Abstract:
On the continued Role of Water Pressure Testing in Grout Design and ImplementationFor decades there has been debate over whether or not Lugeon-style water pressure tests (WPTs)provide reliable information for curtain rock grouting design or indeed for curtain performance verification.Some have advocated that WPTs be dropped from programs as unreliable indicators of the probableperformance of grout injection behaviour or quantities. Some have advocated use of WPTs only fordesign and that final grout injection hole performance should be the measure of completion to targetLugeon acceptability criteria. Others have intimated that the incompatibility of the fluids in the two typesof injection approach compromises direct application of Newtonian based flow parameters derived fromwater based injection methods to prediction of the injection behaviour of modern Bingham style stablegrout mixes.The design issue that a curtain has to perform to retain water has also been cited by many as theprincipal justification why WPTs must be used not only for design but also for final verification of curtainacceptability. Central to this debate is the perceived dilemma often seen on construction sites ondeciding when is enough. Despite the fact that landmark papers (Houlsby, 1982 and others) provideclear guidance on target lugeon acceptability criteria, there often still remains dichotomy of opinionbetween site personnel and design teams on adequacy of perfomance acceptability when balancedagainst skyrocketting costs and significant schedule impacts associated with chasing down the last"leaky" zone.This paper examines some of the pros and cons of retaining WPTs as the sole measure of acceptabilitygiven the major advances that have occurred in site investigation characterization and groutperformance/penetration monitoring. It is argued that with the advent and increasing use of downholeacoustic televiewers during actual grouting and much better design methods for evaluating groutingbehaviour as a function of rock mass fabric and behaviour, coupled with much improved injectionprocedures during construction, that acceptabilty checks can be moved more towards focused verificationrather than routine observance of patterned final stage WPTs