Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Civil and Environmental Engineering


Dr. M. Hesham El Naggar


Geosynthetic reinforcement in earth structures has been used extensively over the last two decades. Extensive research has been carried out to investigate solutions to enhance the lateral stability of pile foundations. This research is motivated by the need to install piles in sites characterized by soft subsurface soil conditions, and often times, in seismic active areas. This research work explores an innovative use of geosynthetics to enhance the lateral performance of pile foundations. The static and seismic soil-structure-interaction behaviors of geosynthetics-reinforced pile foundation systems were evaluated using a series of reduced scale physical model tests performed on a shaking table in a 1G environment. A laminar shear box containing a pile foundation model supporting a single degree of freedom structure installed in different soil bed models was used in the experiments. The soil models included: a layer of synthetic clay (Modified Glyben) underlain by a sand layer (simulating a base case of soft soil); a layer of synthetic clay sandwiched between a sand layer and an aggregate layer (simulating the case of conventional ground replacement for the top soft soil); and a layer of synthetic clay sandwiched between a sand layer and a geosynthetic-reinforced aggregate layer (simulating the case of ground replacement of the top soft soil combined with geosynthetic reinforcement using a microgrid mesh). A series of sine-sweep, harmonic and scaled earthquake tests have been performed to identify the amplification and resonance conditions of the foundation system and to identify various aspects of seismic-soil-pile-geosynthetic reinforcement interaction effects. Lateral static load tests of this system were performed using a one directional load system that was fixed on the laminar shear box. The dynamic and static tests were simulated employing numerical models developed using the finite element program Plaxis 3D. The results of both static and dynamic tests showed that the microgrid reinforcement improved the lateral performance of the pile foundation and reduced the vibration amplitudes of the supported structure. The numerical analysis results were in close agreement with the dynamic and static experimental results. The results of a parametric study for the investigated foundation configuration and seismic loading demands showed that the requirements for engineered backfill can be reduced by more than 50% and the lateral seismic response can be reduced by 50% by using geosynthetic reinforcement.

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