Theoretical and experimental investigation of pressure solution

Abstract

Consideration of the existing thermodynamic theory of pressure solution (PS) shows that this theory is applicable to the development of PS structures as well as to local grain-scale diffusive transfer. Local precipitation of pressure solved material ceases when pores are reduced to equilibrium size, if not before by kinetic considerations. Longer range diffusion may then occur if a site of non-equilibrium porosity is available. Such porosity may be generated by particulate flow or by hydraulic fracturing. Long range diffusion may also depend on greater ease of diffusion, as may occur along stylolltes. Measurement of PS strain rates was attempted by stress relaxation tests (SRTs) at room temperature of both Carrara marble and compacted aggregates of calcite and quartz sands. Neither material gave results indicative of PS although strain rates as low as 10-8.5s-1 were obtained. Work hardening during loading resulted In alternating increase and decrease of strain rate concomitant with steadily declining differential stress during the SRTs. The variation in strain rate, termed cycling, was interpreted to be the result of non-steady state flow during loading. Thermal expansion and contraction were shown to be the cause of pressure fluctuation in a long term quantitative experiment on PS begun during this study. Such expansion and contraction should be avoided In quantitative studies, particularly at low strain rates.