Abstract: The nonmetal acoustic detector type TH204 is used to test P-wave velocity of expansive soil under the condition of constant amplitude dry-wet circulation. The approach of using P-wave velocity to define damage variable of fatigue damage of expansive soils is proposed, and the law of fatigue damage under dry-wet circulation is explored. Results reveal that 1) with the increase of cycles, the damage variable of expansive soil increase nonlinearly under different control moisture contents, and the growth rate tends to be gentle; 2) the greater the control moisture content, the smaller the damage variable. The greater the cycle amplitude, the greater the cumulative damage variable; 3) the control moisture content plays an important role in the damage variation of the first dry-wet circulation, but from the second to the sixth cycles, the damage value variation shows no regularity with the change of control moisture content. Formula of damage evolution proposed in this research could be used to determine the damage extent of expansive soil.

Key words: road engineering, expansive soil, wave velocity, damage variable, cycle amplitude