Relation of the angle of contact between pipe invert and bedding material to the load resisting capacity of pipe

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

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