Microgrid inclusions to increase the strength and stiffness of sand

Presented within this paper are the results and analysis of a series of triaxial compression tests evaluating the mechanical properties of poorly-graded sand mixed with randomly-oriented, small grid inclusions (“microgrids”), of various concentrations and aspect ratios. Addition of the relatively stiff microgrids, coupled with frictional interaction and interlocking of the sand grains within grid apertures enabled improved strength and stiffness of the reinforced composites at low confining pressures. Microgrid reinforcement mixture increased soil internal angle of friction from 5 to 10°, as well as the secant modulus by up to 50%. Aspect ratio and grid concentration exhibited effects on mechanical behavior, presenting the most benefit for large aspect ratios and concentrations of 0.5% by weight. Concentration must be optimized since larger grid concentrations may exhibit interference with one another, realizing less granular interlock and interface friction. Interlock of the microgrids and soil grains employs frictional mechanisms similar to geogrids where large interface friction may be mobilized when grid transverse member thickness and/or aperture are of comparable size to the mean grain size of the surrounding soil. However, unlike geogrids, soil composite behavior is better realized when inclusions are mixed homogenously with random orientations throughout a soil.