Help! Paver Sidewalk Cut-out: Erosion Problems. Retaining Wall?

13 years ago

Hi:

I've posted a separate entry in this forum regarding my sidewalk pavers:

http://bit.ly/bMnELU

Long story short:

I pulled-up and re-laid 18" hex concrete pavers on our city sidewalk due to cracked/broken pavers, uneven surface, etc. It's a sloping hill there, about 4-5%.

As part of this, I had to narrow the sidewalk around a mature pecan tree. I reduced the width there from 6' to 3' to accommodate roots. This left a 3-foot by 15-foot bed around the tree (around 7.5' on either side of the tree). I mulched this area and planted it with hostas and liriope. (shady area)

The problem came with the rain yesterday--I didn't have any kind of border next to the sidewalk pavers. The rain came down the hill, washed-out the mulch, and eroded the sand under some of the pavers, thus compromising the sidewalk.

The question is--can I simply install a wooden border next to the pavers, such as a 1x4 rail or do I need to build a retaining wall and make a level, rather than sloping, bed around the tree to prevent wash-out?

Thanks--rapid replies appreciated, as the rain is returning in a few days!

-Mark-

1. Problem AreaÂFlooded, Before Resetting Pavers

{{gwi:20858}}

2. SidewalkÂAfter Resetting Pavers, Looking Down (pavers at tree were raised subsequent to this photo)

{{gwi:20859}}

3. SidewalkÂAfter Resetting Pavers, Looking Up (pavers at tree were raised subsequent to this photo)

{{gwi:20861}}

4. Plan (Note: bed around tree expanded during construction due to addl. tree roots discovered; now it's approx 3'x15')

5. Sidewalk after rain: mulch washed-out, bed sand at end{{gwi:20880}}

6. Sidewalk after rain: top edge, sand & dirt
{{gwi:20882}}

7. Sidewalk after rain: side edge, erosion, compromised pavers
src=http://homepage.mac.com/bigmark/Sidewalk_Drainage/DSC_0003_2.jpg>;

8. Compromised paver
{{gwi:20885}}

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Comments (5)

