Root piles are very small diameter piles (generally 60 mm to 135 mm). Length of the root piles generally vary within 4 m to 30 m.
The concept of root pile was first introduced by an Italian engineer named F. Lizzi. His primary concern behind root pile development was to do underpinning work. Now days, root piles are also used for slope protection work, where a network of root piles is built to protect the slope. This is called reticulated root piles. Root piles are also used for correction of landslides.
Root piles should not be confused with micro piles. In case of micro piles, a steel pipe is used whereas a single steel bar is used in case of root piles.
Procedure for Construction of Root Piles
Step-1 (Drilling of Hole)
Drill a hole of about 100 mm diameter with or without a drill pipe. The diameter of holes may be changed as per site soil condition or requirements. Drilling is done by rotary drilling method and is advanced by direct circulation of water or bentonite slurry. In the method of direct circulation, the cut pieces formed due to cutting action of bit, come to the surface along with bentonite or water.
Step-2 (Placing Reinforcement Bar)
After completion of drilling operation to the required depth, install a single reinforcement bar of dia. about 15 mm or more. Then install a tremie pipe inside the drill pipe. Tremie pipe is used to place the mortar.
Step-3 (Filling of Mortar)
Fill up the hole with cement sand mortar made of 600 kg to 800 kg of cement for one cubic meter of sand. This type of mortar gives high strength. The mortar is placed by tremie pipe and is filled from bottom to the top. At any time during placing or mortar, the bottom end of the tremie pipe should be just inserted in the mortar being placed.
The process of grouting is done in stages by dividing the grout length into short sections. This is done to adjust the grout volume and injection pressure as per different soil conditions. At every stage, air pressure not exceeding 60 kg/m2 is applied at the top of the drill pipe and tremie are gradually withdrawn. Air pressure makes it easy to withdraw the pipe and improve pile soil contact.
Step-5 (Completion of Pile)
After complete removal of the drill pipe, release the air pressure and allow the mortar to set.