Influence of Geomaterial Heterogeneity on the Results of Hydraulic Pulse Tests

Heterogeneity of a geomaterial can result from a variety of processes associated with depositional effects, chemical alterations and mechanical actions. In contrast to a non-homogeneous geomaterial where the properties vary gradually from point to point, a heterogeneous geomaterial is one that exhibits abrupt variations in the properties. Recent studies on the estimation of permeability, indicate that although spatial heterogeneity exists in geomaterials, the overall or bulk or effective properties can be described by convenient measures based on the statistical distribution of the heterogeneity. For example, when the permeability of a heterogeneous geomaterial exhibits a lognormal spatial distribution, the effective permeability can be estimated through the geometric mean of one dimensional permeabilities measured in three or more arbitrary directions within the heterogeneous domain. In this paper we apply the concept of effective hydromechnical properties to determine the response of hydraulic pulse tests conducted on a heterogeneous low permeability geomaterial. In addition to the permeability distribution, the geomaterial skeletal stiffness and porosity are needed to interpret the hydraulic pulse test. The research focuses on establishing the role of the effective representations of the permeability, skeletal stiffness and porosity on the ability of a mathematical model to interpret a hydraulic pulse test. Such results are compared with computational simulations of a hydraulic pulse test conducted on a one-dimensional element with heterogeneous properties that conform to lognormal distributions. The results indicate that the effective representations provide a satisfactory approach to accommodate hydromechanical geomaterial heterogeneity. Guided by these results, the studies are extended to the consideration of Biot poroelasticity of a heterogeneous fluid-saturated porous medium.