Analysis of dynamic properties and transitional failure of clay-sand mixture in fine-grained soil based on mineral composition

摘要

Reexamining the transitional failure with energy method is a new idea of studying the dynamic properties of finegrained soil. In this paper, a series of undrained cyclic triaxial tests and low-vacuum environmental scanning electron microscopy were employed to study the dynamic properties of two types of clay-sand mixtures with a similar plasticity index at a fine-grained content of 70%. In terms of mineral composition, Toyoura sand constituted the coarse-grained fraction of the clay-sand mixture, and its fine-grained portion was comprised of different mass ratios of quartz, albite, Na-montmorillonite, and kaolinite (Q(c)A(c):M-c:K-c); that is, the specimens were divided into groups TQ(42.5)A(42.5)M(0)K(15) and T-Q(45)A(45)M(2.5)K(7,5). The results showed that T-Q(42.5)A(42.5)M(0)K(15) with an embedded dispersed fabric had a failure mode dominated by the pore water pressure, so it had an inferior cyclic strength compared to T-Q(45)A(45)M(2.5)K(7.5) with an embedded flocculated fabric. Meanwhile, the dimensionless viscous energy dissipation ratio (VEDR) was introduced to observe the history of the differential energy dissipation of the clay-sand mixture and thus reveal the limitations of the plasticity index for the evaluation of the dynamic properties of soil. Furthermore, compared with previously studied artificial marine clay with a clay-like mode of VEDR and low-plasticity fine-grained tailings with a sand-like mode of VEDR, the clay-sand mixture studied herein offered a transitional mode of VEDR. On the whole, this work can make a significant contribution to the research on transitional failure by demonstrating that traditional dynamic properties and energy dissipation can act together as the indicators of the dynamic behavior of soil.

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