Abstract: Studying the permeability characteristics of acid-contaminated undisturbed loess can provide cost-effective engineering measures for the treatment of contaminated sites. Distilled water was used as the exudate. The permeability variation of the undisturbed loess was studied by using GDS triaxial permeameter under erosion by hydrochloric acid, nitric acid and sulfuric acid. The mechanism analysis was carried out from the change of microstructure of acid-contaminated undisturbed loess. The test results show that under the same consolidation stress conditions, the permeability coefficients of different types of contaminated undisturbed loess decrease with the increase of acid concentration. As the of acid concentration increases, the connection mode of contaminated undisturbed loess skeletons changes from point-to-point contact to point-to-surface contact and surface-to-surface contact. The dissipation of large pores and the increase of small pores decreases the effective seepage pores, and therefore decreases the permeability coefficient of the contaminated undisturbed loess. Under the same experimental conditions, the sequence of the permeability of different types of contaminated undisturbed loess is: sulfuric acid

Key words: undisturbed loess, acid contamination, permeability, electron microscopy