Cyclic threshold shear strain for pore water pressure generation and stiffness degradation in marine clays at Yangtze estuary
Xing Xiao, JI Dong-wei, Tianzhu Hang, Zi-Yang Cai, Lei Zhang, Qi Wu, Guoxing Chen
Abstract
Cyclic threshold shear strain is a fundamental property of saturated soils under cyclic loading. To investigate the cyclic threshold shear strain for pore water pressure generation ( γ tp ) and stiffness degradation ( γ td ), a series of strain-controlled multistage undrained cyclic triaxial tests were carried out on in-situ saturated marine clay in the Yangtze estuary with different plasticity index I p . The test results show that both γ tp and γ td increase with increasing I p , and γ tp is larger than γ td for the same marine clay tested under the same conditions, with γ tp = 0.017 ~ 0.019%, γ td = 0.008 ~ 0.012% for I p of 17, γ tp = 0.033 ~ 0.039%, γ td = 0.020 ~ 0.025% for I p of 32, and γ tp = 0.040 ~ 0.048%, γ td = 0.031 ~ 0.036% for I p of 40. Moreover, the development of stiffness degradation may not necessarily require the generation of pore water pressure but can be aggravated by it. Furthermore, the γ tp and γ td of marine clay are compared with terrestrial soils and marine clays cited from the published literature, the results indicate that the special marine sedimentary environment and the combined action of flow and tidal wave system cause the γ tp and γ td of marine clay in the Yangtze estuary to be smaller than that of the terrestrial clays and marine clays in other sea areas.