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Failing retaining wall at existing driveway

Failing retaining wall at existing driveway

(OP)
So someone contacted me and wanted me to come out and take a look at the condition at his property to see what the potential solutions would be. I have attached a pdf of a cross section through the area of concern.
Basically the owners driveway runs along the side of an existing property line retaining wall that is failing. He contacted the owner of the other property who rents out the house to see if they would share half of the cost to replace the wall and they said no.

As you can imagine my clients concrete is developing large cracks and sinking at areas due to the existing failing retaining wall. So he would like me to design a new foundation system that would support a new concrete driveway without imposing any load to the existing wall as well as still support his driveway if the wall fails.

There are a few options I have and my client will be paying for the solution, so I am just looking to refine the options in favor of an economical design:
A new structural slab supported on a grade beam and caissons embedded below the existing wall footing
A new property line retaining wall.
A new concrete retaining wall spanning horizontally between caissons a few feet inside my clients property that extends down to the depth of the adjacent existing retaining wall footing. This wall would be supported by caissons spaced at 9ft on center with the point of fixity assumed to be about a foot below the existing footing

Any of the solutions would disrupt the soil behind the existing wall so it would have to be shored up during construction.

I am leaning towards the solution that supports the new driveway on a grade beam and concrete piers, but if the existing wall fails then the driveway would be freestanding and I would have to design the whole system for lateral seismic loading. (Located in Southern California)

Any thoughts and or suggestions would be greatly appreciated.

Thanks in advance.

RE: Failing retaining wall at existing driveway

While it may not last forever, consider taking a typical drill rig with augers, say 10" diameter and drill a bunch of holes in concrete and soil below down to some reasonable resistance. Then under ream the slab making with a haunch. Fill with concrete. It would provide a temporary solution, perhaps sufficient to unload the existing wall some and not cost a lot. It might even work out as permanent. Decide on spacing of holes by examining the drilling resistance and the soil there, with starter guess at 8 feet x 6 ft. Support then is a combination of these "piles" and the earth now there supporting the whole thing, but less after piles take some load, which also reduces the lateral load on the old wall..

RE: Failing retaining wall at existing driveway

ask for a construction easement and make an MSW.

If the wall was for the benefit of the land owner rather than the neighbor, it seems it would be his expense. I would not read reluctance to pay as unwillingness to participate. Neighbor may not mind not paying for a new wall even if construction temporarily encroaches into the neighbor's property.

Just have to ask.

f-d

ípapß gordo ainÆt no madre flaca!

RE: Failing retaining wall at existing driveway

OG again. Looking at the tight space, only light equipment should be there and even then possibly on planks to spread out loading, assuming the work will not involve replacing the existing tilted wall. Hey that driveway looks to be pretty good shape. Saving it might be worth while.

RE: Failing retaining wall at existing driveway

I assume your client's property is behind the top of the wall. The wall is not very high. So, excavate the soil from behind the wall, under the driveway, and then backfill the wall with better draining, more granular soil or crushed stone. This should reduce the pressure on the wall. Stay off the neighbor's property. Leave the wall alone except for cleaning out the weep holes, if there are any. If no weeps, drill some.

www.PeirceEngineering.com

RE: Failing retaining wall at existing driveway

P.S., as OG said, the driveway doesn't look too bad. How much has the wall deflected or tilted? Also, the driveway cracks appear to run perpendicular to the wall and to what I would expect to see. I recommend monitoring the wall for movement over a few months and possibly the winter. If nothing is happening, maybe nothing needs to be done. Maybe you just have a cracked driveway - not uncommon. Don't forget to check if any of the wall's weep holes are clogged and make sure any downspouts are not discharging water to the back of the wall. If so, re-route them away from the wall area.

www.PeirceEngineering.com

RE: Failing retaining wall at existing driveway

Does he have an updated survey? Looks like you split that wall down the middle as the property line but for $400-600 bucks he can know exactly where that wall is in relation to his property line. If any portion of it is on his neighbors property he has a case to argue but I'm not a lawyer. Building department will probably require a survey anyway when they pull the permit for the repairs.

Have you looked into a geogrid solution? The wall isn't that high which would save on grid material but you would want to be careful with the tight space and the load from the house when you start excavating. Just a thought but it's worth looking into.

Tie backs, soil nails, dead man anchors? There might not be enough room on either side of this wall to install these but you might be able to pour a dead man anchor close to the house and run threaded rods through the wall to stabilize it from moving anymore. Obviusoly this need to be thought of more in depth to see if it possible with the field conditions and access but it's worth a thought. Good Luck!

RE: Failing retaining wall at existing driveway

Seems like a good job for lightweight polystyrene fill. If the existing wall is not structurally damaged then excavate down and replace with lightweight fill. Simple job, not a lot of equipment required either. Would need to be wrapped though as diesel/petrol spills would damage the fill.

But as others said, the driveway looks pretty good to me. A photo of the retaining wall face would be helpfull

RE: Failing retaining wall at existing driveway

Polyurethane injection under the driveway may buy quite a bit of time at a relatively low cost.

RE: Failing retaining wall at existing driveway

"Polyurethane injection under the driveway may buy quite a bit of time at a relatively low cost." How so? Pressure injection behind the wall may push the wall out farther (or over).

www.PeirceEngineering.com

RE: Failing retaining wall at existing driveway

PEinc, I don't know how bad the wall looks. If injection is done carefully to fill voids and not lift the driveway it can be performed without exerting much pressure. That may prolong the life of the driveway. The concern seemed to be damage to the driveway. If the retaining wall is in bad shape or unstable, then this would not be my approach, but if the wall is not bad, then it may be an option.

RE: Failing retaining wall at existing driveway

It seems to me that the original poster's concern is the failing wall, not the driveway.

www.PeirceEngineering.com

RE: Failing retaining wall at existing driveway

PEinc. You suggested that maybe nothing has to be done to the wall. If that is the case and they are concerned about the driveway, then my suggestion may be a way to address the driveway.

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