Underpinning is done on a structure when the foundation needs to be strengthened, secured or built with extra support. When making the calculations of how big the hole should be for this method and how much concrete should be used, employ an engineer for insurance purposes.
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Mark the locations where you will be installing the piles. Use the record or chart given to you by the engineer. Don’t move the places where the piles are to be unless given the okay by the engineer.
Create round or square holes in the ground in the appropriate places adjacent to the building to show the footing, the bottom of the grade beam, the stem wall or the column. It should be at least 24-inches wide and at least 12-inches lower than the footing. The footing should be as smooth as possible, and the vertical and bottom face of the footing should be perpendicular to each other. This will help the pile bracket to be mounted.
Pressed piers and screw piles don’t necessarily need to have holes made, but they do require marked piles. Pressed piers are small sections of steel that are pressed under the footing, while screw piles are small piles that are screwed into the ground with a device that looks similar to an enlarged drill bit. These methods are usually used for newly constructed areas.
For other methods of piling, insert the pile bracket underneath the footing. Use two concrete anchors to attach the vertical face of the pile bracket to the footing. Place the pile lead section and the guide sleeve. Pour the first section of the pile down the bracket sleeve. Attach the hydraulic rams to the pile bracket. Advance the pile, but it don’t let it be more than a 5 degree angle from being upright. Add these pile sections as needed to stabilize the foundation.
Pack the piles with no less than 60,000 pounds of force, and add piles until they reach about 5-inches higher than the pile bracket sleeve. Attach two 1-inch diameter all-three bolts to the pile bracket. Proceed to put a fastening plate on the top of the pile. Secure the fastening plate to the 1-inch diameter all-threads. Use the hydraulic ram to lift the structure. Do not lift the pile with more than one-third of the force that was used to install it.
Once the structure has been lifted, use the 1-inch bolts to attach and firmly secure the fastening plate to the pile bracket. Write a record of all the piles, the depth, the pressure used and any other information pertaining to the completed task. Remove the extra piles and fill the dirt back in with the soil that was removed. For concrete piles, wait three days before packing dirt.