RusHydro has announced it has successfully completed the stabilization of the Zagorskaya pumped storage plant no. 2, a year after subsidence in the project's powerhouse basement led to its partial flooding.
On 17 September 2013, workers at the project noticed the turbine room began filling with water. All 15 employees working at the site left the facility safely. A subsequent survey of the site indicated that the powerhouse has subsided, with water coming in through deformation joints and intakes of half-finished water pipes. Further exploration, including drilling, identified caverns formed by washout of soil as the immediate cause of the subsidence.
Two inquiry commissions - one formed by Rostekhnadzor (the Federal Service for Ecological, Technological and Nuclear Supervision) and another by RusHydro - have studied the incident and both have reached the same conclusion as to its cause: the washout of soil occurred due to the inefficiency of an anti-filtration system located in the tailrace and beneath the pit of the construction site. This inefficiency is explained by particularities of the system design and insufficient exploration of the soil, said Rushydro.
As part of the stabliization work, an isolating earth-fill dam was erected on tailrace side of the building. By June 2014 the area adjacent to the building was been completely drained. Temporary support was also formed beneath the basement plate in order to prevent further subsiding, achieved by drilling holes and injecting more than 20,000m3 of special fluid.
In parallel, the turbine room was cleared of sand drifts, and an assessment of damage to equipment was carried out.
Successful completion of the work means that RusHydro can now start on the next phase of rehabilitation at the plant. The roadmap for restoration of the facility has been developed by Hydroproject Institute, part of the RusHydro Group, and was appraised and approved by an expert community including Lahmeyer International. The final restoration plan will be chosen by Hydroproject Institute jointly with external experts and will be presented for approval to respective government agencies.