roof strata
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Mining ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 13-31
Author(s):  
Lech Stolecki ◽  
Krzysztof Szczerbiński

The paper presents the results of long-term continuous measurements of the deflection of the roof layers in the underground copper mine Polkowice-Sieroszowice, Poland belonging to KGHM Polska Miedź S.A. The measurements were performed with the use of the inclinometric method consisting of continuous registration of changes in the angle of inclination of the roof strata. The measurements were carried out using an inclinometer sensor fixed to the end of a rockbolt in the roof. Measurements presented in the article were made in various regions of the underground mine. The monitoring covered: The exploitation front, machinery chamber and the region of the experimental longwall mining of copper ore. The obtained results proved the usefulness of the developed method in the process of the evaluation of the stability of mining excavations. The sensors were highly sensitive and performed the measurements in a simple way; highly accurate and reliable results were obtained.


Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 4) ◽  
Author(s):  
Qingliang Chang ◽  
Qiang Leng ◽  
Xikui Sun ◽  
Guichen Li ◽  
Biao Zhang

Abstract The aim of this study is to explore a safe mining method to effectively excavate the deep thick coal seams in rockburst-prone mines. Based on the theory of elastic foundation and geological conditions of the Xinhe Coal Mine, the cemented paste backfill (CPB) is proposed to prevent rockburst. In this study, the roof fracture mechanism of block caving mining (BCM) and CPB methods are established. Then, the stress evolution of the surrounding rock and the subsidence of roof strata with these two methods are compared. The results show that the maximum bending moment appears in the middle of the roof, and the value is far below the critical bending moment of the roof by using the CBP. While using the BCM, this value exceeds the critical bending moment of the roof, which may trigger rockburst-related problems. In addition, there is no first weighting and periodic weighting phenomena by using the CPB method as the overburden pressure is gradually transferred to the backfill body, resulting in a safer mining condition. Furthermore, the engineering application indicates that the frequency of daily microseismic events and the burst energy are significantly reduced by using the CPB.


Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Kai Wang ◽  
Bao-gui Yang ◽  
Zhong-kui Wang ◽  
Xiao-long Wang

In order to meet the security and high-efficiency production needs, high-strength bolt (cable) reinforcement technology is usually used to maintain the stability of roadways. However, due to the great variability of lithology and mechanical properties, the failure form and stability of the layered roof in coal roadways are significant differences. The traditional supporting design method of the layered roof support in coal roadways is the engineering analogy method, which depends on experiences rather than theoretical analysis. Based on the theory of the elastic foundation beam and key stratum, this paper establishes a simplified analytical model of layered roof strata in coal roadways. Based on the Mohr-Coulomb theory, this paper gives the failure criteria of the layered roof strata, and the failure range of the layered roof strata is obtained. The length and pretightening force of bolt (cables) of the layered roof strata can be calculated based on the suspension theory and composite beam theory, which providing a quantitative theoretical basis for the determination of supporting parameters. Finally, as a case, the layered roof strata failure range and supporting parameters of the S1301 auxiliary transportation roadway in Gucheng coal mine are calculated.


2021 ◽  
Vol 2021 ◽  
pp. 1-6
Author(s):  
Zhicheng Ren ◽  
Minghui Zuo

For the support problem of the super-large section cut in working face with large mining height, the 1105 cut pilot chamber of Zhaogu No. 2 Mine, the roof strata structure detection and the strata movement rule research were conducted. The results prove that concentrate fracture area, gradually sparse fracture area, and rare fracture area regularly distributed from the surface to the deep area of the roof of 1105 cut, and less fracture exists in the rock stratum of roof above 3.5 m, and the stratum of roof within the range of 4–6 m is stable. Authors propose the long bolt and cable combined supporting technology and optimized the design plan applying theoretical calculation and computer numerical simulation. The scheme has been applied in the field of the 1105 super-large section cut in Zhaogu No. 2 Mine. The monitoring results show that the scheme can effectively control surrounding rock of roadway, and the support with long bolt has good effectiveness.


