Codes & SafetyQuestion 115 of 120
A trench 7 ft deep with a 3 ft wide bottom is excavated in Type C soil and will be protected by sloping the walls at 1-1/2 to 1. How wide must the excavation be at the top?
a.13 ft 6 in
b.24 ft
c.17 ft
d.10 ft 6 in
Explanation
Type C soil is sloped 1-1/2 horizontal to 1 vertical, about 34 degrees from horizontal, so each wall lays back 1.5 x 7 = 10.5 ft. Both walls are sloped, giving 3 + 10.5 + 10.5 = 24 ft at the top. The 13 ft 6 in answer adds the layback to only one side, and 10 ft 6 in is the layback of a single wall with the trench bottom left out entirely. Seventeen feet corresponds to a 1 to 1 slope, which is the ratio for Type B soil, not Type C.
Law Reference: 29 CFR 1926.652(b)Practice all 120 questions free — no signup required.
Related questions on this topic
- A site plan shows the invert elevation of a building sewer as 102.50 ft at the upstream end and 101.90 ft at the downstream end, with 48 ft of run between the two points. What is the slope of the sewer in inches per foot?
- A building sewer runs 62 ft from the building drain to the connection at the main and is to be graded at 1/4 in per foot. The invert elevation at the upstream end is 100.00 ft. What is the invert elevation at the downstream end?
- A crew is setting sewer pipe in a trench 5 ft 6 in deep with vertical walls cut in previously disturbed soil. No sloping, shoring or shielding has been installed. What does OSHA require before a worker enters?
- A trench 5 ft deep and 90 ft long is open, with workers spread along its full length installing pipe. What is the minimum number of ladders required and how must they be placed?
- A trench must be excavated 22 ft deep in Type B soil to reach an existing sewer main. Which statement about the protective system and the excavated material is correct?
- Before anyone enters a 12 ft deep sewer manhole classified as a permit-required confined space, the atmosphere is tested and the meter reads 19.2 percent oxygen. What is the correct interpretation, and in what order must the atmosphere be tested?
Last reviewed: · editorial process
PrepPass Editorial Team · Verified against Journeyman Plumber Licensing Exam (UPC/IPC-based) · How we review