Bearing Pressure for MSE walls?

[MSEMan]

I am concerned that I continue to see bearing capacities for MSE walls quoted in contract documents as single number values such as allowable = 200 kPa, or ultimate = 500 kPa. Given that we are all using similar analytical tools, shouldn't the Engineer/Client be quoting either FOS/load and resistance factors or bearing capacity with assumptions (i.e. allowable = 200 kPA at 5m width and 1.0m embedment.)? Wouldn't it be sufficient to specify phi, gamma and C values for the founding strata?

If anyone asked me to estimate the safe bearing capacity of a formation, I would first want to know whether they were building a pile or a raft.

 

[rochplayer]

What we prefer to give is a table of allowable capacity (or factored resistance) versus Bmod (Bmod = B - 2e). Since bearing and settlement is foundation width dependent, the MSE wall load is eccentric, and the wall vendor will calculate the eccentricity, it has worked well to provide them Bmod so they can have a direct comparision to their applied loads.

Also, we always state our assumtions and provide a table of properties for soil in the reinforced zone, the retained zone, and foundation soil properties. It is only good practice.

 

[jdonville]

MSEman,

I will explicitly state the design parameters for the reinforced fill, retained soil and foundation soil(s). I will explicitly state the top of wall and assumed foundation (levelling pad) elevations and the reinforcement length being assumed for the analyses.

If the allowable bearing is less than the Meyerhof bearing pressure, then I will adjust the reinforcement ratio or provide recommendations for improving the foundation soils in order to make it all work. Any recommended adjustments to the reinforcement ratio are explicitly stated.

As most MSE walls I prepare reports for are for highway retaining structures, the overall geometry of the wall is fairly well-defined by the time I come into the picture.

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.