What is the relation of the angle of contact between pipe invert and bedding material to the load resisting capacity of pipe?

Minimum crushing strength is a commonly adopted parameter for describing the strength of rigid pipes like concrete pipes. This value is determined in laboratory by subjecting the test concrete pipe to a line load diametrically along the pipe length while the pipe invert is supported on two bearers for stability reason. This test is called three-edge bearing test and the load at failure of pipes is expressed in terms of kN per length of test pipes (called minimum crushing strength).

Bedding factor of a pipe is defined as the failure load for the pipe laid in actual ground with bedding to the failure load under three-edge bearing test. The bedding factor is largely related to the angle of contact between pipe invert and the bedding material. The angle of contact between pipe invert and the bedding material increases with the ratio of bending moment at invert (for the case of three-edge bearing test) to the angle under consideration.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.