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In the process of coal mining, when the mine roadways pass through water rich and structurally developed strata, it is easy to expose water channels and cause water inrush hazards. In order to improve the working performance of cement-based grouting materials in water rich environments, this paper used polyacrylamide (PAM) and water glass as additives to modify ordinary Portland cement. Also, using the molecular dynamics simulation method, an interface model of cement and admixture mixed products was constructed, and the number of interlayer water molecules was adjusted to simulate the different water content environments of hydration products. Furthermore, various microscopic characterization experiments were used to verify the simulation results. The results show that the PAM water glass structure exhibits a good hydrophilicity, and the strong hydrophilicity enables its binding with C–S–H to have strong adhesion, which can better adapt to water rich environments. The variation of debonding energy at the interface of cement − water − PAM − water glass exhibits irregularity. At a moisture content of 6%, the debonding energy at the interface of cement − water − PAM − water glass reaches the maximum critical point of 37 465.715 mJ/m2. At higher moisture contents, water molecules penetrate the pore structure and undergo deeper hydration reactions with the interior of the material, enhancing interface stability. The diffraction peaks in the XRD pattern are consistent with the predicted forms of C–S–H and PAM water glass in the computational simulation, confirming that polyacrylamide and water glass will react with Ca2+ and Si4+ generated during the cement hydration process. The SEM images show that there are a large number of hydration particles and micropores, including needle shaped and spherical crystals, at the interface between cement polyacrylamide and water glass. These hydration particles may be hydration products that enhance the interfacial adhesion formed by polyacrylamide and water glass participating in the cement hydration process. The presence of micropores is the main reason for the changes in interaction energy and debonding work observed in the simulation. Through molecular dynamics simulation and experimental results, it can be proved that the floc structure formed by PAM and water glass has good hydrophilicity. Compared with the traditional cement grouting materials, the floc structure in the PAM-water glass modified cement slurry has stronger adhesion properties with the cement hydration products C–S–H, which effectively locks the water between the layers of hydration products, thus improving the stability of the slurry in the water-rich environment.

The micropore structure of porous media (such as natural rocks and man-made materials) is very complex and has strong micro heterogeneity, and pore structure is a critical parameter to estimate the rock quality. However, the pore structure characterization of rocks under load is not studied well. In this paper, sandstone specimens were preloaded to six different stress levels, and then the pore structure of rock was characterized by SEM and NMR, respectively. The results show the following: (1) The damage in sandstone increases with predefined stress, and the rate significantly increases over 0.8 uniaxial compressive strength (UCS). (2) There is a critical value in the process of rock damage (0.8 UCS), and when it is less than this critical value, the microstructure in the rock is mainly composed of pores and micro-cracks, and the length is generally less than 5 μm; when it exceeds the critical value, there are obvious cracks or even groups of cracks inside the rock. (3) The changes in porosity can be divided into three stages, showing a “√” shape tendency. (4) The pore structure can be visually presented using NMR and SEM, and the distribution mode of the pores changes from separated points to concentrated patches to finally interconnected networks of pores with an increase in the predefined stress. Overall, NMR provides a new method for characterizing rock damage and studying rock microstructure.