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RE: Over-Engineering

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I think we're being rather bold in believing the human race will still
be around in 10,000 years?  (Notice the question mark).

I studied those balancing rocks in (New Mexico?).  They were essentially
made of sandstone and the wind would erode only the sandstone substrate
that was not under stress (triaxial load test stuff, remember?)  So the
sandstone directly under the center of gravity of rock was the most
stressed and least eroded, and the surrounding, unsupporting and
unstressed segments of rock eroded away, leaving just the core balancing
the big rock above.

-----Original Message-----
From: David Merrick, Structural Engineer, Merrick Group
[mailto:mrkgp.se(--nospam--at)gmail.com] 
Sent: Wednesday, April 14, 2010 11:04 AM
To: SEAINT
Subject: re: Over-Engineering

http://news.discovery.com/earth/balanced-rocks-earthquak=e-hazard.html

I have had some visits with Jim Brune about 13 years ago. His precarious

rock studies are not new. The commercial interest is to find storage 
sites for nuclear waste. There might be a limit to how high seismic 
accelerations can reach in a 10,000 year event.

Dr. Brune has a personal interest in my Sierra Mountains cabin. There is

a standing precarious rock on the cliffs behind. That rock's position 
might be about 10,000 years old. Storing nuclear wast, with 10,000 year 
half life, in my back yard might make me some money and preserve the 
wilderness like setting! My real interest is in the cabin. It is a 150 
year old two story wood house with stud-less interior walls of 1x24 
vertical planks and news paper.

A precarious rock founded on hard rock soil types and with a low natural

rocking period, might be quite safe from tipping over. That is not the 
issue. When projecting our few hundred hundred years of estimated 
earthquakes into the future of  about 10,000 years, the resulting design

loads are suspiciously high. There might be a limit to how high seismic 
accelerations can reach. Energy dissipation of the soils may increase 
more than the increase of energy for a seismic event that is approaching

a 10,000 year return period. Say, in a 10,000 year event, the landscape 
might move over 20 feet. A balanced precarious rock may prove that it 
did it more gently than expected.

The rock, pictured in the article referenced, is unusual. Dr. Brune's 
studies are of more stable rocks that are of harder composition and not 
as susceptible to wind erosion. I found his test methods interesting. I 
like that he hauled his electronics with horses or mules and camped on 
the way. They attached motion sensors and pushed over large precarious 
rocks a slight amount and released them to create motion.  His first 
estimates were mathematically modeled by hand. The equations are too 
long, increasing the chance of error. I hope he has switch to computer 
modeling of a solid mass with non-linear links to the base. I was 
interested because of my experience with some large concrete blocks used

for a Livermore lab building, rocking but with vertical post-tensioned 
tendons.

I heard President Obama has canceled the nuclear storage project in the 
Yucca Mountain, Eureka County, Nevada. I have not heard what issues have

not been resolved. Is a 10,000 year seismic event part of it?

David B. Merrick, SE
Sacramento, CA

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