Some useful construction tips for installation of Micropiles Foundation
Micropiles refer to deep foundation used when there is shortage of space or headroom exists for implementation with standard pile rigs. These piles are described as minipiles, pin piles, needle piles and root piles.
Micropiles stands for small diameter bored cast-insitu piles with diameter 150 to 300 mm which are developed through rotary drilling machine and grouted with rich grout & fine sand via injection process.
Method Statement of Micropile Installation are:
• A borehole with necessary diameter 150 to 300 mm is drilled by bentonite slurry with the help of a rotary drilling equipment to make the sides of the bore hole stable.
• A liner of full depth up to hard rock / strata is essential. M.S. or HDP pipe liners should be utilized. MS liners are mostly recommended.
• Tor steel reinforcement cage of a bundle of large diameter rebars is supplied as pile reinforcement.
• Pile is grouted through rich grout of cement and fine sand containing water cement ratio of 0.5 and this grout should include least compressive strength of 480 kg/cm2 on 28 days. On the other hand any other appropriate method along with filling the bore by coarse aggregate up to indicated height of about 1m and filling it consequently with cement grout can also be projected.
• The piles are socketed sufficiently into the hard strata / rock necessary to enhance the capability that is primarily available in friction in the socket.
The safe vertical load capacities usually vary from 25 to 35 MT and lateral (shear) capacities are generally vary from 2 to 4 MT.
Sequence of Piling for Micropiles:
The piles must be set up in a perfect sequence so that the load bearing power of formerly installed pile is not minimized. The sequence of piling is based on working drawings. In a pile group, the sequence of installation of piles usually differ from the centre to the boundary of the group or from one side to that the soil is managed from the flowing out throughout operations.