Shear strength and related properties of sediments from experimental mohole (Guadalupe site)

Abstract

In studying the strength properties of preliminary Mohole samples, primary consideration was given to testing samples under conditions as similar as possible to those in situ. For shear strength tests, the triaxial cylindrical compression apparatus and the consolidated undrained test were selected as most suitable. Shear strength was found to vary from 0.07 bar in the upper meter to 2.66 bars at a burial depth of 136 meters. Comparison of test results with previous work on normally consolidated marine clays suggests the Mohole sediments to be similar in most respects to other clays, but having a higher ratio of strength to overburden pressure than do clays from environments of shallower water and more rapid deposition. Comparison of shear strength values with burial depth to values of porosity, particle size, total carbonate content, and content of clay minerals indicates a positive correlation between strength and carbonate and montmorillonite content, but a negative correlation between strength and porosity, per cent clay-sized particles, and illite and chlorite content. The common cause of these correlations is believed to be original rate of deposition of detrital sediments. The section from 85 to 135 meters is believed to have accumulated at a greater rate than the older and younger sediments, thereby lessening the effect of incipient cementation near the water-sediment interface.