One of the key engineering aspects of the “pushed piles” method of foundation repair is what happens to the dirt when the piles are driven into the ground by the weight of the house. So we asked a structural engineer with years of experience in the field of foundations. Below is the answer written in laymen’s terms.
When a standard sized concrete cylinder (a pile) is pushed into the ground it occupies space that was formerly occupied by dirt (or clay soil). The cylinder, usually 12 inches in length and 6 inches in diameter, is pushed into the ground with a hydralic jack under tons of pressure. This pressure causes the dirt to partially “liquify” in a process known as “Thixotropy.” The soil actually has the consistency of a gel, something like toothpaste, and under pressure will be forced into the small natural cavities of the surrounding soil.
Thixotropy or Soil Liquefaction Defined
A state of ‘soil liquefaction’ occurs when the effective stress of soil is reduced to essentially zero, which corresponds to a complete loss of shear strength. ( quoted from the page at https://en.wikipedia.org/wiki/Soil_liquefaction )
“In geology, soil liquefaction refers to the process by which water-saturated, unconsolidated sediments are transformed into a substance that acts like a liquid, often in an earthquake. By undermining the foundations and base courses of infrastructure, liquefaction can cause serious damage.” ( quoted from the page at https://en.wikipedia.org/wiki/Liquefaction )
During the hydralic installation of the concrete cylinders, the partially liquified clay soil or “gook” loses much of its ability to bear weight (load capacity). The “gook” at the bottom of the first concrete cylinder and surrounding other cylinders has roughly 30% to 50% of normal load capacity. This loss of load capacity is to be expected because the clay soil has been transformed from a solid to a partially liquified state. In most cases, the “gook” will gradually flow upward along the sides of the cylinders for a number of months or years after installation. When you need of a professional foundation repair company contact Houston Foundation Pros.
Loss of Load Capacity
As explained to us, immediately after the jacking process of pushed piles the column of concrete cylinders is at its peak load capacity, which is defined with a Factor of Safety = 1. The load capacity will begin to diminish over time and the Factor of Safety will become less than 1, which is the condition of failure of the column of pressed piles. That is, the column of pressed piles can no longer support the weight of the house. If you are thinking “sell my house” then contact Houston Home Buyers.
Factor of Safety is a very important concept that every homeowner should understand. A Factor of Safety of 1 means that the foundation repair method can not support any additional weight in the house or garage. If pushed piles are installed under the garage area the the owner should park all cars inside the garage during the installation process. If pushed piles are installed under a garage area without the weight of the cars inside then it is an invitation to immediate failure of the pushed piles the first time the car(s) are parked inside the garage.