To overcome the problem of not reaching proper depth many of the pressed concrete piling contractors have devised methods to help the pile drive through the soil. One such method is placing a cone shaped piece on the bottom of the leading concrete cylinder. This is supposed to overcome the resistance of pressing a flat surface against the soil. Now you will have a pointed end on the first section decreasing the friction, you will also have a finished pile resting on a pointed end. Obviously when you place the full weight of the structure on this pile it can push the pile even deeper due to the shape of the cone. If the pile drives easier due to its shape it will also settle easier due to its shape.
Another method used to overcome shallow depths is to use high pressure water jetting to lubricate (soften) the soil below the concrete cylinder. A high pressure line is forced down the center of the concrete piles blasting water into the soil making the piles install easier. Common sense tells us that if your home was built on expanding clay soils and you are having foundation issues, the introduction of more water into these soils is not a good solution. Good for the contractor, yes, but good for your home? No!
One of the latest innovations in the segmented concrete pile industry is a spiraled concrete cylinder. The theory is that the spiral shape makes it easier for the pile to drive through the soil and “reach up to 20% deeper”. Deeper than what? Twenty percent deeper than five feet is on one additional foot. This is not going to make any difference if the active layer continues 10-15’ below the surface.
Once again picture in your mind a spiral shaped concrete cylinder, as the cylinder is driven in the ground it turns about 90 degrees per foot of depth. Imagine, if you will, that the spiral on the cylinder causes the soil to move away from the center of the pile creating a void around the concrete cylinder. This sweeping action forces the soils outward in an irregular shape. As more cylinders follow each other a soil void is formed around the pile creating a friction pile that does not have the benefit of soil around itself. Once again this is a fine marketing tool to make your concrete cylinder different from others, but is it causing more potential harm than good?
Once the piles are driven down a couple of feet into the soil, and the soil has been pushed away from the pile, the pile is setting on a muddy mess with a pointed end. Now when they lift of your home, a block of concrete is placed on top of the last concrete cylinder driven and then the now famous car jack is placed on top of the block and they start pumping the handle. After your home is over raised, two small cylinders are placed along side of the car jack and steel shims of various thickness are slid between the new cylinders and the footing. These thin steel shims are now what your home is resting upon. The car jack is then lowered and your home drops down onto a stack of thin steel shims.
Segmented concrete piles were once “King” in Texas, but now due to their shortcomings, homeowners throughout the country are demanding more from foundation repair professionals. As with most home improvement projects information is the key to quality work. Like many foundation engineers throughout the country you to have been educated on foundation repair methods. Remember, do not make your decision based on advertising and cheap prices, if it sounds too good to be true – it probably is.