Reconstruction and building extensions have become popular trends, even being recognized as one of the most appropriate options for homes, especially in high population density areas or crowded cities. Due to the changes in the size of buildings (by applying additional loads), the existing foundations themselves are incapable of resisting extra stresses. Therefore, it is imperative to increase the bearing capacity as well as the overall stability of existing foundations. The paper aims to present a numerical case study on the use of micropile elements for enhancing the performance of the boundary footing of a renovated building in terms of bearing capacity and stability. Moreover, the effect of cohesionless soil types on the bearing capacity of boundary foundations was presented. Numerically calculated results show that the stability of the boundary footing, presented in terms of the safety factor, was increased as strengthened by micropiles. The bearing capacity ratio (BCR) of the boundary footing was significantly improved when the relative distance (S) between the micropile and the boundary footing decreased, and the length of micropiles (L) increased; however, the BCR rose as the micropile’s angle (() with respect to the vertical increase. In other words, the performance of the foundation underneath the boundary footing was significantly affected by some micropile parameters, including length, inclination, and the distance between the micropile and the boundary footing. These crucial factors must be carefully examined during the design of the micropiles’ configuration for strengthening the boundary footing. Lastly, the load-carrying capacity improvement of the loose sand using micropiles was found to be more significant than that of denser ones.

This paper is aimed to address an actual case study on the use of micropile technology for improving the bearing capacity of an old building. The numerical simulation results show that the load-carrying capacity of square footing utilizing micropiles is notably increased. The improvement of the bearing capacity of the foundations depends on the strengthening methods, such as inclination angle ((), length (L), and distance of micropile from the edge of footings (S). Specifically, with the same length value of pile used, the bearing capacity reaches the largest magnitude at the S/B ratios of (0.5(0.75). The use of inclined piles yields a larger magnitude of bearing capacity than the vertical ones, these obtained results are contributed to the contribution of the “confining effects” of soil mass underneaths the footing as subjected to vertical loads. Additionally, if the soil mass below the footing has a high bearing capacity (firm to stiff clayey soils, medium to dense sandy soils…) , the design value of L/B ratio in the strengthening method should be in range of (2.0÷3.0), chosing beyond that optimal range is uneconomical since the improvement of bearing capacity is insignificant. In other words, the relationship between stress bulb in soil under the footing and the length of micropile should be taken into consideration to achieve a higher economic efficiency of the strengthening method.