Excavation in Rock
Excavation in Rock
(OP)
"metavolcanic rock with occasional fracured zones"
Spread footings are to be embedded in the rock. I haven't seen this before, how are excavations in rock done?
Is it practicable to bore holes in rock, for end bearing caissons?
Thanks.
Spread footings are to be embedded in the rock. I haven't seen this before, how are excavations in rock done?
Is it practicable to bore holes in rock, for end bearing caissons?
Thanks.





RE: Excavation in Rock
Rock-socketed caissons are relatively common. Many times the side friction develops before end bearing.
RE: Excavation in Rock
The caisson sounds interesting, that was more or less a passing thought--I was thinking end bearing, and then extending it all the way up as a column. Good stuff.
RE: Excavation in Rock
RE: Excavation in Rock
I was more or less writing in this forum, because I thought someone might have some experiences (things that went wrong?) or web links to the actual construction equipment and projects, pictures are worth a thousand words. There isn't much information on rock excavations in my engineering references DOTs, USACE, Bowles, Das, etc... Almost seems like I should be looking at mining or oil drilling material references?
RE: Excavation in Rock
You may wish to consult this publication:
US Army Corps of Engineers, ROCK FOUNDATIONS, EM 1110-1-2908
link: http://w
Also, http://www.rocscience.com/hoek/Hoek.asp
RE: Excavation in Rock
Another thing to consider is transfer of lateral loads and moments to the rock. Based on these loads, a shallow foundation may not fit the bill.
In any case, your geotechnical engineer/consultant should have recommended a foundation type based on the loads and given construction or design recommendations related to the geometry and method of excavation for the rock.
Scour concerns indicate that this is a bridge or raised structure of some sort. However, the questions that you are asking lead me to suspect that you don't have a geotechnical engineer/consultant on the project. If not, this forum is ill-equipped to give you the kind of specific advice you need, and you had better engage a geotech sooner rather than later.
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Excavation in Rock
RE: Excavation in Rock
Generaly the rock must be over broken, that is the blast zone extends 2-3 feet below the bottom of the footing level. This rock can be cleaned out and filled with concrete or left and the footing built o top of i. This would depend in your structures needs. Generally the rock is blasted prior to removing the overburden as the over burden provides confining pressure, sound dampining and prevention of fly rock. If the surface is fractured, and that is a concern, it generally remidied by slush grouting.
Proerly designed and executed, blasting is generally the most effective way to remove rock.
RE: Excavation in Rock
Most footings and foundations in New York City have to be blasted. Other structures and buildings are inches away at times.
The key is to find a good Geotech firm familiar with blasting. We use GZA, they are excellent. Also, find a blasting contractor that specilizes in this type of work.
All of our research shows that rock hammers open up all of the seams in the rock. If you hammer first, and then have to blast, it is much harder to break the rock and is not as safe due to loss of energy confinement.
I find that people who say "no blasting" do not have much experiance in this area or have had a few bad experiances. This normally happens when going with the lowest bidder.
Remember that vibration damage criteria are based on wave frequency. When blasting real close, the frequencies are in the thousands, so normal limits do not apply.
Frank Lucca M.I.Exp.E.
www.terradinamica.com
RE: Excavation in Rock
I think you all would have liked my response to djonville, but it was deleted from the thread awful fast. I think this is about my 10th handle.
RE: Excavation in Rock
http://www.geoengineer.org/
RE: Excavation in Rock