SEDL / STP / STP777-EB / STP28923S

Effects of Cementation on the Compressibility of Pierre Shale

McKown, AF
Senior engineer, Haley & Aldrich, Inc., Cambridge, Mass.

Ladd, CC
Professor of civil engineering, Massachusetts Institute of Technology, Cambridge, Mass.

Pages: 20    Published: Jan 1982

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Abstract

Natural cementation in cohesive soils can have a significant effect on the apparent maximum past pressure (¯σ^vm) estimated from one-dimensional consolidation tests. Relatively small amounts of calcium carbonate (CaCO³), above a threshold value of about 2 percent by weight, appear to cement the structure of a Nebraska Pierre shale, causing measured ¯σ^vm-values several times larger than the maximum past overburden stress inferred from geological history. However, CaCO³ contents in excess of this threshold value (even up to 50 percent or more) produce little further increase in ¯σ^vm. On the other hand, leaching out relatively small amounts of CaCo³ from a highly calcareous clay shale can increase its compressibility and produce a lower measured apparent maximum past pressure.