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Construction & Contractors/swimming pool and bedrock


We want to build a home in a new community. The long range plan is to add an inground pool. Today we were walking several lots to make a determination on best fit for our future home and pool. The building supervisor mentioned the large rocks they encountered while prepping the nearby lots for home construction. Who would I contact to get an analysis done of the lot as to its suitability for a swimming pool before putting nonrefundable money down in this community?

Unfortunately no engineer or geologist has X-ray vision so in order to give you specific information some actual subsurface testing, in the form of drilling or test pits, would be required.  That is the best answer, and depending on how much the down payment is, it may be cost-effective if for no other reason than if you want to build a pool you will save money in the long run if you do this in a way the avoids a later geotechnical exploration program.  

There are usually local earthmoving guys with a backhoe and a dump truck who can come onto a site for less than $150/hr and do test pits, then fill them back in.  Test pits for pools will be in the 8-10 ft depth range so you'll need a backhoe with an extendable digging bucket.  If the access isn't too bad you can get a site-specific answer for around $1,000.  While you are at it, take good flash pictures of the trench sidewalls (never enter an unshored trench in soil) with a measuring tape in the photos for depth, and collect canvas bags of dirt (50 lb every 3 ft of depth).  You can give the dirt and photos to your pool contractor and I bet he can design you the pool without having to hire a geotechnical engineer to do what amounts to the same thing all over again.  If you run into backhoe refusal at less than pool depth (less than 6-8 ft or so), well, there's your answer.

The first thing I would do, though, is look around.  See any boulders at the surface?  is bedrock shallow in the vicinity?  Then, find out who the earthmoving contractor was for the work the building supervisor was referring to, and contact their Owner, foreman or superintendent (whoever would know) and ask how much rock they found, what sizes, and how much of a problem it was for them.  You might also ask who did the geotechnical investigation for the nearby lots and ask to talk with the geotechnical tech who was on site doing construction surveillance.  If there was no construction surveillance on the neighboring lots, say for the subsurface construction of utilities and general site grading, that will tell you something about what you are getting into.

Failing that, you can call around to local geotechnical firms with experience in the local area and ask questions, but you won't get the site specific info that I think you are looking for.

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Robert Cummings, P.E.


I can answer questions related to rock blasting, rock and soil excavation (such as tunnels and highway cuts), stability of such excavations, and foundations in rock and soil. I can also answer questions related to geology and mining.


30+ years as a geotechnical engineer and minerals engineer. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for mining and heavy construction.

Society of Mining Engineers, Deep Foundations Institute, Association of Engineering Geologists, and International Society of Explosives Engineers.

Mining Engineering, AEG Bulletin.

BS and MS Geological Engineering

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