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Question
I want to install an in-ground pool  however when my pool contractor started to dig he hit rock.  He now suggested using a ram hoe to dig the hole, at a rate of $3,000 a day.  I live just outside of Nashville, Tenn where I am told my property has blue slate limestone and I will never be able to have an in-ground pool.  I do have a home with a full basement and I was told that they blasted for that, however blasting is no longer allowed in my area.  Any suggestions would be helpful.
Thank you
Cindy

Answer
Unfortunately if you have hit hard rock there is going to be a cost escalation.  

$3,000/day for using a hoe-ram is a little bit steep but not totally out of range.  It depends on the capacity of the hoe-ram.  If it's something close to an energy rating of 10,000 ft-lb then it's not too bad because he will probably be able to make some production.  If it's a 3,000 ft-lb machine it could take a while in which case it's not a good deal.  Ideally you would negotiate a cost per cubic yard, because the daily rate makes you susceptible to his rate of production, which depends on the machine and how he uses it just as much as it does the site conditions.  If he refuses, then try to get him to include excavation and haul-away in his hoe-ram rate.  When using a hoe-ram you eventually accumulate a lot of broken rock and have to switch to a bucket to load it out so that you can hoe-ram again.  Otherwise, tell him you are giving up and then seek out a more reasonable earthwork contractor to dig your hole.

You can hoe-ram most rock, the only thing is time and cost.  When people say you can't get through that limestone they were probably using too light a machine, or one run by someone who either was not real experienced or didn't exercise all his options.  Hoe-ram productivity can be improved by pre-drilling the rock, but that will add to the cost.  If the limestone is drilled with, say 3 inch holes on 2 ft centers, it will make the hoe-ram production go much faster.  I have seen some very massive granite excavated with a hoe-ram by pre-drilling.

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Robert Cummings, P.E.

Expertise

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.

Experience

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.

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

Publications
Mining Engineering, AEG Bulletin.

Education/Credentials
BS and MS Geological Engineering

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