Effect of nonplastic silt content on undrained shear strength of sand\u2013silt mixtures

Mohammad Emdadul Karim,Md Jahangir Alam

doi:10.1186/s40703-017-0051-1

Mohammad Emdadul Karim, Md Jahangir Alam

Open Access

https://doi.org/10.1186/s40703-017-0051-1

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Abstract

To assess the behavior of sand–silt mixtures, strain-controlled monotonic triaxial tests were conducted on sand–silt mixtures of specimen size 71 mm in diameter and 142 mm in height at various relative densities but same isotropic effective confining pressure of 100 kPa. Concept of limiting fines content (LFC) was verified by these undrained monotonic triaxial tests. LFC was found to be the very important parameter to understand the behavior of sand–silt mixtures. The behavior of sand–silt mixture changes approximately at LFC. At constant relative density, increase in silt content decreases the undrained peak shear strength till LFC. After LFC the strength becomes near about same till pure silt sample. The reason of behavior could not be explained. At constant global void ratio, the peak shear strength decreases with increase in silt content till LFC and for further increment of silt content the peak shear strength increases. Sand–silt mixtures containing certain amount of silt which is near to the LFC showed flow type as well as brittle behavior. Failure of structure on this type of soil will be catastrophic during earthquake. In the case of permeability decreased with increasing silt content up to LFC. After the LFC, dry density is decreasing with increasing silt content but permeability remains constant till pure silt.

Highlights

Nonplastic silt is a common alluvial deposit in the flood plain of Bangladesh
The undrained monotonic triaxial tests were performed on sand–silt mixtures at 30, 60 and 78% relative densities and effective isotropic confining pressure of 100 kPa
By moist temping method with 10% moisture content, specimen of 30% relative density was possible to prepare, as between each grain there is a little blob of water and the surface

Summary

Introduction

Nonplastic silt is a common alluvial deposit in the flood plain of Bangladesh. It is finer than sand and behaves like sand but different from elastic silt and clay. Sand and nonplastic silt are liquefiable whereas clay and elastic silt are not liquefiable. Nonplastic silt content in sand–silt mixtures controls the behavior of the soil under monotonic and cyclic loading. Many researches are found in literature on the effect of nonplastic silt content in sand–silt mixtures. Their findings are sometimes contradicts each other. Design engineers are not aware of the behavior of nonplastic silt-sand mixtures

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Conclusion