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Consistent with its title, “An overview of the model container types in physical modeling of geotechnical problems” by Esmaeilpour et al. [1], the essence of the paper is literature review, and hence it is particularly important that the review is accurate. The authors have compiled an extensive list of papers relevant to the design of model containers used to study effects of seismic loading on soil behavior in shake table tests. Of course, many more container types exist for “physical modeling of geotechnical problems” beyond shake table testing. Both the paper and this discussion are focused on containers used to contain soils during shaking table tests, whether performed at 1g or on a centrifuge. Unfortunately, we noticed inaccuracies in the way that the authors have characterized the work of others. We present examples below. 

A cone penetrometer was specifically designed for the LEAP project to provide an assessment of centrifuge model densities independent from mass and volume measurements. This paper presents the design of the CPT and analyses of the results. Due to uncertainty in the specifications about how to define zero depth of penetration, about 20% of the CPT profiles were corrected to produce more accurate results. The procedure for depth correction is explained. After these corrections, penetration resistances at the representative depths of 1.5, 2, 2.5, and 3 m (prototype depth) are correlated to the reported specimen dry densities by linear regression. Using the inverse form of the linear regression equations, the density of each specimen could be estimated from the penetration resistance. Kutter et al. (LEAP-UCD-2017 comparison of centrifuge test results. In Model Tests and Numerical Simulations of Liquefaction and Lateral Spreading: LEAP-UCD-2017, 2019b) found that the density determined from penetration resistance was a more reliable predictor of liquefaction behavior than the reported density itself. Finally, the centrifuge tests at different LEAP facilities modeled the same prototype in different containers using different length scale factors (1/20 to 1/44); thus the ratio of layer thickness to cone diameter was different in each experiment. It appears that the penetration resistances are noticeably affected by container width and, to a lesser extent, resistance is affected by the length scale factor. 

Three centrifuge experiments were performed at the University of California, Davis, for LEAP-UCD-2017. LEAP is a collaborative effort to assess repeatability of centrifuge test results and to provide data for the validation of numerical models used to predict the effects of liquefaction. The model configuration used the same geometry as the LEAP-GWU-2015 exercise: a submerged slope of Ottawa F-65 sand inclined at 5 degrees in a rigid container. This paper focuses on presenting results from the two destructive ground motions from each of the three centrifuge models. The effect of each destructive ground motion is evaluated by accelerometer recordings, pore pressure response, and lateral deformation of the soil surface. New techniques were implemented for measuring liquefaction-induced lateral deformations using five GoPro cameras and GEO-PIV software. The methods for measuring the achieved density of the as-built model are also discussed. 

Measuring displacements in model tests typically involves contact-based sensors such as linear potentiometers, where contact between two moving parts occurs at the sensing point. The sensor's finite mass, the limited stiffness of the beams and the clamping mechanism, and the slippage and hinging of the sensor body could affect the object's response and lead to measurement errors. Also, the physical mounting rack required to hold these sensors often obstructs the view and makes significant areas unavailable for conducting some other essential investigations. The advancement in high-speed, high-resolution and reasonably priced rugged cameras makes it feasible to obtain better displacement measurements by image analysis. This paper introduces a non-contact method that works by video recording the projection of laser lines on a test object to measure static and dynamic vertical displacements. The technique produces a continuous settlement distribution along the laser line passing through multiple objects of interest. This paper presents the theory for converting laser line images to displacements. The new method's validity is demonstrated by comparing the results from other measurement techniques: hand measurements, linear potentiometers and three-dimensional stereophotogrammetry. 

The mean squared deviation between acceleration time histories (of soil-system test replicas) is expressed as a unique aggregate of three discrepancy measures associated with shape, phase, and frequency-shift. The shape-measure quantifies the deviations associated with dissimilarities in form and amplitude. The phase-measure estimates the deviations associated with differences in phase angle. The frequency-shift-measure quantifies the deviations associated with differences in frequency components. These measures were used to assess the discrepancies among six replicas of a centrifuge experiment of a liquefiable soil tested at six different facilities. A sensitivity analysis was thereafter used to assess the effects of input motion discrepancies on a liquefiable soil response. The conducted analysis showed that the acceleration response of the analyzed soil is more sensitive to discrepancies in input motion frequency than in phase or amplitude. 

This paper presents numerical liquefaction simulations of a hypothetical sand in cyclic direct simple shear tests for four different constitutive models. The four models are PM4Sand in FLAC, UBCSand in FLAC, Pressure Dependent Multi Yield 02 (PDMY02) in OpenSees, and the Manzari-Dafalias04 model in OpenSees. Parameters published by others for various sands were used for this work to avoid possible introduction of our bias into the calibration process. The material properties were determined by others for different uniformly graded sands, all with a relative density of approximately 50%. The simulations do not pertain to one sand or one set of laboratory data, so therefore, there is no right or wrong answer. Instead, the goal of this paper is compare a consistent set of results that show the implementations of each model behave as expected, and to illustrate basic differences in behavior of the different models. Cyclic strength curves (cyclic stress as a function of number of cycles) illustrate the behavior of the models over a range of cyclic stresses. Each model displays pore pressure build up, softening, and cyclic contraction-dilation cycles associated with cyclic mobility. Two of the models soften to a point, but then stabilize in a repeated hysteresis loop with no additional growth in the cyclic strain amplitude after some number of cycles. 

A decomposition is used to express the mean squared deviation, quantifying the dissimilarities between time histories of input (or response) quantities of multiple replicas of a soil system centrifuge test, as a unique aggregate of three discrepancy measures associated with shape, phase and frequency-shift. The shape measure quantifies the deviations associated with dissimilarities in form and amplitude. The phase measure estimates the deviations associated with differences in phase angle. The frequency-shift measure quantifies the deviations associated with differences in frequency components. These measures are illustrated using simple synthetic motions and used to assess the discrepancies among six replicas of centrifuge input motion achieved at six different facilities. The conducted analysis shows that the proposed decomposition accurately quantifies the different types of discrepancies in input or response time histories.