Geomembrane sealing systems for dams: ICOLD Bulletin 135

Transcription

1 Innov. Infrastruct. Solut. (2017) 2:29 DOI /s TECHNICAL PAPER Geomembrane sealing systems for dams: ICOLD Bulletin 135 Alberto Scuero 1 Gabriella Vaschetti 1 Received: 3 May 2017 / Accepted: 2 June 2017 / Published online: 20 June 2017 Ó Springer International Publishing AG 2017 Abstract The paper presents the contents of the latest bulletin published by the International Commission on Large Dams (ICOLD) on the subject of geomembranes as sealing systems for dams. Bulletin 135, published in 2010, is an updating and expansion of ICOLD Bulletins 38, published in 1981, and 78, published in Bulletin 135 has been prepared, under the aegis of the ICOLD Committee on Materials for Fill Dams, by the ad-hoc European Working Group for geomembranes and geosynthetics as facing materials, composed by experts from nine European countries, with external contribution from USA. Different competences were covered by the group, which included geomembrane scientists, dam designers, geomembrane systems designers, dam owners, and geomembrane specialist contractors. The bulletin is composed of 9 chapters, in total 464 pages for the English and the French versions. The paper outlines the history of the constitution of the working group, the preparation of the database on geomembrane systems in dams all over the world, discusses the topics covered by each chapter, and gives some statistics based on the database. Some case histories mentioned in the Bulletin, and recent developments, are also presented. This paper was selected from GeoMEast 2017 Sustainable Civil Infrastructures: Innovative Infrastructure Geotechnology. & Gabriella Vaschetti gabriella.vaschetti@carpitech.com Alberto Scuero alberto.scuero@carpitech.com 1 Carpi Tech, Balerna, Switzerland Keywords Geomembrane Waterproofing Dams PVC ICOLD Introduction and background The use of geomembranes in hydraulic structures has more than half-century history: geomembranes were first used in canals immediately after the Second World War, in the research and field experimentation carried out by the US Bureau of Reclamation on various types of canal linings since In dams the use of geomembranes started in 1959 at Contrada Sabetta fill dam in Italy. The first applications were made in construction of new fill dams, which being intrinsically pervious need a separate component to provide imperviousness. The concept of using synthetic impervious geomembranes instead than conventional impervious materials such as clay, concrete or asphalt concrete, certainly derived, among other considerations, from the good performance of embedded polyvinyl chloride (PVC) waterstops in the huge number of concrete dams worldwide that rely on their use to stop water infiltration at joints. A geomembrane system on the upstream face of a dam can be considered, from a conceptual point of view, as one wide waterstop sealed at the abutments and bottom. In the early 1970s, the use of geomembranes was extended to the rehabilitation of old concrete dams, and in the early 1980s to the waterproofing of new Roller Compacted Concrete (RCC) dams. At present geomembranes are adopted all over the world to waterproof all types of old and new dams (concrete gravity dams, buttress dams, arch dams, multiple arch dams, rockfill dams with concrete facing, rockfill dams with asphalt facing, earthfill dams, tailings dams, RCC dams), and practically all types of

