Site construction: NASCLA Commercial General Building Practice Questions
Soils and compaction, earthwork quantities with swell and shrinkage, excavation and trenching safety (OSHA Subpart P), grading and drainage, foundations and piles, surveying, site utilities and erosion control.
Often missed
Question 1
At what depth does OSHA generally require a protective system (sloping, shoring or a shield) in an excavation that is not entirely in stable rock?
Correct answer: 5 feet or more
29 CFR 1926.652(a)(1)
Excavations 5 ft deep or more need a protective system unless they are entirely in stable rock. Shallower ones need one too if a competent person sees signs of a possible cave-in.
Question 2
In a trench 4 feet or more deep, what is the maximum lateral travel distance to a stairway, ladder, ramp or other safe means of egress?
Correct answer: 25 feet
29 CFR 1926.651(c)(2)
Trenches 4 ft deep or more need a means of egress located so workers travel no more than 25 ft laterally to reach it.
Question 3
How far back from the edge of an excavation must spoil piles, materials and equipment generally be kept?
Correct answer: At least 2 feet
29 CFR 1926.651(j)(2)
Keeping loads 2 ft back (or using retaining devices) protects workers from material rolling or falling into the excavation.
Question 4
Who inspects excavations and protective systems, and when?
Correct answer: A competent person, daily before work starts, as needed during the shift, and after rainstorms or other hazard-increasing events
29 CFR 1926.651(k)(1)
The competent person checks for cave-in signs, failing protective systems and hazardous atmospheres, and removes workers when a hazard is found.
Question 5
Under OSHA's soil classification, Type A soil has an unconfined compressive strength of at least what?
Correct answer: 1.5 tons per square foot
29 CFR 1926 Subpart P App. A
Type A is cohesive soil of 1.5 tsf or more; Type C is 0.5 tsf or less; Type B falls between. Fissured, vibrated or previously disturbed soil cannot be Type A.
Question 6
Which soil can never be classified as Type A under OSHA, no matter its strength?
Correct answer: Previously disturbed soil
29 CFR 1926 Subpart P App. A
Previously disturbed soil, fissured soil and soil subject to vibration from heavy traffic or pile driving are excluded from Type A.
Question 7
Under OSHA's sloping tables, what is the maximum allowable slope for an excavation less than 20 ft deep in Type C soil?
Correct answer: 1½ horizontal to 1 vertical (34°)
29 CFR 1926 Subpart P App. B
Appendix B allows ¾:1 in Type A, 1:1 in Type B and 1½:1 in Type C for excavations under 20 ft deep.
Question 8
Calculation
A trench is 8 ft deep in Type B soil and is sloped at 1:1 (given) on both sides. If the bottom is 4 ft wide, how wide is the top?
Correct answer: 20 ft
29 CFR 1926 Subpart P App. B
A 1:1 slope sets the wall back 1 ft horizontally for each foot of depth on each side. Counting only one side gives 12 ft.
Worked solution
1
Formula
Horizontal setback per side = depth × 1 = 8 ft
2
Values
Top width = bottom width + 2 × setback = 4 ft + 2 × 8 ft
3
Result
Top width = 20 ft
Question 9
Under Subpart P, a sloping or benching system for an excavation more than 20 feet deep must be designed by whom?
Correct answer: A registered professional engineer
29 CFR 1926 Subpart P App. F
The appendix tables only cover excavations up to 20 ft deep; deeper sloping or benching must be designed by a registered professional engineer.
Question 10
Before opening an excavation, what must the employer do about underground utilities?
Correct answer: Determine the approximate location of all utilities
29 CFR 1926.651(b)(1)
Utility locations must be determined before digging, normally through the one-call (811) system, and exact locations found by safe means as the dig gets close.
Question 11
In excavations deeper than 4 feet where a hazardous atmosphere could reasonably be expected, what must be done before workers enter?
Correct answer: Test the atmosphere
29 CFR 1926.651(g)(1)(i)
Oxygen deficiency (below 19.5 percent) or flammable or toxic gases can build up near landfills, sewers or fuel lines; testing comes before entry.
Question 12
When a trench shield (trench box) is used, how far below the bottom of the shield may earth be excavated?
Correct answer: Up to 2 ft, if the shield is rated for the full depth
29 CFR 1926.652(g)(2)
Digging up to 2 ft under the shield is allowed when the shield is rated for the full depth and no soil is being lost from behind or below it.
Question 13
Under OSHA, what makes an excavation a trench?
Correct answer: Deeper than wide, 15 ft or less wide
29 CFR 1926.650(b)
A trench is a narrow excavation whose depth is greater than its width, with a bottom width of 15 ft or less.
Question 14
Calculation
A basement excavation measures 60 ft by 40 ft by 6 ft deep in bank measure. How many bank cubic yards (BCY) is that?
Correct answer: 533.33 BCY
Estimating math (earthwork)
There are 27 cubic feet in a cubic yard. Dividing by 9 (square feet to square yards) by mistake gives 1,600.
Worked solution
1
Formula
Volume = L × W × D = 60 ft × 40 ft × 6 ft = 14,400 cu ft
2
Values
Cubic yards = cu ft ÷ 27
3
Result
14,400 ÷ 27 = 533.33 BCY
Question 15
Calculation
400 bank cubic yards of clay will be hauled. The clay swells 30% when excavated (given). How many loose cubic yards must the trucks carry?
Correct answer: 520.00 LCY
Estimating math (earthwork)
Excavated soil takes up more room loose than in the bank. Dividing by 1.30 instead of multiplying gives 307.69, which is backward.
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Practice questions are written in our own words and cite code sections by number. Always study from your own copy of the code and the official candidate bulletin.