The disturbed rock zone surrounding underground openings in salt provides a path of increased permeability, which could bypass seals or closure systems. Compliance application performance assessment calculations include characteristics and parameters of the disturbed rock zone which model brine influx into the disposal room and influence important evolutionary processes. Quantification of spatial and temporal characteristics plays a vital role in verification and validation of calculational and predictive methodologies. This paper presents petrophysical evidence derived from laboratory observations and compares the results to hydrological and geophysical measurements. The composite of related studies, when completed, will provide a hydrologic profile for model validation.
I INTRODUCTION 2 PREVIOUS RESULTS
Laboratory approaches to characterize damage in rock salt are discussed in this paper. Properties of the disturbed rock zone (DRZ) have significant consequences in terms of performance assessment and operation of the Waste Isolation Pilot Plant 0hrIPP). In addition, these studies are relevant to cavern storage research programs and to several German waste isolation programs, which engage complementary research to characterize and model salt damage evolution. During the waste disposal (operational) period, rock mechanics research continues in the WIPP underground, in the laboratory, and in model development. Rock mechanics research played a fundamental role in regulatory compliance certification by the EPA and opening of WIPP, a matter of national and international interest.
Disposal room excavation creates stress states that induce fracture. The disturbance is manifested by dilation of formerly competent rock, altering its intact properties. The DRZ enhances permeability in proximal rock and evolves spatially and temporally. Creation, evolution and engineering properties of the DRZ influence nuclear waste repository performance during operations and after closure. Characteristics of the DRZ are particularly important to the WIPP performance assessment conceptual model. The WIPP project supports research of the disturbed zone through mechanical laboratory experiments, in situ permeability testing, petrofabric observations, and modeling. The research goal is to provide a predictive model capable of delineating DRZ evolution and ascribing permeability parameters.
Over the life of the WIPP project, laboratory, field, and modeling studies have examined the mechanics and characteristics of DRZ development. Gas and brine tests have quantified permeability around many horizontal openings at WIPP (Stormont et al. 1987; Stormont 1990). Other techniques, such as visual observations (Bores & Stormont, 1988), ground-penetrating radar (Kannenberg & Roggenthen 1997), and sonic velocity methods (Holcomb 1988; Holcomb & Hardy 2001), have also been applied to characterize the conditions of rock around the WIPP openings. Recently, Roberts & Beauheim (2001) compiled hydrologic profiles surrounding circular and rectangular WIPP underground openings based on age and position. Similar testing of damaged salt around openings is pursued in German research programs (e.g., Wieczorek & Zimmer 1999). In addition, field permeability testing was conducted in the waste-handling shaft (Saulnier & Avis 1988) and the air-intake shaft (Dale & Hurtado 1996) and around small-scale seals (Knowles & Howard, 1996). Laboratory testing of salt cores has provided significant insight into DRZ development (Rath et al. 2000; Hunsche & Schulze in press). Van Sambeek et al. (1993) characterized dilatancy as a function of stress invariants for a large number of rock salt laboratory tests on WIPP salt, as well as salt from the
