A geotechnical report is required by IBC Section 1803.2, and may only be exempted as follows: "The building official shall be permitted to waive the requirement for a geotechnical investigation where satisfactory data from adjacent areas is available that demonstrates an investigation is not necessary for any of the conditions in Sections 1803.5.1 through 1803.5.6 and Sections 1803.5.10 and 1803.5.11." Note that the sections specified for satisfactory do not deal with presumptive bearing capacity of soils (see 1806.2), but with questionable or expansive soils, groundwater, slope setbacks, and seismic design in SDC C-F.
I say the above, because we get a number of engineers who argue against needing a geo report because they believe the only pertinent information is the load-bearing capacity of the soil.
That said, to answer your question.... Geotechnical reports present a set of recommendations. Geo professionals refer to them as recommendations, because the geo report is often (or at least should be) part of a feasibility study. Unfortunately, it is all too often an afterthought, and is done post structural design. Additionally, geo professionals pride themselves in being consultants, not designers (a subtle attempt at limiting liability concerns).
The answer though is that once the structural engineer, as required by Sec. 1803.2, uses the geotechnical recommendations in his/her design, then the report is no longer a set of recommendations, but becomes a referenced set of design assumptions. If the design assumptions change, then further design clarification is required. I.E. - if the geotechnical report is not followed, they get a correction letter indicating that both the structural and geotechnical engineer must approve the change.
In summary, they are recommendations right up until the structural engineer bases his/her design on those recommendations.
