Which method is NOT commonly used to improve bearing capacity?

Adding salt to soil is not a commonly used method to improve the bearing capacity of soil. The primary purpose of introducing salt into soil generally relates to soil stabilization primarily in specific contexts, such as adjusting moisture retention or reducing plasticity in clay soils, rather than enhancing load-bearing capacity directly.

In contrast, deepening the footing, compaction, and densification all serve to improve the soil's ability to support structures. Deepening the footing effectively increases the area in contact with the soil, redistributing loads and often leading to increased stability. Compaction increases the density of the soil particles, reducing voids and enhancing the resistance to settlement and failure under load. Densification improves the soil by rearranging its particles into a denser configuration, thereby increasing its shear strength and overall bearing capacity.

Overall, the use of salt does not typically contribute to these objectives and may even lead to undesirable effects, making it unsuitable for improving bearing capacity in most scenarios.