I found out that the roots of Oak trees do not "grow" under the slab, like the sycamore's or the magnolias. Most likely the problem is the drought and I'm told I need to water the area around the house to keep the clay from shrinking and the tree roots from sucking the water from the clay. The first concrete repair contractor is coming by tomorrow. We'll see what he has to say about the cracked bricks too. Thanks for your comments Jay J.