The micro-piles are small diameter piles with a diameter less than 150~300㎜.Itisgenerally used in the foundation of structures which construction space is not enough and receive both compression and pullout loads at the same time such as tower, chimney and electric transmission tower. It is known that the axial response of micro-piles is affected by soil condition (soil type and density) and construction conditions(W/C of grouting material, grouting pressure and whether to use casing or not). However, since most researches have focused on the change of axial load capacity of micro-piles with its installation angle and spacing, rational design criteria for micro-piles are not founded yet.
In order to investigate the effect of soil and construction conditions on axial response of micro-piles, a series of calibration chamber tests are performed using a non-pressure type chamber and model micro-piles. The modeltest results show that the uplift capacity of micro-piles increases with increasing soil density and grouting pressure. It is also found that the uplift capacity of micro-piles is higher when not using a casing than when using acasing, and reaches a maximum value when W/C of grouting material is 50%.