Temp tie-backs for shoring wall? 1

[piledrvr]

I am looking for ideas on how to tie-back a temporary shoring wall. Our current plan is to cast some rather large deadmen and use coilrod to tie back the pile. The problem with this approach is that the deadmen would be located within a embankment area and will interfere with the placement of the fill. I have looked at the Manta-Ray system, but everything I have seen says that it can only be used in "undisturbed" soils. We have also thought about driving a couple of anchor pile after the fill has been placed and cut these off below grade, but then we lose the piling. Any other ideas?

 

[GeoPaveTraffic]

Depending on the loads you need, I would look at

1. drilled in soil anchors, 12 to 24 inch diameter
2. drilled in belled soil anchors
3. helical anchors

 

[PEinc]

Fill walls are not very good applications for tieback anchors. Usually, a more economical solution is to use an MSE wall for retaining embankment. If the contractor is more comfortable installing sheet piling or soldier beams, then I also would consider tie rods back to some type of deadman or deadmen. You did not say how high the wall will be. Also, with a fill wall, you need to look harder at the intermediate conditions as the fill is being placed. Significant fill needs to be placed before the deadmen are installed but you can't install the deadmen before the fill is installed. The critical design case may not be the final, full-height wall.

Manta Ray anchors are capable of relatively low working loads. Manta Rays and the other anchors that GeoPaveTraffic mentions require various types of equipment to drill-in or drive the anchors. If the wall needs multiple tiers of anchors, it will be difficult to get the drilling equipment to each tieback elevation. I'd look at an MSE wall (with a wire basket facing) or sheeting with tie rods and deadmen unless the wall is less than 12 to 14 feet high and can be cantilevered. Check the bedrock elevation which could interfere with embedment of sheeting. Also consider settlement of the embankment and the additional loads this could put on the tie rods. Tie rods are usually designed for tension, not combined tension and bending.

 

[piledrvr]

Thanks for the info. It looks like this wall pretty much limits us to using either deadmen or anchor pile with tie rods. We are using soldier pile with timber lagging. Pile embedment is averaging 20 feet with about 4 to 6 feet into an extremely dense glacier till layer. The piling are at complete refusal. The wall is a stage wall for a highway project. We are building up the grade to line up with a new bridge. The traffic is currently about 6 feet below the grade of the new alignment. Once this is complete, traffic will be switched onto the new alignment and we demo the existing bridge and build another. The wall will be holding about 6 feet of fill at this point with live traffic.
During the construction of the second bridge we will have a cut of about 14 to 16 feet. It would be at this point that we would attach a waler tied back to the deadmen at the original ground elevation. We will have approximately 22 feet of wall total with a pile embedment of around 6 feet. The soil layer is so dense that we don't have to worry about the toe giving way however, bending is the main issue. Once this phase is completed, we will backfill to the same elevation as the other bridge and pull the soldier pile.

 

[PEinc]

Sounds like the tie rods and deadmen are the way to go. You really have a cut wall rather than a fill wall.