Soil Capacity/SSP Question

[hillaryBCTI]

Hello,

My question is a somewhat strange one. (See picture:

http://files.engineering.com/getfile.aspx?folder=d27329a4-7a53-4506-90fd-034b64454042&file=1142.bmp)

What is pictured is not what the engineer designed, but rather what the contractor determined how it should be installed. What was actually installed was different still, with no bench of soil at the toe of the SSP.

I have determined the original design (with "continuous ground" at the toe) was adequate (per "Design of Sheet Pile Walls" from ASCE and "Principles of Foundation Engineering" Braja M. Das), but now I am stuck as to how to determine if the SSP passed/failed with the soil bench (picture) or if it passed/failed due to no soil in front of the toe.

Any ideas where I should be looking for information or can someone here help me out?

Thanks!

 

[dgillette]

Whoa, that got my attention.

If I understand the drawing and description correctly, only the upper part of the cut face is supported at all, and the tie backs are too short to reach past all possible slide surfaces (so they can't contribute to the stability of a full-height slope failure). It's all soil, right? This means you are looking at the stability of a vertical cut standing only by the strength of the material below the sheet pile. Must be good unfissured, firm clay or something. (That, or somebody has been living a clean life.) If you have a good handle on the strength of the material, you could analyze it using a chart solution for a vertical cut, which may exist in Das's book, or probably in the US Navy's NAVFAC DM-7. For the latter, search around on this site - one of members has posted a link to it as a .pdf.

 

[hillaryBCTI]

I guess I didn't draw in the tie-backs correctly. And in all honesty, I have no idea how far back they went or what size they were (I'm still working on gathering that information). So they very well could have contributed to the stability.

The soil is definitely not a good clay (sad to say). I'm not fully clear on the type of soil, but from the stack of pictures and the little data I have, I'm guessing anywhere between a SW to a GW. (I haven't gotten my fingers on the geotech. report...if one even exists)

Thank you for pointing me in the direction of some more information. I appreciate it!

Just an fyi, the wall did collapse. Thank goodness it was a weekend when it happened.

 

[dgillette]

Maybe the fact of it being on a weekend shows someone was living right.

DRG

 

[PEinc]

My guess is that the wall did not fail. Rather, the soil under the wall failed and the wall fell along with the failing soil wedge. With two rows of tiebacks for the first 17' cut, the sheet was probably stable and needed no toe embedment. As the excavation progressed another 18' below the first 17'cut, the unshored face became unstable and fell out below the sheeting.

Did the tie rods or strands snap off when the slope failed and the wall fell or is the sheet piling hanging by the ties on the failed slope?