Influences on the performance of cement-based grout used to reform the upper Middle Ordovician limestone in Hanxing mining area

Due to the difference in the properties of grouting materials and grout, there is a lack of reasonable selection of grouting materials and effective regulation of grout type and ratio in the practice of grouting, which makes the advance grouting effect difficult to reach the expected target. Therefore, the development of the upper layer of the Middle Ordovician limestone, and the cement, clay, and fly ash used for local grouting are analyzed. The physical and mechanical properties of the cement-based grout were analyzed. Orthogonal tests determined the physical and mechanical properties of cement-based slurry and its main influences. It was found that the water richness and permeability of the seventh member of the Fengfeng Formation at the upper layer of the Middle Ordovician limestone were greater than those of the eighth member. The mesoscopic voids were mainly comprised of closed and micro-tensioned fissures with average widths of 120 μm and 420 μm, respectively. Wide-tension and middle-tension cracks accounted for most of the crack area and provided good ductility. The main factor controlling the setting time of cement grout, cement-fly ash grout, and cement-clay grout is the water glass content. The main factors controlling viscosity are the content of water glass (cement grout) and water-cement ratio (cement-fly ash grout and cement-clay grout). The main factors controlling the stone rate are the water-cement ratio (cement grout and cement-fly ash grout) and water-cement content (cement-clay grout), while the main influence on strength is the water-cement ratio.