Determination method of fatigue strength of cement-stabilized Macadam under three-dimensional stress state using equivalent stress as index

•The strength model under 3D stress state was proposed through conventional tests.•The characterization equation of fatigue characteristics under 3D stress state was established.•The fatigue strength model with equivalent stress as the index was developed. The cement-stabilized macadam (CSM) material is in a three-dimensional (3D) complex stress state in the pavement structure. It is difficult for the conventional test method to characterize the 3D fatigue strength characteristics of the CSM. In order to establish a 3D fatigue strength design criterion through simple strength methods, this work conducted the conventional unconfined compressive (UC), direct tensile (DT), and indirect tensile (IT) tests. The corresponding 3D strength model, including three parameters, was determined based on three strength testing methods. In addition, a normalized fatigue model including one parameter was obtained by three fatigue tests. Finally, the fatigue strength model under a 3D stress state was established by combining fatigue and the 3D strength model. The results indicate that the 3D strength model effectively characterized the CSM strength under any stress state, and the difference between the IT strengths predicted by the 3D strength model and obtained by the test is 18.43%. Moreover, the fatigue normalization model reflected the 3D fatigue failure of CSM in a complex stress state. The proposed fatigue strength of CSM based on the equivalent stress has clear physical meaning. This work provided a practical technology to obtain 3D fatigue strength resistance of CSM, which solved the technical problem of inaccurate measurement of pavement structure resistance.