More often than not, decks are built on or near descending slopes. This requires soils investigation report for a deck and pool structures. In addition, you may need a topographic plan which shows the slope geometry and elevations as well as trees and brushes. Usually the depth of such borings are 10 ft to 12 ft. The soils report will discuss soils stratigraphy, shear strength of soils and seismic design. In addition, it will discuss stability of any slopes, foundation design parameters and setback requirements for drilled piers.
A pool soils report is similar. When you construct a pool, a 5 ft to 8 ft of soil is removed which typically weighs 120 pounds per cubic foot of volume. That is later replaced by pool water which weighs approx. 62 pounds per cubic foot of volume. So in essence, we are unloading the soil. That is we are removing 120 pounds and only bringing back 62 pounds. Therefore, there is no concern for settlement when it comes too pols and spas.