Characteristics of bored piles installed through jet grout layer

When bored piles are installed through a jet grout layer, significant interaction may take place between the piles and the jet grout. Field load tests have indicated that significant enhancement of the pile shaft capacity and axial stiffness was possible for both compression and tension piles. The influence of the jet grout layer was more pronounced for piles under compression loading compared with uplift loading. The effectiveness of the jet grout in transmitting load via shearing action was dependent on the thickness of the grouted zone, the strength of the interlocks between individual jet grout columns forming the grout slab, as well as the interface bond between the pile shafts and the grout. No apparent adverse effect on the performance of permanent foundations was envisaged as a result of the presence of the jet grout layer. However, interpretation of pile behavior from load tests was complicated by the interaction between the test pile and jet grout, resulting in overprediction of pile capacity and axial stiffness. The significance of the interaction has to be carefully evaluated so that a correct interpretation of the true pile capacity and axial stiffness can be made.