Effect of Overburden Stress on Cyclic Resistance of Fine-Grained Materials

In liquefaction analyses, an overburden correction factor (Kσ) is used to account for the dependence of cyclic resistance ratio (CRR) on confining stress (𝜎′𝑣𝑐) due to soil becoming less dilative as 𝜎′𝑣𝑐 increases. Published models are available to evaluate Kσ for sands as a function of relative density (DR) and 𝜎′𝑣c. In contrast, the cyclic strength of clay-like soils is often assumed to normalize by the monotonic undrained shear strength (su), which scales linearly with 𝜎′𝑣𝑐 for constant overconsolidation ratio (OCR). When that occurs, cyclic strength is also assumed to scale linearly with 𝜎′𝑣𝑐, and Kσ = 1.0. However, few studies have been conducted to verify this assumption. Furthermore, the monotonic strength of silty soils does not necessarily normalize with 𝜎′𝑣𝑐, and the influence on Kσ is therefore unclear. This study presents a qualitative assessment of Kσ for normally consolidated fine-grained soils from a dataset consisting of cyclic direct simple shear and cyclic triaxial tests on soils with plasticity index (PI) ranging from 0 to 36.5, fines content (FC) ranging from 35% to 100%, and 𝜎′1𝑐 ranging from 86 to 1,000 kPa. Trends in Kσ are observed to increase with 𝜎′𝑣𝑐 for some materials and to decrease for others. When combined, a slightly increasing trend is observed, but it is not statistically different from Kσ = 1. A framework is presented for modeling Kσ as a function of the slopes of the normal consolidation line (NCL) and critical state line (CSL).