scholarly journals Geoelectric field response characteristics analysis of floor roadway surrounding rock fracture caused due to coal seam mining

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yuanchao Ou ◽  
Pingsong Zhang ◽  
Maoru Fu ◽  
Xiongwu Hu ◽  
Rongxin Wu ◽  
...  
Keyword(s):  
Rock Mass ◽  
Real Time ◽  
Complex Stress ◽  
Surrounding Rock ◽  
The Self ◽  
Geoelectric Field ◽  
Excitation Current ◽  
Response Characteristics ◽  
Working Face ◽  
Self Potential

AbstractThe fracture of rocks surrounding the floor roadway during the mining of the working face of a coal mine is a complicated spatiotemporal process due to the superimposed action of multiple stress fields on the surrounding rock mass. Using the surrounding rock of a floor roadway in the working face of the Huainan Pan’er Mine as the research subject, we conducted real-time monitoring using geoelectric field monitoring technology, and found the spatiotemporal response law of the geoelectric field in the process of regional rupture and damage of engineering rock masses under a complex stress field environment. The results show that (1) the time series response characteristics and spatial distribution of the geoelectric field signal are closely related to the stress distribution and damage evolution of the surrounding rock mass; (2) the rupture and damage degree of the goaf floor significantly increased when the working face was pushed through the monitoring area for 20–40 m. During this process, the excitation current dropped by 4–12 mA, and the self-potential pulse fluctuation amplitude was greater than 400 mV; (3) from the beginning of the monitoring process to the end of the monitoring, the self-potential in the damaged area decreased by 250 mV, and the self-potential in the mudstone layer below the damaged area increased by 140 mV. The electrons released into the environment around the damaged rock mass during the severe impact phase of mining did not flow back to the damaged area, and the positive charge in the damaged rock mass gradually accumulated in the complete rock mass in units of rock strata; (4) when superimposed and supported by anchor rod and cables, the bearing capacity of the shallow bearing circle of the roadway was enhanced, and the excitation current presented a step-like overall increase during mining of the working face with a small drop after every significant increase. This result is of significance in monitoring the evolutionary process of real-time failure of rock masses under complex stress environments using geoelectric field information and in improving the quality of geoelectric field monitoring technology testing applications in the future.

scholarly journals Self-potential response characteristics of red sandstone samples under uniaxial compression

2019 ◽  
Vol 16 (4) ◽  
pp. 742-752
Author(s):  
Cai Yang ◽  
Shengdong Liu ◽  
Haiping Yang
Keyword(s):  
Rock Mass ◽  
Uniaxial Compression ◽  
Inflection Point ◽  
Radial Direction ◽  
The Self ◽  
Potential Difference ◽  
Potential Response ◽  
Red Sandstone ◽  
Response Characteristics ◽  
Self Potential

Abstract Deformation and rupture of rock mass under loading cause the variation of electric potential. Response characteristics of self-potential and stress during the complete stress-strain process of red sandstones play an important role in evaluating the stress state of sandstone on the basis of self-potential. Experimental results demonstrate that the stress of red sandstone under uniaxial compression is linearly correlated with the self-potential difference before the first inflection point in the initial stage of loading. The average variation rate of self-potential difference and stress is 0.1325 mV MPa−1. As the loading pressure gradually increases and enters the softening stage (before the maximum loading point), the catastrophic points of uniaxial loading stress correspond to the inflection point of self-potential. The self-potential of red sandstone varies in a range of 0–45.6 mV in that case and it fluctuates most significantly around the maximum loading point, with a range of 0.3–195.5 mV. In the end stage of loading, the macroscopic rupture of the red sandstone sample is complete, the self-potential of red sandstone fluctuates slightly around the maximum load point and then gradually stabilizes. Moreover, it is found that self-potentials change more significantly in the radial direction than in the axial direction in the uniaxial compression experiment, indicating that self-potentials generated by rock mass rupture are more sensitive in the radial direction. The rupture process of red sandstone can be dynamically represented by the tempo-spatial evolution profiles of self-potential.

scholarly journals A physical model study of surrounding rock failure near a fault under the influence of footwall coal mining

2020 ◽  
Author(s):  
Shukun Zhang ◽  
Lu Lu ◽  
Ziming Wang ◽  
Shuda Wang
Keyword(s):  
Rock Mass ◽  
Physical Model ◽  
Hanging Wall ◽  
Coal Pillar ◽  
Vertical Displacement ◽  
Surrounding Rock ◽  
Pillar Width ◽  
Model Study ◽  
Working Face ◽  
Coal Pillars

