Abstract:
Prediction of jet grout column dimensions was made using a theoretical formulation based on jetting hydrodynamics and soil bearing failure mechanism. The jet penetration distance (lj) can be calculated using lj = 6.25dn(1+M)?[(Pi-Po)/qbu], where dn is the nozzle diameter, M is a jetting coefficient depending on the compressed air shroud, Pi is the nozzle inlet pressure, Po is the nozzle outlet pressure and qbu is the soil bearing resistance at the tip of the jet. The jet grout column diameter is calculated as D = 2lj + dm, where dm is the diameter of the jetting monitor. Due to the high velocity impact of the jet front, the undrained shear strength will govern triggering of soil failure at the tip of the jet. The undrained shear strength of cohesive soils is easily derived from classical soil theory. The undrained shear strength of granular soils however is a function of both the density (void ratio) and in situ confining stress and can be estimated using SPT or CPT correlations. This paper presents the prediction of column diameters for jet grouting field trials in stratified soil deposits. Soil classification and shear strength parameters were derived from CPT profiles obtained through the soils. Three continuous columns were installed up to 90 ft deep through fill, organics, silty sand and varved silt and clay strata using single and double fluid jetting systems. The in-situ dimensions of the continuous test columns were determined using the CYLJJET method employing electric resistivity measurements and computer simulation techniques. Jetting parameters were varied in accordance with the undrained shear strength of the respective soil strata. The study shows that reasonable predictions can be obtained using the undrained shear strength for both cohesive and granular soils.