What type of foundation is typically best for unstable soils?

A floating foundation is particularly suitable for unstable soils due to its design, which helps to counteract the settlement issues that often arise in such conditions. This type of foundation is built to displace an amount of soil equal to the weight of the structure it supports, essentially "floating" on the soil. This minimizes the load on the underlying soil and reduces differential settlement, making it effective in areas where soil stability is a concern.

In contrast, other foundation types such as spread footings, shallow foundations, and deep foundations may not address the issues presented by unstable soils as effectively. Spread footings distribute the load over a larger area but may not prevent excessive settlement in loose or unstable layers. Shallow foundations sit close to the surface and are generally best suited for stable conditions. Deep foundations, while capable of reaching more stable soil layers, can be more complex and expensive and may still be susceptible to issues like lateral movement if the upper soil layers are particularly unstable.