I am building a pole barn this spring in S.E. Michigan (42x48). Last fall a contractor had brought in and bulldozed a base of 18 inches of clay/rock fill over the area intended for the pole barn. He stated that the year of rains, winter snow and freeze/thaw along with the compaction done by driving over it many times with the dozer, "should compact the clay very well and should be great to pour a slab on in the spring". Is he correct? Or do I have to pull out all 18 Inches of fill and back fill with slag sand and compact every 6-8 inches? The fill was put down in August 2010 and the building is to start June 2011 with a slab in July. II am getting conflicting answers. Is there a simple test I can do to see if compacted enough?

It's not too good to guess on whether the soil is compacted enough. In some cases you have rock and in others soil. Unfortunately there is no home test you can do. There are a number of tests done in the field; pin penetrometer, annular ring and Procter. Pin and annular ring put weight on a known surface area and measure the depth of penetration. Procter is more complex. To further compound your question, we don't know if you will be storing hay bales of bulldozers. Check with your local permitting agency and see if they have a soil tester and maybe they will let you borrow it or maybe they will test.

I agree with ma0641 that it is not good to guess about soil compaction or stability. The cost of guessing wrong is too costly. Different material is used in different parts in the country. The contractor may be very correct in his statement. But then he may not be. We couldn't know. We don't know the mixture of stone and clay. We don't know what kind of clay. There are many different types of clay, just like there are many kinds of sand. We also don't know the moisture content of the mixture. Moisture content is critical in compaction of soil.

In my area a mixture of gravel and gravel dust is the most efficient material to use for fill. The gravel dust helps fill the voids between the gravel and limits the amount of ground water that can settle in the fill. This mixture only has to be compacted or vibrated enough for everything to settle firmly into place. The gravel is not going to compress over time. A lot more efficient and less costly than trying to compact soil.

Soil compaction is a tedious and time consuming process. Moisture content is critical.

In the central SC a fill material called sand clay is commonly used. I not sure whether that is a certain type of clay or a mixture of sand and clay. Local contractors have learned over time that this is an acceptable fill material.

Talk to a number of local contractors, builders and concrete contractors. They will be better equipped to advise you. Then, if you still have question try to do some soil compaction test.