well, i'm in southern alberta and aside from not as much humidity as you have, the temps are relatively similar. my concrete deck which completely surrounds my inground pool is approx 5 inches deep. it's a vinyl liner pool that was put in back about 23 years ago and aside from 5 or 6 hairline cracks, it has no heaving, no separation from the coping. it's done very well considering my garage floor and corner pillars on one side sunk 4 inches since the house was built due to heavy rains in june that really compact the soil. the concrete deck ranges from 3 ft around most of the pool to a very wide "path" that comes to the back of the house about 15 ft away. the entire deck has large slate type stones embedded in the concrete. the vinyl surface has retained it's integrity in spite of settling and movement i would have to guess. not sure what material is used for the retaining walls behind the liner as i wasn't here when the pool was built. i had a small tear i repaired a few weeks ago and i tried to get a sense of what the surface behind was. i've always thought it was compacted sand or dirt..it was darn hard, that's for sure..bent the tip of a knife poking it, even with water against it (underwater tear about 3 inches long)