Nonlinear creep properties and time-to-failure prediction of sandstone under saturated and dry conditions

Influenced by the deep high-stress environment, geological structures, and mining disturbance in coal mines, the frequency of rockburst disasters in roadways is increasing. This research analyzed energy evolution characteristics during rockburst development in the elastic bearing zone and energy conversion in the plastic failure zone. The critical energy criteria for structural instability of roadway surrounding rocks were deduced. Numerical software was also applied to simulate the energy evolution during rockburst development in surrounding rocks of rockburst-prone roadways under conditions of different mining depths and coal pillar widths. The occurrence mechanism of rockburst deep in coal mines was analyzed from the perspective of energy in structures of deep roadway surrounding rock in coal mines. The research results show that the critical energy criteria are closely related to the elastic strain energy stored in deep roadway surrounding rocks and the energy absorbed by support systems. The impact energy in roadways is directly proportional to the square of the stress concentration factor k. Moreover, as the mining depth increases, the location of the peak point of maximum energy density gradually shifts to coal ahead of the working face. The larger the mining depth is, the more significantly the energy density is influenced by advanced abutment pressure of the working face and the wider the affected area is. With the increment of the coal pillar width, the distance from the peak point of energy density to the roadway boundary enlarges abruptly at first and then slowly, and the critical coal pillar width for gentle change in the distance is 30 m. Changes in the peak elastic energy density in coal pillars with the coal pillar width can be divided into four stages: the slow increase stage, abrupt increase stage, abrupt decrease stage, and slow decrease stage. The elastic energy density is distributed asymmetrically in deep roadway surrounding rocks in coal mines. Under the action of structures of roadway surrounding rocks, energy evolution in these structures differs greatly during rockburst development under conditions of different coal pillar widths. This research provides an important theoretical basis for the support of rockburst-prone roadways during deep coal mining.

Section: Introductionmentioning

confidence: 99%

Energy evolution mechanism during rockburst development in structures of surrounding rocks of deep rockburst-prone roadways in coal mines

Xuan,

Cheng,

et al. 2023

“…In the process of coal mining, gas disaster is still one of the main disasters in coal mines, which is easy to cause large-scale casualties (Wu et al, 2022;Zou et al, 2023b). Coal and gas outburst is one of the typical gas disasters in coal mines (Cheng et al, 2022;Zheng et al, 2022;Zhao et al, 2023a), and with the mining operation of coal seam extending to the depth year by year (Xie et al, 2022;Ye et al, 2022;Xie et al, 2023), the permeability of coal seam gradually decreases with the increase of ground stress, gas pressure and temperature, which increases the risk of coal mine gas outburst (Liu and Li, 2016;Pan et al, 2020;Song et al, 2022). In recent years, although our defense technology has made remarkable progress, prominent security accidents still occur from time to time (Liu et al, 2021;Ran et al, 2023a;.…”

Section: Introductionmentioning

confidence: 99%

Regional outburst prevention technology of pre-drainage gas area in west well area of sihe coal mine

Zhang

2023

Coal and gas outburst is one of the main factors affecting the safe and efficient production of coal mines. With the increase of mining depth and mining speed, the dynamic phenomena of coal and gas outburst will become more and more serious. Through the study of various outburst prevention measures in the pre-drainage gas area such as surface drilling, bedding (directional) drilling, and cross-layer drilling, combined with the coal seam occurrence and mining technology of the West Mine Area, a feasible regional pre-drainage comprehensive outburst prevention mode suitable for the characteristics of the 3# coal seam in the West Mine Area has been obtained. This mode is based on pre-pumping of surface drilling first, directional long borehole along the reservoir and pre-pumping of cross-zone borehole, which provides reliable guarantee for safe and efficient production in outburst well area.

“…With the development of efficient coal mining technologies (Wu et al, 2022;Li et al, 2023a), the spatial scale of fully mechanized working faces in coal mines in China constantly expands in three aspects: mining depth, horizontal scale (including the working face length and advance length), and vertical scale (mainly the mining height) (Liu et al, 2021;Zou et al, 2022a;Ye et al, 2022;Li et al, 2023b;Ma et al, 2023;Sun et al, 2023). In such context, the mining depth of coal increases at a speed of 10-25 m/a, and the working face length gradually increases from 100-200 m to 300-350 m, and even above 400 m in some cases Zou et al, 2022b;Zhang et al, 2023a;Su et al, 2023;Ye et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

Three-peak evolution characteristics of supporting stress on a super-long working face in a thick coal seam

Wang,

Cheng,

Zhang

et al. 2023

Increasing working face length is the development trend of intelligent and efficient longwall fully mechanized mining. By combining field measurement and theoretical calculation, change characteristics of the frequency, peak value, and range of weighting in a long working face in a 1000 m-deep shaft of Kouzidong Coal Mine (Fuyang City, Anhui Province, China) were studied. Based on the mechanical model of the hydraulic support group of the elastic independent support, force characteristics and posture change characteristics of the support in the 121304 working face of the mine were studied and analyzed. The supporting stress characteristics of the deep super-long working face were revealed, and the theoretical calculation was in good agreement with the actual measurement. Based on the aforementioned model, support parameters and control technology of the 140502 working face were studied. The results show that as the length of the working face increases, the supporting stress gradually transforms from a single peak to multiple peaks and expands to both ends of the working face. The weighting in different areas of the working face is characterized by an obvious time sequence and great difference in intensity. When the working face length is 300 m, the multi-peak characteristic of super-long working faces appears. The M-shaped three-peak characteristic can be used as the criterion for super-long working faces. A reasonable working face length should be determined by comprehensively considering occurrence conditions of coal seams, working face parameter, and equipment ability. According to the different attributes of hydraulic supports in space and function and combining with zonal characteristics of the long working face, the criterion for the super-long working face and the principle of zonal cooperative control of hydraulic support groups were revealed. In addition, a cooperative control method of equipment groups in the working face based on the state error and cost functions was put forward, and the three-level cooperative control strategy and implementation method were formulated. It can effectively guide the equipment group in the super-long fully mechanized working face in deep thick coal seams to achieve optimal coordinated control.