When is a geological engineer required?
A geological engineer is required for new construction, for deep excavation projects, for full foundation replacements, hillside structures, or where there is a known soils behavior like differential settlement causing an existing structure to have sub-optimal performance. It is also helpful to have them one designing retaining walls starting at around 6’ tall, and essential if they’re 10’+ tall.

What role does a geological engineer play?
A geological engineering firm provides information about how a structure will engage a soils threshold and what long term, earth-based risks should be considered during design of that structure.

They will drill borings at your site and physically pull out samples of the soil layers below your proposed project. They perform a range of tests and generate a Soils Report that carries technical information and history about the subsurface conditions with a summary of how they expect the proposed project to perform on a long-term timespan.

They make recommendations for different foundation systems (shallow footings, mat slabs, pier and grade beams, etc) with some design information pertinent to those systems. If the structural engineer is Tiger Woods, the geological engineer is his caddie. 

You usually want to choose a local geological engineering firm with more experience because they’ve probably worked on a site near yours and may understand the neighborhood soils conditions before drilling borings. 

When do they get involved in the project?
If you know you need a geological engineer on your project, start the process immediately. Their work can occur parallel to but independent of the architectural/structural path. They need to know the scope of work in broad strokes (Vertical addition? Horizontal addition? Full foundation replacement? Excavation?) but won’t need exact linework to perform the bulk of their work. 

As will be mentioned in the D-REVIEW section, it is mandatory that the geological engineer review and approve structural drawings, prior to submitting to the building municipality. During construction, they’ll also have an on-site presence to confirm that the exposed soils conditions match their soils report assessment.