All construction works experience different forms of excavation. The purpose for excavation which always involve removal of soil or earth could be to get to a firm soil for foundation works, drilling operations for water demand, collection of soil samples for laboratory tests, removal of top soil or removal of bad soil. The depth of removal of earth and the pattern of removal distinguishes the different types of excavations. Hence, we have four different types of excavations.
The types of excavations include:
a. Oversite excavation – this involves the removal of top soil (see Figure 1).
b. Reduce level excavation – this is carried out below oversite level to form a level surface on which to build or can consist of both cutting and filling operation as seen in road works. the level to which the ground is reduced is called the formation level (see Figure 2).
c. Trench excavation – this consist of narrow excavations primarily for strip foundations and buried services such as pipelines and cables. This trench (see Figure 3) can be made vertical, slanting or stepped to avoid collapse and with their follow-up advantages and disadvantages. This however depends on the type of soil present and the depth of excavation. Trench excavation can be done manually or mechanically.
d. Pier holes – these are isolated pits (see Figure 4) primarily used for foundation pads for columns and piers or for the construction of soakaways or for collection of soil sample.
Adapted from Building Construction Handbook by Roy Chudley and Roger Greeno
