Mining technology and practice of full-solid waste cemented backfilling in narrow strip of extra-thick coal seam under buildings

There is a great amount of coal pressed under buildings in our country, while the discharge of coal-based industrial solid wastes such as coal gangue and fly ash are increasing, which has severely restricted the local economic and social development. Taking Mahuangliang Coal Mine in Yulin as the test mine, aiming at the problems of extra-thick coal seam, coal pressed under buildings and high backfilling cost, the technology of full solid waste continuous mining and filling in extra-thick coal seam is put forward. The four-stage process is adopted and the extra thick coal seam is divided into upper and lower parts for secondary mining to control the ground settlement to the maximum extent. In order to reduce the cost of filling raw materials, the source modification of magnesium slag is carried out with chemical optimizer to restrain the cooling pulverization of magnesium slag and stabilize hydration activity. In collaboration with coal based solid wastes such as fly ash and desulfurized gypsum, modified magnesium-cinder based cementing material is developed. The whole solid waste filling material was prepared by cementing coal gangue and fly ash with modified magnesium cinder based cementing material. According to the requirements of strong and weak filling strength in four stages of Mahuangliang Coal mine, different ratios of modified magnesium slag-based filling materials were designed to optimize the ratio and applied to underground filling. The paste filling system and roof-contact method are introduced. The experimental results show that the average uniaxial compressive strength of the 28-day underground filling body exceeds the designed strength by 27%. The leaching toxicity of the core meets the relevant national standards, which successfully liberates the coal resources under the building and has significant social and economic benefits. The practice of full-solid waste cementation and backfilling in the extra-thick seam of Mahuangliang Coal Mine provides a useful reference for similar mines in China, and provides a new idea for the large-scale resource utilization of “coal-electricity-chemical-metallurgical” solid waste in large coal bases in China.