Adjustment Method of the Hysteresis Damping for Multiple Shear Spring Model

In simulating the behavior of sandy soil under the cyclic loading condition using the multiple shear spring model, it is necessary to adjust the damping constant of the model. We describe a method for adjusting the constant in this paper. If you adopt the conventional Masing rule to decide the unloading curve of each spring, the entire damping constant of this model, which is superposition of those of all springs, would become larger than that measured in the laboratory for large strain level. Though the damping constant of each spring is controllable by amending the Masing rule, there is no obvious way to decide the constant of each spring. In order to reproduce the actual damping constant, we expressed the damping constant of each spring as a function of displacement at which unloading of the spring has started, and determined the coefficients of the expression from the actual damping constant. So we can amend the Masing rule for each spring so as to realize the damping constant for each spring. The method is adopted to the effective stress analysis program FLIP developed by the authors. In this paper we explain the method and show the results of the computer simulations by FLIP program

Effective Stress Analysis for Evaluating the Effect of the Sand Compaction Pile Method During the 1995 Hyogoken-Nambu Earthquake

The effect of the sand compaction pile method as a countermeasure for liquefaction mainly consists of three factors: increase in the density, increase in the horizontal effective stress and stabilization of microstructure. Proper evaluation of the effect of improvement is important for estimating the seismic behavior of the ground improved by the sand compaction pile method. How to incorporate the effect and its factors into an analytical model was investigated by simulating the seismic behavior of the ground at two sites during the 1995 Hyogoken-Nambu earthquake with the effective stress analysis method “FLIP.” It was found that not only the increase in the density but also increase in the horizontal effective stress were important in explaining the effect of the sand compaction pile method. Moreover, a model taking account of both sand piles and the improved ground between them suggested a possibility of reproducing the behavior of improved ground under large ground motions more properly

LEAP-2017 Simulation Exercise: Calibration of Constitutive Models and Simulation of the Element Tests

This paper presents a summary of the element test simulations (calibration simulations) submitted by 11 numerical simulation (prediction) teams that participated in the LEAP-2017 prediction exercise. A significant number of monotonic and cyclic triaxial (Vasko, An investigation into the behavior of Ottawa sand through monotonic and cyclic shear tests. Masters Thesis, The George Washington University, 2015; Vasko et al., LEAP-GWU-2015 Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019) and direct simple shear tests (Bastidas, Ottawa F-65 Sand Characterization. PhD Dissertation, University of California, Davis, 2016) are available for Ottawa F-65 sand. The focus of this element test simulation exercise is to assess the performance of the constitutive models used by participating team in simulating the results of undrained stress-controlled cyclic triaxial tests on Ottawa F-65 sand for three different void ratios (El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019). The simulated stress paths, stress strain responses, and liquefaction strength curves show that majority of the models used in this exercise are able to provide a reasonably good match to liquefaction strength curves for the highest void ratio (0.585) but the differences between the simulations and experiments become larger for the lower void ratios (0.542 and 0.515)

LEAP-2017: Comparison of the Type-B Numerical Simulations with Centrifuge Test Results

This paper presents comparisons of 11 sets of Type-B numerical simulations with the results of a selected set of centrifuge tests conducted in the LEAP-2017 project. Time histories of accelerations, excess pore water pressures, and lateral displacement of the ground surface are compared to the results of nine centrifuge tests. A number of numerical simulations showed trends similar to those observed in the experiments. While achieving a close match to all measured responses (accelerations, pore pressures, and displacements) is quite challenging, the numerical simulations show promising capabilities that can be further improved with the availability of additional high-quality experimental results

Dilatancy of granular materials in a strain space multiple mechanism model

A granular material consists of an assemblage of particles with contacts newly formed or disappeared, changing the micromechanical structures during macroscopic deformation. These structures are idealized through a strain space multiple mechanism model as a twofold structure consisting of a multitude of virtual two-dimensional mechanisms, each of which consists of a multitude of virtual simple shear mechanisms of one-dimensional nature. In particular, a second-order fabric tensor describes direct macroscopic stress–strain relationship, and a fourth-order fabric tensor describes incremental relationship. In this framework of modeling, the mechanism of interlocking defined as the energy less component of macroscopic strain provides an appropriate bridge between micromechanical and macroscopic dilative component of dilatancy. Another bridge for contractive component of dilatancy is provided through an obvious hypothesis on micromechanical counterparts being associated with virtual simple shear strain. It is also postulated that the dilatancy along the stress path beyond a line slightly above the phase transformation line is only due to the mechanism of interlocking and increment in dilatancy due to this interlocking eventually vanishing for a large shear strain. These classic postulates form the basis for formulating the dilatancy in the strain space multiple mechanism model. The performance of the proposed model is demonstrated through simulation of undrained behavior of sand under monotonic and cyclic loading

A simplified method to consider the pile of insufficient length to obtain the support from bearing stratum

Recently, in Japan, there is a case that the pile end of the building did not reach the firm layer because the soil layer was complicated. In such a case with piles with insufficient length, the existing pile modelling method cannot be applied. Therefore, we tried to model the load–settlement relationship of a pile with insufficient length through a two-dimensional (2D) analysis. Firstly, we perform three-dimensional (3D) analyses to examine the load–settlement relationship of a pile with insufficient length. Thus, a degradation parameter to express the effect of insufficient length of the pile is proposed for practical 2D FEM analysis. Finally, we conduct a feasibility study with the proposed parameter in 2D model. It is expected that the proposed model can be used as a reference for verifying the practical performance of buildings supported by incompletely end-supported piles through a 2D analysis