A Full Scale Field Study: Evaluation of the Magnitude and Time Extent of Excess Pore Water Pressure During the Installation of Auger Pressure Grouted Displacement Piles in Downtown Orlando

Abstract

Central Florida’s economy is growing strong and diverse, with that, comes taller structures, hotels, resorts, amusement structures, and public venues. Augered-Pressure-Grouted-Displacement (APGD) piles increasingly became the deep foundation of choice for heavily loaded structures in Downtown Orlando. The combination of favorable subsoil conditions, quick installation, superior skin friction, and minimal drilling spoil made APGD piles very attractive option especially where contaminated soils are encountered. The installation of the APGD piles causes instant increase in pore water pressure at the annulus of the drilled hole during drilling and grouting stages. The subsoil conditions in Downtown Orlando include a unique layer of silty to clayey sands and sandy clays, which exhibits high excess pore pressure during the installation of APGD piles. Piles installed in close proximity to a freshly grouted pile might cause squeezing and occasional grout outflow triggering potential necking. During the installation of 18-inch diameter 80-feet APGD piles for a 23-story mixed-use building in Downtown Orlando, grout outflow was observed when piles were installed closer than 15 ft of a freshly grouted pile. A field study was conducted to evaluate the magnitude and extent of excess pore water pressure during both drilling and grouting stages of APGD piles. Five piezometers were installed between two 60 ft apart piles to depths of 50 to 60 ft with screened section within the clayey soil. Water pressure probes were installed and data was continuously collected. The study showed sharp increase in pore water pressure during drilling and grouting stages. However, the increase in pore pressure was significantly lower than the estimated critical pore pressure needed to cause pile necking. A typical distance of 20 times the pile diameter should be considered for the next pile in the vicinity of a freshly installed pile to completely avoid the potential for pile communication problems in Downtown Orlando.