Rammed Aggregate Pier ground improvement trial and the effects on geologically aged soils

抄録

An in-house research and development (R&D) exercise involving a Rammed Aggregate Pier (RAP) ground improvement trial, was undertaken to determine if RAPs were a suitable ground improvement option to mitigate liquefaction, for a significant infrastructure project located within New Zealand. The Pleistocene-aged volcanic derived pumiceous sands encountered below the groundwater table, were assessed using conventional methods to be susceptible to liquefaction. Considering the results of other trials, conventional large strain Cone Penetrometer Testing (CPT) in conjunction with small strain shear wave velocity testing methods, using the seismic cone penetrometer (sCPT), were carried out prior to and following RAP installation to assist in evaluating the effectiveness of the ground improvement. Although the results of the trial demonstrated that the Pleistocene-aged alluvial sands densified following RAP installation, shear wave velocity measurements were much lower than those undertaken prior to installation indicating that the high energy vibratory hammer used to install the piers had disturbed the soil microstructure. The results have highlighted an interesting effect of dynamic ground improvement techniques in geologically older soil deposits. Comparing the results of the trial, with other RAP ground improvement trials conducted around the world demonstrated that current in-situ testing methods and subsequent analysis methods used in evaluating liquefaction potential of soils are generally based on a large database of case histories involving very young, silica-rich soils which have no bonding/cementation (Robertson, 2015) and therefore there are limitations associated with assessing geologically aged soils.