drilled shaft design for lateral load

huangyhg

drilled shaft design for lateral load
we are designing a drilled shaft soldier pile wall, socketed into bedrock, to restrain a land slide area.  our geotech consultant has run the lateral load analysis and given us the maximum shear and moment on the drilled shaft.
we have designed the shaft for the maximum moment, reinforcing the 36" diameter shaft with #10 bars.  however, we are having trouble designing for the maximum shear.  using the shear capacity of the spiral reinforcing, added to the shear capacity of the concrete, is not providing enough capacity.  instead of increasing the shaft diameter, the suggestion was made to drop a steel section into the drilled shaft to provide more shear capacity. this sounds reasonable, but what area of the steel section is used to calculate the shear capacity?  should only the web depth x thickness be used or the entire section?
thanks for your help with this.
mike
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take it for what its worth, since i don't have experience with it, but i'd use the area of the web for one direction, and the area of the flanges for the other direction.  i'd assume you'll line the steel section up so that the loading is about the strong axis, and the shear will be carried by the web.
i'm sure there is something that documents using composite sections.
can you increase f'c enough to get the shear capacity you need?
web depth x thickness, based on an analogy with (obsolete) steel grillage foundations. even though the steel   
can you decrease spacing of the shafts?
why not use an h pile in the center to increase the shear capacity? this is a quick thought. they use steel beams on thin slabs to increase the shear capacity near columns in flat plate systems. then you would have an increase in the moment capacity as well.
regards,
lutfi
is this a secant-pile wall?
sorry - i hit the button too soon.  i would take it that this is what i alluded too.  why not use tie-backs to take the shear and moments as well?  i would suggest that you get a hold of recent ground engineering magazines.  the february issue has a couple of articles that you might find interesting (monthly topic "slope engineering": page 14 step by step; page 19 sliding scale; page 16 cutting costs).  they also have a couple of articles on soil nailing.  they use a lot of contiguous walls (secant walls) in uk.

how much more shear strength do you need? if you're over by a couple of percent, then that's a lot different than if you're over by 2x.
i like the idea of increasing f'c. if i used the steel shape, then i'd conservatively use the web area only because i don't know of a reference for anything any better.
how tall are these walls? i'm a bit surprised that you can get flexure to work and not shear.
dbd
mike80,
many of the current publications dealing with slope stabilization with drilled shafts assume that the soil slope has failed and that the drilled shafts have to resist the entire wedge of soil above the failure surface.
the ohio dept of transportation has been sponsoring research into this area. unfortunately there is no hard and fast conclusion from the work as of yet - i understand that they will be undertaking instrumented drilled shaft testing as one of the next steps.
there is a slideshow (powerpoint) available online that illustrates the current state of thinking about shaft-stabilized slopes and their analysis. the following link is connected to the final report for one portion of the research.
mike80,
sorry, the powerpoint is no longer online that i can find. i have posted it on my personal web site at