MICROPILES [high pressure grouted] by Foundation Specialists

MICROPILE.info     is a Domain of
                 Foundation Specialists
THE TECHNOLOGY: MICROPILES
Micropile is a small pile with diameter ranging from 3-1/2" (+/- 90mm) to 9-7/8" (+/- 250mm). Micropiles are generally used for underpinning and retrofitting structures.
Micropile can be made by boring or drilling holes in soil or rock, then micropile execution continue by inserting a reinforcing element adequate to the hole size. The micropiles are then grouted by  backfilling the hole from the bottom, using cement mortar (grout). This type of micropile has a small bearing capacity, in accordance to micropile diameter, micropile length and the type of soil to which the micropile has to transfer the loads applied to the micropile itself.
Different types of Micropiles are the "High Capacity Pressure Injected Steel Micropiles" The High Capacity Steel Micropile is made using High Tensile Tubular Steel. The steel micropile is provided with "manchettes". The High Capacity Micropile is drilled, then  fixed into the ground by annular grout. Eventually the steel Micropile is subjected to multi-stage high pressure grouting through the manchettes. Micropiles, due to the very small cross section area are generally skin-friction piles. The Pressure Grouting done through the manchettes provided within the micropiles active length creates series of bulges between the annular grouting of the Micropile and the soil formation surrounding the micropile. The cement bulges protrudring from the micropiles shaft are solidly conneced to the annular grouting of the micropiles. The irregular shapes of the micropiles' bulges have a sizable area which in turn translates to a sizeable increase of the micropile lateral area, creating an increase of the micropiles shaft interface with the medium surroundind the Micropile. The end result of the process is giving this type of Micropile a much higher bearing capacity as compared to non pressure grouted micropiles .
The use of high pressure injected Micropiles is advantageous when using micropiles in doing underpinning of buildings, where the Micropiles have to be installed in areas with limited vertical clearance (for example building basements), or underpinning by means of Micropiles bridge structures with little vertical clearance. Micropiles are generally executed by use of small size equipment, therefore the execution of Micropiles can be carried out in very small areas, and small access. High Capacity Micropiles are done using segmental Steel Micropile reinforcement and injected cement grout. Both materials employed to install micropiles can easily be carried into small spaces, though small access and yet the Pressure Injected Steel Micropile achieves high bearing capacities. In addition, a micropile can be installed through pre-existing foundations, then the micropile head will be properly fixed to the existing structure[ if properly designed and expertly installed], this kind of micropile application can be executed very neatly, and without causing structural damage. Micropiles used for underpinning can be precompressed to be made active from inception. Micropile field of application is very wide. Pressure Injected Micropile is an extremely reliable technology.