Effect of pressurized grouting on pullout resistance and group efficiency of compression ground anchor

The purpose of this study is to investigate the effect of pressurized grouting on pullout resistance and the group effect of the compression ground anchor by performing pilot-scale laboratory chamber tests and field tests. The laboratory test results show that the enlargement of the anchor body diameter estimated theoretically by combining the cavity expansion theory and grout penetration characteristics matches reasonably well with that obtained from experiments. The required injection time as a function of the coefficient of permeability of the ground is proposed. The results of a series of field anchor pullout tests show that the effect of pressurized grouting is more prominent in a softer ground with a smaller SPT-N value for an increase in both anchor body diameter and pullout resistance. The pressurized grouting effect in comparison with gravitational grouting was found to be almost zero if the SPT-N value is more than 50. Based on experimental results, a new equation to estimate the pullout resistance as a function of the SPT-N ₆₀ value is proposed. In addition, based on in situ group anchor pullout test results, a new group effect equation is proposed.