A HYBRID TIME-FREQUENCY METHODOLOGICAL PROPOSAL TO SIMULATE GROUND RESPONSE UNDER HARMONIC ACCELERATIONS IN A MATERIAL-POINT FRAMEWORK

The response of geomaterials to seismic excitations, which are usually described with time history data, can be estimated by solving governing equations in the frequency domain and transferring quantities back to the time domain. However, one limitation of frequency analysis is the simplification of soil response by assuming constant stiffness during the action of seismic input. Therefore, when the frequency approach is used in ground response problems, linear-equivalent models of soil behaviour that allow the description of non-linear stiffness are implemented. In order to simulate large fields of displacements induced by seismic actions, this paper introduces a methodological proposal based upon a hybrid Finite Element (FE) time-frequency approach, coupled with the Material Point Method (MPM). In the FE solution, the soil stiffness changes after certain number of cycles and the equation of motion is solved in the frequency domain while the soil stiffness remains constant. Mapping of kinematic quantities between nodes of the finite element mesh and material points is performed via a Newton-Raphson numerical scheme. Each change of the stiffness matrix is marked by a convective material-point phase and the recalculation of material point locations. By following this approach, large deformations of geomaterials under constant amplitude harmonic accelerations can be simulated using a linear equivalent approach for the non-linear response. A model test case subjected to harmonic shaking is explained

Automatic calibration of the SANISAND parameters for a granular material using multi-objective optimization strategies

peer reviewedThe parameter calibration of a constitutive model is a requisite to counter the uncertainty in the parameters and to approximate the simulation results effectively. Yielding a robust set of parameters for various test conditions is complicated as innumerable parameter combinations have to be investigated. In previous works, this calibration has been performed manually by trial and error without checking the robustness of the chosen parameters. Therefore, the present study introduces an automated calibration procedure using multi-objective optimization techniques. This assists in searching the parameter domain space extensively for better combinations that simulate the experiment results precisely. Though this approach is quite popular in various other engineering aspects, proposing the concept of calibrating the soil parameters and validating their efficiency has been always a challenge and interesting in this framework. In this research, SANISAND model parameters have been calibrated for crushed glass material under different triaxial conditions considering the barotropy, and pycnotropy effects. The results demonstrated that the optimized SANISAND parameters approximated the experiment results far better than manually calibrated results. This calibration approach facilitates in conserving the robust parameters besides dealing with time constraints and motivates the idea of adapting this automation platform to any constitutive model for significant approximations

Numerical investigation of geogrid back-anchored sheet pile walls

peer reviewedIn the last decades, geosynthetic reinforcement has been widely used in geotech-nical applications. Recently, geogrid has also been used to back-anchor sheet pile walls. However, this system has not received sufficient attention neither in research nor in construction. Due to the complex interactions between soil, geogrid and sheet pile wall, the applicability of common design guidelines for conventionally back-anchored walls to this particular system has to be proven. To develop a fundamental understanding about the influence of various components of the system on its behaviour, numerical investigations have been conducted within this study. In this paper the influence of geogrid inclination, design of geogrid-sheet pile connection including prestressing and geogrid position on the earth pressure distribution and wall deformation is discussed. The numerical results revealed that the position of geogrid and design of geogrid-sheet pile connection significantly affect the earth pressure distribution. The wall deformations are mainly influenced by the geogrid position