AbstractA study of the deformation of the surrounding rock and coal pillars near a fault under the influence of mining is conducted on a physical model for the design of coal pillars to support and maintain the roofs of adjacent fault roadways. This research is based on the 15101 mining face in the Baiyangling Coal Mine, Shanxi, China, and uses simulation tests similar to digital speckle test technology to analyse the displacement, strain and vertical stress fields of surrounding rocks near faults to determine the influence of the coal pillar width. The results are as follows. The surrounding rock of the roadway roof fails to form a balance hinge for the massive rock mass. The vertical displacement, vertical strain and other deformation of the surrounding rock near the fault increase steeply as the coal pillar width decreases. The steep increase in deformation corresponds to a coal pillar width of 10 m. When the coal pillar width is 7.5 m, the pressure on the surrounding rock near the footwall of the fault suddenly increases, while the pressure on the hanging wall near the fault increases by only 0.35 MPa. The stress of the rock mass of the hanging wall is not completely shielded by the fault, and part of the load disturbance is still transmitted to the hanging wall via friction. The width of the fault coal pillars at the 15101 working face is determined to be 7.5 m, and the monitoring data verify the rationality of the fault coal pillars.

scholarly journals A New Unified Solution for Circular Opening considering Different Strength Criteria and the Postpeak Elastic Strain Form

2020 ◽  
Vol 2020 ◽  
pp. 1-21
Author(s):  
Xuyang Shi ◽  
Wei Zhou ◽  
Liang Chen ◽  
Qingxiang Cai ◽  
Ming Li ◽  
...  
Keyword(s):  
Rock Mass ◽  
Plastic Zone ◽  
Elastic Strain ◽  
Surrounding Rock ◽  
The Self ◽  
External Boundary ◽  
Circular Opening ◽  
Strength Criteria ◽  
Criterion Equation ◽  
Zone Radius

The strength criterion is an extremely important basis for evaluating the stability of surrounding rock and optimizing the support pressure design. In this paper, nine different strength criteria are summarized and simplified based on the reasonable assumption. Then, a new unified criterion equation is established, which includes all strength theories proposed by this paper. Meanwhile, a new unified closed-form solution for circular opening based on the newly proposed unified criterion equation is deduced with the infinite and finite external boundary combining with the nonassociative flow rule under plane strain conditions. In the plastic zone, four different elastic strain assumptions are applied to solving the plastic zone deformation considering the effect of rock mass damage. The solution’s validity is also verified by comparison with the traditional solution. Finally, the influences of strength criteria, dilation coefficient, elastic strain form of plastic zone, and rock mass damage on the mechanical response of surrounding rock are discussed in detail. The research result shows that TR and VM criteria give the largest plastic zone radius, followed by IDP, MC, and MDP criteria, and seem to underestimate the self-strength of rock mass; The CDP criterion gives the smallest plastic zone radius and may overestimate the self-strength of rock mass; UST0.5, GSMP, GMC, and GLD criteria that reasonably consider the effect of internal principal stresses give an intermediate range and can be strongly recommended for evaluating the mechanics and deformation behavior of surrounding rock; as the dilation coefficient gradually increases, the dimensionless surface displacement presents the nonlinear increase characteristics; the deformation of plastic zone and the ground response curve, which are closely related to the strength criteria, are also greatly influenced by the elastic strain assumption in the plastic zone and rock mass damage degree. The assumption that the elastic strain satisfies Hook’s law (Case 3) may be more reasonable compared with the continuous elastic strain (Case 1) and thick-walled cylinders (Case 2) assumptions; in addition, the Young’s modulus power function damage model seems to give more reasonable solution for the deformation of plastic zone and is suggested to be a preferred method for solving plastic displacement. The research results can provide very important theoretical bases for evaluating the tunnel stability and support design reliability of different lithology rock masses in underground engineering.

