Drilled shaft design for lateral load
Drilled shaft design for lateral load
(OP)
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
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






RE: Drilled shaft design for lateral load
I'm sure there is something that documents using composite sections.
RE: Drilled shaft design for lateral load
RE: Drilled shaft design for lateral load
Reference: "Foundations, Abutments & Footings" by Hool & Kinne, McGraw-Hill Book Co., 1943.
www.SlideRuleEra.net
RE: Drilled shaft design for lateral load
RE: Drilled shaft design for lateral load
Regards,
Lutfi
www.cdeco.com
RE: Drilled shaft design for lateral load
RE: Drilled shaft design for lateral load
RE: Drilled shaft design for lateral load
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
RE: Drilled shaft design for lateral load
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.
http
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Drilled shaft design for lateral load
Sorry, the powerpoint is no longer online that I can find. I have posted it on my personal web site at
http:/
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Drilled shaft design for lateral load
1. The shear exceeds capacity by about 150%, so increasing the f'c doesn't help enough.
2. Our geotech has proposed 36" diameter shafts on 6'-0" spacing, so would be possible to reduce spacing slightly, although it probably would be more economical to use the steel section, either an HP or WF.
3. This is not a secant-pile wall. The shafts will be completely buried and will depend on soil arching between the shafts. The shafts are to prevent further movement of landslide areas.
4. The shafts are about 28 feet long from surface of ground to top of bedrock. In this case the slip plane is at the surface of the bedrock, so the shafts are resisting all the shear forces. We have other walls on the project where the slip plane occurs several feet above the bedrock and the shear forces are significantly lower.
Thanks again for all the help. Based on the responses, we will use the web area for calculating the shear resistance.
Mike
RE: Drilled shaft design for lateral load
RE: Drilled shaft design for lateral load
No wall exposure. The application is the use of discrete drilled shafts to stabilize a slope.
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com