Grouting treatment for safe coal mining beneath thick unconsolidated strata: current status and prospects

Coal mining beneath thick unconsolidated strata faces risks including water and sand inrush, overburden instability, and surface subsidence. Grouting treatment is an important technical means of improving the load-bearing and water-sealing properties of strata. Focusing on the requirements for safe coal mining beneath thick unconsolidated strata, this review traces the development of grouting technology and summarizes the mechanisms and applicable conditions of permeation, fracture, compaction, and jet grouting. It analyzes the properties of cementitious and chemical grouting materials and the requirements for matching these materials to different strata, and presents grouting strategies for typical engineering scenarios. Key aspects of precise grouting construction control are summarized in terms of drilling and borehole wall stability control, dynamic regulation of grouting pressure and flow rate, and construction sequencing and borehole stage control. Research progress in evaluating the effectiveness of regional grouting treatment is reviewed from the perspectives of theoretical calculation, numerical simulation, physical model testing, and field measurements. Current research has several limitations: grouting theory models do not adequately accommodate complex geological conditions, simulation platforms have limited capabilities for reproducing complex operating conditions, grouting materials require improvements in overall adaptability and functionality, construction processes lack precise dynamic regulation, and effectiveness evaluation systems lack specificity. Future development should focus on refined grouting theory models incorporating multiple coupled factors, environmentally friendly high-performance grouting materials, intelligent grouting equipment and sensing systems, digital twins and full-process visual monitoring and control, and multidimensional effectiveness evaluation systems covering the entire life cycle.