Experimental Investigation on the Bearing Capacity of Loose Sand: Effects of Footing Geometry and Cemented Layer Thickness
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Abstract
Shallow foundations constructed on loose sand deposits frequently face significant geotechnical challenges, primarily characterized by low bearing capacity and excessive settlement due to the soil’s punching shear failure mechanism. This study presents a comprehensive experimental investigation to quantify these behaviors and evaluate the efficacy of surface cement stabilization as a ground improvement technique. The experimental program was conducted in two distinct phases. The initial phase established a baseline for untreated loose sand (Dr=30%) by examining the "scale effect" through square footings of varying widths (B=60,70,80, and 100 mm) and analyzing the "shape effect" by comparing square and circular geometries. The results demonstrated a non-linear increase in bearing capacity with footing size, confirming the stress-level dependency of granular soils. Furthermore, square footings exhibited superior performance, yielding approximately a 19% higher ultimate capacity than circular footings of equivalent dimensions due to enhanced confinement at the corners.
In the second phase, the study investigated the performance of a rigid square footing (B=60 mm) resting on a finite cement-stabilized crust (3% cement content, cured for 7 days). The width of the improved zone was fixed at twice the footing width (W=2B), while the layer thickness was systematically varied to thickness ratios (H/B) of 0.5, 1.0, 1.5, and 2.0. The inclusion of the cemented layer fundamentally altered the load-settlement response, transforming the failure mode into a rigid slab action that effectively distributed stresses over the weaker subgrade. The improvement efficiency was substantial, with the ultimate bearing capacity rising from 104.2 kPa at a thin layer of H/B=0.5 to a peak of 325.3 kPa at H/B=2.0. These findings indicate that optimizing the thickness of a finite cemented crust offers a highly effective and economical alternative to deep foundations for structures on marginal granular soils.
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