Once Clayton’s house was successfully elevated 9 feet off the ground, it was time to fill in the basement. I specified the type of fill to use – a crushed gravel that drains well and doesn’t compress – and Clayton ordered 280 cubic yards of the stuff, delivered truckload by truckload. Messier, the house lifting company, also served as the excavator, and it was their job to spread the fill in the basement and perform a compaction.
Fill is typically placed in layers, called “lifts”, 6 to 12 inches deep. Messier placed five lifts, each 10 inches deep, to reach the required total depth of 4 feet 2 inches. Crew member Calvin drove a Bobcat to carry fill into the basement and spread it evenly. Norm operated a backhoe outside the house to keep the fill supply close at hand, and other crew members in the hole checked level using a laser.
But freshly placed fill is quite loose, and the slab for the new ground floor wants a stable surface underneath. That’s what compaction does: it makes the fill denser and stabilizes it. For this part of the job, Messier brought two vibrating plates. You push them like lawnmowers, and they shake and shimmy the fill underneath to make the gravel particles interlock snugly. The vibrator’s effectiveness varies with depth, with the zone of maximum compaction occurring 6 to 18 inches below the surface. (That’s the main reason fill is placed in lifts rather than all at once.) After each lift, the Messier crew slid the vibrators over the entire surface of the fill until it was nice and flat and stable.
It was my job to test the fill and make sure it was compacted properly. How did I do that? I’ll save that tale for next time.