To explore the feasibility of weathered shale as expressway subgrade,the study on the mechanism of shale weathering and its filling strength(CBR test)were carried out.The SEM images of shale samples from Zhang Cheng expressway under different immersion time were obtained and the mineral components and micro-structure were observed and analyzed.The chemical and mineral compositions as well as clay mineral of shale samples were also tested by X-ray diffraction method.Time scope for disintegration,weathering mechanism and micro-structure change of shale samples were discussed.Based on these experiments,California bearing ratio(CBR)tests under different compaction degree were carried out under the optimum water content of shale samples within the range of ±0.8%.The test results show that the most disintegration of shale occurred within 12 hours and the complete disintegration was within 24 hours and micro-structure,mineral and chemical compositions changed dramatically; The CBR value of shale sample after disintegration can satisfy the requirements of subgrade filling on expressway construction.