Is it possible to have an MSE Retaining Wall without Ties

[oengineer]

I have been asked to provide a cost estimate of an MSE Retaining wall with tie backs & an MSE Retaining Wall without tie backs. Is it possible to have an MSE Retaining Wall without Ties? Are tie back Retaining walls different than MSE Retaining walls? Any input is appreciated.

 

[oldestguy]

At low heights and with the wall made up of concrete blocks (3'x3'x5' it is a gravity wall. Go higher than some limit (maybe 6') you need the ties.)

 

[oengineer]

@oldestguy - The maximum height for my wall is 4'-1" and the the minimum height is 1'-0". So, would I not need tie backs for my MSE Retaining Wall? From the literature I have been reading on MSE walls it seems you always need some thing for tensile earth reinforcement.

I do not have much experience designing retaining walls, this is basically my first time.

 

[zlindauer]

MSE means "Mechanically Stabilized Earth" so if you remove the tie backs it is no longer classified as an MSE wall, but rather a gravity wall.

 

[JAE]

I've always seen 4 ft. as a maximum height without ties - but it does, obviously, depend on the size, width and weight of the actual block system you are using.

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[oengineer]

@zlindauer - I was asked to look into determine a cost for MSE Wall (with & without tie backs) and a reinforced retaining wall. It seems, for my given max height, you would suggest just using a reinforced concrete gravity wall or cantilever wall?

@JAE - I haven't seen any information/literature for an MSE wall without some type of tensile earth reinforcement. This project is in Texas and TXDoT calls for tensile earth reinforcement in their specs for MSE retaining walls.

 

[IDS]

As zlindauer said, MSE is mechanically stabilised earth, so the "tie backs" are actually soil reinforcement, rather than ties. A tie-back wall has a different design methodology.

But in answer to the question, you can certainly have a modular block retaining wall without soil reinforcement, and if it is designed properly you can go much higher than four feet.

I suggest you contact some suppliers for cost estimates.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[BridgeSmith]

If you can make a gravity wall work using precast blocks, that is obviously less expensive than a block-faced MSE wall. How high you can go without soil reinforcement (geogrid or metal ladder-type "strip" reinforcements) depends primarily on the backfill material. Specifically, a granular material with a high angle of internal friction (phi) will be stable at a greater height than material with a low phi angle. Block suppliers, such as Keystone and Mesa, have tables for their gravity walls with various backfills.

The choice of a block wall or semi-gravity cast-in-place concrete wall usually depends on whether the top of the wall can be transitioned in 8" steps, which is necessary for a block wall.

 

[oengineer]

@IDS - I have contacted some suppliers and also looked at TXDOT (Texas Department of Transportation) to find out past low bids on retaining walls in order to determine at unit price per sq. ft. Thanks for your input.

@HotRod10 - I am new at designing retaining walls, so I wonder if the geotech report would contain a recommendation of the type of retaining wall to be used? Is it typical for geotechnical engineers to make retaining wall recommendations?

I have an adjacent building about 3 to 4 ft away from my proposed wall. Would this effect the type of wall to be used?

 

[TehMightyEngineer]

oengineer, also take a look at precast modular concrete gravity walls:

https://www.arrowheadprecast.com/images/products/recon/designs/ap-recon-gravity-wall.jpg

https://i.pinimg.com/originals/55/23/64/552364919c34bd9777dbea381e0ef32b.jpg

https://i.ytimg.com/vi/_9ML2tAT2co/maxresdefault.jpg

They're kind of a hybrid between MSE and gravity block walls.

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[BridgeSmith]

"Is it typical for geotechnical engineers to make retaining wall recommendations?"

I wouldn't know. At the DOT where I work, we don't have geotechnical engineers; we have geologists. They give us the soil properties, bearing capacities, etc. and we choose the type of structure, size it for stability and/or capacity, and do the structural design.

"I have an adjacent building about 3 to 4 ft away from my proposed wall."

In front or behind?

 

[oldestguy]

A rule of thumb for gravity walls is this. The material in the wall is solid, generally some kind of masonry, not hollow sections. The width required from front to back is set at 1/3 the height. Using concrete block when the cavities filled with concrete would work, but if filled with earth, this rule would probably say front to back width to be closer to i/2 the height. I'd not consider these rules for heights over 6 feet without a geotech doing a stability analysis. This rule only applies to a level backfill surface. If sloped retained surface, do a stability check.

 

[BridgeSmith]

The block systems we've used for gravity walls have a tail with openings and a flange to be filled with and to lock in the gravel around and within the tail, producing a wall system that can be assumed to be a solid mass the depth of the blocks (generally about 21" for the standard blocks). The design height is in the range you mentioned, from 2 to 3 times the depth, depending on the properties of the retained soil, the backslope, and whether any significant live loads will be present (trucks driving above the wall). The block manufacturers have tables to help (some have design spreadsheets available, although it's not difficult to do the calculations.