This paper presents a real case study of a micropiling process that was developed to stop the continuous tilting of a 9-story residential building in Dakahlia, Egypt. Shortly after the construction of the building, the surface raft foundation exhibited severe settlement problems. In order to carry out a geotechnical investigation, boreholes were drilled around the constructed building. It was discovered that in addition to a thick, soft clay layer in the soil profile, there was also a crucial eccentricity between the centroid of the total building loads and the centroid of the raft. The issue needed to be addressed immediately, and a micropiling system was proposed to satisfy the geotechnical and structural conditions associated with the case history. In addition to describing the field measurements, detailed methodology, and micropile installation process, this paper also presents three different design approaches for determining the number and location of the micropiles. Although the underpinning process itself initially induced some settlement, micropiling the raft proved to be an efficient solution to stop the continuous tilting of the building. A micropile load test confirmed the advantageous effect of the grouting technique used for Type B micropiles, where the grout is injected under high pressure.

The micropiled raft offers a foundation system that combines the advantages of the conventional piled raft and the efficient installation of micropiles. In this paper, a comprehensive numerical analysis was conducted on the behavior of micropiled rafts under combined vertical and lateral loading using finite element modeling. A numerical model calibrated against full-scale axial and lateral field tests is used to conduct the analysis. The soil profile was soft clay soil underlain by a layer of dense sand. Numerous cases were analyzed to assess the lateral performance of micropiled rafts while considering several factors that may affect the performance, such as micropiles spacing, raft thickness, the magnitude of vertical loading, micropiles length, and their arrangement. The difference between the lateral performance of a primary micropiled raft and that of an existing raft enhanced by underpinning micropiles was also investigated. The lateral load capacity of the micropiled raft, the bending moment, and the shear force along the micropiles depth were estimated. Moreover, the load-sharing ratio between the micropiles and the raft was assessed. Based on the parametric study results, significant guidelines for choosing suitable micropiled raft configurations for initial design purposes were provided.

This paper used finite element modeling to evaluate the consolidation effect on the performance of existing rafts underpinned with micropiles under combined vertical and lateral loads. For this purpose, a real-life case study was discussed, in which micropile underpinning was used to stop the continuous tilt of a 13-floor residential building supported by a surface raft. It was found that the building tilted towards the northeast direction because of the consolidation of a deep soft clay layer under the northeast building corner. After discussing the as-built micropiling system, a 3D numerical model, developed using the PLAXIS software, was used to conduct the numerical research. The time-dependent behavior of the raft with and without the consideration of micropiles was assessed. Moreover, the variation of load-sharing ratios with time was investigated. The numerical results emphasize that the underpinning process was effective and reduced the final raft rotation and maximum settlement by 79.9% and 73.9%, respectively, compared to the case of the absence of micropiles. The consolidation process under a steady level of vertical loads enhanced the performance of the micropiled and unmicropiled rafts against upcoming lateral loads. The vertical load-sharing ratio increased during a life span of 20 years by 10.4% due to the consolidation process, but the increase was at a decreasing rate. Comparing all the four directions in which the lateral load was applied, the micropiles carried (57.4–76.6%) of the lateral load.

One of the major disadvantages of micropiles is their low lateral stiffness and flexural rigidity due to the small diameter. This limitation can be handled in current practice, by installing the micropile with inclined condition or providing a steel casing. Additional steel casings will increase the lateral load capacity of micropiles but increase the project cost as well. Thus, inclination of micropile which is relatively simple and cheap is recommended. In this paper, a comprehensive numerical analysis is conducted on the behavior of micropiled rafts installed with inclined condition under combined vertical and lateral loading. A FEM calibrated against full-scale axial and lateral field tests is used to conduct the analysis. The soil profile is soft clay soil underlain by a layer of dense sand. The study investigates the impact of several parameters which are as follows: magnitude of vertical loading, reinforcement type, inclination angle of micropiles, and number of inclined micropiles. The study reveals that increasing vertical loads causes continuous decrease in the lateral load capacity of micropiled rafts. When all micropiles installed are inclined, the positively inclined micropiles carry 79–86% of the total lateral load carried by micropiles, whereas the negatively inclined ones carry 14–21%. Inclined micropiles offer greater lateral load sharing ratio (αh) than that of vertical ones, largest at θ = 45°. The effect of micropile reinforcement on improving the lateral performance is low compared to the effect of micropile inclination angle.

A micropile is a small diameter "cast-in-situ" pile which was initially used to repair historic buildings. In this paper, a numerical analysis was conducted on the performance of micropiled rafts under pure lateral loading using the finite element modelling. The FEM was calibrated against full scale lateral and axial field tests. Numerous cases were analyzed to investigate the lateral performance of micropiled raft on soft clay soil underlain by a layer of dense sand. The factors that may affect its performance were considered such as: the micropiles spacing, the undrained shear strength and thickness of upper clayey soil layer. The lateral load response of the micropiled raft was assessed. Moreover, the variation of lateral load capacity of single free head micropile with the clay cohesion was evaluated. Then, the effect of the micropiles spacing on the group efficiency was studied. The group effect was found to be insignificant for spacing to diameter ratio larger than 2.31.