Slope, soil and drainage
Ideally, you want a swimming pool site that’s level and slightly higher than the land around it. The underlying soil should be stable and easy to dig. Also, you’ll need a dry site, with good surface and subsurface drainage. Good drainage conditions will depend on the slope of the land and the nature of the soil.
By analyzing a contour map of your lot, you can determine where the land sloped and how steep the slopes are. You should also be able to locate any high spots, depressions, flat areas, or drainage paths. If you don’t have a contour map, wander around your property and take note of any of these features; then mark them on your plot plan.
While you’re at it, take a look on the far side of any fences. One might conceal a gully that could turn your sparkling pool into a muddy mess during a storm.
Even if your property has no ideal level area, remember that hillsides can become sites for magnificent swimming pools. Turn to Lots with a challenge for some solution to hillside building problems.
Because soil conditions not only affect the ease of excavating for a pool but also have the potential for damaging or even destroying a pool shell, you must determine the type of soil underlying your property.
Once you’ve zeroed in on a possible pool site, you can have the precise nature of you soil identified – have a hole dug to pool depth. Some soil types require special design features in the pool. Though the pool contractor may have had experience with these conditions, you may want to consult a soils engineer.
Loam, commonly called “garden soil,” is ideal for a pool site in many parts of the country since it’s easy to dig. The walls of the excavation will be stable and not likely to collapse. In other areas, though, it may settle or compact causing damage to the pool shell.
Sandy soil, the bane of pool builders, usually caves in during excavation. Because the walls must be shored up with wood or sprayed with concrete to prevent collapse, the construction cost is increased. Sometimes, a concrete pool in sandy soil must be built with thicker shell or supported on piers or pilings.
Wet soil, whether waterlogged from surface runoff or in an area with a high water table, is best avoided, if at all possible. Excavating for a pool in wet soil is very expensive. And the pressure of the underground water can collapse an empty pool built in such soil, or float the pool out of the ground.
Expansive soil, known as “adobe” in some countries, becomes a problem only when a significant amount of water percolates into the ground. The pressure exerted on the side of even a filled pool can cause it to collapse.
Some communities ban types of swimming pools that cannot be reinforced to withstand the pressure of wet expansive soil. A concrete pool in expensive soil may have to be built with a thicker shell; it may also require expansion joints between the shell and coping, the coping and desk, and within the desk. A trench dug around the pool 1.5 to 3 meters from the walls and filled with loose material can help absorb the soil expansion. Surface drainage must be directed away from the pool area and any drainage lines must be leak proof.
Corrosive soil is no longer a serious problem, now that plastic pipe has replaced metal pipe in swimming pool construction.
Though metal pools and the metal wall panels used with some vinyl-lined pools are treated against corrosion, special precautions may be required in highly corrosive soil. Your pool contractor or soils engineer should be aware of any problems in your area.
Rock, sometimes visible as outcroppings but usually hidden beneath the soil, requires expensive drillings and blasting. If rock underlies the site you must use, consider building a vinyl-lined on-ground pool without a hopper or deep end.
Filled ground is unsuitable as a pool site unless the soil was compacted properly or unless the bottom of the pool will be deeper than the disturbed soil.
The weight of a filled swimming pool built on improperly compacted fill compresses the soil and allows the pool to settle into the ground. If it settles evenly, the shell can pull away from the desk or, in the case of a concrete pool, from the bond beam. Uneven settling can crack the shell of a concrete pool. An expensive solution is to support the pool shell on piers or pilings that sit on solid ground.
Even though you may not see evidence of fill, dig some test holes on your potential sites. If you find layers of different kinds of soil or any manmade debris, you can be sure that the area was filled.
Usually, natural drainage on the surface of your property or a neighbor’s property can be diverted from a pool site; disposing of underground water and pool water is another story entirely.
Surface drainage need not be a problem if you avoid building your pool in a low-lying area from which water cannot drain. During storms, muddy water collecting there can spill over into your swimming pool.
Water running off a slope or down a natural drainage path can fill you pool with mud and debris. If you cannot find a site free from runoff, you can landscape the pool area to divert the water
Subsurface drainage problems – water accumulating just under the surface of your site, or a spring running under your property – may not make a site unusable, but the excavation will be more expensive; in addition, a drainage system may have to be installed under the pool to carry away the water.
Sometimes, a soggy low spot or especially lush vegetation will alert you to an area of poor underground drainage on your property. Most of the time, though, the condition is hidden until you dig a test hole or start excavation you pool.
Ask your swimming pool owning neighbors if they encountered any subsurface drainage problems; you can also consult local soils engineers, pool contractors, and building inspectors.
Pool water drainage involves disposing of the pool water if you have to drain it, and disposing of the water from the filter when it is serviced. Dumping 115,000 liters of chlorinated swimming pool water in your garden would kill all your plants – not to mention the damage it would inflict on your neighbor’s yard and the whole eco-system in your area.
If your community prohibits emptying pool water into the sewer or storm drain system, you may have to construct a dry well to absorb the water.