Applicability of the fully grouted piezometer installation method for transient seepage conditions

ABSTRACT: The use of the fully grouted method (FGM) to install and backfill vibrating wire piezometers has been growing in popularity. Published modelling results from finite element seepage analyses under steady state conditions show the range of grout/soil permeability ratios under which the FGM is considered reliable. There is limited published literature with comparisons between the results of field installations using the FGM and the traditional sandpack with bentonite chip seal method. The earlier published data that formed the basis for widespread adoption of the FGM did not consider situations where transient porewater pressures resulting from application of external stresses (e.g. embankment construction) are induced in a low permeability layer, and there are a range of soil and transient seepage conditions under which the fully grouted installation method may not provide reliable results. This paper reports the results of transient finite element analyses of fully grouted installations in low permeability clay layers where there are adjacent higher permeability soil layers, and provides additional insight into the applicability and limitations of the FGM. The results of several parallel installations using the FGM and the traditional sandpack with bentonite chip seal method are also reported to provide empirical reference cases.