Attila Michael Zsaki

Strengthening of clay by geogrid reinforced granular pile

Abstract In the present work an attempt has been made to study the behavior of a single pile reinforced with the layers of geogrid and installed in soft clay. Laboratory tests have been conducted to study the response of a geogrid reinforced granular pile under a rigid circular footing. The influence of spacing of geogrid layers and reinforced depth of pile (depth of bottom most geogrid layer), on the performance of reinforced pile has been investigated. Finite element numerical analysis has also been carried out employing rocscience, Phase2, version 6 and the comparison of results has been done with those from the experimental study. In order to validate the general findings from the study, results have also been compared with those from relevant published literature. Geogrid reinforced granular pile has been found to result in significant increase in load carrying capacity. The bulge diameter of pile has been found to reduce due to the incorporation of geogrid layers as reinforcement.

Modeling the behavior of a reinforced granular layer overlying soft soil using an integro-differential equation

Abstract Many regions of lowlands contain areas of considerably soft soils where large settlements are observed. As part of reclaiming these areas by placing a fill over the soft soil can induce extensive differential settlements, thus the use of reinforcement is essential.This paper presents a modeling approach to investigate the complex behavior of the soft soil, granular fill and reinforcement system. The response of granular fill in the proposed model is an elastic-plastic constitutive model derived from the CANAsand model, which uses a non-associated flow rule along with the concept of the state boundary surface possessing a critical and a compact state. The model is capable of computing the surface profile of reinforced granular fill over very soft soil due to immediate settlement. A primary ground deformation profile is evaluated prior to filling and is based on a parametric study involving variables such as the height and spacing of embankment fingers, the stiffness modulus of reinforcement and the cohesion of soft soil. Numerical results indicate that these parameters affect the performance of the system in many direct ways. Based on the theory presented an integro-differential equation, written in its finite difference form, was developed to estimate the total displacement field of the system. The model, implemented as an algorithm, generated results showing that larger surface settlements were associated with high void ratios whereas smaller surface settlements were associated with low void ratios. The computed settlements were compared to predictions from an exiting finite element code and the two results are comparable in the context of geotechnical engineering practice.

cutting|Plane: an interactive tool for exploration of 3D datasets via slicing

The interpretation of results of analysis often requires considerable resources; both hardware and human expertise and time. Many disciplines generate three-dimensional volume datasets that need to be explored to observe structure and trends in key variables. This paper presents a coupled hardware-software approach for aiding data interpretation by cutting the dataset with a plane. The developed device can be held by the user and interactively manipulated to re-orient the cutting plane and observe trends in the data. As a practical application of the device, three-dimensional stress analysis results were explored using the device resulting in an increased efficiency of interaction and interpretation.

Accelerated parallel computation of field quantities for the boundary element method applied to stress analysis using multi-core CPUs, GPUs and FPGAs

Abstract Computation in engineering and science can often benefit from acceleration due to lengthy calculation times for certain classes of numerical models. This paper, using a practical example drawn from computational mechanics, formulates an accelerated boundary element algorithm that can be run in parallel on multi-core CPUs, GPUs and FPGAs. Although the computation of field quantities, such as displacements and stresses, using boundary elements is specific to mechanics, it can be used to highlight the strengths and weaknesses of using hardware acceleration. After the necessary equations were developed and the algorithmic implementation was summarized, each hardware platform was used to run a set of test cases. Both time-to-solution and relative speedup were used to quantify performance as compared to a serial implementation and to a multi-core implementation as well. Parameters, such as the number of threads in a workgroup and power consumption were considered and recommendations are given concerning the merits of each hardware accelerator.

Simulation of Tailings Flow Resulting From a Dam Breach Using Smoothed Particle Hydrodynamics

Failure of tailings dams often results in the release of substantial amounts of tailings into the environment causing considerable damage. The flow of tailings presents a complex modeling challenge due to the free-surface flow and large deformations involved, often intractable by conventional finite element or finite difference methods. A mesh-free formulation, based on Smoothed Particle Hydrodynamics (SPH), was utilized to back-analyze documented tailings dam failures. As with any numerical model, the calibration of model parameters to corresponding physical quantities is a requirement prior to any application of a model. In addition to the effect of model parameters, such as the roughness of terrain, that are hard to quantify, the capabilities and limitations of the SPH model itself were investigated using a simple experimental setup of flume flow. In this paper, the calibrated model was applied to literature-reported tailings dam failures. The outflow of tailings interacting with the terrain resulted in considerably good agreement between the simulation results and the reported cases, enabling use of the modeling approach to assess the potential damage cause by tailings dam breaches and predict flow paths of tailings.

Stability assessment of homogeneous slopes loaded with mobile tracked cranes—An artificial neural network approach

Abstract Construction projects often involve the use of mobile crawler cranes to excavate, backfill, dredge or move material and equipment on or near slopes. Crane manufacturers often only provide guidelines for the safe operation of cranes with respect to over tipping. However, the complex interaction of many variables such as the crane, its load, the slope geometry and its geotechnical properties can create slope instability. In this study, an artificial neural network was developed to predict the stability of these slopes loaded by mobile cranes. The neural network was built and trained using a set of slope stability models that were constructed using the above parameters via Monte Carlo sampling. The trained network was capable of predicting the factor of safety of a loaded slope and the location of the critical failure surface with relatively low error. In addition, the quality of the network’s output was investigated using multiple metrics, such as the correlation ratio or the mean squared error and quite high correlation was achieved. Thus, the predicting capabilities of the network can be used with confidence to aid the positioning of mobile cranes on slopes without a need to perform slope stability analysis for each scenario.

Hardware-accelerated generation of 3D diffusion-limited aggregation structures

The diffusion and aggregation of particles in a medium can result in complex geometric forms with an artistic interpretation, yet these aggregates can represent many natural processes as well. Although the method is quite simple, it takes many particles to form an aggregation. If the process is simulated using a computer, it directly translates into lengthy computation times. In this paper, the acceleration of the diffusion-limited aggregation was investigated. The algorithm of aggregation was implemented on a serial single-core CPU, and that served as the base-case. With the aim of reducing run times, the algorithm was implemented on three accelerator architectures using OpenCL as the connecting software framework. Performance testing of the OpenCL implementation was done on a multi-core CPU, a GPU and an FPGA. Metrics such as run time, relative speedup and speedup-per-watt were used to compare the hardware-accelerated implementations. Even though using a GPU is not the most economical alternative energy-wise, its performance resulted in the highest speedup, while an FPGA or a multi-core CPU offered other viable options in accelerating the creation of diffusion-limited aggregation structures. Implementation of diffusion limited aggregation (DLA) on parallel hardware.Use of OpenCL running on multi-core CPU, GPU and FPGA.Performance evaluation of the accelerated DLA algorithm.

A Non-Overlapping Domain Decomposition Method for the Stokes Problem

A domain decomposition method for the Stokes problem using Lagrange multipliers is described. The dual system associated with the Lagrange multipliers is solved based on an iterative procedure using the two-level finite element tearing and interconnecting (FETI) method. Numerical tests are performed by solving the driven cavity problem. An analysis of the number of outer iterations and an evaluation of the cost of the inner iterations are reported. Comparison with the well-known Uzawa algorithm shows a reduction in the floating point operations count of the inner iterations while achieving the same number of outer iterations.Copyright