Retaining wall Pile embedment in rock

[Madziwa]

Hi,

We are about to try to design a retaining wall for a 15+m height of weathered volcanic ash above a 'soft' sandstone. Does anyone know of any simple way to calculate the embedment depth required to achive a cantilever action? All we have is a dynamic probe blow count on the sandstone at the site and general lab data for the sandstone from the local viciinty

Gareth Williams
Geotechnical Engineer,
Auckland New Zealand

 

[jdonville]

Madziwa,

What type of structure are you envisioning to retain your weathered ash? It's not clear from your post.

I would imagine that analysis of a cantilevered wall (sheet, soldier, tangent, secant) would suffice for any of those types, although you will have to evaluate the lateral capacity of the pile-rock system using a p-y (LPILE, COM624P) or Brom's analysis.

See the COM624P User's Manual here (

http://www.fhwa.dot.gov/engineering/geotech/library_listing.cfm)

for some background. See also Reese and van Impe's recent book "Single Piles and Pile Groups under Lateral Loading".

For the retained height that you mention (15m), you may need to install tieback anchors or similar restraints to keep the embedment depth reasonable and reduce moments in the piles. Alternately, you might consider a MSE/RSS wall.

Jeff

 

[SlideRuleEra]

Here is a simple way, from a 1931 Carnegie-Illinois Steel Corporation Catalog:

For walls entirely cantilever, the penetration below bottom should equal approximately the unsupported height above.

Since this would require 15+ meters of embedment for an entire steel sheet pile wall the modern techniques, suggested by jdonville are almost guaranteed to be cost effective.

http://www.SlideRuleEra.net

 

[Madziwa]

Thanks,
We plan on using a barrier pile wall (soldier pile). MSE/SRW walls probably won't work due to limited extent available for geogrid length. Tie backs are under consideration, but again due to limited site width behind the wall, they may not be feasible.

Cheers

Gareth Williams
Geotechnical Engineer,
Auckland New Zealand