The Micropiles was first conceived in Italy in the early 1950s. The use of micropiles has grown significantly since their conception, in particular since the mid-1980s.

Micropiles have been used mainly as foundation support elements to resist static and seismic loads, and to a lesser extent, as in-situ reinforcements to provide stabilisation of slopes and excavations.

Construction/Installation

The micro-pile is constructed by drilling a borehole which can be formed in several ways. Generally, a threaded central reinforcement bar with a sacrificial drill bit is used to form the borehole. The pile is simultaneously drilled, and grout pumped into the newly formed void without requiring casing to control loose or collapsible soils. The sacrificial drill bit also allows for the penetration of boulders and rocks.
Thanks to their self-drilling function, bars can be drilled into most ground conditions for tension, compression, or alternating load applications. The pile is installed using relatively small rotary and pumping equipment therefore the benefit being the ability to mobilise within confined spaces,up steep slopes and into remote locations. Micropiles are installed by methods that cause minimal disturbance to adjacent structures, soil, and the environment. They can be installed where access is restrictive and,in all soil, types and ground conditions.
Micropiles can be installed at any angle below the horizontal using the same type of equipment usedfor the installation of ground anchors and for grouting projects.

Commonly used

Hollow-stem augers are continuous flight auger systems with a central hollow core similar to those commonly used in auger-cast piling or for subsurface investigation. These are installed by purelyrotary heads. When drilling down, the hollow core is closed off by a cap on the drill bit. When the hole has been drilled to depth, the cap isknocked off or blown off by grout pressure, permitting the pile to be formed as the auger is withdrawn. Such augers may be used for drilling cohesive materials, very soft rocks, and are commonly used in sands. Various forms of cutting shoes or drill bits can be attached to the leadauger, but heavy obstructions, such as old foundations and cobble and boulder soil conditions, are difficultto penetrate economically with this system.

Alternative methods

Single-Tube Advancement-External Flush (Wash Boring)
Rotary Duplex
Rotary Percussive Duplex (Concentric)
Rotary Percussive Duplex (Eccentric or Lost Crown)
Double Head Duplex
Sonic

Subsurface Conditions

Micropiles can be installed in areas of particularly difficult, variable, or unpredictable geologic conditions such as ground with cobbles and boulders, fills and miscellaneous debris, and irregular lenses of competent and weak materials. Unlike conventional drilling the micro-pile is conductive to soft clays, running sands, and high groundwater and commonly used in karstic limestone formations. Load Capacities Micropiles can withstand relatively significant axial loads, ultimate loads as high as 4,500kN has been achieved. These capacities continue to increase as experience and knowledge increases. Moderate lateral loads can be achieved, however, the addition of CHS outer casing can be utilised to significantly increase the lateral capacity. Design Overview Selection of Micropile Length An individual micro-pile total length si selected considering where the geotechnical capacity is developed by skin friction (or side resistance) between the grout and theground embedded within a suitable stratum over a appropriate length. Additional consideration regarding total length is the required penetration depth to accommodate resistance to downdrag and uplift forces.

Selection of Micropile Cross

Section In order to accommodate axial loads it is common for up to one half of the cross sectional area of the micropile to comprise steel casing and/or steel reinforcing rod(s). GTL commonly use of common (CHS) casing sizes to mitigate procurement associated with material availability. In general, it is preferable to install fewer higher capacity micropiles as compared to a larger number of lower capacity micropiles to resist a given set of foundation loads. With this approach, less total drilling is required thus reducing overall costs. Also, it is more efficient to resist lateral loads, minimize lateral deflections, and/or achieve relatively high axial load capacities using steel casing as compared to steel reinforcing bars alone. The bond between the cement grout and the reinforcing steel bar allows the composite action of the micropile, and is the mechanism for transfer of the pile load from the reinforcing steel to the ground.

Advantages

The main advantage of a micropile is its ability to figure in terribly engorged and low height areas and on any soil surface regardless of its sort. Fast ballroom dancing installation even in environmentally-challenging conditions. They’re little and comparatively lightweight. they’re comparatively cheap. Simultaneous drilling and grouting allow low overhead, restricted access installation. Micropiles are typically preferred to “H” piles attributable to overhead physical constraints. Improves the bottom (densification) Offers higher skin friction minimize lateral deflections, and/or achieve relatively high axial load capacities using steel casing as compared to steel reinforcing bars alone. The bond between the cement grout and the reinforcing steel bar allows the composite action of the micropile, and is the mechanism for transfer of the pile load from the reinforcing steel to the ground.

Micropile Vs Typical Pile

Micropiles are engaged in any difficult conditions involving soil and rock. Micropiles are custom and applied for tough terrains and applications. Micropiles are used for rehabilitation. Micropiles penetrate any surface and might be put in even though an existing foundation creating it one of the simplest doable solutions for foundation rehabilitation and strengthening works. Small piles are used for slope stabilization, hill stabilization, and different soil improvement and any kind of ground improvement works. Micro piles are employed in areas wherever geological formation is high, urban backfills, areas having floating boulders or different tough terrains that can’t even be accessed with a traditional pile. Used extensively within the rehabilitation of monuments, recent structures, sinking structures, etc altogether components of the globe.