Post Cyclic Volumetric Recompression Response of Carbonate Sediments-Paper

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The study investigates post-cyclic volumetric compression in carbonate sediments, an important source of additional settlement beneath offshore structures as excess pore pressure dissipates after cyclic loading.<br /><br />Laboratory tests were conducted on two reconstituted sediments from Australia’s North West Shelf: coarse-grained carbonate silty sand (CG) and fine-grained calcareous clay (FG). The programme included classification and constant-rate-of-strain consolidation tests, plus monotonic and cyclic simple shear tests at effective vertical stresses of 40 and 80 kPa.<br /><br />Both sediments experienced post-cyclic compression during pore-pressure dissipation. Volumetric strain generally increased with the excess pore pressure generated during cyclic loading, and also tended to increase with the maximum cyclic shear strain. The FG sediment showed greater post-cyclic compression than the CG sediment and the comparison data for non-carbonate soil.<br /><br />A standard critical-state-based estimate using the recompression index from consolidation tests substantially underpredicted measured strains. Fitting the results required an empirical multiplier, α, of approximately 6.0–13.5—well above the value of 1.5 reported for non-carbonate clay. The authors attribute this difference to particle reorientation and the crushable nature of carbonate sediments, which can produce additional compression not captured by standard consolidation parameters. The multiplier also varied with sediment type and stress level.<br /><br />The findings indicate that post-cyclic settlement in carbonate sediments may be significantly underestimated if conventional recompression parameters are used without adjustment. The authors recommend site-specific testing when designing offshore foundations on these sediments.

Keywords

post-cyclic compression

carbonate sediments

excess pore pressure

cyclic loading

offshore structures

volumetric strain

simple shear tests

calcareous clay

carbonate silty sand

offshore foundations