Cementitious Material Fatigue Damage

Bottom-up fatigue damage in cementitiously stabilized materials is driven by the tensile stress at the bottom of the layer. The model for fatigue life is:

where N_ft is the fatigue life, k₁, k₂ and k₃ are model parameters, s_t is the tensile stress in the transverse direction, and MOR is the current modulus of rupture after accounting for curing. Once the fatigue life is determined for each axle load, the fatigue damage is accumulated following Miner’s Law:

where w_ft is the fatigue damage, N_i is the number of passes for the i^th axle load, and N_fti is the crushing life corresponding the i^th axle load. The stiffness is then reduced by the following ratio:

where SR_fatigue is the stiffness ratio due to fatigue damage, m₂ and n₂ are model parameters that depend on the material type, UCS_28,psi is the 28-day UCS in psi, and w_ft is the crushing damage. Damage is updated after every set of loads following the incremental-recursive procedure in CalME.