A Study on the Effect of Temperature on PAM-Improved Shield Tunneling Sandy Slurry

Polyacrylamide (PAM) is widely used to improve sandy muck in shield tunneling due to its excellent physicochemical properties. During shield excavation, the temperature of excavated soil varies with geological depth and equipment heat transfer, making it necessary to investigate the temperature effect on the performance of PAM-modified sandy muck. In this study, molecular dynamics (MD) simulations are employed to construct a (PAM, H2O)/α-SiO2 interfacial model. The microstructural evolution and interfacial interaction characteristics between PAM molecules and the α-SiO2 substrate are analyzed at the nanoscale under different temperature conditions. A structure–performance–mechanism relationship is established, forming a conceptual framework of the “configuration–interaction energy–stability” mechanism for PAM-modified sandy muck. The main findings are as follows: (1) The PAM exhibits the most stable interfacial bonding with α-SiO2 between 278 K and 318 K, primarily governed by electrostatic attraction and hydrogen-bond synergy. (2) Within this temperature range, PAM forms a dense and stable interfacial adsorption structure, whereas both thermodynamic stability and structural integrity decline outside it. (3) At 318K, the PAM/α-SiO2 system shows the most favorable hydrogen-bonding behavior, with orderly alignment of PAM and H2O molecules and optimal chain flexibility and adhesion capacity. Therefore, 318 K is the upper temperature limit reference point at which the improvement effect of PAM remains the most stable, providing theoretical guidance for temperature-controlled soil conditioning in shield tunneling.