Soldier Pile wall design using LPILE4 and lateral subgrade modulus

[GeotechRic]

I conducted a "basic modeling" type analysis using LPILE4 in order to determine depth of embedment and deflections. The piles are 24 feet long, with a 15 feet embedment into 3 feet of medium dense sand and the remaining 12 feet in very stiff clays.

The structural engineer now has returned saying he needs two things:

1) lateral subgrade reaction modulus and

2) the lateral bearing capacity of the soil where the h piles are embedded.

I've been reading previous topics for a while now but don't seem to get a good understanding of what these values consist of and how to estimate them.

What I've understood from previous posts, the engineer wants the lateral subgrade modulus in order to model linear reaction springs along the pile length using a program such as STAAD. the modulus being just p/y at the given depth of the spring, in units of stress/cubic length such as what you would get from performing a plate load test.

Lateral bearing capacity is something I've never dealt with.

Hopefully I can get a good explanation (Focht3, BigH, etc.) of what the parameter consists of and what is the best way of estimating them (NAVFAC 7.2-235?).

NAVFAC suggest a linear increase of kh in the sand starting at 0 at the dredge line and then a constant kh in the very stiff clay ranging from 35c to 70c.

 

[jdonville]

GeotechRic,

You may want to use simple passive pressure - as in AASHTO's simplified design method for cantilevered retaining structures with discrete elements (see AASHTO Standard Specifications for Highway Bridges 2002/17th Edition, chapter 5).

Unfortunately, if you can't get a copy from a friend, the entire book costs 100's of dollars available from AASHTO (

http://www.aashto.org).

However, these are based on Teng's simplified method, if you can get a copy of Teng. These concepts are also presented (although not as clearly as might be hoped) in the Caltrans bridge design manual Chapter 5

http://www.dot.ca.gov/hq/esc/techpu...ridge-design-specifications/page/section5.pdf

Hope this helps,

Jeff




Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[BigH]

Sorry Focht3 - but you might look, as a start, in Bowles - section 13-3.3 (5th Edition). Not quite sure why he needs the "lateral bearing pressure" if he has the appropriate modulus of subgrade reaction. For the former to fully develop (assuming as capacity rather than allowable) I would think that the deformations required would be much larger than what the appropriate modulus of subgrade reaction would permit.