There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A serious rock burst (“4.19” event) occurred on 19 April 2016 in the No. 4 working face of the No. 10 coal seam in Da’anshan Coal Mine, Jingxi Coalfield. According to the China National Seismological Network, a 2.7 magnitude earthquake was simultaneously recorded in this area. The “4.19” event resulted in damage to the entire longwall face and two gateways that were 105 m in long. In addition, several precursor bursts and mine earthquakes had occurred between October 2014 and April 2016 in the two uphill roadways and the No. 4 working face. In this paper, the engineering geological characteristics and in situ stress field are provided, and then the rock burst distributions are introduced. Next, the temporal and spatial characteristics, geological and mining conditions, and other related essential information are reviewed in detail. The available evidence and possible explanations for the rock burst mechanisms are also presented and discussed. Based on the description and analysis of these bursts, a detailed classification system of rock burst mechanisms is established. According to the main causes and different disturbance stresses (i.e., high/low disturbance stresses and far-field/near-field high disturbance stresses), there are a total of nine types of rock bursts. Thus, some guidelines for controlling or mitigating different types of rock bursts are provided. These experiences and strategies not only provide an essential reference for understanding the different rock burst mechanisms, but also build a critical foundation for selecting mitigation measures and optimizing the related technical parameters during mining or tunnelling under similar conditions.

Case Studies of Rock Bursts Under Complicated Geological Conditions During Multi-seam Mining at a Depth of 800 m

Rock burst assessment and prediction by dynamic and static stress analysis based on micro-seismic monitoring

Progressive mitigation method of rock bursts under complicated geological conditions

Effective evaluation of pressure relief drilling for reducing rock bursts and its application in underground coal mines

Investigation and analysis of the rock burst mechanism induced within fault–pillars

Rock burst is one of the most catastrophic dynamic hazards in coal mining. A static and dynamic stresses superposition-based (SDSS-based) risk evaluation method of rock burst was proposed to pre-evaluate rock burst risk. Theoretical basis of this method is the stress criterion incurring rock burst and rock burst risk is evaluated according to the closeness degree of the total stress (due to the superposition of static stress in the coal and dynamic stress induced by tremors) with the critical stress. In addition, risk evaluation criterion of rock burst was established by defining the “Satisfaction Degree” of static stress. Furthermore, the method was used to pre-evaluate rock burst risk degree and prejudge endangered area of an insular longwall face in Nanshan Coal Mine in China. Results show that rock burst risk is moderate at advance extent of 97 m, strong at advance extent of 97–131 m, and extremely strong (i.e. inevitable to occur) when advance extent exceeds 131 m (mining is prohibited in this case). The section of two gateways whose floor abuts 15-3 coal seam is a susceptible area prone to rock burst. Evaluation results were further compared with rock bursts and tremors detected by microseismic monitoring. Comparison results indicate that evaluation results are consistent with microseismic monitoring, which proves the method’s feasibility.

Risk evaluation of rock burst through theory of static and dynamic stresses superposition

