Cyclic Pore Water Pressure Generation and Stiffness Degradation in Compacted Clays

Abstract

Cyclic hollow cylinder torsional tests were performed in undrained conditions on 12 compacted clay specimens collected from two types of dams (an earth-core rock-filled dam and an earth-zone dam) in Thailand. The cyclic degradation, cyclic pore water pressure generation, and volumetric cyclic threshold shear strain were studied via multistage strain-controlled tests. The testing program encompassed five overconsolidation ratios (OCRs), 1, 1.5, 2, 3.5, and 4, where six to eight cyclic strain-controlled stages were applied in each test with frequency f=2 Hz. The results reveal that the volumetric threshold shear strain amplitude of these compacted clays ranged between approximately 0.009 and 0.025% and generally increased substantially with the plasticity index (PI). The cyclic pore water pressures normalized by σc′ are consistently lower than previous ones using other types of clays tested with other types of devices at comparable cyclic shear strain amplitudes. The cyclic degradation and cyclic pore water pressure in compacted clay are significantly affected by the OCR.