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Re: GEOTECH: Requirements for Rock

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Bill-
That's a pretty broad question but I'll give it a shot with some general comments.
 
You are looking at strength parameters of course, depth of weathering, effect of water, depth to water, type of rock, etc. for vertical loads. 
 
Excavation parameters become important because they will determine if you can use machine excavation or will have to resort to blasting or hydraulic fracturing. This can have a large effect on project cost. 
 
Where rock becomes more challenging is if you have excavations or tunnel type structures. Then, fracture patterns (spacing, orientation of fractures and bedding planes) can result in enormous differences in pressure exerted (from none to very large).  Expansivity of the rock is important with tunnels because "squeezing ground" can be difficult to handle. Faults and bedding planes are important to locate as are shear zones. 
 
Here in California, there is a heavy emphasis on the rock constituents.  Common issues are the presence of asbestos type fibers (chrysotile) (which are released with excavation and compaction and create both worker safety and public safety issues), heavy metals may require expensive hazardous waste disposal techniques.
 
Permeability can become an issue if you are below the ground water levels.
 
Common excavation techniques may include machine excavation using crawler tractors, roadheaders, backhoes, shovel excavators, draglines, etc. or blasting (which can open several cans of worms if nearby residents are present) or hydraulic fracturing (more expensive and slower than blasting but without some of the vibration issues).
 
This is a start but it would be easier to answer your question if we knew what type of facility you were contemplating.
 
Regards,
Bill Cain, S.E.
Berkeley CA
 
 
-----Original Message-----
From: Bill Polhemus <bill(--nospam--at)polhemus.cc>
To: seaint(--nospam--at)seaint.org
Sent: Mon, 15 Aug 2005 16:06:57 -0500 (CDT)
Subject: GEOTECH: Requirements for Rock

Just don't know much about rock since almost all my engineering life has
been spent with construction on the Gulf Coast.

But what is typically required in field investigation, testing and
reporting regarding rock by the Geotechnical engineer?


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