A case study of liquefaction: demonstrating the application of an advanced model and understanding the pitfalls of the simplified procedure

Abstract

The complexity of advanced constitutive models often dictates that their capabilities are only demonstrated in the context of model testing under controlled conditions. In the case of earthquake engineering and liquefaction in particular, this restriction is magnified by the difficulties in measuring field behaviour under seismic loading. In this paper, the well documented case of the Canterbury Earthquake Sequence in New Zealand, for which extensive field and laboratory data are available, is utilised to demonstrate the accuracy of a bounding surface plasticity model in fully-coupled finite element analyses. A strong motion station with manifestation of liquefaction and the second highest peak vertical ground acceleration during the Mw 6.2 February 2011 event is modelled. An empirical assessment predicted no liquefaction for this station, making this an interesting case for rigorous numerical modelling. The calibration of the model aims at capturing both the laboratory tests and the field measurements in a consistent manner. The characterisation of the ground conditions is presented, while, to specify the bedrock motion, the records of two stations without liquefaction are deconvolved and scaled to account for wave attenuation with distance. The numerical predictions are compared to both the horizontal and vertical acceleration records and other field observations, showing a remarkable agreement, also demonstrating that the high vertical accelerations can be attributed to compressional resonance. The results provide further insights into the underperformance of the simplified procedure. Keywords liquefaction; dynamics; field instrumentation; numerical modelling; bounding surface plasticity model; validation; simplified procedure; horizontal and vertical records List of notation A Plastic hardening modulus (BSPM) A d Dilatancy coefficient (BSPM) A 0 Dilatancy constantmaximum value of the dilatancy coefficient (BSPM) Κσ Overburden correction factor K 0 Coefficient of earth pressure at rest k Permeability k c b Parameter defining the size of the bounding surface k c d Parameter defining the size of the dilatancy surface k max Maximum permeability at the time of liquefaction k 0 Initial static permeability as measured in conventional laboratory testing Μ c c Stress ratio (q p′ ⁄) defining the critical state shear strength in triaxial compression Μ e c Stress ratio (q p′ ⁄) defining the critical state shear strength in q-p′ space in triaxial extension

Cyclic liquefaction resistance of sand under a constant inflow rate

“…Moreover, they show that deep layers overlain by nonliquefiable layers can liquefy rapidly, isolating the rest of the deposit. Tsaparli et al (2020) demonstrate how current simplified liquefaction susceptibility assessments led to a false negative case during the same series of earthquakes, due to not accounting for water drainage that led to void redistribution in proximity to the interface of a liquefiable with a lower permeability layer. The occurrence of localised volumetric expansion below a lower permeability layer, to the point of the formation of a water film, was first identified by Kokusho (1999).…”

“…However, to the authors knowledge, no data are available on cyclic element tests under specified, non-zero, volumetric expansion rates. Of particular interest is the condition of volume increase due to water inflow, which can occur in proximity to the interface of a liquefiable layer with an overlying layer of low permeability; a condition that is not accounted for by current simplified assessments (Cubrinovski et al, 2019) and can lead to false negative predictions (Tsaparli et al, 2020). This paper makes a first step in addressing such issues, by presenting results from cyclic triaxial experiments under a condition of water inflow.…”

Structure–soil–structure interaction (SSSI) of adjacent buildings with shallow foundations on liquefiable soil

“…Several constitutive models have been developed, aiming to capture the response of liquefiable soil (e.g., Refs. [10][11][12][13][14][15][16][17]). Such models typically contain a large number of parameters, which have to be carefully calibrated against soil elements tests (e.g., Ref.…”