Behavior of Footing Resting above Dual Circular Cavities in a Rock Mass: Insights from an AFELA Study

Abstract

The current study investigated the ultimate bearing capacity (UBC) of a uniformly distributed loaded strip footing with a width, B, situated above two circular-shaped cavities in a rock mass following the generalized Hoek–Brown (GHB) failure criteria. The reduction coefficient, Rc, which evaluates the impact of the presence of dual cavities on the decrease of the UBC of a strip footing for multiple cavity configurations, was quantified through the application of adaptive finite-element limit analysis (AFELA). This study included six distinct configurations (CF-1–CF-6) based on the location relationships between two cavities (C1 and C2), with a normalized spacing between the dual cavities represented as S/B. The configurations varied based on the vertical distance between the footing base and the crest of the cavities, denoted by Z (i.e., Z1 and Z2 for cavities C1 and C2, respectively) and the normalized horizontal distance between the footing’s central vertical axis and the centers of the cavities, represented by X (i.e., X1 and X2 for C1 and C2, respectively). The effect of parameters, including Z1, Z2, S/B, X1, and X2, on the magnitude of Rc for all configurations was analyzed. The outcomes revealed that the presence of dual cavities is insignificant on UBC of footing for CF-1: Z ≥ 3.5, S/B ≥ 3; CF-2: Z ≥ 3.5, S/B ≥ 2; CF-3: Z ≥ 3, S/B ≥ 2; and CF-4: Z ≥ 3, S/B ≥ 3. Additionally, significant reduction in UBC for CF-5 and CF-6 were noted when Z2 ≥ 2.5, 4 ≤ X2 ≤ 4 and Z2 ≥ 1, S/B ≥ 6.0, respectively. The potential failure curves associated with each configuration were identified, providing insight into the foundation’s behavior in the vicinity of the dual cavities. Rock is generally a reliable foundation material, but the presence of cavities poses risks to nearby structures. Understand the impact of these cavities on the stability of foundations resting above them is crucial to ensure structural safety and minimize potential hazards. This study investigates the effect of underground cavities on foundation stability and evaluates how the depth and spacing of the cavities in relation to the foundation influence its stability. The research focuses on dual circular cavities and provides practical insights for engineers and geotechnical professionals, particularly in the case of dual unsupported parallel tunnels in rocks. The findings can be readily implemented in foundation design to enhance structural safety. Engineers can utilize the research findings to make informed decisions regarding foundation design and suitability, thereby improving structural safety. Geotechnical investigations can also apply these findings to evaluate the impact of dual cavities on the ultimate bearing capacity of foundations. By anticipating challenges and implementing appropriate design measures, the safety and stability of structures can be enhanced. Furthermore, the research contributes valuable knowledge about failure modes associated with different cavity configurations. This information supports risk assessments and aids in implementing reinforcement techniques to mitigate potential risks.