Influence of Recycled Aggregate on the Settlement Behaviour of Circular Footing Resting on Gypseous Soil
DOI:
https://doi.org/10.65204/djes.v3i3.797Abstract
This study examines the settlement behavior of circular footings on gypseous soils with different gypsum contents under dry and saturated conditions. Three types of soils have been considered: S1, S2 and S3 with gypsum contents of about 30%, 47% and 69% respectively. The soils were improved with recycled concrete (RC) at dry weight proportions of 5%, 10%, 15%, 20% & 25% and the effect of treatment depth (0.5D, 1D & 1.5D where D is the diameter of footing) was investigated through the model tests in the laboratory. The results show that RC addition significantly ameliorates the settlement and increases the load-carrying capacity of the soil -footing system. Under dry conditions, the reduction of settlement was about 28-58%, 8-54%, and 7-53% for S1, S2, and S3 respectively depending on RC contents and treatment depths. The improvement was greatest at higher RC contents of 20 to 25% and greater treatment depths (1D-1.5D). Under saturated conditions, the improvement was still obvious but was of a comparatively lower value due to gypsum dissolution and collapse behavior. The settlement reduction was noted for about 21% to 68%, 10% to 45% and 10% to 50% for S1, S2 and S3, respectively. The effectiveness of RC reduced with an increase in gypsum contents with saturation effect since the loss of natural cementation decreased the overall stiffness of the soil. The results further show that by increasing the treatment depth the performance is significantly improved, i.e. more of the stress influence zone is incorporated within the treated layer, thereby improving the distribution of the loads and reducing deformation. The improvement mechanisms are principally attributed to void filling, improved particle interlocking, increased stiffness of soil matrix and the potential self-cementing effect of residual cementitious materials in recycled concrete. In conclusion, recycled concrete is a great and sustainable material to enhance the engineering behavior of gypseous soils. Optimal performance was obtained under dry conditions at 25% RC and a treatment depth of 1.5D while the unfavorable condition was obtained under saturation in highly gypseous soil (S3). These results point out the importance of the gypsum content and the moisture conditions in design and stability of foundations built on gypseous soils.
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