Uncompacted bedding for concrete pipes

In the middle third of the base of precast concrete pipes, bedding layers are suggested to be left Uncompacted since it helps to decrease the reaction force at the invert of the pipes and intensifies the effect of shear forces. Furthermore bending moment at pipe invert is increased by compaction of bedding layer. General rule for this region of bedding layer is that it must be firm enough for the pipes to rest on. 

Sides of haunch and bedding directly under the haunch must be compacted since this will decrease the bending moment at the invert that is the critical failure location for pipes. The compacted haunch helps to resist the pipe load and sustain level and alignment.