toe/heel proportions

[scherry]

I have a wall with a property line so close to the face of the wall that it isn't funny. is there any reason I cannot use a retaining wall without a toe if I can meet all of the soil pressure and stability requirements? I cannot think of one...but then...

thanks.

 

[Focht3]

You can. It's harder, but it's possible to do.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[gandersen]

scherry:

One approach to retaining walls on property lines is to tie them back (install tiebacks or anchors into the backfill to restrain the wall).

Another approach is to use a Mechanically Stabilized Earth (MSE) wall built out of internal reinforcement that acts like a gravity wall and gets its stability out of its own weight.

Another approach is to use a cantilever wall that gets stability from internal bending moment capacity and is "anchored" by the underlying soils.

I hope this helps.

Glen

 

[scherry]

thanks to everyone. i am afraid i am really only familiar with cantilevered retaining walls and some of their closest relatives not having done much stabilized earth or ties although i am basically familiar with the concepts. i think i have worked it out, but i appreciate the input from all. the biggest issue i had here was that there is also a fire lane at the top of one of the walls and the moments due to that are quite high, despite the fact that the walls are not particularly tall. i think the ties would still work, but am guessing the stabilized earth might not...anyway, unless I did the math wrong last night at 1:00 AM i am done with it for now, with a small toe. of course when I wake up I will recheck all of my math. Again.

thanks for thre input.

 

[cdh61]

scherry,

I have placed a segmental retaining wall 25 mm from a property line, with a toe load. Depending on the type of wall (or blocks) you are using, a vertical wall near the property line with toe load can be used, followed by a batter (if required).

Check out the segmental retaining wall blocks by risistone.com., many be the Durahold II blocks will work, they did for me along a property line with some truck traffic.

regards

 

[Focht3]

A MSE wall can work for your situation; these can be very cost effective if the grade change is relatively small (i.e. 6 ft or less.) This approach avoids the use of concrete or steel to carry the loads, so the facing wall is present to protect the geogrid or geotextile, not to carry load.

I've done far more conventional walls, but it's pretty clear to me that MSE is the way to go on "short" walls where the underlying support quality is good to excellent.



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[PEinc]

scherry,
What is the finished height of your proposed wall? The height can greatly influence the type of wall needed. Are you placing fill behind the wall, above original grade, to create a new higher finished grade? I would not worry about tiebacks, tie rods, geogrids, etc., until I knew the wall height, soil conditions, required surcharge loads, and if this is a fill wall or a cut wall. Fire lane loading should still meet HS20 or HS25 loading, shouldn't it? You need to consider more than the location of the property line when picking wall type.

gandersen,
you make good points. By "cantilever" wall, did you mean a cantilevered soldier beams/sheet pile wall?.

 

[scherry]

Actually this is garbage soil to the point where the geotech has recommended removal and replacement of the native soil to the rock horizon (2 to 4 feet below natural grade) they are building up the site substantially and have been directed to do so with select fill. the retainage on the walls is rather low - 6.25 max. And based on the above, the retained soil is fill rather than cut. the wall height varies from that where there are curb requirements in some cases, and I have gone a little deeper below the finished grade in the areas where the walls form part of the detention pond, so the max design height for stability analysis is 7.75. the fire lane is HS20 loading and another wall carries a parking surcharge - passenger cars. A dumpster pad is at one corner where two walls meet - the highest point of the walls naturally. There is also a 6 foot privacy fence required and the architect has stated that he intends to place this fence - hurricane with slats -on top of the wall. i am fighting this wherever possible. the walls are drained. the active soil pressures are not extreme because the backfill is select fill. I may be conservative in some of the friction values because of the replacement of the native soil, but that is what i have been given to work with. I am using a reduced pressure wheel load at the "deeper" section, and a modified boussinesq for the wheel closest to the wall the wheel further inside the wall for the cumulative lateral pressure on the wall.

 

[PEinc]

How close will wheel load come to the back of the wall? AASHTO requires retaining walls to be designed for a minimum traffic surcharge equal to 2 feet of earth overburden or 250 PSF vertical surface pressure. This may give lateral loads less than a Boussinesq wheel load. It is rare that a wheel load will be right at the back of the wall unless the vehicle is crashing over the top of the wall.

Your wall isn't very high. You may be able to install a soldier beam wall with either precast concrete lagging or precast panels. These can have an architectural finish. Drilling rock for soldier beam embedment below finished grade could be expensive. Check AASHTO specifications for highway bridges. The manual contains pressure envelopes for cantilevered soldier beam and sheet pile walls.

Your best wall choice could be a segmental retaining wall made of blocks with geogrid, probably founded on rock. This would require a temporary, shallow, sloped excavation onto the adjacent property. It just wouldn't make much sense to install sheeting along the other property line in order to maintain it while making a 2 to 4 feet deep wall excavation. If you have to sheet the excavation, you might as well build a cantilevered soldier beam wall.

 

[cdh61]

scherry,

You still have several options of retaining walls based on discription. But, from what I read, it may be best to use a cast-in-place wall anchored to bedrock with tie backs also anchored to rock. With the rock only 2 - 4 ft below grade, this is not a problem or big cost to excavate.

I would assess the cost of a few options, including maintenance costs and potential cost associated with damage to the wall should this occur. Also see if there is a preference by the owner. I mention this becasue the SRW mentioned before came about due to construction costs and potential long term maintenance costs. And on another project, the opposite occurred.

regards

 

[scherry]

unfortunately in regards to the distance from the wall to the wheel load, the architect placed the 21 foot fire lane starting at the face of the wall. so theoretically the wheel could be right at the wall. however given the fact that if it is, no one can get off or get to equipment, and other considerations (that is the closest my tables go to give me the design loads...) I set it 2 feet from the face of the wall - but I did not skin the factors of safety, either.

 

[g7mann]

Sheery:

I was faced with a virtually identical situation about two years ago. In this case there was a [three] tiered Keystone block wall located just inside the property line. The wall not only provided the "edge" to a site but it also "retained" a buried circular metal detention tank. In addition, the local [County] agency required a fire truck loading immediately along the top of the wall.

The wall reinforcement was installed per design, in itself a somewhat unusual event, but the backfill was a relatively poor quality silty sand wiht "junk", although it was reasonably well compacted in-place.

The contractor built the wall before installing the detention tank. Then, because he wasn't paying attention, he dumped his trackhoe through the top of the tank. This required the removal and replacement of the tank. This replacement process resulted in loaded and unloaded dump truck traffic along the top of the block wall. In all, we counted a total of three thousand four hundred passages of trucks, many of them "overfilled" since they did not have to use a public street. This traffic resulted in about an inch of movement in only the top blocks. Based on this experience I will firmly recommend the use of a geogrid reinforced Keystone [standartd] block wall to you for this project. Providing you engineer the wall appropriately, and closely observe the construction process you should be fine.

Best of luck
g7mann

 

[DRC1]

If you are putting the wall primarily in a fill, why not use a gravity wall? That way you don't need a toe, you can leave a parapet for a curb, and have good connection for the fence. Plus it can easily accomidate the dumpster pads. You could go cast in place, or use stacked concrete blocks (the 2'x3'x4' size)- some are now made to be interlocking - or you could use preast concrete bins such as Doublewal.