Codes & Safety第 115 / 120 题
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
解析
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.
法律依据: 29 CFR 1926.652(b)免费刷完整 120 道题库 — 无需注册。
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