Self-potential monitoring of a salt plume

Geophysics ◽  
2010 ◽  
Vol 75 (4) ◽  
pp. WA17-WA25 ◽  
Author(s):  
P. Martínez-Pagán ◽  
A. Jardani ◽  
A. Revil ◽  
A. Haas
Keyword(s):  
Real Time ◽  
Current Density ◽  
Potential Method ◽  
The Self ◽  
Contaminant Plume ◽  
Salty Water ◽  
Source Current ◽  
Self Potential ◽  
Over Time ◽  
Source Current Density

Nonintrusively monitoring the spread of contaminants in real time with a geophysical method is an important task in hydrogeophysics. We have developed a sandbox experiment showing that the self-potential method can locate both the source of leakage and the front of a contaminant plume. We monitored the leakage of a plume of salty water from a hole at the bottom of a small tank located at the top of a main sandbox. Initially, the sand was saturated by tap water. At a given time, a hole was opened at the bottom of the tank, allowing the salty water to migrate by diffusion and buoyancy-driven flow in the main sandbox. The bottom of the sandbox contained a network of 32 nonpolarizing silver-silver chloride electrodes with amplifiers, connected to a multichannel voltmeter. The self-potential response associated withthe migration of the salt plume in the sandbox was recorded over time. A self-potential anomaly was observed with amplitude varying from a few millivolts at the start of the leak to a few tens of millivolts after a few minutes. The self-potential data were inverted using a time-lapse tomographic algorithm to reconstruct the position of the volumetric source current density over time. A positive volumetric source current density was associated with the position of the leak at the bottom of the leaking tank, whereas a negative volumetric source current density was associated with the salinity front moving down inside the sandbox. These poles were well reproduced by performing a finite-element simulation of the problem. Using this information, we estimated the speed of the salt plume sinking inside the sandbox. Therefore, the self-potential method can be used to track, in real time, the position of the front of a contaminant plume in a porous material.

scholarly journals Study on the Effect of Isotropic Initial Stress on the Anchoring Performance of Self-Expanding Bolts

2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Jie Liu ◽  
Hongya Li ◽  
Yunzhou Li ◽  
Yunan Yang ◽  
Tao Sun ◽  
...  
Keyword(s):  
Rock Mass ◽  
Energy Consumption ◽  
Surrounding Rock ◽  
Interface Stress ◽  
The Self ◽  
Additional Stress ◽  
Confining Stress ◽  
Internal Interface ◽  
Pull Out ◽  
Anchoring System

In order to study the anchoring performance of a new type of self-expanding, high-strength, precompression anchoring technology with a large amount of expansion agent (ω ≥ 5) cement slurry as anchoring solids under confined surrounding rock conditions, a rock mass anchoring device and methods that simulate in situ stress are developed, and real-time monitoring of expansion stress and anchor pull-out tests are carried out. The results show that the internal interface stress has a loss effect over time, and the stress loss value shows a linear increase trend with the dosage, but the loss rate shows a linear decreasing relationship with the dosage. This paper defines the coordinated additional stress and obtains its temporal and spatial evolution law in the rock mass. It is pointed out that there is a lag time difference between the peak of internal interface stress and the peak of coordinated additional stress, explaining its mechanical mechanism from the perspective of stress transfer. The strong restraint of the sealing section of the anchor hole causes the anchor solid to form a “shuttle-shaped” microexpanded head with thin ends and a middle drum under the expansion stress. During the drawing process, the microexpanded head is “stuck” in the anchor hole and moves upward to form the unique “load platform effect” of the anchoring system. And the mechanical mechanism diagram of this effect is obtained. It is pointed out that this effect can greatly improve the ductility of the anchoring system and the ultimate energy consumption value of damage. A prediction model for the ultimate pull-out force of self-expanding bolts is established. It is pointed out that the initial confining stress value has an exponential effect on the ultimate pull-out force. It shows that the surrounding rock with strong confinement constraints can greatly increase the ultimate pull-out resistance of the bolt. The self-expanding strengthening coefficient λ and the surrounding rock stress influence coefficient k are introduced, the bolt interface mechanics formula and energy equation of the self-expanding anchor system are established, and the feasibility of the formula is verified by the calculation example. It is concluded that the ultimate pull-out resistance of the anchorage with ω = 30 is increased by 3.38 times compared with the ordinary anchorage under the initial confining stress condition of 0.7 MPa, the prepeak displacement of the bolt is increased by 2.08 times, and the prepeak energy consumption of the anchoring system is increased by 7.34 times. The cost only increased by 0.023% based on the literature example.

