About Lifelong Learning - Contact Us - DonateFree-Ed.Net Home   Bookmark and Share

 

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.

MACHINE EXCAVATION

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:

  • The total yardage to be move.
  • The working time available.
  • The type of excavation.
  • The nature of the area.

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

Equipment Type of Material Average Output,
in Cubic Yards per
Hour
Power shovel
(1/2 cu yd capacity)
Sandy loam
Common earth
Hard clay
Wet clay
70
60
45
25
Short-boom dragline
(1/2 cu yd capacity)
Sandy loam
Common earth
Hard clay
Wet clay
65
50
40
20
Backhoe
(1/2 cu yd capacity)
Sandy loam
Common earth
Hard clay
Wet clay
55
45
35
25

Hand 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

Types of
Material
Average Output Yards Per Hour
Excavation With Pick and Shovel to Depth Indicated Loosening
Earth-One
Worker
With Pick
Loading in
Trucks or
Wagons-
One Worker
With Shovel,
Loose Soil
0 to 3 ft 0 to 6 ft 0 to 8 ft 0 to 10 ft
Sand 2.0 1.8 1.4 1.3 - 1.8
Silty sand 1.9 1.6 1.3 1.2 6.0 2.4
Loose gravel 1.5 1.3 1.1 1.0 - 1.7
Sandy silt-clay 1.2 1.2 1.0 .9 4.0 2.0
Light clay .9 .7 .6 .7 1.9 1.7
Dry clay .6 .6 .5 .5 1.4 1.7
Wet clay .5 .4 .4 .4 1.2 1.2
Hardpan .4 .4 .4 .3 1.4 1.7

David L. Heiserman, Editor

Copyright   SweetHaven Publishing Services
All Rights Reserved

Revised: June 06, 2015