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RE: Hillside foundation question.

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Robert, 

I have been out of town so I am a little late in responding to your
question. 

I had somewhat of a similar situation happen to me, And if you do not
take care of this NOW!!!, it will cost you an arm and a leg in the long
run and you have a high potential for cost over runs.

You have a classic case of overbuilding. If you are on decomposed
bedrock there is not one reason why you need all the stuff that your
geologist is recommending unless your house was poorly designed. 

First find another geologist or double check his work. Read through the
first 16 pages and it will give you a wealth of information about your
lot and its geology. 

Talk with a geologist like an interview. The first 3 geologists that I
interviewed were trying to push caissons and grade beams and all kinds
of overbuilding on me. Why do you need caissons and Grade beams when
your house is on Solid rock? You Shouldn't. Once again I have not seen
the design of your house but it nay be cheaper to change your house
design than to do all of the things that you are speaking about in the
letter.

I am assuming that your bedrock is rated at around 5000psf. If he put
1000psf make him check his calcs OR find a new geologist immediately.
That means he is going way to conservative and he not thinking of your
pocket book. Do not be scared to argue with the geologist otherwise he
will not have any respect for you.

Your structural is making recommendations based on what the geologists
had recommended so do not blame your structural. Everything starts with
the geologists if your geologist did not do a good job you are in for a
long project.

Now I have not seen your plan but I do not take the word of the first
recommendation I went through 5 Geologists before I found one that would
listen to me. Then I went thru 3 civils and many structurals before I
got a hillside project rolling.

It took 9 months for my report to get through the city of Los Angeles
but they approved it on 3 ft wide Spread footings. 

I just drove 14 hrs from Colorado without stopping so I have to stop
writing now I don't feel so good... Bye I will have to finish this
later.

Kevin
http://WelcomeLending.com







-----Original Message-----
From: junk01(--nospam--at)sgds.com [mailto:junk01(--nospam--at)sgds.com] 
Sent: Thursday, June 16, 2005 3:23 PM
To: seaint(--nospam--at)seaint.org
Subject: Hillside foundation question.

Let me first say that I am not a structural engineer and I apologize for
the
length of this post. I am a property owner that is trying to build a
hillside home, in Southern California, without "breaking the bank". I
came
across this list as I was researching hillside foundations and have been
following it for a few days and reading through some of the archives.
You
have a great wealth of information and expertise here. Although I am
capable
of learning and doing many things, I am fully aware that a hillside
foundation design is well outside of my expertise. Given enough time and
training (and not to mention the legal ability to stamp my plans) I
would
love to engineer my own house, but that's not going to happen (at least
not
in a timely manner and without ending up divorced). 

I have a couple of questions regarding hillside foundations. I designed
this
house myself and tried to simplify the design to make it as economical
as
possible (like aligning upper and lower story walls and windows,
providing
plenty of shear wall space, etc). I have done a lot of research in
various
areas and am trying to work my way through a very steep learning curve.
After interviewing a few recommended structural engineers, I hired one
and
he has been working on the foundation design (I am self-contracting the
construction). We have a great working relationship and he has made some
good additional recommendations to cut costs. I want to make sure I do
not
offend him by questioning his design.

Where I am stuck is on the basic design of the foundation. The engineer
has
come up with a system composing of 24" grade beams and 10-12 24"
friction
piles located at the corners and main interior walls. I would not even
question this design if it were not for a) that many piles sounds like
too
many, and b) Arthur Levin's book "Hillside Building: Design and
Construction" implies that many engineers over design hillside
foundations
and use too many friction piles. I have read through Levin's book
numerous
times over the last few years in anticipation of building this house.
Specifically, Levin says "Grade beams can span and cantilever farther
than
most engineers expect". I realize the book is over simplified and hardly
touches on the actual mathematical engineering of a design, but with the
increased costs of steel and concrete, I am trying to be as efficient as
possible.

What I am looking for are some generalizations regarding grade beam
spans
and the number of friction piles. I realize that no one here can know
enough
of the details of my project to make any firm recommendations. In
Levin's
book he talks of designing 30'x50' hillside buildings with 4 piles by
increasing the size of the grade beams and cantilevering them. He also
talks
about a design that spec'd 24 piles, but only needed six. I understand
these
are general examples not relating to the specifics of my design. As a
lay
person, am I wrong to second guess my engineer's preliminary design? I
know
I am only basing my opinion on Levin's book, which may be totally
outdated
(second edition, 1999). Perhaps codes have changed significantly since
then.
I only want to end up with reasonable foundation costs so I can afford
to
build the rest of the house. I could easily live with six friction
piles.

Project details:
2 story hillside home composed of two appx. 30'x20' sections (the second
one
angled and intersecting the first one by about 25 degrees to match the
angle
of the hillside). Floor area about 1300 sq ft per floor. The building
pad is
relatively flat (+/- 4'). No special loads except for some cantilevered
decks on the downhill side. (The engineer is recommending a concrete
floor
on the first level with a cantilevered deck to help mitigate any fire
hazard.) 

Hillside height 135', average slope angle 45 degrees.
Friction piles along the top of the hill will need to be 40' deep to
meet
the H/3 requirements (40' to daylight). The back row of piles would be
about
20' deep since they are set back about 20' from the slope edge. The
engineer
said that without the H/3 requirement the front piles would be about 32'
deep. 

Soils Report:
Soil consists of competent, granitic bedrock (decomposed granite)
starting
at about 1.5' in depth and is considered suitable for building.
Seismic zone: 4, Soil profile type: Sc
Recommended to use friction piles, minimum 24" diameter. Minimum 10'
into
bedrock and minimum of H/3 (not to exceed 40')
Skin friction of piles: 700psf

Since I have to have these 40' deep friction piles, it seems like I
should
get something back for that additional depth. Am I wrong for thinking
that a
larger, more rigid, grade beam design with fewer friction piles, might
be a
more efficient way to go, rather than designing a simpler plan of a
friction
pile at every major wall? The current design has the piles about 15'
apart.
Is it horribly complex to design a foundation where the piles do not
necessarily line up with the building shear walls? How did Levin design
30'x50' foundations with only 4 piles? He says "Use 4 piles wherever
possible. Grade beams are relatively easy to construct, can be increased
in
depth to span farther, and can be cantilevered a considerable distance".


I'm sorry this is so long, but would appreciate any input I can get. If
this
is the wrong place to ask a question like this then just say so and I
will
leave you all alone.  :)

Robert


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