2 29 Page 2 of 17 Innov. Infrastruct. Solut. (2017) 2:29 hydraulic structures (canals, hydraulic tunnels, surge shafts, pumped storage reservoirs, forebay reservoirs, underground tanks, etc.). The issue of the use of geomembranes on dams, which are among the most demanding and critical hydraulic structures, has been addressed by ICOLD, the International Commission on Large Dams, in two theme bulletins. Bulletin 38 (1981) Bulletin 38, Use of thin membranes in fill dams [1], was published in Bulletin 38 defined geomembranes as a thin product with a thickness from one to a few millimetres, constituted of a flexible watertight material [that] may be prefabricated at works and then transported to the site, or prepared and positioned directly on the site (in situ) ; it considered a cover layer mandatory for a geomembrane system; and recommended a height of 30 m, and a surface of modest dimensions. Increasing the limit height to 40 m was deemed to be based on foreseen future improvements in technique and materials. Bulletin 78 (1991) As the use of geomembranes increased and gradually extended to the rehabilitation of all types of existing dams, and to waterproofing of the new Roller Compacted Concrete dams which began being built in the early 1980s, the need for an updating of the bulletin was felt. In 1991 ICOLD published a new theme bulletin, Bulletin 78, Watertight geomembranes for dams State of the art [2]. Bulletin 78 considers geomembranes an established technique for new construction and rehabilitation of fill dams, as an emerging application for rehabilitation of concrete and masonry dams, and as Future prospects in application to new RCC dams; the cover layer is no more considered necessary; and concerning the limit height There is no reason to recommend a specific height limitation on the use of geomembranes in embankment dams. After 1991, the use of geomembranes to waterproof new dams and to restore imperviousness in old dams further increased. Europe, where the majority of dams are old, was one of the main users and developers of geomembrane systems. In European countries the need for increased information on current practice and trends was more deeply felt. In 1993, during a symposium on dam rehabilitation organised by the ICOLD French National Committee in Chambery, a European Working Group for geomembranes and geosynthetics as facing materials was established, with the mission of investigating the behaviour of geomembrane systems installed in previous times, and of ascertaining and assessing the most recent developments in new projects. The Group was formed by members of the ICOLD National Committees of Austria, France, Germany, Italy, Portugal, Switzerland, and the United Kingdom, and by experts from the Czech Republic, France, Italy, and Spain. All competences were covered: the group included geomembrane scientists, dam designers, geomembrane systems designers, dam owners, and geomembrane specialist contractors. The decision was taken to create a database collecting the most relevant information on geomembrane systems already in service on dams. The next chapter details how the database was compiled. In the years that followed, the database included [80 European dams, and then it was gradually extended to include case histories also from countries outside Europe. The start and completion process of Bulletin 135 At the ICOLD Executive Meeting in Antalya in 1999, the ICOLD Committee on Materials for Fill Dams, under whose aegis Bulletins 38 and 78 had been published, discussed the data collected by the working group and decided to amplify the information and make it available to the international dam community. The Committee extended the working group to include worldwide leading experts in the field of geomembranes, and gave it an official mandate to prepare a new bulletin on geomembranes, addressing design, manufacturing, installation, quality control and contractual aspects, and to extend the database to the whole world. Database The database was implemented starting from some data already included in Bulletins 38 and 78, and from the initial database created by circulating through the members of the working group among owners of dams the technical form elaborated for this purpose. The technical form is a 6-pages document consisting of: Section A: Main information, containing data on the dam (characteristics and service conditions), type of geomembrane and characteristics of the geomembrane system, and the owner s comments on efficiency, durability, technical and economical effectiveness of the system Section B: Additional information, mainly adding data on features of geomembrane system, and on geomembrane installation, quality control and costs. To implement incomplete forms, or to collect data of dams for which forms were not available from the owner or its consultants, data from international literature (Proceedings of ICOLD Congresses, Executive Meetings, Conferences of National Committees, Conferences of ASDSO, the US American Society of Dam Safety Officials, articles in specialised publications such as Reservoirs

