Low Energy Compacted Concrete Grout Micropiles

Results from a series of small diameter vertical drilled and compacted grout micropiles that were installed and load tested to failure in axial tension are presented. Tests were performed in the clay crust at the National Geotechnical Experimentation Site at the University of Massachusetts. Micropiles with a diameter of 76 mm and length of 3.05 m were tested. The micropiles were constructed by incrementally applying dynamic compaction energy from the SPT hammer of a conventional drill rig to the concrete grout as the hole was filled. The results of the tension tests showed that in comparison with a micropile constructed using gravity free-fall placement of the concrete, the pullout capacity of the micropiles was significantly increased when compaction energy was used. This increase is primarily due to the increase in lateral stress produced by the compaction.