STEADY-STATE ANALYSES OF MULTISCALE PNEUMATIC INJECTION TESTS IN UNSATURATED FRACTURED TUFF

Numerous single- and cross-hole pneumatic injection tests have been conducted in unsaturated fractured tuff at the Apache Leap Research Site (ALRS) near Superior, Arizona. The results form a unique data set representing a multiplicity of scales. Steady-state analyses of single-hole tests conducted by Guzman et al. (1996) have yielded values of air permeability at various locations throughout the tested rock volume, on a nominal scale of about 1 m. We complement these by steady-state analyses of several larger scale cross-hole tests. Steady state analyses are much easier to conduct than transient type-curve analyses, which have therefore been limited to relatively few single-hole (Illman and Neuman, 2000) and cross-hole (Illman and Neuman, 2001) tests. The former have yielded equivalent directional air permeabilities and pneumatic connectivities (ratios between observed and generated pressure signals) for fractures that connect pairs of monitoring and injection intervals over distances ranging from meters to tens of meters. Both parameters were found to vary considerably from one pair of test intervals to another, reflecting their nonuniform nature at the ALRS. The permeabilities also exhibit a pronounced scale effect. We present a preliminary statistical analysis of these parameters and discuss their implications vis a vis the pneumatic characterization of unsaturated fractured tuff.