# Calibration of Finn Model and UBSCAN Model for Simplified Liquefaction Analysis Procedures
###### Abstract  
Soil-liquefaction-related hazards can damage structures or lead to an extensive loss of life and property. Therefore, the stability and safety of structures against soil liquefaction are essential for evaluation in earthquake design. In practice, the simplified liquefaction analysis procedure associated with numerical simulation analysis is the most used approach for evaluating the behavior of structures or the effectiveness of mitigation plans. First, the occurrence of soil liquefaction is evaluated using the simplified procedure. If soil liquefaction occurs, the resulting structural damage or the following mitigation plan is evaluated using the numerical simulation analysis. Rational and comparable evaluation results between the simplified liquefaction analysis procedure and the numerical simulation analysis are achieved by ensuring that the liquefaction constitutive model used in the numerical simulation has a consistent liquefaction resistance with the simplified liquefaction analysis procedure. In this study, two frequently used liquefaction constitutive models (Finn model and UBSCAN model) were calibrated by fitting the liquefaction triggering curves of most used simplified liquefaction analysis procedures (NCEER, HBF, JRA96, and T-Y procedures) in Taiwan via FLAC program. In addition, the responses of two calibrated models were compared and discussed to provide guidelines for selecting an appropriate liquefaction constitutive model in future projects. Finn model; UBSCAN model; model calibration; soil liquefaction; numerical simulation; FLAC  
12 April 202126 May 202127 June 202126 May 2021  
**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. **Published:** maps and institutional affiliations. model should have a consistent liquefaction resistance with the simplified liquefaction analysis procedure or experiment results used in the first step of the evaluation to obtain reasonable and comparable evaluation results in the second and third steps. Therefore, the input parameters of the liquefaction constitutive model should be calibrated to capture key aspects (liquefaction triggering and post-liquefaction deformation) of the simplified liquefaction analysis procedure or the cyclic test results [1]. In the past few decades, liquefaction constitutive models were improved from loose coupled effective stress models (e.g., Finn model) to fully coupled effective stress models (e.g., UBCSAND model and PM4 SAND model). However, it remains a difficult task for engineers to choose an appropriate liquefaction constitutive model and representable values of model input parameters. Given that the techniques for sampling undisturbed sand samples (e.g., frozen sampling) are expensive and difficult, most projects do not obtain undisturbed sand samples; as such, reliable cyclic test results cannot be achieved. Therefore, the results of site-specific cyclic tests are usually not available; instead, the simplified liquefaction procedure is used to evaluate the occurrence of soil liquefaction on a site. When numerical analysis is needed for subsequent evaluations, many engineers assign the input parameters of the liquefaction constitutive model following the model's default values without performing a proper model calibration. This practice results in an inconsistent liquefaction resistance (cyclic resistance ratio, CRR) between the simplified liquefaction analysis procedure and the liquefaction constitutive model, leading to numerical simulation results that are not representable and comparable. Among all liquefaction constitutive models, the Finn model and the UBCSAND model are widely used to explore liquefaction behaviors or liquefaction-related hazards in research or practical projects [2; 3; 4; 5; 6; 7; 8; 9]. In these projects, the Finn model or the UBCSAND model were calibrated against dynamic test results [2; 5; 6; 9], physical modeling test results [2; 4; 5; 8], or data from real earthquake cases [4; 7; 9].