Experimental Deformation of Sedimentary Rocks Under Confining Pressure: Tests at Room Temperature on Dry Samples

Abstract

Common engineering experience is not very helpful in picturing the mechanical behavior of ordinarily brittle materials under the influence of high confining pressure. The facts that rocks become stronger and more ductile as the mean pressure is raised have been known for many years, but only a few different rocks have been tested under conditions corresponding with those existing in the crust at depths reached by the drill. It seemed worth while therefore to investigate the mechanical properties of a number of typical sedimentary rocks in a simulated natural environment of high pressure and temperature and hydrothermal solutions. In this first paper are recorded the results of triaxial compression tests on twenty-three dry rocks at room temperature and at various confining pressures ranging from 0 to 2,000 atmospheres. Stress-strain curves and curves for ultimate strength and ductility as functions of confining pressure are given for each rock, and some generalizations are made for each rock type investigated: siltstone, shale, sandstone, limestone, dolomite rock, and anhydrite. In all tests, marked increases in strength and ability to deform permanently without fracturing were found. It is planned to include studies of the effects of temperature, time, and interstitial solutions, and it is hoped that ultimately it will be possible to predict the mechanical properties of sedimentary rocks deeply buried in the crust.