Recent rapid urbanization has led to an increase in tunnel construction, escalating the prevalence of ground collapses. Ground collapses, characterized by large deformation and strain-softening, pose a significant challenge for classical numerical theories and simulation methods. Consequently, a numerical framework combining the material point method (MPM) and strain-softening Drucker–Prager plasticity is introduced in this study to more accurately describe the evolution process and failure mechanism of the subgrade during tunnel excavation. The proposed numerical framework was validated against an analytic solution employing a typical ‘dry bottom’ dam model with solid non-linearity and large deformation; some of the results are also compared with those of the SPH method and centrifugal modeling tests to verify the validity of the MPM method in this paper. The validated model was used in this study to conduct a comprehensive analysis of surface instability and ground collapse under varying soil conditions. This included factors such as strata thickness, cohesion, internal friction angle, and a quantitative description of the development of longitudinal subsidence of the surface. The aim was to clarify deformation responses, failure patterns, and excavation mechanisms, providing insights for underground tunneling practices.

Traditional disposal methods such as landfilling and land reclamation are insufficient to mitigate the environmental impact of construction spoil, making non-sintered blocks a promising approach for resource utilization. This study investigates the production and performance of steel slag soil blocks as an alternative to conventional cement-based materials for non-sintered blocks. The optimal manufacturing parameters were identified as a sodium silicate solution with 6% Na₂O, 30% steel slag content, a liquid/solid ratio of 0.18, and a forming pressure of 10 MPa, achieving a peak compressive strength of 14.46 MPa. Further, the synergistic combination of alkali activation and carbonation enhanced compressive strength to 17.4 MPa, attributed to the development of a compact microstructure characterized by a honeycomb-like C-(A)-S-H gel and well-crystallized, triangular-shaped aragonite. However, durability tests under freeze-thaw and wet-dry cycles revealed that carbonation can detrimentally affect performance. The transformation of C-(A)-S-H gel into calcium carbonate, with relatively weaker cementitious properties, led to internal cracking and surface detachment. Micro-CT analysis confirmed ring-like patterns under freeze-thaw conditions and diagonal cracks during wet-dry cycling, whereas reference blocks incorporating 30% ordinary Portland cement maintained superior compactness with no cracks. These findings suggest that although the alkali activation and carbonation process enhances early strength, further optimization is necessary to improve long-term durability before broader application can be recommended.

Iron-based shape memory alloys (Fe-SMAs) have considerable potential for the active strengthening of concrete structures, yet convenient externally applicable non-destructive methods for identifying local fatigue damage under cyclic loading remain limited. To investigate the weak magnetic response of notched Fe-SMA and its correspondence with local damage evolution, static tensile tests and constant-amplitude fatigue tests were conducted on Fe-SMA specimens with a semi-circular notch. Weak magnetic signals were continuously monitored at a fixed point throughout loading, and surface magnetic-field scanning was performed after fracture. Under static loading, the magnetic signal evolved consistently with the deformation response. Under fatigue loading, the fixed-point magnetic signal exhibited a clear three-stage evolution corresponding to the development of residual deformation. Compared with deformation hysteresis loops, magnetic hysteresis loops contained richer information on local damage evolution. After fracture, abrupt changes in the scanned magnetic field coincided with the actual fracture location, and the magnetic anomaly gradually attenuated as the scanning path moved away from the notch. These results indicate that weak magnetic signals can effectively characterise the evolution of local fatigue damage in notched Fe-SMA, with the normal magnetic component showing greater sensitivity to damage localisation and state assessment.