Well Points

Each of the 3 years we've owned our pool, we have had occasional instances when the liner lifts in the same area of the deep end of the pool. The total size of lifted area is about 3ft x 1ft. There were no ground water issues during the installation in spring, and the liner lifting wasn't evident until later in the summer (when water table should be lower)

I have no reason to believe that ground water is the cause, but I don't know of any other rationale, so I have been investigating installing a well point beside the pool

Can you help me understand this problem as it will determine whether I live with it or fix it. I'm trying to understand if I need to dig down a couple feet, or to the depth of the bubble (~8ft)

My understanding is that the bubble is formed when the pressure behind the liner is greater than the pressure in the pool at the same depth. The water pressure in the pool is the depth of the water, the water pressure on the back side is the pressure of the soil and water.

If I assume water saturated soil is around the same density as water, then the water table would have to be at or above the waterline of the pool. To decrease the pressure on the backside of the bubble, I would only need to dig down ~1-2 foot deeper than the waterline and pump out the water

The other way I've rationalized this assumption is that the pool walls held without any problem during construction the walls support themselves even without water pressure.

Thanks for you help.