A drilled pier is also known as a caisson, a drilled shaft, Cast-in-drilled-hole piles (CIDH piles), or Cast-in-Situ piles. They vary in diameter from 24 to 144 inches and can be installed in a wide range of soil and rock conditions for foundation repair.
They are installed by advancing an auger (a drill tool), to the required depth using open hole, casing, or slurry techniques. Once the desired tip elevation has been achieved, the drilled pier reinforcement is set in place, and the drilled shaft is filled with concrete.
When it comes to foundation repair, a drilled pier is the preferred method for working with lightweight structures where using a hydraulic press for installation might cause damage. A drilled pier is also the ideal solution where depth will either surpass or equate to that of steel or a concrete piling. The construction of drilled piers involves the excavation of piers, providing supports, and concreting.
The auger drill is used for the excavation of a drilled pier; however, if it’s needed, other drilling equipment can be used, such as rotary systems and hydraulic power. The auger drill is attached to a shaft, and then it is rotated under pressure and put into the soil to dig. When it is eventually filled with soil, it is lifted above the ground and then emptied.
In cases of foundation repair where the soil stratum does not have the adequate bearing capacity, belled piers are usually used. To form the bell, the auger is replaced by an under-reaming tool that consists of a cylinder with cutting blades that are hinged at the top. The cutting blades will be in the folded position when the under-reamer is lowered into the hole, and then when it reaches the bottom of the hole, the blades spread outward by a mechanism, and as the under-reamer is rotated, the bell is formed. The loose soil falls into the cylinder, and then when full, it is raised and emptied. This process is repeated until the bell is completely formed. This method is convenient for hard clays where the hole can be left open for a few hours without any support.
The cons of this foundation repair method are the limited amount of depth that can be reached. A limited access rig or skid steer is effective in reaching a depth of ten to twelve feet, but both are limited beyond this. In areas where the other pier systems average more depth, we will typically recommend another system over a drilled pier.
The concrete is also required to cure for a minimum of five to seven days, so the overall process takes longer to complete.
Pier drilling is very important as it is crucial to many structures, as it provides a strong and sturdy foundation. After being drilled, the shafts are filled with concrete to provide a deep foundation beneath an above-ground structure. These can then be reinforced with steel, or they can be unreinforced depending on the loading conditions of the structure.