While waiting for the new trailer to be delivered, we decided to convert part of this strip of lawn next to the carport into a gravel parking pad. This would be the proverbial "before" picture.
After much reading we opted for a pad topped with decomposed granite, or DG, as an effective DIY project. Unfortunately, the soil in our front yard is heavy clay silt, not a particularly stable base to build on. Further down the grade of the yard, this gives way to layered river pebbles as I discovered in my observatory project.
First step was to excavate out some of the clay. We rented our friend the front loader and scrapped off layers of the clay ...
... depositing in out in the "wild" part of our back yard.
We excavated a section 12 ft by 70 ft leaving plenty of room to maneuver the trailer into place next to the carport. Overall depth is about 10" on average with a few over-zealous spots down 14".
Once the area was dug out, we cleaned up the edges and the two ends where the front loader couldn't reach by hand. This took several weeks.
In the process, we discovered the fabled sewer clean-out that the plumber insisted must exist. We knew from the utility department flag where the sewer line must run but not where the clean-out was. Naturally it ended up in the middle of the project area. We will treat this as a "feature" and use it as a dumping point to clean the RV tanks at home.
One of the design dilemmas was how to edge between the trailer pad and the surrounding lawn. When it came time to put in the base material, we only wanted to rent the front-loader one day to reduce rental costs. We needed something we could build ahead of time that would act as a temporary retaining wall and remain as an edging.
We decided to build edging that looks like an ancient fort. We fastened 6 foot sections of side-by-side 4" PT rounds. Every 6 foot we buried a couple in a bit of concrete to hold the assembly up. Here is the complicated rounded-corner bit in progress.
Once done, we had a self-standing basin in which to fill with material. The outside will eventually be backed by top-soil to within a few inches of the top. This will be less of a retaining wall and more of an industrial-grade edging when all is done.
Next step is to take care of that sewer clean-out which will be right in the path of the truck. We created forms with spare Sonotubes and rebar making a protective sleeve around the clean-out. We should be able to drive on it without stressing the plumbing.
We filled with a couple of bags of high tensile strength ready-mix concrete with a temporary wooden cap. This will form a lip into which I can drop a plate or other cover.
We are now ready to put in the base material. We had 28 yards of "road-base" delivered. This stuff is a combination of limestone "fines" and coarse rock up to 1" size. We had a couple of yards left-over at the end.
The two of us were able to complete the job of laying and compacting the road base in one very long day. This was done as a series of layers or "lifts", each about 2-3" deep. We placed the material in with the front loader, and raked it out by hand. We moistened it slightly as necessary and compacted each layer down with a steel-plate vibratory compactor. All of our reading emphasized the need to compact thin layers to make a solid base, especially when we are working with such a small compactor.
Though small, this model of compactor was surprisingly easy to use and minimized the vibrations transmitted to our hands. It vibrates in such a way that it moves forward on its own. The hard part is not pushing it forward, it is holding it back when we reach a tight corner.
Once all of the road-base was in, we came back to add some drainage features. The driveway is sloped downhill toward the house and off to the right. That places most of the run off at the bottom end of the trailer pad. Furthermore, the soil in the yard beyond is built up and does not drain very well. Previously heavy rains caused a pool under the carport.
Along the driveway side of the pad, we dug out a trench to lay a french drain. I guess technically this is a "curtain drain" since we are catching and redirecting flow rather than draining out sub-surface moisture. I forgot to snap a picture, but we drilled 1/2" holes in a 3" sewer-and-drain PVC pipe, placed it in the trench on top of a heavy geo-fabric, filled with clean rock, and wrapped it up.
This will catch and divert some of the run off and will also be tied to the gutter down-spout for the carport. This would not have been a great idea if this were a real french drain, but in this case it should work.
The trench is the over-filled with more rock awaiting the arrival of the decomposed granite.
Beyond the end of the trailer pad, along the fence line, we started digging another drain system. This is to divert all of the water that makes it to the end of the driveway as well as to drain the bottom end of the pad. We will finish this project on the second round. In the meantime, when it rains, we have a mucky catch-basin.
The process starts again, this time with the decomposed granite or DG. We had 7 yards of this material delivered. Again, we had about 1 yard left over.
The total height to fill with DG was 2". Again, are reading indicated that thinner is better in terms of getting a solid surface that does not get mushy. We ended up doing 7 separated lifts. More than necessary but it was easier to rake out that way. We did not have the front loader this time so the transfer was all shovel and wheelbarrow and took a bit over 2 days to finish.
Once completed, we rebuilt the gutter down-spout and tied it into the drainage.
We were very pleased with the result of the compacted decomposed granite. We did not use any of the fancy additives due to cost but the surface is still very hard. It has weathered one strong rain so far with no surface erosion or softening.
Here is the "after" picture of the pad.