Common-Origin Approach to Assess Level-Ground Liquefaction Susceptibility and Triggering in CPT-Compatible Soils Using ΔQ
Steven R. Saye, Scott M. Olson, Kevin W. Franke
Abstract
Current engineering practice employs clean sand–based procedures to evaluate liquefaction triggering in nonplastic, coarse-grained soils and low-plasticity, fine-grained soils below level or mildly-sloping ground. Furthermore, existing empirical liquefaction triggering procedures treat all clean sands (fines content <5%) as identical (i.e., employing a single liquefaction resistance boundary). To improve these practices, this paper presents a new ΔQ common-origin method to assess level-ground liquefaction susceptibility and triggering for cone penetration test (CPT)–compatible soils ranging from nonsensitive clays to clean sands using the soil classification index ΔQ (described elsewhere). This procedure was developed using 401 documented case records of liquefaction and nonliquefaction in clean sands, silty sands, sandy silts, and low-plasticity fine-grained soils combined into a single data set. Importantly, the proposed procedure implicitly couples the evaluation of liquefaction susceptibility and triggering and does not require estimating fines content or converting measured CPT tip resistance to an equivalent clean-sand value. Rather, the proposed procedure yields unique estimates of liquefaction resistance for soils based on compressibility (as reflected in ΔQ) such that factors that affect penetration resistance (e.g., mineralogy, grain shape, density, overconsolidation) are incorporated. The new deterministic and probabilistic procedures are illustrated using examples of liquefaction and no liquefaction in clean sands, silty sands to sandy silts, and low-plasticity fine-grained soils.