3.3 Prototype of Deep Excavation

In a densely built-up area, there is usually not enough space around the construction site and in soft ground condition, some nearby structures are sensitive to the ground movement caused by excavation. In such cases, rigid retaining structures like contiguous bored pile and diaphragm wall with heavy lateral struts are commonly employed. Figure 2.1 shows a cantilever contiguous bored pile wall supporting an excavation of 7.5 m high at a large construction site. The diameter of bored piles normally ranges from 600 mm to 1000 mm. Figure 2.2 shows a 600 mm thick diaphragm wall supporting a 14.5 m deep excavation. Top-down construction refers to cases where the basement is constructed from the top to the bottom and the diaphragm wall is normally a part of the permanent structure with the slabs and beams working as lateral supports during excavation. A typical process of top-down construction which consists of three stages is as shown in Figure 2.3. The top slab was first cast, excavation was then carried out to a desired depth before the second slab was installed. The subsequent floors were constructed in a similar fashion. Based on these features of retaining structures for deep excavation commonly adopted in practice, the centrifuge model for the present study was designed.