Determine the dead load:
A 250 mm diameter sewer is placed in a 2.75 m deep rectangular trench that is 0.65 m wide. This trench is backfilled with saturated clay having a unit weight of 20.4-kN/m3. Determine the dead load due to the backfill that the sewer must support. What class of bedding is to be specified if the crushing strength of this pipe is 23.2 kN/m, and the value of safety factor to be used is 1.5?
Here, H = 2.75 m - 0.25 m
= 2.50 m
∴ H/B = 3.85
From Figure 6.16, we read C = 2.65
We have W = 2.65 × 20.4 × (0.65)2 = 22.84 kN/m
Safe Supporting Strength = (Load Factor × Crushing Strength)/Safety Factor
Load factor = 1.48
Therefore, we specify Class C bedding for the given sewer line.