Exploring Novel Lightweight Backfills for Geotechnical Structures

About This Grant

This project supports research that looks to build upon concepts from aerospace composites engineering to create new geo-composites that combine geosynthetics and lightweight backfill materials with contrasting stiffnesses (lightweight cellular concrete, LCC and tire derived aggregate, TDA) in different geometric architectures with characteristics designed to reach desired objectives. Retaining walls have been constructed recently with TDA (a ductile recycled material that has high shear strength and damping but low modulus) and LCC (a brittle cementitious material that can be placed rapidly as a flowable fill) due to their lightweight nature, rapid construction, low cost, and good static response. However, there are fundamental concerns about the response of these materials during earthquakes, including excessive deformations of TDA, fracturing or loss of contact with reinforcements of LCC, and lack of clarity in whether lightweight backfills will behave as a rigid body due to their lower inertia or distort internally and dissipate energy. New infrastructure opportunities are sought by combining LCC together with TDA and geosynthetic reinforcements or separators to form geo-composites with features like high axial stiffness to support infrastructure but high shear flexibility to provide seismic or vibration isolation, accommodate earthquake loading, or absorb blast impacts. This research seeks to advance the seismic and static design of fill-type retaining systems with lightweight backfills. In addition to a training program for graduate students integrating aerospace composites and geotechnical engineering, high school and undergraduate students will be introduced to the concept of geo-composite backfills in construction through the development of an instructional shake table educational module that demonstrates the impacts of inertia and energy dissipation on the deformation of different backfills. The research objective of this project is to understand how TDA and LCC can be combined with geosynthetics to reach different geotechnical goals while at the same time addressing shortcomings identified in each of the individual backfills. This objective looks to be achieved by learning from composites engineering concepts to combine materials of different stiffness in creative geometries. This project will involve advanced numerical analyses using the discrete element model-bonded particle method (DEM-BPM), calibrated using results from element-scale experiments, to study the deformation response of different geo-composite configurations (e.g., mixtures, laminates, checkerboard, etc.) of LCC and TDA with geosynthetic interfaces under different modes of loading. The goals of the DEM-BPM simulations are to understand the deformation response and fracture initiation of LCC containing compressible air bubbles within brittle cement, and the deformation response of the planar, flexible TDA particles with high interface friction and edge interactions enhanced by exposed steel wires. The DEM-BPM analyses will be up-scaled and integrated into continuum-based constitutive models that looks to be used in commercial finite element software to design the geo-composite backfill materials to have different responses to static and seismic loading. The finite element simulations will be validated using shake table and vertical loading tests on scale-model geo-composites with TDA, LCC and geosynthetics in different configurations. Insights from the validated design simulations will be presented in industrial seminars that bring geotechnical engineers and TDA and LCC specialists. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.