Three-Dimensional Performance of a Deep Excavation in Sand

A 27 m deep excavation in a pyroclastic sand has been constructed in the urban area of Napoli (Italy). The main excavation is supported by T-section reinforced concrete (RC) diaphragm walls. The presence of valuable historical edifices on one side of the excavations suggested the selection of a top-down construction procedure. Maximum settlement recorded at the building façade was about 25 mm [i.e., 0.09% of the free excavation depth (He)]. Full settlement troughs were observed along three different alignments. As a matter of fact none of the monitored alignments could be interpreted exactly as a normal or a parallel settlement trough. A shape function based on the complementary error function was thus proposed to fit the observed settlement data in the plane considering both the distances x and y respectively parallel and normal to the excavation. This approach is actually a combination of existing independent methods.