Earthwork & Excavation

Question 1

What is the earthwork process, and why is excavation necessary? (4)

Answer 1

• virtually every construction site is accompanied by some form of earthwork
• construction may begin with grubbing and clearing
• next, organically rich topsoil may be scraped off the pad site and stored for use later
• excavation is necessary for basements, shallow footings, utilities, and/or to remove unstable or undesirable soil

Question 2

What is the difference between benched excavation and sheeted excavation?

Answer 2

sloped or benched excavation is less expensive than sheeted excavation, but requires a site without nearby property lines, adjacent structures, or other limits on excavation

Question 3

What is the purpose of excavation support?

Answer 3

on constricted sites, the soil surrounding an excavation must be held back by some type of excavation support system

Question 4

What is the angle of repose? (2)

Answer 4

• the steepest angle at which a sloping surface formed of loose material is stable
• depends largely on soil type and characteristics

Question 5

What factors impact the type of excavation support to be used? Provide some examples. (2)

Answer 5

• excavation support can take many forms, depending upon the soil type, depth of excavation, type of construction, proximity of surrounding roads/buildings and presence of groundwater
• examples include tiebacks, crosslot bracing, and rakers

Question 6

What takes on the role of resisting soil pressures once the excavation support is removed?

Answer 6

completed building foundation

Question 7

What is one advantage of the tieback excavation support?

Answer 7

leave the excavation unencumbered

Question 8

What are the three steps of tieback installation?

Answer 8

• drill hole into stable rock or soil
• insert steel prestressing tendons or rod into hole and grout
• after grout has hardened, place steel tendons/rods under tension with hydraulic jack and anchor to waler/steel plate

Question 9

What methods of shoring are used to support the sides of an excavation? (4)

Answer 9

• soldier beams and lagging
• sheet piling
• shotcrete
• shoring can be temporary or left in place

Question 10

What are two methods of ground/earth improvement?

Answer 10

• soil mixing

- rammed aggregate piers

Question 11

What is soil mixing? (2)

Answer 11

• columns of soil strengthened with portland cement and water are created prior to excavation
• always remains in place

Question 12

What are rammed aggregate piers? (4)

Answer 12

• form of “earth improvement”
• constructed solely with crushed rock
• as the rock is compacted in lifts, the surrounding soil is densified
• finished piers may be up to 36 inches in diameter and 30 feet deep

Question 13

What is one great advantage of rammed aggregate piers?

Answer 13

permits shallow footings to be used where deeper types would otherwise be required