Backfill slope
Backfill slope
(OP)
I am designing a 10' cantilevered retaining wall.
I have a geotechnical report on the soil. They provided an equivalent fluid pressure of 47 pcf for level back fill and 78 pcf for a backfill sloping up to 2:1.
The retained soil will be level for the first 10 feet then slope up the hill. Can I consider this a level backfill situation and use the lower equivalent fluid pressure or should I use the more conservative EFP for sloped backfill?
To accurately model slopes what horizontal distance from the wall should be used to determine the slope?
Thanks for your help.
David
I have a geotechnical report on the soil. They provided an equivalent fluid pressure of 47 pcf for level back fill and 78 pcf for a backfill sloping up to 2:1.
The retained soil will be level for the first 10 feet then slope up the hill. Can I consider this a level backfill situation and use the lower equivalent fluid pressure or should I use the more conservative EFP for sloped backfill?
To accurately model slopes what horizontal distance from the wall should be used to determine the slope?
Thanks for your help.
David





RE: Backfill slope
RE: Backfill slope
The position of the overlay is important, you don't want to neglect any loading nor to count it twice. With backfill slope of 2 Horizontal: 1 Vertical and 10' Horizontal setback to toe of backfill, I get a maximum pressure of 625 Lb/SF (at the toe of the 10' high wall).
Total pressure on the 10' high wall comes out at 2738 Lb/Ft of Wall Length. Let me know if you can't confirm.
www.SlideRuleEra.net
RE: Backfill slope
RE: Backfill slope
With the lower # I have a more econimical design.
David
RE: Backfill slope
RE: Backfill slope
However, for the active pressure, the angle of the 'sliding' wedge is less than the 45 deg angle (taken from the vertical). If phi = 30 to 35 deg, then the angle is (90 - (45 + phi/2)) or about (90 - (45+17,say) or 28deg from the vertical (or approximately at an angle of 2V:1H - see Tomlinson's Foundation Design and Construction book - 6th Edition, Figure 5.10 which gives a set-back of 2V:1H for which no underpinning would be normally required). The 'sliding wedge' will not intersect the slope and therefore does not come into play in the active earth pressure on the retaining wall. However, the slope may very well have an influence on the global stability - which needs to be checked as part of any retaining wall design (and many times is not).
RE: Backfill slope
RE: Backfill slope
RE: Backfill slope
As an aside - like the Pinebrook Dam (link in another of the geotechnical threads) - they have a web cam installed that updates every 5 minutes. Interesting for monitoring purposes, perhaps!
RE: Backfill slope
and the sites cleared back to prevent such load calculations being effective, that from many slips encountered.
If the contractor knows you have placed a design that might incur contract implementation and force at later date and the authority may come after him for remediation
he may sue you for damage
I would
and as the authority I would prosecute you
and that could include criminal damage and loss fo life prosecution.
Calculations are for checking things when they are partial as all these are
and well dated and unreliable.
Convenience does not avoid the responsibility for detailing the site. The client is going to be much happier and the authority satisfied if the site stays up, if it falls down, its your neck, that is why we design and anybody suggesting you should dump this on the contractor when the contractor does not know the site and structures should be dumped, as you will be from Institution if you agree with them !