Our 22' x 42' x 8' in-ground, free-form vinyl pool was built in an area of heavy clay. The first three feet below the ground surface are sand and gravel, with up to 13 feet of clay below that. A waterfall feature and series of low walls are built into a hill along one side of the pool that rises almost seven feet above the top level of the pool over a distance of just 20 feet or so. We have had the liner float off the steel walls at the end of each summer, and are seeking a permanent solution to the problem.
The water behind the liner does not drain out, despite being in direct contact with the soil, leading me to believe that there is a significant drainage issue extant. We had an engineer look at the situation, and he is thinking that the surface water is pushing the liner off the walls and we need to evacuate the water before the liner moves. One solution is to create a wick under the deep end of the pool, filling an area with permeable material until we hit sand under the clay, so that the water will collect there and flow to the sand below the clay accordingly; another is to put a dry well and pump at this lowest spot under the pool. Anyone have advice or previous experience as to which is most suited to our circumstance?