Micropiles, also called mini piles, are often used for soil improvements, slope stabilization and underpinning. They are also used to create foundations for a variety of project types, including highway, bridge and transmission tower projects. They are especially useful at sites with difficult or restricted access, or with environmental sensitivity. Micropiles are made of steel with diameters of 60 to 200 mm. Installation of micro piles through topsoil, sand and cobblestones overburden and into soil rock can be achieved using Air Rotary or Mud Rotary drilling, impact driving, jacking, vibrating or screwing machinery. Micropiles can also be used to construct a grout column around the shaft of a standard Helical Pile system, allowing for use in higher load applications.