Repairing earth dam drainage systems

Introduction: when reconstructing or overhauling dams, great attention should be paid to drainage systems as the most critical components of the installations. The article describes the typical malfunctions of earth dam pipe drainages. The research considers geological and hydrogeological features that were not taken into account when developing projects. Materials and methods: control and measuring instrumentation (piezometer network), full-scale experiments on disabling pipe drainage and mathematical modelling were used as the filtration regime research methods. Results: analysis of the hydrogeological features of the base of the right-bank floodplain dam of the Nizhegorodskaya hydroelectric power plant and field filtration observations revealed a strong drainage effect of the base on the filtration flow at several areas of the dam body. At the other areas, a high groundwater level position at the dam downstream and its outlet into the pipe drainage at the downstream were recorded. Substantiated by filtration calculations, the proposed repair of the drainage system consisted in designing open drainage along the dam axis and backfilling the territory at the downstream by 2.0 m that excludes impoundment of the territory without the pipe drainage. Conclusions: the following engineering solutions can be recommended for repairing earth dam drainage systems: construction of backfill drainage trenches in the dam downstream, new pipe drainage at higher elevations or an open drainage channel in solid reinforced concrete arranged along the axis of the dam. The proposed version of the pipe drainage repair provides for constructing an open drainage channel in solid reinforced concrete on a reverse filter with an arrangement of gravel-filled asbestos-cement pipes in the dam slopes and bottom. Such a design solution allows repairing the drainage system without dewatering and, if necessary, completely refusing the existing pipe drainage.