Building the foundation

I really don't remember trenches and piles being dug in California before starting the slab of a home. Our structural engineers told us that we would need to dig 6 ft below the slab, create "trench piles" (concrete forms) and build up from there. Amazingly enough, this was probably the one time that I didn't question why...and now it has me all curious.

Is it because we are so close to the water? Is it because the development previously was covered in mangroves and then filled in? Is it because concrete is a heavier building material than wood? If there is any insight out there among the girls, please share the knowledge!

This was the state of the land two weekends ago (yes, I am a weekend behind...shame on me). The trenches had been dug in the shape of the house and then big boulders were placed in the bottom 2-3 feet. At the time, I was a bit worried that the boulders were being used instead of the trench piles, but the next day we arrived to see that they filled in the boulders and place dre-barb (um, how do you spell that anyway?) on top of the fill.

Alrighty, we're on our way!