Foundation Excavations

There are many different types of excavations performed during the construction of a project. For example, soil may be excavated from the cut or borrow area and then used as fill (see Art. 6.10). Another example is the excavation of a shear key or buttress that will be used to stabilize a slope or landslide. Other examples of excavations are as follows:

1. Footing Excavations.

This type of service involves measuring the dimension of geotechnical elements (such as the depth and width of footings) to make sure that they conform to the requirements of the construction plans. This service is often performed at the same time as the field observation to confirm bearing conditions.

                               FIGURE 6.43 Typical pile configurations

2. Excavation of Piers.

As with the excavation of footings, the geotechnical engineer may be required to confirm embedment depths and bearing conditions for piers. Figure 6.44 presents typical steps in the construction of a drilled pier.

3. Open Excavations.

An open excavation is defined as an excavation that has stable and unsupported side slopes. Table 6.16 presents a discussion of the general factors that control the excavation stability, and Table 6.17 lists factors that control the stability of excavation slopes in some problem soils.

4. Braced Excavations.

A braced excavation is defined as an excavation where the sides are supported by retaining structures. Figure 6.45 shows common types of retaining systems and braced excavations. Table 6.18 lists the design considerations for braced excavations, and Table 6.19 indicates factors that are involved in the choice of a support system for a deep excavation.