Disturbed Rock Zone and Reconsolidated Salt Analyses

D. Michael Chapin, Jr. and Frank D. Hansen

Sandia National Laboratories

4100 National Parks Highway

Carlsbad, NM 88220


The disturbed rock zone (DRZ) surrounding underground openings in salt can provide a path of increased permeability, by way of a shallowly connected network of narrow fractures, which could bypass seals or closure systems installed within geologic radioactive waste repositories. Compliance application performance assessment calculations for the Waste Isolation Pilot Plant (WIPP), and other salt repositories, rely, in part, on the quantification of spatial and temporal characteristics and parameters of this DRZ that both model brine influx into underground waste disposal rooms and that influence important evolutionary processes within these repositories. Here we delineate the DRZ while presenting petrophysical and geophysical evidence of the structural and textural state of this zone, using cores drilled from the WIPP repository and from the German Asse Mine. Secondly, reconsolidated (crushed) salt studies are fundamental to salt repository applications in sealing systems design and analysis, underground cavity stability and rock mechanics evaluation. Reconsolidated salt is also of great interest to international collaborators, where an understanding of the compaction behavior of crushed salt is necessary to perform engineering calculations, such as modeling convergence effects and quantifying backfill consolidation for closure of abandoned mines. WIPP currently applies such information to assess panel closure system redesign. Crushed salt constitutive models are greatly enhanced by the documentation of physical, mechanical and hydrological properties of the reconsolidating material. For this purpose, we examined US, German and Canadian granular salt samples that

experienced reconsolidation in a full-scale application. We then applied a multi-port gas permeameter and scanning electron microscopy to characterize, document and compare properties such as permeability, porosity and mineralogy, as well as structural, textural, compactional and hydrologic features inherent to each sample. By performing these experiments, we can better assess the transport potential of radioactive waste through both the DRZ and through reconsolidated backfill materials in underground repositories excavated in salt.