Research and application of heap spraying technology based on safe and high-efficiency supporting structure

Aiming at the special characteristics of underground coal mine operation environment and the deficiency of existing support technology, heap spraying technology was proposed, technological parameters were determined, heap spraying admixture (S2) was developed, the mechanism of S2 was revealed, and a complete set of heap spraying construction technology was formed and applied to gob-side entry retaining. The results show that: ① Heap spraying technology can be used to construct the supporting structure according to need, which is not restricted by operating space and the operator is far away from the danger zone, so that the surrounding rock can be controlled safely and efficiently. ② Heap spraying material tide mixing and conveying pipeline segmentation with water process, wetting materials in advance, can promote material hydration, enhance adhesion and workability, reduce dust and rebound rate. ③ The accelerating components of S2 include NaAlO₂, Al₂(SO₄)₃, NaF, Al(OH)₃ and fast-hardening sulfoaluminate cement (SAC-42.5), and the viscosifying and anti-cracking components are silica fume (GS), polymer propylene fiber (JB), S2 improves the compressive strength of the supportintg structure material and has micro-expansion properties. ④ Uniaxial compressive strength of the standard specimens molded by heap spraying is 12.0 MPa at 1 d, 18.0 MPa at 3 d, 27.5 MPa at 7 d, 42.1 MPa at 28 d and 42.3 MPa at 90 d, with high strength supporting capacity, and late strength does not shrink, the strength growth process is divided into three stages: the initial rapid growth stage (age 0−14 d), the medium sustained growth stage (age 14−28 d), and the later stable stage (age>28 d). ⑤Heap spraying technology can build the isolation wall along roadway to realize gob-side entry retaining, having a positive effect on expanding the construction method of supporting structure.