Ascertaining Grain Scale Effects Of Seismic Or Aseismic Stimulation Upon Strength Of Near Surface Geological Materials

Abstract

Certain peculiarities of inelastic nonlinearity of unconsolidated near surface stressed granular media contributed at micro- scale are investigated to ascertain anomalous time dependent strength behaviour macro-effects, with geotechnical/geo-environmental implications. Comparative examination of ultrasonic P- and S-wave pulse stimulated repeatable displacement response wave-forms of confined dry and fully saturated ceramic grains analogue, endorsable by pertinent theory, hint certain persistive time and frequency restricted occurrences vouching vital insights. Examination aimed at both understanding “louder” response of “quieter” seismic and aseismic events in granular sediments, and imparting enhanced conceptual substantiation of some previously published results, show that subtle acoustic emission and/or stick-slip type micro events do occur, and, when spread over time and/or space are collectively capable of altering granular material macro strength behaviour. It is clearly deducible from resonant type spectral results that material fragmentation or force chain formation type phenomenon occurs possibly due to macro-scale friction mobilization by grain scale events. It is further speculated that invisible high frequency events may irreversibly alter grain scale surface properties and/or intergranular friction as enhanced elasticity type effect, more elusive with saturation. Temporal morphology of stick-slip type events when stimulated by P- and S-wave modes is posited to be non-identical in characteristic sense.