2013 M.Sc. Graduated Mohammad H. Monemi

Numerical study of pile dynamic stiffness of complex piers by local scour

Abstract

Bridges failures because of local scour at piers are common occurrences. Local scour occurs as the result of interaction between water and soil, either naturally by the changes of rivers morphology or artificially, as the result of structures constructed by human. Most bridges includes complex piers that are supported by deep foundation and includes groups of piles. As the maximum of depth of scour in not reached suddenly, the loading capacity of bridges piles are reduced before the occurrence of the maximum depth of scour.

To study the capacity of a single pile loading during the local scour process, a dynamic analysis is necessary. There is not any numerical model that is capable of simulating the local scour and the dynamic analysis of a pile simultaneously. The present work developed procedures for studying the loading capacity of a single pile during the scour process. SSIIM software is used for estimating the scour process and dynamic analysis is then modeled in ABUQUS software. The behavior of the pile during the scour process is studied by linking these two softwares. The result of dynamic modeling is verified by DYNA5, before linking to SSSIM. The link program was written in MATLAB software and verified by comparing the outputs with the inputs of the program. In addition, method are presented based on simplification of the scour hole shape.

The numerical results of the scour pattern around the single pile using SSIIM software are deviates considerably from those of the experimental data. The maximum scour depth was also compared with the experimental data and it was observed that SSIIM software is capable of estimating the maximum scour depth within acceptable errors. The comparison of results in ABUQUS and DYNA5 models displayed minor errors for stiffness than those of attenuation. The results of ABUQUS model show the operation of piles at lower frequencies are better than those at higher frequencies. With linking ABUQUS and SSIIM, it was observed that during the early stages of scour, the dynamic stiffness has less variation as compared with the final stages of scour process.