Micro piles are small steel pipe piles and are commonly used in situations where ordinary piles (especially displacement piles) are not feasible.
Micro piles are many times combined with rock anchors to provide tension capacity.
An example of the use of micro piles is for foundation retrofit. Usually while retrofitting displacement pile cannont be used either for damage to the existing facility or low headroom.
Some sites to find micropile or minipile applications would be Hayward-Baker or Nicholson. Both are large geotechnical/construction firms.