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RE: soils pressure

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Joe,
For what it is worth, I was told that a local tunnel
under a canal, after it was built, was found to be
subject to squeezing rock.  Apparently, they had to
drill a series of vertical holes and fill them with
Bentonite in order to relieve the pressure.  Strictly
second hand information, but it appears to have some
validity due to the work that had to be done after
the tunnel was finished.
Gary



On 21 Apr 2004 at 16:25, Joe Grill wrote:

> I am told the cut will be in rock and will be a vertical rock face.
> The actual condition remains to be seen.  I also understand that the
> purpose of the gravel fill is to relieve the hydrostatic pressure.  I
> to have designed many basement walls. My question (which I just talked
> to a geotech. about) is?with the vertical rock face about 24? (give or
> take) behind the basement wall, what lateral soil pressures will the
> wall design be required to resist?  I have never had this situation
> before.
>
>
>
> My other problem after the soil pressure question is answered (by the
> way, the geotech. said I ?done good?) is that I did all the required
> design for the connections to the diaphragm and the diaphragm check
> for restraining the top of the wall, and the contractors are telling
> the architect that I am crazy and that they have never seen that sort
> of requirements before.  Of course the architects are agreeing with
> the contractors.
>
>
>
> Another problem is I now live in an area where the typical
> construction for basement walls is primarily CMU.  I am seeing some
> deep cuts, therefore some large restraint forces at the top of the
> wall to deal with and reinforcing that seems heavy to them.  I am new
> to this area, so I can only guess that other engineers around here in
> the past have not looked at the diaphragm and the connections to
> transfer the restraint forces to the diaphragm as closely as I do.
> They are also totally against using full retaining walls since they
> don?t want to use concrete.
>
>
>
> -----Original Message-----
> From: hadiprawira djohan [mailto:hadiprawira(--nospam--at)yahoo.com]
> Sent: Wednesday, April 21, 2004 3:58 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: soils pressure
>
>
>
> If i understand your question correctly, the purpose of free draining
> fill, which usually wrapped around by mirafi filter fabric is only to
> release hydrostatic pressure. It will not counteract  full lateral
> soil pressure against the wall.
>
> In the past, I have designed many retaining wall as a basement wall by
> assuming additional support at the top of the wall. To determine if
> the top support (floor diaphragm) is sufficient, it really depends on
> the condition of the other end of the room. Keep in mind that the
> pressure at the top of wall is less than on the bottom of wall due to
> triangular soil loading.
>
> I would be skeptical if the soil would be able to stand almost
> straight up for 12? (+ footing thickness) without any means of shoring
> during the duration of the construction.
>
> I hope this help.
>
> Hadi Djohan, P.E.
>
> Brooker Engineering, NY
>
> Joe Grill <jgrill(--nospam--at)swiaz.com> wrote:
>
> I have been asked to design a basement wall with a 12' retained height
> of soil. There has been no geotechnical review of the residence, but
> the architect, who has done other work in the area, tells me the cut
> will probably stand almost vertical. If this near vertical face is
> just a couple of feet away from the wall and the backfill is a free
> draining fill, will the fill be able to achieve full lateral soil
> pressure against the wall. The architect/contractor/owner wants to use
> the floor diaphragm to restrain the top of the wall. If the full
> lateral soil pressure is achieved then the diaphragm doesn't have the
> capacity to restrain the wall. I have suggested a geotech be brought
> in to look at the excavation and make recommendations at that point,
> but of course that hasn't been received very well. If the full soil
> pressure is not activated will there be any pressure at all and how is
> it calculated.
>
> Any ideas?
>
> Joseph R. Grill
>
>
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