Repair and waterproofing of the San Juan reservoir dam, Madrid.

Repair and waterproofing of the San Juan reservoir dam, Madrid.

The reservoir, located in the extreme south-west of the Community of Madrid and south-east of Ávila, was built in 1955 and has a total storage capacity of 138 million cubic metres. It covers an area of 650 hectares, distributed longitudinally along a narrow valley in the vicinity of the San Juan pass.

The San Juan reservoir is used to supply water to the south-western part of the Madrid region, as well as to generate electricity. In addition to these uses, it also has a recreational and sporting function, which has made it a popular place for tourists and hikers.

It is the only reservoir in the Community of Madrid where bathing and motorised water activities are permitted, as well as other water sports such as water skiing and wakesurfing. The reservoir has a total of 14 km of beaches.

It has 2 bodies of dam, the main one following the course of the Alberche river and the lateral one, which is the one that has been the subject of the intervention. Reason for the intervention The dam had cracks with very evident water seepage from the back of the dam where a car park is located. The Confederation had received numerous warnings from individuals alarmed by the water leaks observed in the car park area. Challenges and limitations One of the main limitations of the work was the essential emptying of the affected area of the reservoir in order to be able to carry out the intervention. This meant that the work had to be carried out in cold weather, as the draining had to be done in December or January, when the volume of water is at its lowest. Another major challenge was the size of the body of the dam: with its approximately 5,000 m2 it represented a challenge in the coordination of the execution, and had to be carried out in sections.

Molins Solution

Implementation was planned in two phases:

– In the first phase, joints and spalling were repaired with PROPAM® REPAR 40 class R4 structural repair mortar in accordance with UNE-EN 1504-3 and cracks and singular points were treated with BETOFIBER GLASS fibreglass mesh embedded between two layers of FLEXITEC.

– The second phase consisted of waterproofing the body of the dam by spraying two layers of FLEXITEC two-component cementitious mortar, certified as suitable for contact with drinking water in accordance with RD 140/2003 and classified as C-(PI)-(MC)-(IR) in accordance with the UNE-EN 1504-2 standard.

FLEXITEC waterproof mortar was chosen in order to achieve a high quality waterproof and flexible coating that would allow for the movements in the substrate caused by the thermal cycles and by the emptying and filling cycles of the reservoir.