2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Jianqiang Liu ◽  
Guangpeng Qin ◽  
Jing Cao ◽  
Minghua Zhai ◽  
Yunxin Pei

The upper part of high gas coal seam often has a hard and thick sandstone roof, which provides the condition for the occurrence of gas accident in goaf caused by the friction effect for the sliding and instability of hard quartz sandstone. Based on the engineering background of the 1007 working face of Xiakuotan Coal Mine, the conditions of sliding instability of hard quartz sandstone and the possibility of the friction effect are discussed by combining theoretical analysis with the laboratory test. When the ratio of span to thickness is less than 2∼2.56, the hard-thick sandstone strata may slip and lose stability. The influence of friction velocity and gas concentration on the induced gas of quartz sandstone is analyzed and compared. The results show that the point spark, the spark beam, and the gas explosion time are inversely proportional to the relative friction velocity, and the intensity of the gas explosion is directly proportional to the gas concentration and the relative friction velocity. This paper provides the basis for the prevention and control of gas disasters in goaf and the control of hard and thick sandstone roof strata under similar engineering geological conditions. It is of great significance to promote the safe and efficient production of coal mines and to ensure the safety of personal and property.


Author(s):  
Cancan Liu ◽  
Qinjian Zhan ◽  
Lu Yang ◽  
Xigui Zheng ◽  
Peng Li ◽  
...  

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Chao Xu ◽  
Gang Yang ◽  
Haoshi Sun ◽  
Liangliang Qin ◽  
Kai Wang ◽  
...  

The thick and hard rock strata (THRS) exist widely in coal measure strata, which control the movements of overlying rock strata in stopes. When THRS break, great energy is released, which could aggravate the risks of coal and gas outburst, rock burst, and other dynamic disasters. Therefore, the foundation and key of preventing dynamic disasters are to distinguish the THRS that could induce coal-rock dynamic disasters and to analyze the laws of rock stratum breaking and energy releasing. The paper proposed the theoretical calculation methods of the energy accumulation and attenuation of rock breaking which is greatly affected by the hanging length of rock strata and the spreading distance. One or more roof strata that play a leading role in inducing dynamic disasters of the underlying coal mass are defined as the key disaster-inducing strata (KDIS). The disaster-inducing coefficient (DIC) is defined and used as the criterion of KDIS. The greater the source energy, the shorter the spreading distance, and the smaller the attenuation coefficient are, the easier the roof strata are to become KDIS. The disaster-inducing ability of the main THRS was analyzed, and the igneous sill was judged as KDIS, taking the Yangliu Coal Mine as project background. The breaking laws of the igneous sill were obtained by the methods of UDEC numerical simulation and microseismic monitoring, which verified the criterion of KDIS.


2020 ◽  
Author(s):  
Xiaowei Feng ◽  
Fei Xue ◽  
Qun Wei

Abstract W straps are important surface supporting components. When they cooperate properly with inner supporting components, such as rock bolts and cable bolts, they can enhance the supporting effects and bridging bolting units with integrity. Unfortunately, relevant studies regarding this topic have not been extensively reported. In this study, the failure characteristics of the W strap in the field are discussed and different types of distortion are proposed. Followed by the detailed failure patterns of the strap, a possible mechanism and solution are hypothetically put forward, which are then both numerically and experimentally verified. Afterwards, a loading apparatus capable of examining the mechanical behaviours of the strap is designed, which can similarly recreate the loading environment of the strap to the situation in the engineering field. By virtue of the designed loading device, a series of failure patterns of the bolting system are presented, and the distortion degree of the strap is evaluated using a 3D scanning method. The major findings in this study are as follows: 1) a domed face plate is better than a square domed face plate; 2) the existence of a hole beneath the strap in engineering applications can easily induce failure; and 3) cracked but compacted gravel-like roof strata beneath the strap may not cause damage to the strap-bolt supporting system. These ideas present new understandings in terms of the working conditions of W straps in coal mine roadway supporting systems, and the results can be referred to by practitioners.


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