11 ◽  
Author(s):  
Haiping Yuan ◽  
Chenghao Chen ◽  
Zhongming He ◽  
Yixian Wang
Keyword(s):  
Rock Mass ◽  
Mining Area ◽  
Calculation Model ◽  
Rock Bridge ◽  
The Road ◽  
Ore Body ◽  
Safety And Reliability ◽  
Mining Disturbance ◽  
The Stability ◽  
Seepage Channel

Mining disturbance will induce further weakening of faults and rock bridges, improve rock mass permeability and, in serious cases, conduct surface rivers to cause disasters. A numerical calculation model of river-fault in the mining area is established. Based on the fluid-solid coupling theory of rock mass, the influence of mining disturbance on the development and evolution process of rock bridge rupture and river-fault-stope potential seepage channel is simulated and calculated. Research studies show that under the disturbance of ore body mining, it is possible to form a channel from the river to fault to seepage and drainage in the stope. The disturbance of ore body mining has no great adverse effect on the stability of the rock mass at the top of F2 fault. The rock mass damage caused by mining is only distributed in local areas, and the rock bridge between the river, fault, and stope is not completely connected. The fracture of mining rock mass leads to the increase in permeability of rock mass, and seepage tends to spread in the direction of the fault, but there is no obvious through drainage channel from surface water to the stope. The results of research provide technical guidance for the mine to use the filling mining method after the river does not change the road safety and reliability certification and can also provide reference for similar mines.

scholarly journals Failure Mechanism of Rock Bridge Based on Acoustic Emission Technique

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Guoqing Chen ◽  
Yan Zhang ◽  
Runqiu Huang ◽  
Fan Guo ◽  
Guofeng Zhang
Keyword(s):  
Acoustic Emission ◽  
Failure Mechanism ◽  
High Speed ◽  
Large Scale ◽  
Small Scale ◽  
Failure Behavior ◽  
Long Distance ◽  
Rock Bridge ◽  
Rocky Slope ◽  
Landslide Model

Acoustic emission (AE) technique is widely used in various fields as a reliable nondestructive examination technology. Two experimental tests were carried out in a rock mechanics laboratory, which include (1) small scale direct shear tests of rock bridge with different lengths and (2) large scale landslide model with locked section. The relationship of AE event count and record time was analyzed during the tests. The AE source location technology and comparative analysis with its actual failure model were done. It can be found that whether it is small scale test or large scale landslide model test, AE technique accurately located the AE source point, which reflected the failure generation and expansion of internal cracks in rock samples. Large scale landslide model with locked section test showed that rock bridge in rocky slope has typical brittle failure behavior. The two tests based on AE technique well revealed the rock failure mechanism in rocky slope and clarified the cause of high speed and long distance sliding of rocky slope.

scholarly journals Geologic and geomorphologic study of the Terra Murata and Centane-Panoramica Sites (Island of Procida, Naples Bay, Southern Tyrrhenian Sea) aimed at solving some applied geological and geotechnical problems

2021 ◽  
Vol 4 (2) ◽  
Author(s):  
Gemma Aiello
Keyword(s):  
Middle Ages ◽  
Tectonic Setting ◽  
Geological Survey ◽  
Tyrrhenian Sea ◽  
Pyroclastic Deposits ◽  
Coastal Cliff ◽  
Coastal Cliffs ◽  
Naples Bay ◽  
Strong Control ◽  
Geotechnical Problems

A geologic and geomorphologic study aimed at solving some geological and geotechnical problems, regarding the massive seepage of meteoric waters in the coastal cliffs of the Island of Procida (Naples Bay, Southern Italy) composed of both tuffs and loose pyroclastic deposits, has been carried out in the geosites of Terra Murata (Middle Ages village and coastal cliff towards the Corricella Bay) and Centane-Panoramica (coastal cliff facing on the Tyrrhenian Sea).A detailed geologic and geomorphologic survey has allowed to suggest solutions to the applied geological and geotechnical problems related to the occurrence of massive seepages of waters at the physical interface between pyroclastic rocks and loose pyroclastic deposits, characterized by different density, permeability and porosity and also controlled by a dense network of fractures, involving the pyroclastic deposits cropping out in the selected areas.Field sampling and geotechnical laboratory analyses have been carried out to calculate the values of main geotechnical parameters of the yellow tuffs cropping out at the Terra Murata Promontory. At the same time, a detailed monitoring of the seepages of waters has been carried out through a detailed geological survey of the tuff outcrops of the promontory. The obtained results have suggested a strong control from both the geomorphologic instability of the coastal cliff and tectonic setting. At the Centane-Panoramica geosite, the geological survey, coupled with geotechnical analyses and standard penetrometric tests, has accordingly evidenced that the geomorphologic instability was mainly concentrated in the sectors of the tuff coastal cliffs facing seawards towards the Tyrrhenian Sea.

