Rock Burst Mechanism under Coupling Action of Working Face Square and Regional Tectonic Stress

With the development of faults in many coalfields, many large faults will form a relatively independent area, forming regional tectonic stress concentration. Under the influence of mining, it is easy to induce fault activation, produce mine tremor, and then induce rock burst. Through field investigation, theoretical analysis, numerical simulation, and engineering verification, the overburden movement model of No. 3504 working face square and fault activation in Liangbaosi Coal Mine was established. The stress variation and energy release law of working face advance and fault area were analyzed, and the mechanism of rock burst under the coupling action of working face square and regional tectonic stress was revealed. The results show that the regional stress adjustment and fault activation are caused by the large-scale overall movement of overburden during the working face square, and there is a peak value of elastic energy release during the fault activation, which is easy to produce large energy mine earthquake. The energy level of the daily maximum energy event is higher than that of the initial mining stage in the square period, and the location of on-site large energy microseismic event is basically consistent with the predicted fault strike. The study provides a theoretical basis for the prevention and control of rock burst during the working face square under the condition of regional tectonic stress.

Ground Response and Mining-Induced Stress in Longwall Panel of a Kilometer-Deep Coal Mine

In order to improve ground control of the longwall mining, ground response and mining-induced stress in the longwall panel of a kilometer-deep coal mine are investigated in this study. Field measurements on abutment stress, roof displacement, and fracture development indicate that the region influenced by the longwall mining reaches 150 m ahead of the longwall face. Failure scope of the coal seam, where mining-induced fractures are well developed, ranges from 10 to 13 m inward the face line. Vertical stress concentration coefficient reaches 2.2. Based on the field measurements, a numerical model is moreover developed and utilized to examine the response of the principal stress to the longwall mining. The concentration coefficient, peak point location, and influence scope of the principal stress gradually become stable with an increase in face advancement. Regarding the major principal stress, the concentration coefficient and influence scope are 2.4 and 152 m, respectively, and the peak point locates 13 m inward the face line, which are consistent with the field measurements. With respect to the minor principal stress, the referred coefficient and scope are 1.5 and 172 m, respectively, and its peak point location is 21 m ahead of the face line. The major principal stress in the coal seam rotates from vertical to horizontal direction in the vertical plane parallel with face advance direction. The maximum rotation angle reaches 20°. The minor principal stress first rotates into the referred vertical plane and then it rotates from horizontal to vertical direction at the same speed with the major principal stress in the same plane. Rotation angle of the principal stress in roof strata is greatly enlarged, the rotation trace of which is influenced by the longwall mining and vertical distance above the seam. Based on the relation between rotation trace of the principal stress and face advance direction, the influence of stress rotation on the stability of roof structure is discussed.

Coal and Gas Outburst Affected by Law of Small Fault Instability during Working Face Advance

To analyze the effect of small faults in the working face on coal and gas outbursts, the coal and gas outburst accident in the 21431 working face was studied with the 3DEC numerical simulation method, and the main research contents were the change laws of both stresses at the small fault and the overburden strata movement rate in the small fault zone of which the drop height and the strike were designed into different groups. The results show that the risk of small fault slip increases with the advancing working face. In addition, there is a positive correlation between the risk and the small fault throw. The movement rate of overburden strata in the small fault zone increases along with the rising of the small fault throw, which increases the energy transferred to the coal seam from the surrounding rock under the effect of the small fault. Hence, the effect of small faults on the working face on coal and gas outbursts was positively correlated with the small fault throw. Under the influence of a small fault strike, the closer it is to the small fault along the dip distance at the same working face, the greater the risk will be of a coal and gas outburst. And the bigger the small fault strike is, the greater is the stress concentration degree in front of the working face and the more the elastic energy is stored and the greater is the possibility of an outburst. The paper analyzes the influence of small faults on coal and gas outbursts in the working face, which has reference significance for the prediction and prevention of coal and gas outburst disaster in the working face.

Determining the Permissible Longwall Face Advance in the Protective Pillar Conditioning the Liquidation of a Mining Shaft

The presented research subject involved the assessment of the possibility of mining operations within the area of shaft protection pillar with simultaneous liquidation of the shaft. In such a situation, the basic condition is to avoid damage to shaft lining, which can hinder or even prevent safe liquidation of the shaft by backfilling. The procedure to follow in order to assess the possibility and scope of mining exploitation within the shaft protection pillar is demonstrated on the example of shaft X. The applied assessment method involving the possibility and scope of mining exploitation within the protective pillar of the shaft was based on the forecast of rock mass deformation at the shaft site, which was the basis to calculate vertical stresses in the shaft lining and then to compare them with permissible values. The carried out calculations allowed us to determine the permissible face advance of longwall No. 5 at which no damage to the lining and its equipment would occur, ensuring the planned safe liquidation of the shaft by backfilling.

Study on the Ground Movement in an Open-Pit Mine in the Case of Combined Surface and Underground Mining

The combined surface and underground mining method is typically used in an open-pit mine for better production and profits. However, the improved scale of mining operations at the combined mining conditions results in even more intensive strata movement and massive ground damages. This paper assesses the progressive development of the characteristics of roof movement with the longwall face advance and its influence on the ground movement at the slope area using physical models. The identification of strata zones at the combined mining conditions is also included. The results show the following: (1) the failure of the competent strong roof creates an inverse arch-shaped rock block structure, which compacts the loose rock fragments in the caved zone; (2) a bed separation occurs above the inverse structure at the top of the disturbed strata configuration and extends upward with the face advance until it approaches the continuous bending zone; (3) more intensive strata movement and ground damages are produced by the large-scale multiseam mining operations, while regular and more distinct strata zones in the disturbed configuration are identified for less intensive single-seam mining; and (4) the intensive and massive underground mining activities increase the slope strata movement at the surface mining side. This research suggests that a less intensive mining activity is preferred in the combined surface and underground mining conditions from the point of view of ground control.

“Being healthy and living life as if I never had cancer”: The meaning of “living well” from adolescents with cancer.

e22532 Background: Extensive resources are devoted to discovering novel cancer treatments. Meanwhile, patient priorities and experiences must also be addressed. Specifically, among adolescents with cancer, patients’ definitions of “living well” may elucidate treatment preferences, guide care teams and families, and influence future behavioral interventions. The objective was to develop an empirical definition of “living well” for adolescents with cancer to enhance shared decision-making. Methods: Video recordings were analyzed from the Next Steps: Respecting Choices interviews with n = 30 adolescents ages 14-21 years with cancer and their families, a subsample of N = 126 adolescent/family dyads participating in a randomized clinical trial, FAmily CEntered (FACE) Advance Care Planning. Interviews were transcribed, verified and anonymized. A phenomenological analytic method was used to identify psychological meaning in participants’ statements. Results: Adolescents with cancer conceptualize living well as meaning maintaining physical, mental and emotional health, while engaging in purposeful, typical, adolescent-appropriate activities with people important to the adolescents. This has four components: living mindfully; living an identity as a healthy adolescent; spending time with friends and family; and living a purposeful life without depression. Living well means most often enjoying these activities while spending time with family and friends. An exemplary quotation is, “...being able to have a life where everything is going good, and being able to live healthy...gets rid of some of your worries not only for yourself but for your friends and family...less worries means a less stressful life...” Conclusions: By determining what “living well” means to adolescents with cancer, care teams and families can more easily understand patients’ priorities. A firm grasp on patients’ definitions of “living well” could relieve significant burden from families and increase families’ willingness to honor adolescent treatment preferences. Findings may guide future psychosocial interventions. Clinical trial information: NCT01670461.