Abstract
This laboratory investigation has been conducted to elucidate how the fines fraction affects the undrained residual shear strength and liquefaction potential of sand-silt mixtures (Algeria). A series of monotonic and cyclic undrained triaxial tests were carried out on undrained, reconstituted, saturated samples of sand with varying fines content ranging from 0 to 50%. These were undertaken in order to evaluate the effect of the fines fraction on the undrained residual shear strength and liquefaction potential of loose, medium dense, and dense sand-silt mixtures (Dr = 17%, 53%, 62% and 91%), under an initial confining pressure of 100 kPa. The results of the monotonic tests indicate that the stress-strain response and shear strength behaviour is controlled by the percentage of the fines fraction and the samples become contractive for the studied relative density (Dr = 17% and 91%). The undrained residual shear strength decreases as the gross void ratio decreases, and the fines content increases up to 30%. Above this level of fines, it decreases with increasing gross void ratio. Moreover, the undrained residual strength decreases linearly as the fines content and the intergranular void ratio increase. Cyclic test results show that for the studied amplitude, the increase in fines content leads to an acceleration of liquefaction. The liquefaction resistance decreases with the increase in gross void ratio and the loading amplitude.
Highlights
On October 10th, 1980 at 13:25:23.7 local time (12:25:23.7 GMT) a destructive earthquake took place near Chlef City, Algeria
Three series of stress-controlled cyclic triaxial tests were carried out on isotropically consolidated soil specimens with different fines contents ranging from 0–40% and alternated symmetric deviator stress under undrained conditions, simulating essentially undrained field conditions during earthquakes, in order to produce liquefaction potential curves of the sand-silt mixtures
A series of undrained monotonic and cyclic triaxial tests were carried out on silty sand collected from liquefied sites on the Chlef River, Algeria
Summary
On October 10th, 1980 at 13:25:23.7 local time (12:25:23.7 GMT) a destructive earthquake took place near Chlef City, Algeria (formerly known as El-Asnam). In several places in the affected area, especially along the Chlef river banks, huge masses of sandy soils were ejected on to the surface. Strain properties and pore pressure generation in silty sand samples are quite different from clean sand. These new discoveries emphasize the specific important features of deposits with a mixture of sand and silt. The behaviour of silty-sandy soils such as hydraulic fills during earthquakes is not clearly understood. Further study of the behaviour of silty sand is needed for liquefaction assessment of silty sandy soils. Post-earthquake behaviour of silty sand and, the stability of structures founded on liquefied soil depend on the post-liquefaction shear strength of soil.
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