Study on grouting diffusion and water-plugging mechanism of clay–cement slurry in water-bearing fractured rock mass

Grouting reinforcement of the Carboniferous Taiyuan Formation L8 limestone karst-fissure aquifer beneath the No. 2-1 coal seam in the Jiaozuo Mining Area still leaves persistent local seepage. This study addresses the problem by investigating clay–cement slurry from three perspectives: slurry working properties, theoretical diffusion in fractured rock masses, and dynamic-water physical simulation. Laboratory tests on fluidity, bleeding rate, stone-formation rate, setting time, rheology and uniaxial compressive strength were conducted for 20 mix proportions with clay dosages of 0–75% and water-to-solid ratios of 0.6–1.5. A grouting-diffusion model for a Bingham slurry in a porous broken rock mass is derived from a Buckingham–Reiner-type generalised Darcy law that retains the yield-stress (threshold-pressure-gradient) term. Within the laboratory envelope, its small-yield limit reduces to a closed-form expression for the symmetric diffusion-radius baseline – with the following- and counter-flow asymmetry described by a calibrated advection offset – while the full form is retained for field-scale extrapolation. A 1 000 mm × 1 000 mm × 100 mm dynamic-water grouting platform was developed. Six U* 6 (6 4 ) uniform-design experiments then quantified the effects of water-to-solid ratio, flow rate, hole number and grouting sequence on stone-body morphology, diffusion range and plugging ratio. The results show the following. (i) At a water-to-solid ratio of 1.5, increasing clay dosage from 0 to 75% reduces the bleeding rate from 41.6% to 15.5% and raises the stone-formation rate from 57.4% to 81.7%. (ii) Raising the water-to-solid ratio from 0.8 to 1.0 and then to 1.25 increases the mean diffusion distance by 43.4% and 19.9%, respectively (averaged over the along-flow and the two lateral measurement directions of the single-hole tests), a progressively diminishing effect. (iii) Sequential grouting produces ∼46% thicker stone bodies and 27–35% higher plugging ratios than continuous grouting. (iv) Single-peak, multi-peak and plateau seepage-pressure curves are identified, the latter two indicating satisfactory plugging. At the model scale, an optimal square grouting-hole spacing of about 190 mm × 190 mm produces a continuous water-plugging curtain. Because grouting diffusion is a process-controlled problem, this spacing is not converted to the field by the geometric ratio. Instead, the study yields a scale-independent design rule, S = η(R p + R m ), in which field-calibrated following- and counter-flow diffusion radii are substituted to obtain the prototype spacing. The findings provide a reference for parameter optimisation of grouting reinforcement in similar water-bearing fractured floor strata.