SECTION III. EXCAVATION
EXCAVATION AND SHORING CONSIDERATIONS
5-13. When the building site is cleared, drained, and outlined, cut the land to the proper elevation for placing footings. Use suitable equipment for the initial excavation, but excavate to the final depths by hand. The excavation should extend beyond the exterior wall edges to allow for placing forms and applying waterproofing material. Even if you excavate too much earth, place the concrete to the actual excavation depth. Attempts to refill an excavation to the depth specified are not recommended unless an elephant-foot tamper is used to properly compact the fill, because it is difficult to compact the fill surface properly. Some type of lateral provides support for both safety and economy whenever excavation is at such a depth that the slopes become unstable. Good engineering practice dictates using shoring whenever slope stability is questionable. The type of shoring varies with the depth and size of the excavation, the physical characteristics of the soil, and the fluid pressure under saturated conditions. Sandy soils and wet earth generally require more extensive shoring than firmer soils.
5-14. Machines are a necessity for large projects requiring substantial excavation. The most suitable types of equipment include power shovels, dragline buckets, and a backhoe. When selecting equipment consider:
Due to the many variables, it is not possible to give generalized rates of excavation for various types of equipment. However, Table 5-1 gives some typical rates of excavation for specific conditions that still will vary considerably in practice.
Table 5-1. Machine excavation
5-15. Table 5-2 gives hand excavation rates which vary with soil types and excavation depth. Clear out and shape the last 6 inches of bottom excavation by hand; it is extremely difficult to excavate that closely with a machine.
Table 5-2. Hand excavation
|David L. Heiserman, Editor||
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Revised: June 06, 2015