The Roadway Surrounding Rock Delaminating Displacement Monitoring Technology Based on Moiré Technique

2011 ◽  
Vol 58-60 ◽  
pp. 2101-2104
Author(s):  
Fang Liang Luo ◽  
Li Qian An ◽  
Ling Tao Mao ◽  
Jian Cheng Xu ◽  
Lei Li ◽  
...  
Keyword(s):  
Real Time ◽  
Measurement Theory ◽  
Surrounding Rock ◽  
Rock Deformation ◽  
Displacement Monitoring ◽  
Monitoring Technology ◽  
The Real ◽  
Working Face ◽  
Roof Fall ◽  
Safety Production

With the coalface excavates, surrounding rock of roadway will occur deformation in different degrees. When the rock deformation exceeds a certain limit, roof fall and spalling would occur. To prevent such accidents, it is very important to monitor deformation of the surrounding rock in real-time. In this paper, Moiré measurement theory is elaborated. The displacement device (GWG200(C)), based on moiré technique, are applied in ventilation tunnel of 1015 working face in Xing Ge Zhang Mine to monitor deformation. The real time datum of deformation are obtained. The system provides technique safeguard for safety production.

scholarly journals Rockburst Identification Method Based on Energy Storage Limit of Surrounding Rock

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 343 ◽  
Author(s):  
Zhiqiang Zhang ◽  
Chun Luo ◽  
Heng Zhang ◽  
Ruikai Gong
Keyword(s):  
Rock Mass ◽  
Energy Storage ◽  
Minimum Energy ◽  
Surrounding Rock ◽  
Underground Engineering ◽  
Tunnel Excavation ◽  
Working Face ◽  
Excavation Process ◽  
Storage Limit ◽  
The Impact

Rockbursts are one of the prominent problems faced by deep underground engineering. Not only do they affect the construction progress, but they also threaten the safety of construction personnel and equipment, and may even induce earthquakes. Therefore, the prediction of rockbursts has very important engineering significance for the excavation of deeply buried tunnels. In this paper, a new indicator for stability and optimization evaluation of hard, brittle surrounding rock under high geo-stresses, namely the minimum energy storage limit of surrounding rock induced by transient unloading, is proposed. In addition, the time for erecting support for tunnel excavation in the rockburst area and the impact of excavation dimensions on rockburst are investigated. The results show that transient unloading during the tunnel excavation process will reduce the energy storage limit of the rock mass. When the strain energy density of the local surrounding rock exceeds the minimum energy storage limit of the rock mass, the rock mass energy is suddenly released, and rockburst occurs. Rockburst is most likely to occur at 0.42–0.65 D away from the working face. The increasing length of a round adopted in high geo-stress areas will make the surrounding rock unstable and increase the probability of rockburst.

scholarly journals Stability of a Roadway below a Coal Seam under Dynamic Pressure: A Case Study of the 11123 Floor Gas Drainage Roadway of a Mine in Huainan, China

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Pingsong Zhang ◽  
Yuanchao Ou ◽  
Chang Liu ◽  
Binyang Sun ◽  
Chong Xu
Keyword(s):  
Rock Mass ◽  
Coal Seam ◽  
Dynamic Pressure ◽  
Time Domain Reflectometry ◽  
Surrounding Rock ◽  
Monitoring Method ◽  
Gas Drainage ◽  
Gas Outburst ◽  
Working Face ◽  
Seam Mining

Coal and gas outburst is an important risk faced by coal seam mining in the Huainan region of China. In order to control gas outburst, the gas is predrained by digging a floor gas drainage roadway. To study deformation due to dynamic pressure, the failure characteristics of the floor, and their effect on the stability of the floor gas drainage roadway, a comprehensive monitoring method combining Brillouin optical time-domain reflectometry- (BOTDR-) distributed fiber optics and self-potential exploration was adopted. Dynamic data monitoring of the rock strata between the 11123 working face floor and the floor gas drainage roadway of a mine in Huainan was carried out. The field data obtained showed that, when stabilized by rock bolts and other fixed components in the surrounding rock mass of the floor gas drainage roadway, under the influence of mining, the area of concentrated stress appeared at a depth of 20.7 m, when cracks eventually formed, but the overall structural stability of the surrounding rock mass remained good. The stress distribution and crack evolution of the bottom plate under the influence of dynamic pressure showed spatiotemporal characteristics. Of these, the effect of the lead support stress was 107.48 m, and the range of effect of the hysteresis stress was 34.42 m. When the working face mining position arrives and is far from the monitoring station, the failure depth of floor rock stratum shows the following rule: unchanged in the early stage, deepened continuously in the middle stage, and finally remained stable. It takes about eight days for the dynamic adjustment of this process to finally stabilize. The results of this study can provide guidance for devising suitable procedures for carrying out intelligent green safety mining and for warning about the hazards of roadway damage.