3 Innov. Infrastruct. Solut. (2017) 2:29 Page 3 of and Dam of the UK National Committee, Bulletin of the Australian National Committee), and personal communications by designers and University professors, were used. Work method After the contents of the bulletin had been discussed and agreed by all members in the first plenary meetings, smaller groups were created to prepare the various chapters in function of their competence. Periodical meetings were used so that all or most of the members of the group could peruse, make comments and refine the parts prepared by the smaller groups. The findings of the database served as permanent comparison and also to evaluate evolutions of the geomembrane sealing systems if any. Drafts of completed chapters were circulated internally to gather comments from all members. When the first complete draft in English was ready, it was submitted to the Committee on Materials for Fill Dams, during the Executive Meeting of The final version in English was approved by the Committee in The French National Committee requested that the 209 pages of the approved final English version be translated in French and the bulletin published in both languages. The final French version was completed in More than 1 year was required for final revision and approval. Bulletin 135 was published in 2010, with the title Geomembrane Sealing Systems for Dams Design principles and review of experience. In total 464 pages, inclusive of 17 pages of terminology and 14 pages of bibliography and most common standards. Bulletin 135 The foreword of the bulletin [3], written by Mr. Marulanda, Chairman of the Committee on Materials for Fill Dams, is well in the context of the history of geomembranes sealing systems in dams. Foreword of the bulletin The first edition of this Bulletin was issued in 1981 as Bull. 38 (*). It was a precise, detailed technical guide with comprehensive references: types of membranes along with their features were reviewed as well as theoretical and actual strains involved; procedures to be developed were detailed with examples. In 1991, the new Bulletin 78, Watertight Geomembranes for Dams. State of The Art (**) cited 70 dams incorporating geomembranes and it focused on new and improved materials which in the meanwhile became available and on the experience gained which has resulted in a better understanding of their use and in advanced engineering skills in this field so that they have been used in higher dams than before. The Bulletin 78 dealt with new areas such as enhancing the water retaining performance of other facings, repairing old gravity dams and the deteriorated upstream concrete facings of fill dams. Finally, Bulletin 78 reported new ideas regarding drainage, supporting layer and protective covering and geomembranes which were at that time (1990) under consideration for the upstream facings to roller compacted concrete dams. This new edition in 2010 cites 280 dams and updates the data and recommendations of the first two 38 and 78 Bulletins. It reviews the new information and practices that have appeared in the meantime, which include application of geomembrane as the only watertight element in fill dams (Bovilla, Albania, 91 m, 1996), in RCC dams (Miel 1, Colombia, 188 m, 2002), as external joints on RCC dams (Porce II, Colombia, 118 m, 2000), as underwater repair of dams on gravity dams (Lost Creek, USA, 36 m,1997) and on RCC dams (Platanovryssi, Greece, 95 m, 2002). This new Bulletin also deals with application of geomembranes for dams affected by AAR (Pracana, Portugal, 65 m, 1992). The Bulletin reports about sealing of defective joints and cracks in the upstream face of CFRDs by strips of geomembranes mechanically fastened (Strawberry, USA, 101 m, 2002). The 280 dams incorporating geomembranes cited in this new Bulletin are 188 fill and 91 concrete? RCC (?1 of unknown type). Out of the 280 dams 48 are in USA, 47 in China, 42 in France, 35 in Italy, 10 in Spain and in Germany, 9 in Austria, 6 in the Czech Republic, 5 in Portugal, 4 in Bulgaria and in UK, 2 in Belgium, Cyprus, Romania, Slovakia and Switzerland, 5 scattered in other European countries. Europe and USA account for[67% of the total (188 dams). Because of the large experience gained in Europe, this revision was prepared by the European Working Group on Geomembranes as Facing Materials for dams, appointed by the International Commission on Large Dams, with the assistance of some experts from USA. This bulletin conveys to the reader a real worldwide experience on use of geomembranes, with the oldest now dating more than 45 years and still in service. The authors deserve our warmest appreciation, and in particular Alberto Scuero, co-ordinator of the Group, Gabriella Vaschetti, Secretary, and some members of the Group, in alphabetical order, Blanco, Cazzuffi, Girard, Koerner, Lefranc, Millmore, Schewe, Sembenelli, Vale. A.M. MARULANDA Chairman, Committee on Materials for Fill Dams (*) Report prepared by R. Corda and H. Grassinger, members of the Committee on Materials for Fill Dams, with the assistance of K. Rienössl (Austrian National Committee) and J. Combelles, J. Couprie, P. Huot, V. Lelu, D. Loudière and P. Paccard (French National Committee).

