Using the Micropiles Technique as a Settlement Control Tool in the Underpinning of Limited Headroom Cases

The micropiles technique plays an important role in ground improvements. This technique can be used effectively in both new and existing buildings to treat foundation problems. Micropiles are often installed in restricted access and limited headroom situations. Micropiles are used in most soils to transfer the building loads to bearing layers. As a result of progress in drilling equipment it has become possible to design and execute micropiles with load capacities in excess of 300 tons and diameters in excess of 25 cm. This research focuses on the feasibility of using micropiles technique in the underpinning of foundations of existing buildings. A site located in Mansoura, Egypt was selected for this study where micropiles were installed to underpin the foundations of a building consisting of 13 floors. There was a significant bidirectional eccentricity caused a nonuniform stress distribution under the raft foundation. In presence of thick soft clay layers a large amount of differential settlement occurred followed by fast sudden tilting of the building. Micropiles were installed in a specific arrangement to transfer that part of the applied load to the sand layer and to reduce the applied stress on the upper clay layers. As a result the overall bearing capacity of both raft and micropiles was significantly increased to an extent enough to accommodate the applied loads safely. To evaluate the micropiles improvement technique both settlement and tilting results were routinely recorded for ten months after installation. The results showed that the settlement has completely stopped and the building has stabilized.