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Experimental and Numerical Investigation of Impact Loads on a Group of Piles
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Groups of in-line piles connected by beams are being used to contain errant vehicles for perimeter protection of infrastructures. Moreover, piles can be used as roadside safety devices resisting against impact loading. The effectiveness of in-line groups of piles to safely redirect or stop the approaching vehicles, however, has not been well investigated from the geotechnical point of view. The seriousness of the failure of such systems requires the development of reliable design guidelines for functional and cost-effective impact resistant systems. To date, such guidelines are limited and new barrier configurations rely mostly on full scale crash testing to be certified before they can be used. However, the extensive test setup, instrumentation and considerable cost of such crash tests have limited the practicality of running many of those tests. Numerical simulations are very useful to extend the values of the crash tests. In this research, the performance of such barriers is examined through full-scale crash tests and numerical simulations. The full scale crash tests consisted of two different configurations of piles and beams: one was in loose sand and the other in hard clay. Both barriers were subjected to vehicle impact: one by a 6800 kg medium-duty truck traveling with the approaching velocity of 80 km/h and the other by a 2300 kg pickup truck with an approaching velocity of 100 km/h. Both barriers successfully contained the impacting vehicles. Detailed finite element models of the barriers and the soil were developed using LS-DYNA a powerful numerical package and then combined with the vehicle models to simulate the dynamic events. Comparison between predicted and measured behavior was used to calibrate the models. Once calibrated, additional simulations were performed to create a comprehensive database to further study the impact response of these systems. Practical recommendations are drawn from the experimental and numerical work. Using the numerical simulation results and the experimental data, a simple yet effective model TAMU-POST (Group) was successfully developed to predict the lateral response of in-line piles embedded in any soil type subjected to impact of a vehicle through a nonlinear impact analysis. It was shown that the developed simplified mass-spring-dashpot analogy method with the calibrated constants for damping gives a remarkably good estimate of the barrier deflection measured in the tests and simulations. Two full scale impact experiments and approximately 100 numerical simulations of impact events using LS-DYNA were used to assess the precision of TAMU-POST. After calibration against the full scale crash tests, additional numerical simulations were performed to study the influence of important design parameters including mass and velocity of vehicle, soil strength, pile spacing and embedment depth was performed. Finally, the uncertainties in estimates of the model inputs such as soil properties and the model parameters were acknowledged through a reliability analysis and the probability of failure provided. It is believed that the research outcome including the testing datasets, numerical experience and the proposed model serve a reliable means to design impact-resistant barriers and, in particular, facilitates future studies on impact performance of piles in better protecting assets.
Asadollahipajouh, Mojdeh (2015). Experimental and Numerical Investigation of Impact Loads on a Group of Piles. Doctoral dissertation, Texas A & M University. Available electronically from