Micromechanics of sand grain failure and sand compaction

While there exists a considerable body of theoretical and experimental work regarding the time-independent compaction and compaction creep behaviour of sands under near-surface and upper-crustal conditions where brittle processes are important, a number of important questions remain unanswered. In particular, the brittle failure behaviour of single sand grains is poorly understood at the microphysical level, and previous experimental studies performed on sand aggregates have not systematically investigated the effect of applied stress, grain size and chemical environment on either time-independent compaction or compaction creep behaviour. In addition, theoretical models for compaction of sands by time-independent grain scale cracking lack a true micromechanistic basis and no microphysical models have been developed for compaction of sands by timedependent grain scale cracking. The present study is concerned with the development of a fundamental understanding of the micromechanical processes controlling the compaction behaviour of sands under conditions favouring brittle and elastic phenomena. The approach adopted involves theoretical and experimental investigations into the failure behaviour of single sand grains and into the compaction behaviour of sand aggregates, and addresses both time-dependent and time-independent processes. The results help provide the understanding of the fundamental processes operating during sand grain failure and sand compaction needed for on-going progress towards micromechanically based constitutive relations suitable for modelling natural and man-induced deformations of both sands and sandstones.