H-Pile in rock

[Cosimo]

When designing a temporary soldier piling/lagging system where rock is encountered below the excavation/dredge line, what are reasonable Kp values, assuming the h-piles are set in augered holes filled with lean concrete? Any reference sources you can suggest? Thanks you.

 

[jdonville]

Cosimo,

AASHTO Standard Specifications for Highway Bridges 17th Edition or LRFD 3rd Edition have guidance.

For permanent walls, AASHTO allows a total force per discrete vertical element of Fp, such that:

Fp = sD*(D+b^0.5)/[1+tan(B')]

where

s = unconfined compressive strength of rock mass
D = embedment depth of element in competent mass (AASHTO recommends discounting top 1 foot of embedment for permanent walls)
b = width of vertical element
B' = angle of dredge line measured from horizontal (sloping downward away from wall is considered positive angle in this case)

Determination of 's' can be tricky, as many AASHTO formula assume a RQD of 60%+. If the RQD is less than this amount, it is unclear what is the best course of action.

Hope this is helpful.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[PEinc]

Check out AASHTO's Standard Specifications for Highway Bridges.

Check out FHWA's Geotechnical Engineering Circular No. 4, FHWA-IF-99-015, Ground Anchors and Anchored Systems.

 

[DRC1]

Say Phi = 45-50 deg. and you will get reasonable embedments

 

[PEinc]

You will also get pretty reasonable embedment results if you treat the rock below subgrade as a very stiff clay.