PSI - Issue 84

Marco Barla et al. / Procedia Structural Integrity 84 (2026) 441–448

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and excavation sequencing defined in the project technical reports: each construction sub-phase was modelled and for each phase, the maximum admissible ground load induced by construction equipment was evaluated. This load corresponds to the maximum value that does not trigger instability, i.e., does not result in safety factors lower than unity. As shown in Fig. 6, the numerical analyses indicated that individual stabilization measures could only produce limited increases in the slope safety factor; however, their combined effect results in a substantial improvement in overall stability, achieving final safety factor (FS) values consistent with acceptable safety margins. Moreover, the influence of the soil saturation level can be observed while comparing the results for the same scenario in different water table conditions, e.g.: scenarios 5a (high water table condition) and 5b (low water table condition). The construction of the motorway and the original stabilization works significantly reduced slope stability, a condition further aggravated by long-term structural degradation, bringing the system close to limit equilibrium. The emergency measures then implemented on site led to moderate but cumulative improvements, resulting in FS values of approximately 1.2 (high water table) and 1.42 (low water table). While these values indicated a condition of overall stability, they still reflected a sensitivity to intense rainfall events. This interpretation is consistent with monitoring data collected since November 2024, which show no significant displacements under relatively dry conditions. Finally, the completion of the planned interventions produces a marked increase in stability, with FS values reaching approximately 1.58 and 1.94 under high and low groundwater conditions, respectively. These improvements are attributed to a reduction in slope inclination, restoration of anchoring efficiency, and enhanced groundwater drainage. Consequently, the proposed stabilization works were considered capable of ensuring adequate long-term slope stability, provided they are implemented in accordance with the modelling assumptions and properly maintained over time. The detailed analyses of dismantling operations for the anchored slabs and excavation of the overlying slope sectors produced the maximum admissible loads that construction equipment may apply while maintaining adequate stability conditions. Exceeding these thresholds would result in insufficient safety factors and potential instability. These results can be intended as specifications for the execution phase of the works.

Fig. 6. Results of numerical analyses: evolution of the factor of safety and of the critical potential failure mechanism across the analyzed scenarios. HW = high water table condition; LW = low water table condition.