Improved cyclic load resistance of sand beds with geogrid-reinforced dense gravelly layers

Foundations bearing on uncompacted coarse-grained soil deposits (e.g. aeolian fine sands) can experience excessive settlements under monotonic and cyclic loading conditions. Straightforward strategies for improving their geomechanical behaviour include mass replacement of the uniform fine sand with high-quality soil (typically coarser sand-with-gravel (S-G) material), along with including geosynthetic reinforcement layers, although this approach may prove uneconomical in practice. The present study advocates an alternative approach employing geogrid-reinforced thin dense S-G layers incorporated at discrete depths within the backfilled fine-sand deposit. A comprehensive programme of 1 g testing was performed to investigate the relative performances of fine sand beds incorporating geogrid layers, unreinforced thin dense S-G layers and geogrid-reinforced thin dense S-G layers compared to the plain (fully unreinforced) fine sand bed. A 150-mm dia. footing bearing on the surface of the sand beds was subjected to a combination of static loading followed by 2000 load cycles of different intensities. The experimental results confirmed that compared to the unreinforced/geogrid-reinforced sand beds, the sand beds with geogrid-reinforced dense S-G layers demonstrated superior performance in terms of limiting the cumulative footing settlement. The demonstrated concept could be of practical use in the economic construction of reinforced soil walls, reinforced foundation beds, and so on.