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eltbee

building up lawn area in front of retaining wall for grass (w/ pi

eltbee
11 years ago

Background: North Texas area (Collin County). Slab on grade. No basement. Soil is clay. Existing grass is Bermuda. We have a small backyard. It is roughly 30'x40'. The corner of the property sloped off towards the alley as you would expect to promote drainage. It had excellend drainage but the slope was too great to be usable. There was an existing 2' retaining wall on one side of this yard area that also sloped down to the corner. And there was a soon to be large Cedar Elm tree right in the corner. The upshot is we wanted to reclaim the space, however small, for use as a play area for the kids. I have done a few things:

1) Removed the tree.

2) Extended the 2' retaining wall around the back of the yard so that it is level with the existing retaining wall, back-filled the wall with about 12 inches of 3/4 angular limestone gravel in a landscape fabric envelope, and put a fence on top. BTW, the height of the retaining wall at the highest point was 20 inches so I didn't do a draintile - just gravel.

3) Installed 4 inch sewer pipe (white) for all of the gutter outlets to this area and daylighted them through the wall in the corner.

4) I put in a 12x12 basin + drain grate in this back corner. In fact, my gutter drainage pipe is all tied in to the basin. Not sure that it will actually be useful as a drain though.

5) I redid the entire sprinkler system from scratch in the area so the heads can be properly adjusted to the new level (time consuming holy cow!).

Now I am at the stage where I am bringing the back yard up to level with the retaining wall and re-setting the grading. The area will be topped with turfgrass (Bermuda). Since it is a blank slate, I want to get the soil and grading right for drainage and grass. In general I am trying to do it right since this area is effectively built up from scratch. Since it is a small area, cost is no object. I have at my disposal anything from local landscape vendors. Most people use living earth stuff here. I have been filling the area with Texas Black which is very fine, clean, clay fill dirt. This is going on top of the existing soil which is almost all clay and rock. I know that I can't put grass down on the clay fill dirt so I must leave room for topsoil. The existing Bermuda had very poor topsoil. As near as I can tell, they just laid sod on top of the clay fill dirt which I think is normal for new construction.

Few questions:

1) I have the Texas Black (clay) as primary fill dirt. How much room should I leave for Topsoil?

2) When I put the topsoil on top, should I mix it in with the clay to create a transition? If so how much transition and how much pure topsoil?

2a) Any particular topsoil I should use? I have access to Topsoil+Compost mix which is the plan so far.

3) Should I grade the clay layer first and then put topsoil on top or grade the final clay+topsol mix from above?

4) Should I seed or sod? Cost doesn't really matter but the sod I have seen so far it grown in clay which might not be so ideal to layer on top of what I am preparing?

4a) If seed, it is basically 1st of August. Too late to seed? Any particular seed to use?

5) Since my regrading will encompass existing Bermuda areas, is it ok to just cover it with the dirt mixture I am asking about above? Do I need to cut out the old grass?

6) From the base of the foundation to the most distant point in the corner of the retaining wall where the drain is (roughly 40 feet), the elevation change is about 10 inches. This is about 2% gradient. Do I grade 2% evenly the whole way or do I put in more gradient near the house and less through the lawn. The existing codes recommend 6 inches in the first 10 feet from foundation. Because this area doesn't see any runoff from the roof now, it should only handle the water from the lawn surface itself if that matters.

7) My basin + drain sits about 4 inches below the retaining wall in the most distant corner of the yard. Not sure that it is necessary now. Any tips on how to grade the lawn to incorporate it? Or should I pull it out (cover it)? Could I create some swales to direct the water to it?

8) In preparing my area to take soil or sod, anything else I should mix in? Local guy said use some Texas greensand.

Any other questions I should be asking?

Thanks in advance!

eltbee

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