4 29 Page 4 of 17 Innov. Infrastruct. Solut. (2017) 2:29 (**) Report prepared by R. Corda, member of the Committee on Materials for Fill Dams, with the assistance of G. Degoutte and C. Bernhard (CEMAGREF, France), L. O. Timblin and W. R. Morrisson (USCOLD) and D. Cazzuffi (ENEL, Italy). Contents of the bulletin The bulletin has been structured in 9 chapters and 3 appendixes: Chapter 1: is an introduction to geosynthetics, to their classification in several families according to their function, and in general to their field of application Chapter 2: describes classification and characteristics of the various types of geomembranes, and discusses materials specifications and testing Chapter 3: discusses the loads and stresses to which geomembranes are exposed, criteria and recommendations for design, construction and operation. The loads and stresses relevant to a particular type of dam are addressed in the relevant dedicated chapters. Chapter 4: discusses application of geomembranes in construction of new fill dams, application of geomembranes to repair of asphalt-concrete sealing facings, bituminous geomembrane facings, and concrete facings in CFRD Chapter 5: discusses application of geomembranes to repair of concrete, shotcrete and masonry facings of gravity dams and arch dams. The chapter addresses repair in the dry and underwater Chapter 6: discusses application of geomembranes to RCC dams as watertight upstream facing in new construction, and as repair of existing RCC dams Chapter 7: discusses special applications as watertight element at joints and cracks, and as an underwater repair measure Chapter 8: dedicated to quality control Chapter 9: gives recommendations for specification for design, supply and construction, including guidance to technical contents of contracts Appendix 1: the database, related to the ICOLD definition of large dam. Appendix 2: a list of geomembrane technology terms and definitions (according to IGS International Geosynthetics Society) Appendix 3: bibliographic references and references on testing standards. The following paragraphs state, more formally, the contents of the nine chapters and of the three Appendixes, explaining the main issues for of each chapter. Chapters 1 and 2: introduction and materials The chapters address all geomembranes, i.e. materials prefabricated in a factory, either in relatively thin continuous polymeric sheets (polymeric geomembranes, with a large predominance of PVC geomembranes), or by impregnation of geotextiles with bituminous materials (bituminous geomembranes). The geomembranes considered are factory-made polymeric and bituminous geomembranes. In situ impregnated geotextiles and sprayed liners based on polyurethane and polypropylene resins, which are closer to the family of the resins and less and less frequently used, are not subject of the bulletin. The few existing examples have notwithstanding been included in the database. The chapters discuss materials composition, configuration, supply, seaming, testing, durability and ageing, with some statistics for each type of geomembrane (Table 1). Overall, polymeric geomembranes account for[91% of the total, out of which about 60% are PVC. Bituminous geomembranes have been used only on 20 dams, of which 17 in covered position. Chapter 3: loads acting on the GSS This chapter describes the stresses and constraints to which geomembranes are exposed when used as sealing element in dams: mechanical, physical, chemical, biological and other types of attacks. It offers criteria and recommendations to consider in the design, construction and operation of dams with having a geomembrane as water barrier. Identification and relevant and comprehensive characterization of all the stresses to which the geomembrane sealing system will be submitted is essential to ensure the success of the project. Chapter 4: fill dams This chapter deals with applications of geomembranes in fill dams, where geomembranes have been used in 60% of cases in new construction, in 40% as rehabilitation measure of asphalt concrete facings and of concrete facings (CFRDs). Approximately in 90% of dams, the geomembrane was installed in upstream position, to minimise uplifts and uncontrolled water presence in the dam body, improving stability and safety. Generally speaking, the application of a PVC geomembrane system in new fill dams has the significant advantage that, being the geomembrane very deformable (typically [230%), it can accommodate without breaking

5 Innov. Infrastruct. Solut. (2017) 2:29 Page 5 of Table 1 (Table 3 in Bulletin 135)-Synthetic materials more frequently employed as geomembranes Type Basic material Abbreviation Thermoplastic Chlorinated polyethylene Ethylene vinyl acetate copolymer Polyethylene Polypropylene Polyvinyl chloride CPE EVA/C PE a PP PVC Thermoplastic rubbers Chlorosulfonated polyethylene Ethylene propylene copolymer CSPE E/P Thermo-set Polyisobutylene Chloroprene rubber Ethylene-propylene diene monomer Butyl rubber Nytrile rubber PIB CR EPDM IIR NBR a Within the group shown, polyethylene and polypropylene are collectively called polyolefins the not negligible movements that are typical of this type of dam, especially at the junctions between the deformable dam body and the rigid concrete structures (e.g. spillways, intakes, plinth), and the settlements that may still occur after impoundment. New fill dams with geomembrane systems are behaving quite well. In new construction, the chapter discusses the various configurations: upstream exposed, upstream partially or totally covered, and internal position, including the cases of heightening of existing dams, and giving examples for each configuration. At publication of Bulletin 135, the most recent face anchorage technique for upstream exposed geomembranes was by seaming the PVC composite geomembrane liner to PVC anchor strips embedded in porous concrete curbs against which the fill was placed. Sar Cheshmeh tailings dam raising was the first embankment dam adopting this type of face anchorage system. Sar Cheshmeh existing tailings storage in Iran, owned by National Copper Industries Co., included a 75 m high main embankment consisting of an inclined clay core as impervious element, and of outer colluvial gravel shells. The production escalation required a set up comprising a 39.5 m high and 1000 m long downstream raise to the main embankment, in four separate stages, of which IIB and IIC have been completed so far. Stability analysis showed that the seismic stability of a raised clay core was not sufficient, due to the geometry of the raising. Furthermore, no suitable clay based materials were available at site. ATC Williams, designers of the dam raising, considered as alternative solutions an asphaltic core, an upstream bituminous membrane, and polymeric geomembranes. An upstream exposed PVC Geomembrane Facing Rockfill Dam (GFRD) was selected because of superior safety in respect to earthquakes. ATC Williams deemed the GFRD system would be the most stable, efficient and buildable arrangement. The finishing layer of the dam is made with extruded porous concrete curbs illustrated in the schemes of Fig. 1. The face anchorage for the waterproofing liner is the patented method with PVC anchor strips discussed above. As the embankment and curbs were being raised, the PVC strips were nailed to the curbs and then permanently anchored by the fill compacted against the curbs. Overlapping PCV strips were joined by heat-seaming. The procedure is shown in Fig. 3. The PVC geocomposite used for the anchor strips and for the liner is SIBELON Ò CNT 4400, consisting of a 3 mm thick PVC geomembrane, heatbonded during manufacturing to a 500 g/m 2 non-woven polypropylene geotextile (Fig. 2). The PVC strips heat-welded at the overlap, form continuous anchor lines. The SIBELON Ò geocomposite liner sheets were then deployed from the crest, after having been secured at top by a stainless steel batten strip on a conventional concrete curb. After cleaning the PVC anchor lines, the PVC geocomposite sheets were temporarily anchored at the crest of the first stage, stage IIB, and then unrolled down the slope (Fig. 4 on left). The PVC geocomposite sheets were heat-welded to the PVC anchor strips (Fig. 4 on right). Adjoining PVC geocomposite sheets were watertight heat-welded at overlapping, as shown in Fig. 4 at bottom. The bottom seal of stage IIB was made by embedding the PVC geocomposite in a trench excavated in the clay core of the existing dam, and then backfilled with clay (Fig. 5 on left). The bottom perimeter seal at the concrete plinth of the abutments is mechanical, referred to as the tiedown type. In tie-down seals, watertightness against water in pressure is attained by compressing the PVC geocomposite unto the concrete with flat stainless steel batten strips secured by stainless steel anchor rods embedded using chemical glass anchoring capsules at regular spacing. Smoothing epoxy resin, rubber gaskets, stainless steel bat

