Feasibility of a Polymer Foaming Agent as a Grouting Material for Broken Coal Masses

A new soluble polymer foaming (PF) grouting material was developed by using hydrophilic amino resin as the base material and adding other cross-linking, foam, foam stabilizing, toughening, and coupling agents. The PF material exhibited low viscosity, excellent adhesion, and strong penetration. The grouting reinforcement effect of the proposed PF material on broken coal masses was investigated and compared with that of traditional superfine cement (SC) through simulation experiments. Results showed that after grouting, fractures, joints, and other failure planes inside raw coal were filled and bonded, and the mechanical strength of the grout-coal concretion improved relative to the residual strength of raw coal. The average uniaxial compressive strength of SC specimens was 6.16 MPa, whereas that of PF specimens was 10.85 MPa. Moreover, the PF specimens presented an obvious characteristic of plastic strengthening. Analyzing the reinforcement effect of the grouting materials on the basis of single structural plane theory revealed that at the critical state, the average sigma(3) value of SC specimens was 1.43 MPa, whereas that of PF specimens was 3.09 MPa. In addition, coordination between the lateral and axial deformations of the PF specimens during compression promoted the formation of a bearing structure that can adapt to deformation. This structure is crucial for the safe operation of coal mines.