Micro piling is an innovative foundation technique which uses small-diameter piles. This method is often used for underpinning of structures and can be a cost-effective alternative to other stabilization methods. It is also commonly used for repairing damaged foundations and seismic retrofitting. This construction technique is particularly useful in difficult ground conditions such as karstic geology, poor soil with limited accessibility or low headroom and for buried structures.

The load capacity of micropiles can be very high and they can resist both compressive and lateral loads. Depending on the design and site conditions, they can be installed in a variety of configurations including vertical, inclined or horizontal (see figure below).

Micro Piling: A Closer Look at Its Applications and Advantages

A key aspect of designing a micropile system is determining the appropriate pile diameter, length and spacing to ensure adequate load-bearing capacity. In addition, it is crucial to consider the interaction between the piles and the surrounding soil. Generally, the piles are connected to the soil by means of a reinforced interface element which follows the Mohr-Coulomb failure criterion. This ensures that the soil/pile composite is strong enough to resist the applied loads without the formation of excessive plastic deformations in the surrounding soil.

The installation of a micropile typically starts by drilling a hole into the soil or rock using a temporary casing. After reaching the predetermined depth, the drill is removed and a reinforcing steel bar is inserted into the hole. Grout is then injected through the hollow bar to form the micropile. The casing can remain in place for permanent reinforcement, seismic design considerations or to facilitate structural connections.