Huge retaining wall ideas

[TigerGuy]

I need to design a reconstruct of an area damaged by erosion. The area in question is at the top of limestone bluffs overlooking a major river. Total elevation difference is 120 ft.

The only thing I can think of is to excavate the material loosened by erosion, then build a drainage path for the water and retaining wall with soil nails into the limestone for tiebacks and work up from the base.

I'll be getting some soil borings, including coring into the rock. Any ideas or suggestions would be greatly appreciated. In the words of the owner, "I'm not looking to save money on this. I want a solution to last 100 years."


M-I-Z

 

[PSlem]

There was a rock slide area on I 40 repaired by a local company that used rock climbing techniques for workers and equipment. A search should turn up their name.

 

[msquared48]

Getting a Geotech involved is a very, very good idea here, particularly considering what the owner wants.

I would consider rock bolts though rather than soil nails to stabalize the rock face. As for the necessity of soil nauils, ythat would be for any loose material that might sluff off in the future or exists now. Depending on what the Geotech says, perhaps a combination of the two would be your best approach.

Maybe even adding a gunnite surface over a cyclone fence mesh secured by rock bolts could be considered here.

Mike McCann
MMC Engineering

 

[RFreund]

So is this more slope stability or retaining wall? I guess really a retaining wall is just a form of slope stability so maybe this question in invalid.

EIT

 

[cvg]

You seem to indicate the slope is unstable, not just an erosion problem. Assuming that is the case, then:

1) perform slope stability analysis to determine global stability or not
2) based on results of investigation and analysis, you might do one or more of the following:
a) remove some of the overburden to reduce the stress
b) surface dewatering at the top of the cliff (divert and remove surface water going over the slope or into the ground near the top)
c) groundwater dewatering to lower the pressure on the cliff wall (wells, toe drains etc)
d) blast the slope back to an acceptable angle or buttress the bottom
e) rock bolts with shotcrete facing on the bad parts
f) rock fall netting on the loose parts
g) just monitor the slope

 

[BigH]

TigerGuy - why not draw up the existing cross-section and shown the "intended" finished product - then post it so all can visualize what it is you really are looking for. Are you wanting to stabilize the whole slope - or just the upper part?

 

[TigerGuy]

Maybe I can clarify: The area at the top of the bluffs consists of about 5 feet of loess on top of limestone bedrock. An access road was graded to permit maintenance. However, the grading created a low area. Stormwater now ponds in this low area and flows over the side, causing the erosion problem.

The erosion has partially loosened some of the limestone, so the area of concern extends farther down the slope.

My question is about the constructability of such a tall retaining wall. Typically, I see Geogrids extending back from MSE walls. However, with a 120 ft wall, the Geogrids would not be able to extend far enough before running into the limestone. That is why I was thinking about soil nails/micropiles for the tiebacks.

Does anybody have experience with retaining walls this tall?

 

[oldestguy]

Can you build a gravity wall or MSE wall on the top of the slope resting on rock? Then, by means of the wall, raise the grade up there to then be able to divert surface and any collected ground water off to the side somewhere.

Reminds me of some treatments I have seen along the Mississippi, specifically DuBuque, IA. There the walls are made of local stone blocks.

I did one like this at McGregor, IA at the Fish and Windlife headqtrs.

 

[InDepth]

Sketch would be nice.

 

[crcivil]

I think Rock bolting (cement cartridges and steel bars) and Shotcreting (fiber reinforced) is the way to go as msquared48 has already pointed out. Enough number of weep holes will be a must.