Stress-deformation behavior of chalk

When strong rock masses, with discontinuity patterns parallel and perpendicular to the ground surface, are subjected to normal loads, linear or concave stress-deformation curves are produced. In contrast, chalk rock masses with the same discontinuity pattern, produce convex curves. This paper investigates the underlying mechanisms, which may be responsible for such differences. Experimental results are presented for profiled chalk specimens in which the contact area at the discontinuity boundary is approximately 15% of the specimen cross-sectional area. It was found that these low contact area specimens exhibited both concave and convex behavior. This behavior was attributed to discontinuity closure and yielding of the intact material, respectively. The overall trend in behavior was found to be a function of the contact area at the discontinuity boundary, the initial discontinuity aperture, and the yield stress. © 2007 ASCE