Tests of Strength Parameters of Hydro-Mixtures Based on Ashes from a Fluidized Bed Boiler in the In-Situ Approach

Abstract

The paper presents the practical use of a solidifying hydro-mixture based on ashes from fluidized bed boilers under hard coal mine conditions for filling an incline connecting the headgate and tailgate of a longwall running along the strike with roof caving. The reason for filling the incline with a material of preset strength parameters was to minimize the methane hazard in the extracted coal seam. Due to a great demand for fill material, which translates into economic considerations, the option of applying fine-fraction waste material was selected. Preliminary laboratory tests of the physical and mechanical properties of hydro-mixtures based on ash obtained from a fluidized bed boiler of a power plant, allowed us to select a specific hydro-mixture meeting the requirements. After 95 days, the incline filled with the proposed hydro-mixture was subjected to exploitation along with the advance of longwall working. This enabled the in-situ collection of a number of fill material samples from various places along the entire length of the incline. Then their strength was tested and the results compared with the obtained test results of identical material seasoned under laboratory conditions. The obtained results constitute a unique research material since it is practically impossible to verify the laboratory-determined strength parameters of the solidifying fine-fraction hydro-mixtures under in-situ conditions. Thsis results mainly from the lack of technical capabilities and poor access to the places where fine-fraction hydro-mixtures are applied, mostly abandoned cavings or parts of workings separated by dams.