Abstract: To investigate the water seepage characteristics and formation mechanism in an ancient building base (ABB), site investigation, in situ monitoring, laboratory test and numerical methods are employed to study the water field in an ABB. The causes of water seepage, spatial-temporal distribution and migration of water during the rainfall are analyzed in detail. The research results show that the causes of water seepage of the ABB are rainfall infiltration rather than plants irrigation. The rainfall has a greater influence on 2.0 m depth rammed soil underneath the base top than the influence at the other positions, and the water has a tendency to migrate from the base top to base bottom. It is indicated that the impervious layer has been in disrepair for long years and the leakage pathway in the rammed soil has been generated. During 2 hydrological years, 3.0 m depth rammed soil adjacent to the side wall of ABB was saturated and was easily influenced by the rainfall infiltration, which caused bloom of the crystalline materials and occurrence of peeling and water seepage. After 10 hydrological years, the water migrated from the base top to the crown of city-gate, and water seepage and peeling happened. The evolution law and formation mechanism of water seepage hazards are analyzed in details through different approaches, and the results can provide scientific base for seepage prevention and restoration measures of the ABB.

Key words: ancient building base, seepage hazard investigation, water field, rainfall infiltration