Experimental investigation on the grouting characteristics of fractured sandstones under different confining pressures

Grouting is an important technical method for anti-seepage reinforcement in underground projects, and it is important to study the strength and deformation characteristics of grouted rocks under different confining pressures (σ3). The time-varying characteristics of urea-formaldehyde resin slurry (UF-RS) with different oxalic acid concentrations and volume ratios were investigated for the selection of suitable ratios. The mechanical properties and damage characteristics of the yellow sandstone and its grouted rock were investigated, and their fractal dimension were studied. The results showed that for higher oxalic acid concentrations, the span of the low-viscosity stage was shorter and lesser time was required to reach the initial setting state of the slurry for the same volume ratio. The span of the low-viscosity stage was longer for a greater volume ratio of modified UF-RS to oxalic acid. The strength recovery ratio of grouted solids was found to be proportional to the σ3, and the cohesion of grouted solids had a larger gap than that of intact yellow sandstone. The fractal dimension and strength recovery ratio of the grouted solids showed an opposite trend with changes in σ3, and the fractal dimension showed a decreasing trend with increases in σ3.