Minipiles, also called micropiles, (and less commonly as pin heaps, needle stacks and root heaps) are deep foundation elements constructed using high-strength, small-diameter steel casing and/or threaded bar. Capabilities vary based on subsurface profile and the heap size. Allowable heap capacities in excess of 1,000 tons have been reached.
Commonly, the casing is improved to the layout depth using a drilling technique. High-power cement grout is subsequently pumped into the casing. The casing may extend to the complete depth or terminate with the reinforcing bar going to the depth that is total above the bond zone.
The technique was used to support most types of structures. Micropile drill rigs enable installation in limited access, low headroom interiors, permitting facility upgrades with minimal interruption to regular operations.
Where excavation walls are required in other enclosed areas and low headroom lines of micropiles spanned by wooden lagging can be ideal. Post- frictional forces can increase thereby achieving greater ability. Micropiles can function to “stitch” the land together, in foreseen shear zones to enhance stability that is mass. Underpinning of foundations adjacent to excavations that are planned is another application that is heap.
For planned bases in places with multiple underground utilities, the price of a cast-in place piling system may frequently be considerably increased by the expense of utility re routing, creation of decent access, and occasionally even a shutdown of facility operations. While avoiding existing utilities little diameter micropiles can be installed.
Another program for micropiles is for deep foundations in subsurface conditions which have natural or manmade obstructions. The drill systems developed for these rigs that are smaller diameter are capable of more easily penetrating cobbles and boulders than the traditional driven or drilled pile systems. In challenging subsurface states, micropiles can be cost effective for new structure construction.
Potential Uses of Micropiles
- Limited Accessibility /Headroom or A Distant Place;
- Support System Close to Existing Construction;
- Auxiliary Support For An Existing Structure;
- Hazard of Liquefaction From Heap Driving;
- Need To Minimize Vibration or Sound;
- Have To Reduce Or Eliminate Spoil At Dirty Or Unsafe Sites
- Where Piles Penetrate Rock as Alternate Deep Foundation Type, Notably;
- Where Spread Footings Are Possible but There’s Potential For Erosion or Scour