If the soil condition is predominantly compact sand, base preparation is fairly straightforward. The goal is proper compaction free of undulations (i.e. an uneven base). First, install screed rails using stakes. Adjust the screed rails to the proper height using a transit. Then, spread a layer of recommended compaction material evenly over the bottom of the excavation. Compact the material and screed the floor flat, filling any low spots during this process. Repeat several times as necessary. On projects where sand or engineered fill is used, the completed area will resemble a slab of finished concrete.
Additional work will be required when dealing with muddy, clay-laden soil. In this case, the hole should be excavated deeper and the base firmed up using 13- to 19-mm (0.5- to 0.75-in.) stone (typically limestone) to create a solid foundation. On installations that have breached the water table, and the soil is extremely muddy and unstable, the hole should be excavated an additional 152 to 305 mm (6 to 12 in.). Then, larger stones (i.e. road base) should be used to build the base before covering it with smaller 13-mm (0.5-in.) rocks or gravel. Geotextile fabric should be placed on top of this base to serve as a filter. Finally, place a layer of backfill on top of the fabric which will allow water, but not the fill, to filter through.
The same technique should be used if there are any voids in the excavated base; for example, if a tree stump had to be removed or solid granite had to be blasted out. Fill the void with road base, then smaller gravel, then fabric, and build the base on top.
In some cases, where soil conditions are severe (e.g. comprising a soupy tar mix), the only answer is to pour a cement base. In these instances, a foundation must be created similar to what is used to build slab houses, using 254 mm (10 in.) of cement with 25-mm (1-in.) rebar.
Extreme freeze/thaw conditions
In Canada, climate is always an issue for pool builders. During the winter, multiple freeze-thaw cycles have the potential to cause damage to any type of inground pool as water expands when it turns to ice. That said, fibreglass pools are no more susceptible to freeze-thaw damage than any other type of pool. One particular advantage they have in this regard is the flexural strength of the fibreglass shell, which allows it to bend without breaking.
By far the most important step to help maintain equal pressure inside and outside of the pool during freeze-thaw cycles is to never drain the pool during the off-season (or ever). This cannot be over-emphasized and should be communicated to the homeowner. Even in extreme conditions, a full pool will ensure hydrostatic pressure remains equalized.
By following these recommendations and installing a sump pipe or daylight drain, it will help keep melting snow and ice away from the pool. Another important factor to an incident-free winter is the proper construction of a standard cantilevered concrete deck. A typical 0.9-m (3-ft) (minimum) deck will be designed to slope 6 mm (0.25 in.) per 305 mm (12 in.) away from the pool. This angle will allow melting snow and ice to naturally flow away from the sides of the pool. Needless to say, the manufacturer’s instructions pertaining to deck construction should always be followed.
What immediately caught my attention was that fiberglass pool installation would have to be done in a hole dug almost to pool size. This saves on materials and labor, which is one of the reasons why fiberglass pools are increasingly gaining popularity. When the contractor installs a new pool in our aunt’s backyard, I’ll try to chat with them if they’re using fiberglass. Thank you for the heads up. http://www.hydroscapeinc.com/pools