Concrete Lagging as Earth Retaining Wall

[Expotek]

I have a dilema. On my project, soils report calls for a Permanent Soldier Pile Lagging (SPL) to remain in place to retain the earth excavated about 6ft. high on the property line. In front of this SPL, we are to build CMU retaining wall.
Question is why build a retaining wall, if we need to have a SPL to retain the earth. Since Lagging is good for only 10-15 years, what if I use Concrete Lagging? then I see no reason to build another concrete retaining wall in front of it?

slope of retained earth is about 2:1 or less. Wall and the excavation is on my property line, so no access on the other side of the wall. Soil is Expansive silty Clay in Southern California.

Any HELP will be appreciated. What is my leat expensive but correct solution?

 

[PEinc]

First, no matter what type of wall you build, you will need a good determination of earth pressures caused by the expansive silty clay.

Secondly, if you use precast lagging which is tucked behind the soldier beam flanges, you will need to make a full depth, open excavation in order to place (by stacking) the lagging from subgrade up to the top of the wall. This means an open, unsupported, and possibly vertical cut about 6 feet minimum in height. Will this cut be safe, legal, stable? Can you temporarily slope back the excavation onto the adjacent property so that the precast lagging can be stacked? Precast lagging will also need either a footing beneath it or some supports welded to the soldier beams, beneath the bottom lagging planks, in order to prevent settling of the heavy, thin precast.

Timber lagging is usually and properly installed from the top down using progressive excavations of 5 feet maximum. This is not easily or attractively done with precast concrete lagging.

 

[Expotek]

Thanks PEInc. Neighbors property is illegally gradred to less than 2:1 slope, therefore, I have to have the Shoring to retain his slope from failing? He is not cooperative at all, so no chance to go offsite even for temporory grading. Prooosed Soldier beams are to be set in drilled 2ft. dia. X 5ft deep hole, set with Lean concrete mix, possibly using Concrete covered steel "I" flanges. Then concrete lagging has to be installed (front of rear flage)just the same as Timber lagging, Top down using progressive excavation.
My understainding is that the CMU block retaining wall is using county standards for footing etc.
I am looking for some one who will review the soild report and support the opinion that Permanent Shoring is not necessary, only temp. shoring while CMU wall is built and cured. Any guidance on how to get this done and avoid Shoring expense completely?

 

[PEinc]

Your wall is not very high. Therefore, several wall types could be used. However, these different walls would take up more space and require a front face which would be farther from the property line, into your property.

Five feet soldier beam embeddment is not very deep for a wall six feet high. Is 6 feet the finished wall height or does the six feet include any depth below finished grade in front of the wall?

If the CMU wall facing and its connections to the soldier beams are designed for the full earth pressures, the lagging could possibly be "temporary" but left-in-place wood lagging, either treated or untreated, instead of being precast lagging.

I am not sure what you mean when you say, "I am looking for some one who will review the soild (soils?) report and support the opinion that Permanent Shoring is not necessary, only temp. shoring while CMU wall is built and cured." A CMU wall with a finished height of six feet, with a sloping surface behind, but without the soldier beams, will probably need geogrid reinforcement (an MSE wall). This type of wall will require considerably more space (6 or 8 feet wide vs. +3 feet wide).

 

[Expotek]

My walls range from 2 ft. to 6ft.in finished height along finished driveway. When I say CMU wall, I mean Concrete Masonry, grout filled, steel reinforced, solide concrete wall. Blocks used would be 8" and 12" concrete blocks, steel rebar reinforced with proper drainage, waterproofing and backfilled with rocks etc.

Gravity type MSE with geogrid is NOT an option, since I am on the property line (only 2ft. from property line to the front of the wall).
If I had a second opinion from another Soils engieer indicating that fancy SHORING is not necessary, and Concrete block retaining wall should do the job, once build and cured. Then all I have to do is to have Temp. shoring ( which is also required by OSHA) to retain the dirt while we build the wall. Then I can convince my existing Soils engineer to withdraw Shoring requirement form the Soild report suggesting that CMU block retaining wall is sufficient to retain the 2:1 backfill slope.

Rohit
1-800-854-2658 ext: 6534
expoteksvc@netzero.com