Liquefaction and post-liquefaction properties of sand-silt mixtures and undisturbed silty sands

• Published in: Soils and foundations Vol. 59; no. 6; pp. 2311 - 2323
• Main Author: Enomoto, Tadao
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2019
• Subjects: Fine sand containing non-plastic silt; Liquefaction; Post-liquefaction behaviour; Triaxial compression; Undisturbed and non-plastic medium-fine sand containing fines; Fine sand containing non-plastic silt; Triaxial compression; Undisturbed and non-plastic medium-fine sand containing fines; Liquefaction; Post-liquefaction behaviour
• ISSN: 0038-0806
• DOI: 10.1016/j.sandf.2019.09.005

Severe damage to earth structures mainly consisting of fine sands containing non-plastic silt has often occurred due to the liquefaction of the fill materials. However, the changes in the liquefaction susceptibility and post-liquefaction undrained behaviour of fine sands associated with the increase in the amount of non-plastic silt have not been well understood under a constant degree of compaction which has been employed as the construction management index for these structures. To clarify this point, a series of undrained cyclic triaxial liquefaction tests, followed by monotonic loading, was conducted on seven sand-silt mixtures with fines contents ranging from 0 to 100% in the present study. Undrained triaxial compression tests without precedent cyclic loading were also performed on the same materials for comparison purposes. In these tests, cylindrical specimens with an initial degree of compaction of 95%, prepared by the wet tamping method, were employed to simulate the construction conditions of earth structures. The test results showed that: (1) the liquefaction resistance, and the static strengths of specimens with and without precedent cyclic loading history decreased with increasing fines content ranging from 0 to 50%; however, they increased afterward, and (2) sand-silt mixtures with fines contents of 30, 50, and 65% consistently exhibited extremely small post-liquefaction strengths without showing any significant changes in the excess pore water pressure generated in the precedent liquefaction tests, which may lead to the post-liquefaction flow failure of earth structures. From these results, the risk of employing a uniform degree of compaction irrespective of the fines content was presented. In the present study, similar triaxial liquefaction tests, with measurements of the shear wave velocities by means of bender elements, were also conducted on both undisturbed and reconstituted non-plastic medium-fine sands containing fines which were retrieved from road embankments damaged possibly due to liquefaction brought about by the 2011 off the Pacific coast of Tohoku earthquake. The soil ageing effects were briefly discussed from the test results.