A field study on the behaviour of driven and drilled micropiles implemented in clay

Micropiles are often implemented through drilling, steel pipe installation, reinforcement and grouting. However, in some parts of the world, especially in areas with fine-grained soils, these shafts are implemented by steel pile driving, followed by reinforcement, and grouting has been expanded considerably. In this study, micropile shafts were installed at the site by both driving and drilling methods. Reinforcement and grouting were carried out by two-step grouting and applying different grouting pressures in the micropiles. Some boreholes (at a distance of 0.3 m from the micropile axis) and test pits were drilled to investigate the penetration radius of the grout at different grouting pressures. Results showed that the bearing capacity of driven micropiles is about 4 to 14% more than that of drilled micropiles due to the soil compaction impacts. The average uniaxial compressive strength of the soil samples after micropiles grouting was dependent on the applied grouting pressure and increased from 25 to 56%. In addition, the direct shear test results showed an increase of 15% in the soil cohesion and an increase of 4° in the internal friction angle for the soil after grouting of the micropiles.