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Dams age at different rates and in a different way, depending on various parameters. Dams are always at high risk because of internal erosion, ageing, ground movements, failure of material properties used in construction etc. Some dams may remain safe for a thousand years while others may start to crack and leak after less than a decade. Regular operation, maintenance and inspection of dams are necessary to increase the life span of a dam.

ICOLD, the International Commission on Large Dams, has been addressing the use of geomembrane in dams since the end of the 1970ies. Dedicated bulletins have been issued to provide information and guidelines in 1981, 1991 and 2010. The most recent one, Bulletin 135, “Geomembrane Sealing Systems for dams – Design principles and review of experience”, is the world's reference guideline for design, installations and behavior of geomembrane systems. Bulletin 135 also gives guidance to technical contents of contracts, and to the minimum requirements that should be asked for the waterproofing systems and for the bidding contractors.

Geomembrane waterproofing systems are an effective method for seepage control and plays a very important role in the safety of the dam and increasing the life span of the dam. Geomembrane waterproofing systems are an established technique for long-term waterproofing. The technical assets of geomembranes are tabled below:

The design of the geomembrane sealing system must be always made in conjunction with the overall dam design, stability and safety of the dam. The success of Geomembrane system is attributed to the various parameters considered in designing the application in every type of dams.  In simple terms, the fixation on a concrete dam is different from a masonry dam and is different in a earthen dam. The parameters to consider in designing are:

While various possible loads are discussed about, we will discuss in detail on how an effectively designed waterproofing system In Dams continues to function well even after many years with reference cases of Indian projects. This is apart from 160+ dams rehabilitated by Carpi worldwide.

Kadamparai dam in India, owned by Tamil Nadu Electricity Board (TNEB) was constructed in 1983, is a composite structure consisting of a central stone masonry gravity section and two earthen embankment sections. The masonry section is 67 m high and 478 m long, with a central spillway, a scour vent tower and one inspection gallery. Since 1990's, seepage rates gradually began to increase, reaching a maximum of 38,200 l/minute at around 80% of FRL. Repeated local repairs by re-pointing at selective locations, vertical drilling from the crest and grouting at close intervals, and underwater treatment of the leaking areas by chemicals and cement, were carried out from 1990 to 2000 but none could give a permanent solution. 

The owner TANGEDCO after a detailed study of the technology available in the international market finally decided to go in for exposed PVC geocomposite system. The system was approved by leading institutes like IIT Delhi, Anna University. 

The Carpi system installed in 2005 provided for Kadamparai consists of an impermeable PVC geocomposite liner, mechanically fastened to the Dam body, tensioned and drained to provide an effective and long lasting water-poofing liner from crest to heel on the upstream face of the masonry dam. To mitigate the roughness of the masonry, a 2000 g/m2 needle-punched nonwoven anti-puncture geotextile was placed over the facing. 

The waterproofing liner is a prefabricated geo-composite SIBELON CNT3750 made by an impervious geomembrane 2.5mm thick with a backing of an anti-puncture drainage geotextile 500 g/m2. The geocomposite sheets are anchored to the Dam face by vertical anchorage assemblies (patented) bolted into the dam upstream face at regular 5.7 meter intervals. The anchorage system is designed to maintain the liner in a stable position on the upstream face and to tension the liner, avoiding formation of slack areas and folds and to keep the liner independent from the Dam face allowing and facilitating drainage of water between the Dam and the geo-composite by creating an air space between the surface of the structure and the geo-composite liner. 

Drainage System: A double mechanical perimeter seal at bottom, and separate drainage compartments for various areas of the upstream face and for the area between the two bottom seals, provide accurate monitoring of the efficiency of the system 

The whole system installation covering more than 17,000 m2 including the monitoring system has been completed in 3 months, 6 weeks ahead of schedule. Total seepage has been reduced from nearly 35,000 l/m to about 100 l/m. It is more than 15 years

now and still the measured leakage rate stands around 100 l/m against >35,000 l/m before installation of Carpi's PVC Geomembrane System. The recent visit by IIT has concluded on the efficacy of the system when properly designed and installed and the experts opined the system will continue to function for another 2 decades. The success of the project lies in its meticulous planning and designing with inputs provided by the owner and the engineers involved in the project.

“Carpi was awarded India Power Award for the year 2008 for this project in recognition for Excellence in water & Energy Management”.

Servalar Dam is a Stone Masonry Dam constructed in the year 1984. This is one of the two reservoirs that supplies water to the entire district of Tirunelveli in the state of Tamil Nadu. 

The leakage was beyond control on the left flank with the gallery recording 743 Lpm (liters/minute) and a complete wet downstream side (which is unmeasured - Can be approximated as around 6000 Lpm).  Most of the vertical drain shafts were choked. This continued leakage resulted in bulging of the entire dam on the left flank downstream which posed a serious risk to the dam. 

Several repair attempts were undertaken but without much success including Racking/Packing and Pointing with Cement Mortar & Chemical Mortar/Epoxy, grouting and joint chemical treatment.

Carpi was finally selected to install the PVC Geomembrane waterproofing System in the year 2016.  

The waterproofing liner is a flexible synthetic geocomposite, SIBELON® CNT 3750, consisting of a 2.5 mm thick PVC geomembrane plasticised with high molecular weight branched plasticisers, thermally bonded during extrusion to a 500 g/m2polypropylenegeotextile. Each sheet has a length such as to cover the dam section where it is placed. The geocomposite has been installed in exposed position, with the PVC geomembrane in contact with the reservoir's water.

The drainage system is divided into several compartments for ease of monitoring the efficiency of the system even after several decades.  The drain system  is achieved using a band of transmissive geonet materials placed above the primary bottom seal. 

The Face anchorage of the SIBELON® CNT geocomposite to the dam is obtained by the Carpi patented system of stainless-steel tensioning profiles allowing continuous linear fastening and pre-tensioning of the geocomposite. 

The Submerged perimeter seals (at heel and around the inlet gates - Scourvent and Power Vent)  are made with 80 x 8 mm flat stainless-steel profiles tied to the dam with anchor rods. At the crest a seal is  made with 50 x 3 mm flat stainless-steel batten strips tied to the dam with mechanical anchors.

Upper Bhavani dam, a stone masonry dam of 80 m height, located in The Nilgiris District, TamilNadu (India) is the second project for Carpi in the DRIP program (Dam Rehabilitation and Improvement Project). The dam constructed in the year 1965 faced severe leakage in shaft surrounding the spillway inspite of the temporary repair solutions done between 2003 and 2010. The project is being executed in 3 phases out of which 20% of geomembrane installation was completed in first phase and 30% in second phase.  The third phase will commence once the monsoon ends. Despite the challenges of extreme cold weather and location of dam in deep reserved forest and threat of extremists, 50% of work has been planned to be completed in third phase.  The water from the Upper Bhavani Dam acts as the main source for a series of cascaded power houses with a total power generation capacity of 600 MW. Thus saving water is of utmost importance for the client TANGEDCO (Tamil Nadu Generation and Distribution Corporation Ltd)

The performance of the above applications has shown that exposed geomembrane systems, adequately designed and installed, provided a technically effective solution to restore imperviousness in the dam body.

*Target Reference

Besides the technical results, Carpi has acquired the most important achievement by gaining appreciation and confidence of designers and owners of various hydraulic structures worldwide with the installation of geomembrane systems in these 60 years