oilpainter
13 years ago
This is city land. Anything you do can be ripped out by the city if they don't like what you do. Water careening down a slope is sure to wash out the soil under pavers that are not set in concrete. You don't need a retaining wall to prevent the mulch being washed away by that amount of water. A low concrete or wood edger would do. It would do nothing to prevent the washout of the sidewalk though
oilpainter
13 years ago
I also see a problem with that piece of 2 foot sidewalk. Anyone in a wheelchair or pushing a baby stroller would be stopped dead when they got to that spot. I'll bet there will be complaints to city hall> think you should call the city and let them deal with it.
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Please note that the walk grade slope along its length does not matter at all, only that it should be a smooth walking surface. The important part is the cross slope that carries the water over the curb to the gutter, which should closely match the grading detail I provided. The transition areas can deviate from the standard cross slope if the area is higher in grade than the adjacent areas with the proper cross slope. Looking at your latest graphic I see a 10% slope from point B to C. This looks suspect to me, since this area should be one conforming to the standard grading detail and the lengthwise slope of the walk edges should be the same as the slope along the curb. Since the overall street slope is around 4 to 5%, it seems unlikely that any section of the curb would have a 10% slope. On the subject of cost, I would think you might need around 2 cy yd of fill to bring the walk up to grade. The best fill would be a something like a select road base material. In my area the cost runs around $15/yd from the crusher and up to twice that from a material supplier, plus trucking cost. Here we have some mineral soil types with clay (not top soil!) that can be compacted to support walks and drives that only carry light loads. Never use a clay with lumps. It will leave voids and result in settlement. You might want to look at renting a plate compactor for this project. A thin layer of sand on top of the base material can facilitate getting the pavers set for a smooth surface.
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"Does this address your concerns enough?" Not really, because you are not adequately describing degree of severity. A picture would give an idea of HOW MUCH slope and what things and how much space are in the area. It would be a better way for me to predict complications, or to determine if there is an easier way than what you are proposing. I want to see how much slope and what other things there are in the work vicinity. Is there a fence between the properties? How far to the next property? A simple picture would probably show all these things without me needing to think and ask about each thing. There are aspects to your drawing that I don't understand. A picture of the site would likely make it easier to speculate what you are proposing. It sounds like you're building a retaining wall. Is this really necessary? (A picture would probably tell!) I'm going to speculate that it isn't unless the grade change is severe. In that case it would be preferable to have the wall outside of the paved area ... not underneath the edge soldier course. Placing it under adds complication to the compaction process. What is the paver pattern? If minimal cutting is a goal, the retaining wall will create another complication. For pedestrian and light duty vehicular use, 6" base is overkill. 4" is sufficient. If you're going to be driving a skid-steer across on a routine basis, then 6" well compacted base might make sense. Where are you located?
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@partim and @gardengal48 and others Hi there. Thank you for all of the comments. I really appreciate them. Here are a few better pictures of the trees. The road rash that I am talking about is the ability to see through them now. On the road side that abuts the busy street. Over the years, I have added just a few inches of mulch not touching each of the trunks. Just to clarify, I’ve planted 40 of these same arborvitaes at a friends house, and we haven’t lost one, there. My main concern here at my house, is the fact that they are looking worn and tired! Not symmetrical for my ocd eyes ha! And the reason why I haven’t cleaned them up, is because when I have tried to weed them, I get a bunch of roots up with the weeds as well! Hard to just do a quick weed job on them! Passers by seem to think they are there to throw stuff into, so I’m constantly picking crap out of the base of them! My main concern was the looks of them like I said, but also the fact that the base of the retaining wall is getting pushed aside and out from the looks of it. And roots are showing from that side. The rocks are starting to ease their way loose. Hope this helps! All the advice is so appreciated!!
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Would probably leave the fencing in place for insurance/liability reasons. I see a shadow that suggests the walls are north/south -- that the sun rises/sets front/back of the house? Easiest and least expensive way to deal with the visual on the front is to plant a hedge of shrubs that will look good year round -- grow thick and keep their leaves. You should also probably waterproof the exposed (middle/interior/visible) side of the front yard. you could do the same for the back wall or the next easiest way to "finish" the center space is to extend the concrete floor of the existing step/stoop and add a full width, high roofed (gable topped) screened porch or sun room, covering the concrete wall sides with faux stone panels. Depending upon what is in the basement and how you want to use this space, you could waterproof just the first eight-to-twelve feet or so of the exposed wall and then remove the rest of the wall and the dirt that is to its left (behind it -- using that dirt to level your back yard) and build a new wall (toward the left/back of the yard) at a right angle to the original wall and have that wall include steps leading to/toward this space from your back yard patio above the new wall (as far away from your house as the new wall extends).
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ken_mce
13 years ago
This is a lovely and creative way to deal with one of the classic sidewalk problems. The other posters are correct in that technically it probably is city property and the city can do what it wants.

My experience in similar situations is that the city guys have more work than they can handle, and if I improve something and no one complains, well they have real work to do someplace else. The same goes for the utility companies. In that narrow area, is there room for a stroller or wheelchair to pass through? If so, odds are you're fine. If not, can you widen towards the uphill side, away from the tree?

You might look into switching from sand to small gravel and see if it will resist washing. In this setting I think a masonry edge would look better and hold up longer than wood. However wood will do.
mrmambo
Original Author
13 years ago
Thanks to all for your feedback; in short:
- the property is City-owned, but the maintenance of same is left to the home owner. The City does not maintain residential sidewalks and generally does not deal with them unless public construction requires it, a homeowner requests assistance, or a formal complaint is lodged.
- the width of 3' is considered standard for sidewalk cut-outs, as far as I can tell. The City of Los Angeles, among other municipalities, approves of this width as a standard minimum for pedestrians, strollers, wheelchairs, etc.
- I decided to try using plastic paver edging, which is held in by metal stakes. This seems to be a standard solution and should provide a solid edge next to the pavers to prevent wash-out.
- I've decided to forego the construction of a retaining wall, as the landscaping is really secondary to the sidewalk pavers. Construction of this terraced "box" is probably an extraordinary effort for what is a public walkway.
- I may use gravel in place of the mulch in the landscaped area, as it should be more resistant to wash-out and allow some dispersion of the water flow.

Thanks again-

-m-
mbright
13 years ago
If the pavers don't work out for you, you could try rubber. Our city has used flexible panel sidewalks around trees for years and they work really well with uneven surfaces and above roots like yours.

Help! Paver Sidewalk Cut-out: Erosion Problems. Retaining Wall?

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oilpainter

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Help! Paver Sidewalk Cut-out: Erosion Problems. Retaining Wall?

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oilpainter

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