Can't solve it - retaining wall next to creek in very poor soils

[Calif_Eng]

I have an 11 foot wall to support a road next to a creek in an alluvial floodplain in very poor soil. The geotech engineer is not allowing any bearing, only 200 psf in slip friction for nine feet of sandy strata beginning two feet under the lagging for nine feet in depth (13-22ft). Under that its liquefiable until you get down 40 feet. With the LFRD STR I condition I have lateral loads of 1.35EH + 1.75LL + 1.25DC. I was planning a soldier pile single tieback wall, W12x53 r=1.25 @ 8 ft centers, but the vertical resistance factor of the soldier pile for slip friction is .55 which results in 1.25DC exceeding the .55* 200psf slip friction resistance on it's own. The tieback exerts additional downforce on the soldier pile. Alternatives: I can't do RSP as it will get into the creek and environmental review will reject. Intuitively, I'm very leery of a deadman at an angle down to provide additional resistance. About forty feet down the geotech hit some decent material but they only went two feet into it so we'd have to do more geotech. Then I maybe could do piles and and double tiebacks. Any thoughts?

 

[Calif_Eng]

Talked to managing engineer. We just got blanket NEPA approval for 20+ sites, but no driven piles are allowed. So no SSPs. Gabions have also been rejected for environmental reasons, apparently trap and kill small animals. He's good with going 38 feet to better material with drilled soldier piles, concrete around steel, water starts at 15 so have to be in caissons. Double tie backs up top for lagging wall for lateral forces. That's better than I hoped for.

Geotech came back again and was okay with helical anchors and shotcrete slope at 1:1 or a floating soldier pile wall on a grade beam with double tieback, but irrelevant not I have the okay to go down to the good material.

I'm off the design for now and doing paperwork to get concept approved for funding in the next couple weeks.

 

[amlinerrichard]

Years ago, 1980's, we built a retaining wall with some very large concrete blocks. They were offset as we went up. It was on the Park Board Headquarters in Mpls at 38th St. and Bryant Av. So. I do not recall the official name of the product. It was used as a wall for a flood control pond. Also it was built with designs from the Sewer Design Dept. of MPLS. They could also be called.

 

[BridgeSmith]

Redi-Rock supplies the forms for the large block walls. StoneStrong is a similar system. I'm not sure if either one is suitable for a location with low bearing capacity, though.

 

[dik]

Can you use a geogrid reinforcement?d

Dik