scholarly journals Cascade effect of rock bridge failure in planar rock slides: explicit numerical modelling with a distinct element code

2020 ◽  
Author(s):  
Adeline Delonca ◽  
Yann Gunzburger ◽  
Thierry Verdel
Keyword(s):  
Numerical Modelling ◽  
Distinct Element ◽  
Failure Process ◽  
Rock Block ◽  
Critical Position ◽  
Plane Failure ◽  
Rock Bridge ◽  
Rock Bridges ◽  
Cascade Effect ◽  
Dip Angle

Abstract. Plane failure along inclined joints is a classical mechanism involved in rock slopes movements. It is known that the number, size and position of rock bridges along the potential failure plane are of main importance when assessing slope stability. However, the rock bridges failure phenomenology itself has not been comprehensively understood up to now. In this study, the propagation cascade effect of rock bridges failure leading to catastrophic block sliding is studied and the influence of rock bridges position in regard to the rockfall failure mode (shear or tensile) is highlighted. Numerical modelling using the distinct element method (UDEC-ITASCA) is undertaken in order to assess the stability of a 10 m3 rock block lying on an inclined joint with a dip angle of 40° or 80°. The progressive failure of rock bridges is simulated assuming a Mohr–Coulomb failure criterion and considering stress transfers from a failed bridge to the surrounding ones. Two phases of the failure process are described: (1) a stable propagation of the rock bridge failures along the joint and (2) an unstable propagation (cascade effect) of rock bridges failures until the block slides down. Additionally, the most critical position of rock bridges has been identified. It corresponds to the top of the rock block for a dip angle of 40° and to its bottom for an angle of 80°.

scholarly journals Influence of Freeze-Thaw Cycles on Acoustic Emission Characteristics of Granite Samples under Triaxial Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhandong Su ◽  
Ke Geng ◽  
Fubiao Zhou ◽  
Jinzhong Sun ◽  
Huayan Yu
Keyword(s):  
Acoustic Emission ◽  
Triaxial Compression ◽  
Peak Frequency ◽  
Dominant Frequency ◽  
P Wave ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Ae Signal ◽  
The Stability ◽  
Granite Samples

Understanding the acoustic emission (AE) characteristics of rocks that have undergone freeze-thaw cycling is of great significance for the use of AE technology to monitor the stability of rock masses in cold regions. A series of freeze-thaw cycling experiments and triaxial compression AE tests of granite samples were performed. The results show that, with an increasing number of freeze-thaw cycles, the P-wave velocity and peak AE intensity of granite show a substantial downward trend. The AE ringing counts during triaxial compression can be divided into three stages: abrupt period, calm period, and failure period. The overall change of the characteristic AE signal of granite samples that underwent different freeze-thaw cycles is the same. The AE signal during the destruction of granite occurs in clear dual dominant frequency bands. The peak frequency increases with increasing load time, and this trend becomes less clear as the number of freeze-thaw cycles increases. Overall, the peak frequency distribution tends to change from high to low with an increasing number of freeze-thaw cycles. The results provide basic data for rock mass stability monitoring and prediction, which is of great significance for engineering construction and management in cold regions.

Effect of TiN Addition on the Low Temperature Degradation of Ceramic Tool Materials 3Y-TZP

2006 ◽  
Vol 315-316 ◽  
pp. 40-44 ◽  
Author(s):  
Jing Sun ◽  
Chuan Zhen Huang ◽  
Jun Wang
Keyword(s):  
Phase Transformation ◽  
Elastic Modulus ◽  
Low Temperature ◽  
Grain Boundary ◽  
Volume Expansion ◽  
Monoclinic Phase ◽  
Boundary Phase ◽  
Ceramic Tool ◽  
Tool Materials ◽  
The Stability

Ceramic tool materials, 3Y-TZP added by TiN particles, were fabricated through hot-pressing techniques. The effects of TiN on their low-temperature degradation at 220# in air were investigated. It is shown that TiN can improve the stability of t-ZrO2 and inhibit the transformation from tetragonal to monoclinic phase, and that the content of TiN affects the stability of tetragonal phase and the propagation of tetragonal-to-monoclinic transformation into the specimen interiors. It is suggested that the grain-boundary phase prevents the nucleation of transformation, and that the high elastic modulus of TiN can prevent the propagation of phase transformation by resisting the volume expansion of transformation. When the content of TiN is 20wt%, the ceramic material shows better low temperature degradation resistance.

Sign in / Sign up

Export Citation Format

Share Document