Abstract

Model tests were designed to simulate tectonic loading during cementation. Mixtures of sand, Portland cement, and water were subjected to uniaxial confined compression until solidification was complete. After unloading, the mortar blocks were tested to measure residual stress effects. Results of the model tests were compared with data measured on tectonically compressed sandstones.Sandstones which have been subjected to a tectonic force during the process of cementation preserve the direction of the force through a residual stress effect; on relaxation of the tectonic force a plane of low tensile strength, formed by preferentially oriented microcracks, develops perpendicularly to the direction of the tectonic force. The plane of microcracks is detectable by point- and line-loading, and through measurements establishing variations in compressional wave velocity and in stress–strain characteristics. A secondary weaker alignment of microcracks may develop in a plane perpendicular to the primary alignment. Load-parallel microcracks may form during the loading cycle. Alternatively, the lateral residual stresses may be large enough to produce microfractures parallel to the relaxing tectonic force. It is demonstrated that most microcrack alignments have macroscopic equivalents in the form of joints.

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