Segmented concrete piles also known as pressed concrete piles, have been used for many years around the country, especially in Texas. They were originally designed for foundation repair in Texas due to the expansive nature of the clay soils located in many parts of the state. People were looking for an alternative to poured in place concrete pilings, hence the precast concrete segments. This solution became very popular and migrated throughout Texas and other southern state regions due to fantastic marketing and cheap pricing. Just now has the other shoe fallen.
With unprecedented lawsuits and educated engineers, the trend is flowing away from these stacked concrete pilings for foundation repairs. Instead of the soils being blamed for continued movement of homes, people are now blaming foundation repair contractors that use this process for their never ending foundation problems. The engineering community has become aware of these issues, many engineers are now demanding that any foundation repair system to be installed shall be driven below the upper active regions of the soils down to a load bearing stratum that is not affected by fluctuating moisture levels. This issue can be easily seen in areas with expansive clay soils. As the hot summer sun dries the clay soils, the concrete press piles cannot penetrate past the active soil layers like steel push piers can.
With the realization of these factors steel pier systems have become the favorite for homeowners and engineers alike. Steel piers that incorporate a synchronized lifting system eliminate the problems that segmented concrete piers have had while also providing an accurate way to measure pressure, depth and force on the structure. These variables allow a trained installing contractor to precisely drive pier sections to a load bearing layer of soil then lift the structure in a uniformed and controlled manner under the supervision of an engineer.
The segmented concrete piles have always had some problems but many these issues have been ignored or circumvented with shortcuts. The general impression was it is not perfect but it is cheap! For homeowners that had to live through these shortcomings, answers like these have not been satisfactory. The number one issue with these cabled or stacked concrete piles is the method and the depth that they are driven.
First, a red flag should be raised anytime a car jack (bottle jack) is used to lift a structure. Car jacks are fine for cars or trailers but should never be used in foundation repairs. Their capacities are very limited along with the fact that there is no way of determining the pressure that they are exerting on the home. In the installation of pressed concrete piles, car jacks are used to drive the concrete cylinders into the soil. Car jacks have a very small saddle that contacts the footing hence placing a much localized force on the concrete foundation. Many times footings will crack or crumble due to this method of foundation repair.
Next, the flat bottom 6” diameter concrete cylinders are pushed against the soil causing shallow drive depths. Picture in your mind the amount of force required to press a concrete cylinder into your front yard. Now picture, in your mind, that you are using a 1” diameter metal shaft to accomplish this task. The 1” shaft is using your footing to press the cylinder through the soil, obviously not a good situation. Not only are the 6” cylinders not going to drive very deep but the duress that is being placed on the footing is unacceptable.
Every foundation repair contractor worth his weight in salt calculates the weight of the structure before prescribing a method of repair. This information is necessary for driving pier sections along with lifting structures when there is a means of controlling hydraulic flow and pressure. Without being able to control flow or pressure, as with car jacks, foundation repair becomes a guessing game. Proper depth and soil conditions cannot be met when the structures weight and strength are not calculated.
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, 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?
The lift, now things really get interesting. Once the piles are driven down a couple of feet into the soil, the soil has been pushed away from the pile, the pile is setting on a muddy mess with a pointed end. Now for their 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, yes 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.