(b) Figure 2 – Plan view of (a) Case One and (b) Case Two for the three spacings. In the first set of simulations, both shafts were left open, and their center‑to‑center distances were varied at 6, 10, and 14 meters (Table 2).The behavior of Shaft 1 under these configurations was evaluated against a control case where it was the only shaft excavated. In the second set, Shaft 1 was filled after excavation while Shaft 2 remained empty, using the same spacing values. The outcomes were then compared with a scenario in which Shaft 1 was the sole shaft to be excavated and backfilled. Assessing the contrasts between these two modeling setups across all spacing intervals made it possible to clearly determine how the spacings alters shaft interaction and overall stability. Table 2 – Test case configuration by name, spacing, and case labels # Name Spacing (m) Case One Case Two 1 S1 6 S1-U S1-F 2 S2 10 S2-U S2-F 3 S3 14 S3-U S3-F 6 1Sh 1 shaft 1Sh-U 1Sh-F 3. RESULTS AND DISCUSSION To assess the influence of spacings, the outcomes of Case One (unfilled shafts) and Case Two (Shaft 1 backfilled) were systematically compared (Figure 3). The analysis first examined the single-shaft scenario (1Sh scenario in both Case One and Case Two), where stress–strain responses along the cut line revealed that increasing the spacings consistently lowered stress magnitudes across all parameters, including von Mises stress and the first, second, and third principal stresses. Strain values also decreased in the higher spacings condition, confirming that stability can be controlled through the spacings.
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