Influence exerted by underground excavation shape and by effective stresses on the formation of a tensile strain zone at a depth greater than 1 km

2020 ◽  
pp. 67-75
Author(s):  
Van Min Nguyen ◽  
V. A. Eremenko ◽  
M. A. Sukhorukova ◽  
S. S. Shermatova
Keyword(s):  
Rock Mass ◽  
Cross Sections ◽  
Tensile Strain ◽  
Rock Fracture ◽  
Strain Analysis ◽  
Surrounding Rock ◽  
Underground Excavation ◽  
Secondary Stress ◽  
Principal Stresses ◽  
Mining Depth

The article presents the studies into the secondary stress field formed in surrounding rock mass around underground excavations of different cross-sections and the variants of principal stresses at a mining depth greater than 1 km. The stress-strain analysis of surrounding rock mass around development headings was performed in Map3D environment. The obtained results of the quantitative analysis are currently used in adjustment of the model over the whole period of heading and support of operating mine openings. The estimates of the assumed parameters of excavations, as well as the calculations of micro-strains in surrounding rock mass by three scenarios are given. During heading in the test area in granite, dense fracturing and formation of tensile strain zone proceeds from the boundary of e ≥ 350me and is used to determine rough distances from the roof ( H roof) and sidewalls ( H side) of an underground excavation to the 3 boundary e = 350me (probable rock fracture zone). The modeling has determined the structure of secondary stress and strain fields in the conditions of heading operations at great depths.

scholarly journals Stress and deformation analysis of gob-side pre-backfill driving procedure of longwall mining: a case study

2021 ◽  
Author(s):  
Rui Wu ◽  
Penghui Zhang ◽  
Pinnaduwa H. S. W. Kulatilake ◽  
Hao Luo ◽  
Qingyuan He
Keyword(s):  
Rock Mass ◽  
Stress Distribution ◽  
Coal Seam ◽  
Abutment Pressure ◽  
Longwall Mining ◽  
Vertical Stress ◽  
Floor Level ◽  
Working Face ◽  
Floor Heave ◽  
Stress And Deformation

AbstractAt present, non-pillar entry protection in longwall mining is mainly achieved through either the gob-side entry retaining (GER) procedure or the gob-side entry driving (GED) procedure. The GER procedure leads to difficulties in maintaining the roadway in mining both the previous and current panels. A narrow coal pillar about 5–7 m must be left in the GED procedure; therefore, it causes permanent loss of some coal. The gob-side pre-backfill driving (GPD) procedure effectively removes the wasting of coal resources that exists in the GED procedure and finds an alternative way to handle the roadway maintenance problem that exists in the GER procedure. The FLAC3D software was used to numerically investigate the stress and deformation distributions and failure of the rock mass surrounding the previous and current panel roadways during each stage of the GPD procedure which requires "twice excavation and mining". The results show that the stress distribution is slightly asymmetric around the previous panel roadway after the “primary excavation”. The stronger and stiffer backfill compared to the coal turned out to be the main bearing body of the previous panel roadway during the "primary mining". The highest vertical stresses of 32.6 and 23.1 MPa, compared to the in-situ stress of 10.5 MPa, appeared in the backfill wall and coal seam, respectively. After the "primary mining", the peak vertical stress under the coal seam at the floor level was slightly higher (18.1 MPa) than that under the backfill (17.8 MPa). After the "secondary excavation", the peak vertical stress under the coal seam at the floor level was slightly lower (18.7 MPa) than that under the backfill (19.8 MPa); the maximum floor heave and maximum roof sag of the current panel roadway were 252.9 and 322.1 mm, respectively. During the "secondary mining", the stress distribution in the rock mass surrounding the current panel roadway was mainly affected by the superposition of the front abutment pressure from the current panel and the side abutment pressure from the previous panel. The floor heave of the current panel roadway reached a maximum of 321.8 mm at 5 m ahead of the working face; the roof sag increased to 828.4 mm at the working face. The peak abutment pressure appeared alternately in the backfill and the coal seam during the whole procedure of "twice excavation and mining" of the GPD procedure. The backfill provided strong bearing capacity during all stages of the GPD procedure and exhibited reliable support for the roadway. The results provide scientific insight for engineering practice of the GPD procedure.

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