dirt collapsing from under pier

I have inherited a mess. a local contractor added on both ends of my wife's one story house before we met. when he did he forced water to flow under the house instead of around it. Now I have stopped the water flow and dried up under the house, but damage has already been done. The house is on the side of a steep hill, the builder cut a notch in the side of the hill and set pads to stack cinder blocks for the outer wall. on top of the notch he placed his pads and stacked cinder blocks for his 2 center beams and the front wall. As a result of the water the top of the notch he cut is colapsing from under the pads. One is already no longer supporting the beam at all. I want to pour some 4 inch diameter 1 foot long cement columns with rebar running down the center for support and set so that it will protrude 1 inch from the bottom and leave a 1 inch depression in the top so the individual pieces will not slide of one another. I will drive these into the ground with a air/hydrolic jack to the sandstone aprox 6 feet below the ground surface. I want to set a steel plate on top of this to disperse the weight over the entire area of the cement pad I will set on top to stack the cinder blocks. My question is how thick of a steel plate should i use.

 

Welcome to the forums.

How about some pictures?
http://www.doityourself.com/forum/el...-pictures.html

 

Your plan is seriously flawed. A 4" dia. concrete column, with rebar down the middle, will spall and fracture as you try driving it into the ground. And exactly how do you intend to drive a 1 foot long column 6 feet into the ground?

Far better to use longer, steel pipe columns, which can be hammered on forever without fracturing.

 

As bridgeman said, your plan is seriously flawed. Provided some pictures as suggested earlier and some of us here can provide you with a better plan. Quite possibly driving steel pipes down to the rock might work but also you may be better off with a spread footing to support the columns.