This study uses ordinary Portland–sulfate–silicate composite cement as the matrix and investigates the effects of water–cement ratio, HPMC dosage, and PCS dosage on the performance of specialized grouting materials for subway structure repair during operation through single-factor experiments and orthogonal experiments. Multifactorial variance analysis was employed to quantitatively evaluate the sensitivity of each factor and their interactions to slurry flowability, setting time, anti-dispersibility, and compressive strength. The results show that the water–cement ratio is the most critical factor affecting the performance of the grouting material, with extremely significant impacts on all performance indicators; HPMC dosage significantly affects flowability, setting time, and anti-dispersibility; PCS dosage primarily influences 2 h compressive strength; the interaction between water–cement ratio and HPMC dosage has a significant impact on anti-dispersibility. Principal component analysis revealed the trade-off relationship between flowability, setting time, and strength. The study established a sensitivity ranking for the performance of specialized grouting materials: water–cement ratio > HPMC dosage > PCS dosage > interaction, providing a theoretical basis and methodological reference for the formulation optimization of specialized grouting materials for subway structure repair during operation.

Emergency leakage repair in subway shield tunnels requires a technique to encapsulate highly reactive sodium silicate that is simple and field-deployable, yet no mature solution currently exists. The challenge lies in sodium silicate’s strong alkalinity and high osmotic pressure, both of which corrode most shell materials. This study proposes a “composite core” concept—functionally re-engineering the core rather than relying on complex shell chemistries. Using hydroxypropyl methylcellulose (HPMC) as the key material, temperature-triggered microcapsules with a nano-silica shell and sodium silicate–HPMC core were fabricated via low-temperature shear. Low temperature (10–15 °C) is critical: it suppresses side reactions and tunes viscosity to 2000–5000 cP, facilitating shear dispersion. The resulting microcapsules exhibit well-defined morphology with a dense shell. Temperature response tests reveal distinct release onset at ~30 °C (HPMC’s LCST): HPMC chain collapse generates internal stress that ruptures the shell, driving progressive sodium silicate release. Alkaline resistance tests confirm that intact microcapsules remain stable in high-pH environments (pH ≈ 13.2) for 30 min. This work validates the “composite core” concept and provides a simple, field-operable route to fabricate temperature-triggered microcapsules for emergency repair applications.

To overcome the performance shortcomings of disconnectable couplings in foundation pit support systems, a threaded-sleeve-type disconnectable coupling was designed and developed in this study. An axial loading test was performed to investigate the bearing capacity of the coupling. Its yield load, initial compression stiffness, load–displacement curve, stress distribution, and failure mode were determined. A finite element analysis parametric study was performed and formulae for calculating the yield load and compressive stiffness proposed. The following conclusions were drawn from the results: (1) The coupling has good bearing performance. The yield load is 10,509.96 kN, the ultimate load is 12,980.2 kN, and the initial compression stiffness is 4215.17 kN·mm⁻¹. The failure of the coupling is characterized by an outward bulging of the nut part and shearing of the thread. (2) The coupling has good ductility. Strain concentration occurs at the screw. (3) The bearing capacity of the coupling is positively correlated with the outer diameter of the nut, nut thickness, and screw thickness and linearly inversely related to the elongation and screw pitch. (4) The established calculation formulae can accurately estimate the yield load and initial compression stiffness of the coupling.