Base Grouted Bored Pile on Weak Granite

An instrumented bored pile was installed and load tested to clarify the mechanism of base grouting and determine its effectiveness. The load transfer characteristics, and mobilization curves for skin friction resistance and end bearing resistance were determined from the strain gauge data. The performance of the base grouted bored pile was compared with data for two conventional slurry stabilized bored piles and a barrette installed in similar ground conditions. Significant increase in pile toe stiffness and skin friction resistance was observed for the grouted pile. Analysis of the results suggests that, in addition to improvement of the pile toe bearing condition, it was possible for grout to flow upwards along the pile shaft-soil interface during grouting at very high pressures, thereby enhancing the skin friction resistance as well. Both toe resistance and shaft resistance were simultaneously mobilized right from the start of loading. A review of base grouting records for 32 working piles indicated that there was an approximate correlation between cement consumption, the number of grouting stages and the volume of pile shaft.