Micropiles are small diameter foundation (300mm or less) elements drilled by means of small leader mounted rigs such as the Klemm KR 806 (modified) or the Hutte HBR 202. Those small diameter structural elements are drilled fully cased through the use of segmental drill pipes to depths. A high yield stress steel rods and then inserted into the fully grouted cased hole before the segmental casings are removed.
The use of micropiles becomes an advantage in situations where the use of larger piles is not recommended such as in soil conditions containing large boulders at depth, in areas where conventional rotary bored piles could affect the neighbouring structures or perhaps in low headroom conditions and/or karstic geology. They can also be used to augment or replace deteriorating foundation elements or for supporting slopes, embankments or general soil stabilisation.
There are several types of micropile installation techniques such as ‘double rotary head system’, percussive system or rotary system with the assistance of drilling fluid or polymer. Notwithstanding the method of installation, all micropiles rely on the friction between the grouted element and the soil/rock interface to resist the vertical loads. NSCC has the experience with installing micropiles with a working load of 2500kN.