Hydrostatic and shear consolidation tests with permeability measurements on Waste Isolation Pilot Plant crushed salt

Crushed natural rock salt is a primary candidate for use as backfill and barrier n:aterial at the Waste Isolation Pilot Plant (WIPP) and therefore Sandia National Laboratories (SNL) has been pursuing a laboratory program designed to qiJantify its consolidation properties and permeability. Variables that influence consolidation rate that have been examined include stress state and moisture content. The experimental results presented in this report complement existing studies and work in progress conducted by SNL. The experiments described in this report were designed to 1) measure permeabilities of consolidated specimens of crushed salt, 2) determine the influence of brine saturation on consolidation under hydrostatic loads, and 3) measure the effects of small applied shear stresses on consolidation properties. The laboratory effort consisted of 18 individual tests: three permeability tests conducted on specimens that had been consolidated at Sandia, six hydrostatic consolidation and permeability tests conducted on specimens of brinesaturated crushed WIPP salt, and nine shear consolidation and permeability tests performed on crushed WIPP salt specimens containing 3 percent brine by weight. For hydrostatic consolidation tests, pressures ranged from 1.72 MPa to 6.90 MPa. For the shear consolidation tests, confining pressures were between 3.45 MPa and 6.90 MPa and applied axial stress differences were between 0.69 and 4.14 MPa. All tests were run under drained conditions at 25°C. Results of the hydrostatic consolidation tests on brine-saturated specimens show, not surprisingly, that consolidation rate increases with pressure. These data alone cannot be used to infer a difference in coasolidation rate between damp and saturated specimens subjected to hydrostatic load, although that result has been observed in previous studies by SNL. Shear consolidation tests show that for small axial stress differences there is no systematic correlation between the magnitude of the stress difference and the consolidation rate. Permeabilities decrease as specimen density increases. Fits to the permeability-versus-density data show that permeability decreases approximately two orders of magnitude as fractional density increases from 0.9 to nearly 1.0. Values of permeability over this range of fractional density were between 6 x 10-18 m2 and 3 x 10-22 m2. OISTFM80TION OFTl-lilI DOCLiMd~r It;Wt • This report was prepared by REISPEC Inc. for Sandia National Laboratories under Contract No. 69-1725. fR