Currently, rock bursts pose a serious threat to the safety of miners and equipment in underground coal mining operations, especially in China. The number of coal mines with rock burst hazards is increasing year by year with no signs of letting up. By 31 December 2013, there were 142 coal mines in China which had experienced rock bursts. Each year, rock bursts cause considerable economic loss and enormous casualties. For instance, a rock burst induced by a large thrust fault caused 10 deaths and trapped 75 people on 3 November 2011 during the headgate excavation of LW21221 in Qianqiu coal mine, Yima City, China (Cai et al. 2014a, b; Li et al. 2014). Rock bursts are serious not only because the hazard itself can cause damage, but because it can cause a series of secondary disasters, such as coal and gas outbursts, and gas explosions. The most serious gas explosion recorded to date killed 214 people, injured 30 people, and caused a direct economic loss of U49.689 million. It happened on 14 February 2005 in Sunjiawan coal mine, Fuxin City, China. Investigation revealed that the gas explosion was induced by a rock burst (State Administration of Work Safety, State Administration of Coal Mine Safety 2005). Existing research mainly concentrates on the monitoring, prediction, and prevention of rock bursts (Adoko et al. 2013; Cai et al. 2014a, 2014b; Kornowski and Kurzeja 2012; Mu et al. 2013). Control measures against rock bursts are usually passive and include: de-stress blasting (Konicek et al. 2013), directional fracturing (He et al. 2012a), large-diameter drilling (Li et al. 2014), etc. These measures are time-consuming and only reduce rock burst potential without complete elimination of the hazard. The latest statistical data (Pan et al. 2013) show that 87 % of rock bursts occurred in roadways in China’s coal mines. Compared with the 72.6 % seen from previous statistics (Dou and He 2001), this proportion has increased. Among roadway rock bursts, gob-side rock bursts (GRBs) (i.e., rock bursts occurring in gob-side roadways) account for the majority. For example, the eight rock bursts in the No. 17 coal seam of Xing’an coal mine, Hegang City, China, caused damage to the tailgate and the longwall face eight and two times, respectively. However, the headgate was not damaged at all (see Fig. 1a). The 22 rock bursts in the No. 17 coal seam of Junde coal mine, Hegang City, caused damage to the tailgate, the longwall face, and the headgate 18 times, five times, and once, respectively (see Fig. 1b). Both tailgates in the two coal mines are gob-side roadways. It is common in other coal mines that GRBs account for the majority of rock bursts because gob-side roadways bear a higher stress. If GRBs are controlled effectively, rock burst hazards will be significantly mitigated. In this work, a case study of Yuejin coal mine (YCM) in Yima City, China, was analyzed to ascertain whether, or not, roadway staggered layouts could control GRBs. The aim of this study was to deduce whether, or not, this & Lin-ming Dou lmdou@cumt.edu.cn; kdlzl2010@163.com

Roadway Stagger Layout for Effective Control of Gob-Side Rock Bursts in the Longwall Mining of a Thick Coal Seam

Combination of coal mining dynamic load and high static stress can easily induce such dynamic disasters as rock burst, coal and gas outburst, roof fall, and water inrush. In order to obtain the characteristic parameters of mining dynamic load and dynamic mechanism of coal and rock, the stress wave theory is applied to derive the relation of mining dynamic load strain rate and stress wave parameters. The in situ test was applied to study the stress wave propagation law of coal mine dynamic load by using the SOS microseismic monitoring system. An evaluation method for mining dynamic load strain rate was proposed, and the statistical evaluation was carried out for the range of strain rate. The research results show that the loading strain rate of mining dynamic load is in direct proportion to the seismic frequency of coal-rock mass and particle peak vibration velocity and is in inverse proportion to wave velocity. The high-frequency component damps faster than the low-frequency component in the shockwave propagating process; and the peak particle vibration velocity has a power functional relationship with the transmitting distance. The loading strain rate of mining dynamic load is generally less than class 10−1/s.

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In Situ Test Study of Characteristics of Coal Mining Dynamic Load

List of symbols A, B, C Rock blocks A0, B0, C0 Action points of lateral thrust H, L, W Thickness, length and width of rock block (m) h0 Thickness-to-length ratio of rock block (h0 = H/L) Lx Length of fault-pillar (m) a Thickness of voussoir arch (m) d0, d1 Vertical deflections of rock blocks B and C (m) aA, aB, aC Rotation angles of rock blocks A, B, and C ( ) h Angle of fault plane in vertical direction ( ) u, uf Friction angles of rock and fault plane ( ), 0.85 for most rocks and faults c Unit weight of rock (N/m), 2.5 9 10 N/m for most rocks p Applied stress on rock block from overlying strata (Pa) q Total applied stress on rock block from overlying strata and the rock block (q = p?cH) (Pa) rc Uniaxial compressive strength (UCS) of rock (Pa) r, s Compressive stress and shear stress at fault plane (Pa) f(lx) Static stress within fault-pillar (Pa) P Total load on rock block (P = pLW ? cHLW = qLW) (N) T Lateral thrust (N) R0–0, R0–1, R1–2 Shear forces between rock blocks (N) R, R1 Resistance forces of collapsed and broken strata (N) Tf, Rf Normal force and shear force at fault plane (N)

Yan-lu Ding

Papers

Investigation and analysis of the rock burst mechanism induced within fault–pillars

Risk evaluation of rock burst through theory of static and dynamic stresses superposition

Roadway Stagger Layout for Effective Control of Gob-Side Rock Bursts in the Longwall Mining of a Thick Coal Seam

In Situ Test Study of Characteristics of Coal Mining Dynamic Load

Mechanical Analysis of Static Stress Within Fault-Pillars Based on a Voussoir Beam Structure