Building an Vinyl Liner Inground Swimming Pool on Rock
Everyone wants an inground swimming pool build to go smoothly, but things always come up when you least expect it . . . usually when you start digging. The biggest variable is usually what you are going to find once you start digging over 3′ in the ground. 
Penguin Pools often comes across rock or bad fill in many newer subdivisions. Builders take fill from one site and put it on another site until they don’t have any more sites to hid the fill. Rock and buried construction trash makes building an inground pool very challenging. When building a vinyl liner pool, the walls have to sit on virgin ground so there is no worry about settling. When you hit soil or earth that doesn’t hold its form / collapses, you need to find away to create virgin soil. The way Penguin Pools of Milwaukee & Minneapolis builds vinyl liner pools on rock is fairly simple.
1. Dig your pool like normal to spec. The earth will fall and crumble making your dig shelf and ramps useless . . . Like the above picture.
2. Order Traffic Bond (usually 1/4″ with fines) and fill in the hole you just dug. This is the same material that gets compacted under your concrete flat work.
4. Once you pool dig is level along the entire dig shelf, leave it sit until it is completely dry. It is usually fine to work with the next day, but may take up to 24 hours.
5. Now you can re-dig your pool to specs and the walls will hold. The compacted TB dries like concrete and you now have virgin ground to build on. Your vinyl liner inground swimming pool will not settle or have issues due to poor soil. Just be aware that hand forming will be difficult due to the strength of the compacted TB.
*** Just an FYI, this requires a lot of TB 10 – 15 full dump trucks (quads). Don’t worry, this can then be used as backfill if you so choose.
Here is another slideshow of a pool we did in 2004.
Many pool builders will just use a patch to cover a wound. Using vermiculite to patch voids is an easy and cheap way to rectify the problem, however it isn’t the correct way to do it. You need to create the correct earth to build on so you pool will not have issues 5, 10, 30 years down the road. This costs more, but it is the correct way to do it.
If you have any questions, feel free to contact Penguin Pools of Milwaukee or Minneapolis.