حسام الدين جابر حسن
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2022-07-07
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Abstract
ABSTRACT
The soil beneath the foundation is subject to moments and vertical forces, resulting in eccentric loading; as a result, the stability of the total foundation is reduced, along with differential settlement, foundation tilting, and heaving of the underlying soil, and in consequences, this may causes to a reduction in soil bearing capacity (BC). The study is conducted to improve the importance of utilizing reinforcement to enhance the BC of clay soil and reduce the impact of eccentricity ratio (e/B). This improvement should lead to a reduction in the use of the common, costly, and time-consuming methods of increasing the footing size or replacing the underneath soil and increasing the use of reinforcing materials, especially the reeds that are available locally in abundance.
This study aims to examine and evaluate the BC of centrically and eccentrically loaded square footing with the soil beneath reinforced. Two materials, the first one synthetic (Biaxial geogrid) and the other natural (reed grid), were used as reinforcement for the clay soil. Reed was selected because of its local availability in southern Iraq, cheap, and suitable mechanical properties. Reed stems are interconnected to form grids of similar dimensions to geogrids. To assess the influence of reinforcement and eccentric load, 43 laboratory model tests are performed. The used eccentricity ratios (e/B) are 0.05, 0.1, 0.16, and 0.25. Also, the aperture size of the reed grids and footing tilt angle were examined.
The results prove that the BC increases when using reinforcement for both materials in the cases of central and eccentric loading. Also, it is concluded that the best reinforcement layout which gives the best BC has been observed at 0.35 for (u/B) and 1.4 for (d/B) in cases of soil reinforced with geogrid and 0.35 for (u/B) and 1.5 for (d/B) in cases of soil reinforced
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with reed. The test findings indicated that the number of reinforcing layers plays an essential role in BC enhancement until a certain value for both geogrid and reed situations, with the optimal values obtained as 4 at 2.27 BCR and 3 at 1.93 BCR for geogrid and reed, respectively. A new equation relating BCR to reinforcing layer number is proposed for both geogrid and reed situations. When the ratio of (e/B) is beyond the footing core boundary, BCR is reduced, and this reduction is greater at 44 % and 32% for the geogrid and reed cases, respectively. In the case of using four reinforcing layers of (e/B) equal to 0.16, the BCR reaches 1.84 and 1.38 for geogrid and reeds, respectively, compared to non-reinforced soil at the same (e/B). Under eccentricity, the tilt angle of footing is linearly increasing with (e/B) in both reinforcement materials, and this increasing rate when (e/B) inside the core boundary is less by 16% than beyond the core boundary for the geogrid case. For the reed case, when (e/B) within the core is less by 28% than at the core, and less by 9% between at the core and outside the core. Previous models that related to the study topic are evaluated with the experimental results of the present study.