6 29 Page 6 of 17 Innov. Infrastruct. Solut. (2017) 2:29 Fig. 1 Upstream exposed geomembrane with PVC anchor strips (Carpi patent) Fig. 2 Deployment of waterproofing geocomposite sheets on the PVC anchor strips Fig. 3 PVC anchor strips embedded in curbs ten strips and splice plates achieve even adequate compression necessary for watertightness, as extensively described in international literature (Fig. 5 on right). The intermediate seal between stage IIB and stage IIC is made by watertight welding the geocomposite of the upper stage on the geocomposite lower stage, and covering the

7 Innov. Infrastruct. Solut. (2017) 2:29 Page 7 of Fig. 4 Deployment and heat-welding of geocomposite sheets on PVC anchor lines, and heat-welding of adjacent sheets Fig. 5 Bottom perimeter seal-embedded type (left) and the tie-down type (right) Fig. 6 Intermediate seal between stage IIB and stage IIC (left) and top perimeter seal at stage IIC (right) weld with a PVC geomembrane strip. The seal top of stage IIC is made by embedding the geocomposite in a trench then ballasted with conventional concrete as shown in Fig. 6. Stage IIB and staged IIC raisings reached 20 m of height. Total surface was 38,500 m 2. Installation of the waterproofing system took 14 weeks in total (Fig. 7).

