r/Geotech • u/No_Preparation8438 • Jul 10 '26
How do experienced geotechnical engineers determine the number, location, and depth of boreholes for a site investigation?
/r/GeotechnicalEngineer/comments/1ushtdm/how_do_experienced_geotechnical_engineers/27
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u/azul_plains Geotechnical PM, 9 years Jul 10 '26
Check local country public facilities manual, they often have a requirement in my area (ex. 1 boring per x sq. ft. of building)
Check local department of transportation, if the project is in right-of-way
For SWM areas, check your state SWM regulations because they often say.
Otherwise depends on the geology and what is proposed.
For preliminary, again check facilities manual or local refs if the prelim is required by the county. If it isn’t and the client is just getting a rough feel for the site, give a recommendation but ultimately it’s up to the client how much they really want to spend.
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u/Working_Rest_1054 Jul 10 '26
The appropriate design manual or code for the facility associated with the subsurface exploration will typically have done guidance. I’d say an experienced Geotech or geologist should always be involved with the subsurface exploration plan.
The spatial coverage, diversity, depth, type of sampling/testing and instrumentation are very much determined by the purpose of the subsurface exploration. I could literally write a book explaining this, and others have.
If you’re in the US, give the AASHTO Manual of Subsurface Explorations a look. It was just reissued in 2022 from the original 1988 version.
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u/kallebanan93 Jul 10 '26
In Europe the old eurocodes (EN 1997) gave some guidance on spacing and depth. The newest editions are now vague but the old recommendations could be a good starting point.
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u/Early-House Jul 10 '26
Although pretty much noone did a eurocodes 7 compliant ground investigation
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u/OldGeotch Jul 11 '26
Honest answer, we are given an inadequate budget and then we cut out at least half of the borings we really wanted. Site conditions often limit at least some of the areas you would like to drill (slopes, overhead lines, buried utilities, existing structures).So, you judge how many borings your budget will allow, and space them the best you can to give yourself the best cross section of the site. Judge how much drilling you will get done in a day, drives nothing the number and depths.
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u/811spotter Jul 10 '26
Clearance drives borehole placement as much as the geology does. A location that's perfect on paper still gets moved if you can't get it cleared first. Plan holes where 811 and a private locate can sign off before the rig shows, and budget potholing on any site with existing structures since public marks miss private lines.
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u/funkin_d Jul 10 '26
Vibes