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Abstract

The deformation and failure law of stope roofs is more complicated than horizontal coal seams affected by the angle of the coal seam during the mining process of steeply dipping coal seams. This study focused on and analysed the working face of a 2130 coal mine with steep dipping and large mining height. Through the use of numerical calculation, theoretical analysis, physical similar material simulation experiments, and field monitoring, the distribution characteristics of roof stress, as well as the threedimensional caving migration and filling law, in large mining height working faces under the dip angle effect was investigated. The influence mechanism of the dip angle change on the roof stability of large mining heights was investigated. The results revealed that the roof stress was asymmetrically distributed along the inclination under the action of the dip angle, which resulted in roof deformation asymmetry. With the increase in the dip angle, the rolling and sliding characteristics of roof-broken rock blocks were more obvious. The length of the gangue support area increased, the unbalanced constraint effect of the filling gangue on the roof along the dip and strike was enhanced, and the height of the caving zone decreased. The stability of the roof in the lower inclined area of the working face was enhanced, the failure range of the roof migrated upward, and the damage degree of the roof in the middle and upper areas increased. Furthermore, cross-layer, large-scale, and asymmetric spatial ladder rock structures formed easily. The broken main roof formed an anti-dip pile structure, and sliding and deformation instability occurred, which resulted in impact pressure. This phenomenon resulted in the dumping and sliding of the support. The ‘support-surrounding rock’ system was prone to dynamic instability and caused disasters in the surrounding rock. The field measurement results verified the report and provided critical theoretical support for field engineering in practice.
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Authors and Affiliations

Panshi Xie
1 2
Baofa Huang
1 2
Yongping Wu
1 2
ORCID: ORCID
Shenghu Luo
2 3
ORCID: ORCID
Tong Wang
1 2
ORCID: ORCID
Zhuangzhuang Yan
1 2
Jianjie Chen
4

  1. Xi’an University of Science and Technology, School of Energy Engineering, Xi’an 710054, China
  2. Xi’an University of Science and Technology, Key Laboratory of Western Mine Exploitation and Hazard Prevention Ministry of Educat ion, Xi’an 710054, China
  3. Xi’an University of Science and Technology, Department of Mechanics, Xi’an, 710054, China
  4. Xinjiang Coking Coal Group Corporat ion Limited, Xinjiang 830025, China
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Abstract

The article presents the results of experimental research aimed at recognizing the impact of the design of energy dissipation devices on the formation of bed local scouring below the sluice gate. The experiments were carried out on a model of a sluice gate built in a rectangular flume with a width of 0.58 m, with the outflow of the stream from under the slider to a horizontal bed 0.80 m long. Behind the dam gate valve three different constructions of energy dissipation devices were used: flat, horizontal slab, slab equipped with baffle blocks arranged in two rows and rip-rap. The experiments assumed forming a scour hole in 480 minutes downstream the sluice, where the bed was filled with sorted sand. The depths of the scour were measured in the longitudinal profile after 30, 60, 90, 120, 180, 240, 300, 360, 420 and 480 minutes. The deepest scour holes of the bed, both in terms of depth and length, occurred on the structure model with energy dissipation devices made as a flat, horizontal plate. At the same time, in this case, the hole was developing the most rapidly, and its shape and size posed the greatest threat to the stability of the structure. The use of baffle blocks arranged in two rows or a rip-rap behind the structure slide noticeably reduced the size of the scour and delayed the erosion of the bottom in time, as compared to the course of this process on a model with a flat, horizontal slab.

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Authors and Affiliations

Janusz Urbański
ORCID: ORCID
Marta Justyna Kiraga
Sławomir Bajkowski
ORCID: ORCID
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Abstract

Incorporation of air-entraining agent has improved recycled concrete freeze-proof durability. However, it is very lacking to study the role of the entraining agent. In this paper, the influence of an air-entraining agent on freeze-proof durability for the ordinary C30 recycled coarse aggregate (RCA) concrete and air-entrained C30 RCA concrete was investigated with the laboratory comparative tests. The mass loss, the dynamic modulus of elasticity, ultrasonic wave velocity and cubic compressive strength were measured during freeze-thaw cycles. The test result showed the concrete’s performance was similar to the ordinary concrete and was better than that of other recycled concretes when the content of RCA was 50% and 0.03% of air-entraining agent was added for C30 RCA concrete. Meanwhile, the addition of air-entraining agent has an improved effect on the performance of recycled concrete, but the effect was limited.
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Authors and Affiliations

Xianghui Deng
1
ORCID: ORCID
Yiyuan Liu
2
ORCID: ORCID
Rui Wang
1
ORCID: ORCID

  1. Prof., School of Civil and Architecture Engineering, Xi’an Technological University, Xi’an, 710021, China
  2. Ms., School of Civil and Architecture Engineering, Xi’an Technological University, Xi’an, 710021, China

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