The open cut section of an excavating intercity railway tunnel in Nanjing crosses the backfill area of a large abandoned mine. Due to the influence of extremely heavy rainfall and excavation unloading of open cut tunnel foundation， many deformation cracks appeared in the intercepting and drainage ditch at the lower part of the steep cliff on the south side of the mine. Therefore， the stability of thebackfill gentle slope is related to the construction and operation safety of the railway under construction. In order to solve this problem， on the basis of geological analysis， the numerical method is used to simulate and analyze the changes of the seepage field， displacement field and the slope stability of the gentle backfill slope under continuous heavy rainfall. The influence of different rainfall types on the stability of the gentle slope is discussed. The results show that under the condition of continuous heavy rainfall， precipitation infiltration makes the sliding force of the gentle slope increase gradually， and forms temporary confined water in the aquitard， which results in seepage force and buoyancy force. Under the combined action of the two forces， the slope stability decreases significantly and the slope instability occurs. Besides， it is found that the early-peak rainfall and uniform rainfall will affect the slope stability in a short time， while the influence of the mid-peak rainfall and late-peak rainfall on the slope stability gradually appears in the later stage. Therefore， it is necessary to reinforce the foundation of the open cut tunnel and take effective measures to intercept and drain water in order to ensure the safety of the intercity railway during the construction and operation periods.
