I too have a question to pose to the group. I am now dealing with a project on
the Oregon coast which will use pipe piles to support a shipway (this is a new
ship repair facility), some piles driven on land and some in the (salt) water.
The soil profile consists of fine to medium sand (dune sand), with SPT = 12
blows per foot at the surface increasing to over 100 blows per foot at about
40-50 ft. A good site for 200 ton piles!
But--a local piling contractor has advised the owner that he can vibrate the
piles in provided they use a plug about halfway down the pile. He, the
contractor, claims that he can vibrate an open ended pipe pile "to the center of
the earth" unless there is a diaphragm or plate to block the pile. I have a
problem understanding that. I feel that when he vibrates an open-ended pile to
the 100 blow per foot zone, he will effectively reach "vibration refusal." Does
anyone out there in cyberspace have any experience with a similar situation?
How do I answer this owner and his contractor advisor?
"Bleakney, Michael (DOT/STR)" wrote:
> Never having seen chalk outside of a classroom I was going to let this pass
> without comment, but after Steve Corbet's comments which sort of expanded
> the scope of the discussion I thought I would throw my 2 cents worth in.,
> and hopefully hear from someone with a similar experience.
>
> We routinely drive closed end pipe piles, usually 0.5 or 0.6 m diamater,
> with 12.7 mm wall. We have seldom had any trouble with these. They have
> been driven through silts/clayey silts, boulder clays/tills, cobbles,
> gravels, to bearing in mudstones, shales, sandstones, etc. Lengths can be
> in excess of 30 m. The end plate is welded to the bottom of the pile. I can
> fax you a standard detail drawing if you like, or I think you can access our
> Standard Specifications at
>
> http://www.dot.gov.nb.ca/dot/specs/dotsps99.pdf
>
> after first completing a form at
>
> http://ftp.dot.gov.nb.ca/specs/default.html
>
> You will want to look at Standard Drawing 312-1. Of particular importance,
> in my opinion, is that the plate diameter is not larger than that of the
> pile, otherwise the installation is somewhat akin to dropping the pile down
> a prebored hole, at least as far as shaft resitance is concerned.
>
> On occasion, though rarely, if a particularly nasty stratum of boulders must
> be penetrated, an H-pile stinger is welded to the bottom of the pipe pile.
>
> Sometimes these are driven from the top, but this is unusual, because of the
> large size of hammers required which are not always available in our small
> market. For a couple of jobs we have tested top driving with a Pile
> Dynamics Inc. Pile Driving Analyzer. If my memory serves me correctly, when
> CAPWAP analysis was performed on the test results, we came up with a plug
> weight at the toe roughly equal to a hemisphere of dense soil with a
> diameter about equal to the pile diameter. No pile damage was detected, nor
> separation of the plate from the pile detected.
>
> Most frequently, our pipe piles are driven by a method that resembles the
> installation of an expanded base pile (Franki), except that the toe plate is
> installed on the pile. A "plug" of "dry" crushed rock and cement (about 5:1
> ratio I think) is dropped into the bottom of the pile (about 1.5 m in
> length) and a piece a ship's drive shaft is dropped against it, by simply
> allowing it to slide down the inside of the pile. This is continued, with
> occasional replenishment of the "plug" material, until the pile cannot be
> driven any further. Typical "ram" weights are 30 kN with a 5 m drop. These
> are easy and cheap for the contractors to acquire, and they all seem to have
> some version of it. Sometimes the ram has centring fins so it doesn't get
> jammed in the pile. I have a devil of a time trying to estimate capacity
> from observations of this method, and since we never do any load tests (for
> "calibration" of observations) have settled on a combination of Gates
> dynamic formula and static analysis using a target toe elevation.
>
> While difficult (for me anyway) to model, the method does seem to work well,
> and advances the pile deeper than top driving seems to be able to. I think
> part of the reason for this is the compressive stiffness of the relatively
> short length of pile below the point of impact, and that the upper part of
> the pile is loaded in tension as it is pulled down through the soil,
> reducing the normal stress between pile and soil, and hence the frictional
> resistance to driving. Even though I can't explain how well or why this
> works, or estimate capacity with it, I can't argue with the fact that it has
> been used around here for at least twenty years, and there has never been a
> problem with structure performance that I am aware of.
>
> I would really be interested in hearing from anyone else who has used this
> method to install pipe piles, and would particularly be interested in
> discussing how they estimate/verify/predict capacity, and especially if
> anyone is modelling this with wave equation methods. Unfortunately I have
> never seen this described in any text book, code, technical journal, etc.,
> so I wonder if this is the only place in the world where this is done.
>
> I am looking forward to seeing where this discussion goes.
>
> Michael R. Bleakney, P. Eng.
> Geotechnical Engineer
> New Brunswick Department of Transportation
> Structures and Materials Branch
> PO Box 6000
> Fredericton, New Brunswick
> E3B 5H1
> CANADA
>
> Phone: (506) 453-2674
> Fax: (506) 457-6714
> Email: [log in to unmask]
>
>
>
> > -----Original Message-----
> > From: Steve Corbet [SMTP:[log in to unmask]]
> > Sent: Thursday, April 08, 1999 10:53 AM
> > To: moulds, rob
> > Cc: Geotech Mailist (E-mail)
> > Subject: Re: Driven Piles
> >
> > "moulds, rob" wrote:
> >
> > > Does anybody have any experience or references / information relating to
> > > driven tubular steel piles with end bearing plates. The plates are
> > > however not welded across the base but are positioned approx. 5-8
> > > metres up the inside of the pile.
> > >
> > > The piles are to be driven through chalk gravel into a moderately weak
> > > to moderately strong chalk
> > >
> > > Particular concerns relate to the effectiveness of the plate to create a
> > > 'plug'.
> > >
> > > Thanks
> > >
> > > Rob Moulds
> >
> > Rob and others on the list
> >
> > I have two experiences of driving tube piles with end plates, both of
> > which
> > were problems and which are unpublished.
> >
> > The first in the UK at Lowestoft with the plate about 1.0m inside from the
> > toe with a pile dia of 750mm. The piles were driven through Made ground
> > (cohesive and granular), Med dense fine sand into a dense clayey silt at
> > about 20m. The piles pulled up immediately they reached the silt, for
> > various reasons it was necessary to drive to depth for lateral stability
> > and
> > to make driving easier we cut out a hole 350mm dia in the plate to relieve
> > some of the end bearing.
> >
> > The second was in Dubai driving 750mm dia piles again with the end plate
> > about 1.0m from the toe. Here the piles were driven through loose sand
> > into
> > weak calcisitite with band of weak sandstone, ground water at ground
> > level.
> > The piles drove to about 10m when the driving suddenly eased and the piles
> > filled with water. The piles were extracted and it was found that the end
> > plates had been blown in, presumably by the pore water pressures generated
> > by the hammer. The problem was cured bu burning four 100mm dia holes in
> > the
> > pile wall just below the end plates, all piles then drove to the required
> > depth / set without any problems.
> >
> > Hope that helps, photo available for the Dubai case
> >
> > Regards
> > Steve Corbet
> > Associate Maunsell Ltd
> > [log in to unmask]
> >
> >
--
S. Joseph Spigolon
Coos Bay, Oregon 97420
Phone: 541-267-4371
Fax: 541-267-8224
E-mail: [log in to unmask]
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