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RE: Bridge Abutment Replacement

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Steven,

You've got an interesting problem.

Best solution I can come up with is building a temporary
cap with the supports OUTSIDE the edge of the bridge.  
However, this would be a 62 ft span and probably pretty
hefty in size.  It's going to have to be close to the ends of 
your girders.  Typically specifications call for pick-up
points to be within 30" of bearing points.  I'd stick close
to that with the bearing on the temporary bent.  You also might
consider an interior support of your temporary bent, placed
to avoid the future battered piles.  

Another option you might want to consider is the use of drilled
shafts in lieu of battered piles.  Your geotech could give
you a better opinion on this.  

I don't think that the demolition and rebuilding of your existing
abutments will be as big an issue as the location of the temporary
bent.  You'll probably need to leave room for sheet piling to
provide temporary shoring, but staged construction isn't too
impossible to deal with.  Just leave enough room between existing
and new construction to provide for adequate bar laps.

Good Luck!





-----Original Message-----
From: Steven Mallett [mailto:smallett(--nospam--at)dillon.ca]
Sent: Thursday, June 14, 2001 8:50 AM
To: seaint(--nospam--at)seaint.org
Subject: Bridge Abutment Replacement


We are looking at designing to replace an existing bridge abutment. The
existing concrete abutment is 30 years old and is supported on steel
pipe
piles founded on bedrock (well, some of them anyway which has
precipitated the replacement) with H-pile batter piles. There has been
gradual settlement over the years and repairs to suit. Settlement also
due
to embankment fill consolidation and resulting downdrag on piles.
Geotechnical investigation will determine if consolidation is near
completion.

Bridge is three span with pre-stressed concrete girders (8) and
concrete deck. Middle span over a railway line. End spans (45 ft.) are
over embankment slope. Overall width is 62 feet with two travel lanes.
The kicker here is that one lane must remain open to traffic at all
times
during the construction. No detour routes are available.

I am seeking comments for:

1. Suggestions/past experiences for temporary support of the girders
during  construction of the new abutment. 

2. Suggestions/past experiences in building abutment in separate pieces,
i.e. demolish one half, then re-build half and re-seat girders for
traffic
lane, then demolish and re-build other half. We also have to worry about
avoiding the existing piles when driving new piles.

Thanks in advance,

Steven A. Mallett, P.Eng.
Dillon Consulting Ltd.


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