Swimming pools blog

Where pools are constructed with the pool floor below the water table
a vertical drain pipe should be installed to which suction can be
connected to evacuate water from behind the shell when the pool is
emptied or partly emptied. If the pool is a fibreglass one you may
need to dig down beside the shell at the deep end as you empty the
pool and install a drain so you can suck out water from around the
shell to stop the pool floating. There may still be problems if water
can not pass easily down to the suction point.
With a liner pool in a concrete shell it is usually possible to slide
a pipe down behind the liner in a corner at the deep end, as you
lower the pool water level and pump out water that would otherwise
float the liner, if you do not want the liner to move. Otherwise,
allow the water to fill the shell up to the watertable, this will go
some way to balancing the soil pressure, and pump it out when work
needs to be done, or the new liner fitted.

With concrete pools, hydrostatic relief valves are needed to prevent
water pressure collapsing the walls and floor, but even the weight of
surrounding soil can cause damage.
Emptying a pool always risks such damage, and work which necessitates
the emptying of a pool should be planned to minimise the time that
the pool has to be empty. Even a 30 x 15 foot pool av 4 feet deep
contains water weighing 50 tons so the loss of this mass creates
unusual stresses on the pool structure.