Defining Clay‑Seam Behavior in Salt Formations

Accurate predictions of the long‑term behavior of waste are essential for managing underground facilities like the Waste Isolation Pilot Plant (WIPP), where bedded salt naturally seals fractures and closes openings. Clay seams and geologic contacts within bedded salt formations can influence how the rock deforms and responds over time, but reliable, representative test data have been scarce.

The lack of available data prompted Sandia National Laboratories (Sandia) to partner with RESPEC to collect and test core samples from a nearby potash mine. RESPEC carefully retrieved large, minimally disturbed cores that preserved natural clay seams and contacts, providing a rare opportunity to study these features under realistic conditions.

Testing Real and Simulated Conditions

At RESPEC’s Materials Testing Laboratory, cores were prepared into smaller samples with intact interfaces. RESPEC tested the samples under pressures similar to underground conditions at WIPP. The results showed many natural interfaces were stronger than expected, partly because salt crystals had bonded across the seams.

To better understand the full range of underground conditions, RESPEC and Sandia expanded the study to include engineered clay seams. The seams were created and tested to represent weaker conditions that may also exist in the field.

Supporting Better Long‑Term Predictions

By testing both natural and fabricated samples, the project established realistic upper and lower bounds for the strength and stiffness of clay seams in salt. These results gave Sandia the data needed to refine its models of how WIPP will perform over time.

For further information on this project, please see the publicly available reference below.

• Sobolik, S. R., S. A. Buchholz, E. Keffeler, S. Borglum, and B. Reedlunn, 2019. “Shear Behavior of Bedded Salt Interfaces and Clay Seams,” ARMA 19-040, 53rd US Rock Mechanics/Geomechanics Symposium, New York, New York, June 23–26.