The usual approach for settlement analyses is to first estimate the amount of earthquake-induced total settlement (ρmax) of the foundation. Because of variable soil conditions and structural loads, the earthquake-induced settlement  is rarely uniform. A common assumption is that the maximum differential settlement Δ of the foundation will be equal to 50 to 75 percent of ρmax (i.e., 0.5 ρmax ≤ Δ ≤ 0.75 ρmax ). If the anticipated total settlement ρmax and/or the maximum differential settlement are deemed to be unacceptable, then remedial measures are needed. One alternative is soil improvement, which will be discussed later.

Instead of soil improvement, the foundation can be designed to resist the anticipated soil movement caused by the earthquake. For example, mat foundations or posttensioned slabs may enable the building to remain intact, even with substantial movements. Another option is a deep foundation system that transfers the structural loads to adequate bearing material in order to bypass a compressible or liquefiable soil layer. A third option is to construct a floating foundation, which is a special type of deep foundation where the weight of the structure is balanced by the removal of soil and construction of an underground basement. A floating foundation could help reduce the amount of rocking settlement caused by the earthquake.

1 Shallow Foundations
2 Deep Foundations

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