| Summary: | In the geotechnical engineering applications, precise understandings are yet to be established on the local displacement fields of the soil grains and the evolution of failure envelopes in strip footing structures interacting with different soil profiles. Several theoretical and experimental approaches have been used to measure the ultimate bearing capacity of homogeneous and layered soil systems in the past, but with a significant level of differences depending on the failure envelopes of the soils assumed. The ultimate bearing capacity refers to the ability of the soil to sustain the maximum load on the footing before the soil collapses. Finite element method (FEM) could help to study such large-scale problems but depends on the continuum assumption and the type of the constitutive relation of the soil. This research contributes new advancements on both the experimental and computational fronts in the field of soil-strip footing structure interactions under plane strain condition: (i) experimentally digital particle image velocimetry (DPIV) is used to measure the grain-scale (local scale) displacement fields, and they are used to characterise the failure envelopes of key footing-granular soil interaction problems. For the first time, such outcomes are generated in terms of the relative density of the sand, interference effects of the strip footings, accounting for the layering characteristics of sand and under static and cyclic loading environments. The experimental results are compared with corresponding finite element analysis and a good level of agreements are reported between them and (ii) in the finite element analysis (FEA), it was shown that, using an inbuilt(/existing) model of constitutive relation of sand does not produce the displacement fields of sand grains (local scale) that are comparable with DPIV outputs. Hence, a new approach of using the global experimentally-derived constitutive relations are represented as an input in the FEM simulations. The localised subsoil deformations from FEM are validated experimentally using DPIV outputs. It is worth mentioning that, such an approach results an excellent level of agreements between the above said experimental and finite element analysis approaches at both local and global scales. Furthermore, using the displacement fields obtained using DPIV, where applicable the existing theories for calculating the ultimate bearing capacity of the strip footing on layered sand are refined for achieving a better accuracy of the predictions. The computational and the experimental approaches developed in this research programme provide a strong basis in terms of methodology and findings for analysing other complex soil profiles in the ground-structure interactions in future.
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