Abstract: The variation law of meso-structure and average P-wave velocity of expansive soil under the condition of drying-wetting cycles was studied through CT technology and TH204 nonmetallic acoustic test.Through defining CT-damage variable by research methods of damage mechanics,the relationship between the changes of meso-structure and the average P-wave velocity resulted from drying-wetting cycles was established.Results show that the first to the fourth drying-wetting cycles have big influence on the meso-structure of expansive soil,and the development of internal micro-crack was obvious; whereas the seventh and the eighth drying-wetting cycles have little influence on the meso-structure.The average P-wave velocity of expansive soil attenuates non-linearly with the increase of cycle times,and finally tends to be stable.With the increase of drying-wetting cycle times, the damage variable of expansive soil increases gradually,and the evolution of meso-structure damage is a non-linear accumulating process.CT damage variable is in a good exponential attenuation relationship with average P-wave velocity.

Key words: CT technology, expansive soil, drying-wetting cycles, meso-structure, average P-wave velocity