Micropiles are widely used as a part of foundation support systems. Stabilization and support of bridges, buildings, highways, towers and nearly every man made structure imaginable is greatly enhanced with the utilization of micropiles. The names “micropile’ and “minipile”, are clearly size specific, representing the delineation between micro(pile) at 2-5” and mini(pile) within a parameter of 6-12”. Installation of minipile is accomplished within the process of drilling and grouting. Both micro and mini piles can be drilled to great depths, as deep as hundreds of feet and have the capabilities to support hundreds of tons of structural weight.
Reinforcement of micropiles using large diameter threaded bars increases load capacity. Overhead physical restrictions lead frequently to the use of either the mini or micro piles rather than H piles. Both micro and mini pile support systems are an economical alternative to large diameter drilled shaft foundation work. Some difficult soil conditions or impediments to access prelude the use of large diameter drilling. Micropiles are therefore extremely useful in situations involving restricted physical space. Simultaneous insertion of short length casing and drill rod can do wonders in such situations.
The setup of micro and mini piles follows particular procedures sequentially. Load transfer to the wall is accomplished by drilling into bedrock and bonding to rock sockets. Minpiles are deposited into bedrock by drilling. When the drill is removed the setting of the minipile into the rocksocket is accomplished. Grout is sent through pressurized pumps into the minipile casing from the bottom. These minipiles rise to the entry mouth of the rocksocket which allows bonding to occur. Micropiles can then be cut to conform to elevation requirements and may be fabricated and manipulated into the foundation rebar. Tests of load capacity enable efficient design specific to engineering requirements.
Micropiles can also be called needle, pin or root piles as well as minipiles. These smaller increments are quite helpful when building within restricted spaces. The small diameter piles (150-300mm) are cast in situ. They are constructed with the use of a rotary drilling machine, richly grouted with fine sand when injected. Bentonite slurry stabilizes all sides of the borehole and then pipe liners made from M.S or H.P are used. Pile reinforcement is enhanced using steel cages bundling large diameter rebar. A number of methods can be used in grouting by altering the cement, fine sand and water ratios. Filling the borehole with cement grout or aggregate are options to attain specified heights if any project. The socketing of the piles into rock or hard strata is an extremely important part of ensuring safe vertical load factors.