Experience with stepped excavations for LCC Back fills for Retaining Walls

[cmoreride]

Huge project approximately 130 retaining walls. Many of the walls are using LCC back-fills.
The basic excavation uses a "base slope" of 2:1 and requires steps (default horz of 5' and a vert of 2.5').
Every Ret Wall design "h" change results in a different footing size and elevations and resultant stepped excavation.
A literal interpretation of the design drawings result in excavations that look like stadium seating.
This is impractical to excavate. I like to see how others have addressed this issue.

 

[oldestguy]

Seems quite impractical. I'd expect a lot of loose material moving down the slopes getting into the way of the work there. Likely the cost of the work will be much more than using a simple slope of 30 degrees.

 

[cmoreride]

using LCC was a solution to eliminate piles and footings with piles. agreed on the soil holding the steps etc. it's turning into a real bugaboo. Thus far the best idea is to after some variability at the bottom get all the steps on the same grade. The idea is to do the base excavation build the footing and walls and then come back and step the slope. The LCC must be keyed into the native ground therefore it can't be placed on a slope. I would have thought if we used a slope greater that 2:1 we could eliminate the steps altogether but according to Geotek No! I'm thinking a second Geotek opinion on that is worth thew cost for sure!

 

[oldestguy]

How do you get a typical earth mover to stay or even get on a 5 foot wide place?

 

[cmoreride]

a dozer top down with the steps in place from the start during wall construction or a excavator digging benches after wall is constructed into the base excavation basin. My role is to model the excavations and provide staking data to survey. I started this thread in the hope that folks had encountered these issues and found practical solutions

 

[oldestguy]

OK, suppose the site has clean sand or clean sand layers. No way will this work due to continuing raveling with time. Darned if I can figure how you can start on wall construction before you get excavation full width down to footing grade. OH, leave steep earth cut walls. Apparently no government rules on safe construction, huh?

 

[cmoreride]

Got that right.
And in some cases it has to be opened up more for pile rig and it's access.
Other locations have to backfilled. Where the LCC mass is higher than OG and then stepped excavation created.
And the LCC is placed in 3ft max lifts and must remain free of debris

"another day in paradise"

 

[cvg]

benching is generally required bottom up for embankment construction with compacted fill. It removes the loose outer layer and "keys in" the new compacted fill on top. If the wall and concrete backfill is stable (and it should be) than I am having difficulty understanding the purpose for the benches. just strip the top 6 inches off the slope and run a sheeps foot over the slope to prep the subgrade and then build the wall.

 

[cmoreride]

Geotek, Structure Designers, DOT, Special Provisions and Specifications thus far have us in a box.

 

[oldestguy]

This Old Guy is assuming you are to supervise in one way or the other how you place the LCC in layers so that the edge 5 feet width into the FINAL cut is all on undisturbed ground. Do not do that staking. Instead stake and have the cut slope made so there then is a 5 foot horizontal dimension from the main cut surface staked surface back into the slope that meets a 30 degree line to be the bottom corners of all those layers when completed. Make that cut, and no cuts farther into the slope yet. After the wall is built and filling of the LLC starts, one layer at a time. When the completed first layer is done, excavate for the next layer into the slope that 5 foot distance beyond the edge of the just placed LCC all in undisturbed ground. Place the next LCC layer. So then continue up the slope, one layer at a time with the edge 5 foot width excavation made immediately before placing the next LCC layer. It means handling that 5 foot width earth cut material for each layer, one cut at a time, just before placing the next LCC layer How you do that can be by many means. I'd look at some form of "dental" excavating method such as an elevating excavator as used for roadway final finishing of subgrade excavation, using trucks or other earth hauling equipment to get that material out of that area. Maybe a back-hoe would do it. How you stake that original cut to get down and build the wall, I'd bet some simple device at top of slope can serve as a guide for the bulk excavators. I'd not try to stake the completed bottom corners edges of those LCC layers for the first bulk excavation. In summary, do the final 5 foot edge width excavation of the LCC zone one layer at a time only after the previous lower LCC layer below is done and set. Due to possible mistakes or actually doing the first bulk esxavation, that final 5 foot width may not be exactly 5 ft., maybe 7 or maybe 4. At least its position can be firmed up at the final excavation and filling step.