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Excavator Operator Certification Exam Prep · Question

A trench is being excavated in cohesive soil to a depth of 3.5 metres. The soil analysis indicates a Type C soil according to CSA Z275.5. What is the minimum allowable slope angle for the unshored sides of this trench to ensure worker safety?

According to CSA Z275.5, the maximum allowable slope for Type C soil is 1.5 horizontal to 1 vertical, which translates to an angle of 33.7 degrees relative to t

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Question: A trench is being excavated in cohesive soil to a depth of 3.5 metres. The soil analysis indicates a Type C soil according to CSA Z275.5. What is the minimum allowable slope angle for the unshored sides of this trench to ensure worker safety?

Answer options:

  • 45 degrees
  • 34 degrees
  • 26 degrees 34 minutes ✅ 18 degrees 26 minutes

Correct answer: 18 degrees 26 minutes

Explanation: According to CSA Z275.5, the maximum allowable slope for Type C soil is 1.5 horizontal to 1 vertical, which translates to an angle of 33.7 degrees relative to the horizontal. However, this is for Type B soil. For Type C soil, the maximum allowable slope is 2 horizontal to 1 vertical, which is approximately 26 degrees 34 minutes. Wait. For Type C soil, the maximum allowable slope is 3 horizontal to 1 vertical, which corresponds to an angle of 18.4 degrees or 18 degrees 26 minutes. A 45-degree slope is 1:1, suitable for stable rock, not Type C soil.

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