Comparison of Strain-rate Dependent Stress-Strain Behavior fromK_o-consolidated Compression and Extension Tests on Natural Hong Kong Marine Deposits

Abstract

This article presents results from a series of K o -consolidated compression and extension triaxial tests on specimens from undisturbed samples of Hong Kong Marine Deposits (HKMD). To investigate the strain-rate effects, a total of seven K o -consolidated triaxial tests were conducted including four compression tests and three extension tests. After K o -consolidation, the triaxial test specimens were sheared at step-changed axial strain rates under three different confining pressures of 50 kPa, 150 kPa, and 400 kPa, respectively. The step-changed strain rates were applied in the following order: þ2%=h, þ0.2%=h, þ20%=h, À2%=h (unloading) and þ2%=h (reloading) for the four compression tests and À2%=h, À0.2%=h, À20%=h, þ2%=h (unloading) and À2%=h (reloading) for the three extension tests. The results are reported and analyzed in the paper. The results show that the strain rate effects, the stress-strain characteristics, and the effective stress paths of the specimens for tests in a compression state are different from those for tests in an extension stage. One order of magnitude increase in axial strain rate causes an average 8.6% increase in undrained shear strength for compression tests and a 12.1% increase for extension tests. It is also found that the failure mode of the specimens in compression is different from that in extension. The stress-strain behavior of specimens shows strain-softening and a clear shear band in compression tests, but strain-hardening without any clear shear band in extension tests for the same absolute value of axial strain.The territory of Hong Kong located in the south of China is very hilly. Approximately two-thirds of the territory's land is considered unsuitable for development. Due to the increasing need of land for buildings and infrastructure, a number of large-scale marine reclamation works have been constructed in Hong Kong over the last two decades. This trend will continue for the near future.

Nonparametric Estimation of Undrained Shear Strength for Normally Consolidated Clays

“…Therefore, FVT is often considered as the reference test for undrained shear strength and it has often been used in the establishment of empirical correlations . It should be emphasized that the undrained shear strength depends substantially on the testing method and testing conditions (Yin and Cheng 2006;Mayne et al 2009;Ching and Phoon 2013). Therefore, 6 results of this study are only comparable with other FVT-based studies, such as the ones in Skempton (1957) and Bjerrum and Simons (1960).…”

An anisotropic elastic–viscoplastic model for soft clays

“…9. Field vane test profiles for St. Herblain clay (after Zentar, 1999;Rangeard, 2002;Yin and Cheng, 2006). …”

“…Fig. 6 shows the normalized effective stress paths for HKMD by Yin and Cheng (2006). C150 and C400 are the tests under a confining pressure of 150 kPa and 400 kPa, respectively.…”

“…C150 and C400 are the tests under a confining pressure of 150 kPa and 400 kPa, respectively. The critical state line was estimated using three undrained triaxial tests at one constant strain-rate (see Yin and Cheng, 2006). In these two step-changed tests, stress path overpasses the critical 0.7 0.8 0.9 1 2 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4…”

“…The time-dependency of stress-strain behaviour of soft clays has been experimentally investigated through one-dimensional and triaxial test conditions by numerous researchers (i.e., Bjerrum, 1967;Vaid and Campanella, 1977;Mesri and Godlewski, 1977;Leroueil et al, 1985Leroueil et al, , 1988Nash et al, 1992;Sheahan et al, 1996;Rangeard, 2002;Yin and Cheng, 2006).…”