8 29 Page 8 of 17 Innov. Infrastruct. Solut. (2017) 2:29 Fig. 7 Upstream exposed geomembrane at Sar Cheshmeh tailings dam in Iran Fig. 8 Stage 1: stage 1? stage 2 waterproofing system completed in 52 days More dams have now been constructed with the same system. A recent (2015/2016) example is Nam Ou VI 88 m high rockfill dam, which is part of the Nam Ou VI Hydropower Project in Lao PDR, and the highest GFRD in Laos. The PVC geocomposite selected to ensure long-term watertightness in exposed position is SIBELON Ò CNT 5250, consisting of a 3.5 mm thick PVC geomembrane, heat-bonded during manufacturing to a 700 g/m 2 non-woven polypropylene geotextile. The system was the same of Sar Cheshmeh. The dam body and its waterproofing system were constructed in three separate stages: stage 1 from the bottom of the excavation at El. 427 m to El m, stage 2 to from El m to El m, and stage 3, comprising a 3 m high parapet wall, to reach El m. Installation of the geomembrane system of stage 1 was completed in 24 days for 13,700 m 2 of upstream water barrier; installation of the geomembrane system of stage 2 was completed in 28 days, for about 23,000 m 2 of upstream water barrier. In total, 52 days to construct a watertight upstream facing of almost 37,000 m 2, a fraction of what a concrete facing would have required (Fig. 8). An outstanding application of the same technology is ongoing at Las Bambas copper mine currently developed in Peru. Tailings from the mine processing plant are pumped to a Tailings Storage Dam (TD) located within a broad valley and formed by a large Tailings Retaining Embankment on the southern and eastern sides. The TD will contain all tailings generated from processing operations, all bleed water released from the deposited tailings, and all water runoff from the TD catchment. For mine start-up purposes, the TD will be the primary water storage for the commissioning of the concentrator plant. The TD will continue to be utilized as water storage throughout the operating life of the mine. The Tailings Retaining Embankment, therefore, needs to be a water retaining embankment, and is being built from rockfill and waterproofed with an exposed PVC geocomposite, to construct a GFRD. The Tailings Retaining Embankment is being raised in stages, and when completed will be 230 m high. Stage 1A has an approximate height of 58 m, and total surface lined is 39,767 m 2 ; stage 1B has raised the embankment to a maximum height of 88 m, and total surface lined is 138,129 m 2. After completion of stage 1B the Carpi crews were placed in standby until construction of the embankment embedding the anchor strips in the curbs from

9 Innov. Infrastruct. Solut. (2017) 2:29 Page 9 of Fig. 9 Stage 1: Las Bambas tailings dam at stage 1, and the dam pictured in November 2016 Fig. 10 Upstream exposed geomembrane anchored by deep grouted anchors (Filiatrinos hardfill dam, Greece 2015, left) and by trenches (Bulga earth dam, Australia 2016, right, Panama Canal Expansion Water Saving Basins, bottom) elevation 4020 m to elevation 4050 m was completed, around middle of November. Carpi started to install the geocomposite system of this stage on 19 November Installation is at present ongoing. Total surface to be lined in this stage is 172,512 m 2. The installation of the geomembrane has already reached a height of 118 m from the foundation (Fig. 9). New patented technologies are recently being used for upstream geomembrane systems in new fill dams, which were not available at the time of publication of the bulletin. Such technologies include face anchorage of the geocomposite by deep grouted anchors, such as adopted at Filiatrinos hardfill dam, and face anchorage by PVC anchor strips embedded in trenches, such as adopted at Bulga earthfill dam. The same systems were adopted at some of the 18 Waters Saving Basins of the Panama Canal Expansion. See Fig. 10. Design aspects such as the characteristics and stability of the various layers, the anchorage at boundaries, the anchorage over the dam face, and installation techniques, are analysed. Specific aspects for rehabilitation are the anchorage systems, designed depending on the type and strength of

10 29 Page 10 of 17 Innov. Infrastruct. Solut. (2017) 2:29 Fig. 11 Upstream covered geomembrane (Bovilla gravel dam, Albania 1996, left) and central zigzag geomembrane (Gibe III cofferdam, Ethiopia 2009, right) the existing facing (asphalt concrete or concrete). The various aspects to consider when deciding if to place a cover layer on the geomembrane in a new fill dam are discussed, as the possibility of damaging the geomembrane when placing the cover was well known. The chapter discusses also available alternatives for geomembranes in central position, of which no photos were available at that time. See Fig. 11. The rehabilitation of fill dams with concrete facing (CFRD) and with asphalt concrete facing (ACFRD) is also addressed. The exposed system (conceptually the same described in Chapter 5: concrete and masonry dams ), and the covered system are described. Chapter 5: concrete and masonry dams In concrete and masonry dams, geomembranes have been used for rehabilitation. Only in one case of partial application at heel, the geomembrane was used since new construction. Almost all concrete and masonry dams that have used geomembranes for rehabilitation have been waterproofed with the systems patented by Carpi. Performance history of this system is at present approaching 40 years, and field results have proven its capability of extracting and discharging water already permeating the concrete, for example at Pracana dam, where the exposed PVC geomembrane has helped slowing the alkali-aggregate reaction. Both the cases that follow are reported in Bulletin 135. Pracana is a 65 m high buttress dam in a seismic and hot region of Portugal, built between 1948 and Anomalies in the behaviour of the dam were evident since first impoundment: cracks appeared at the upstream and downstream faces, significant seepage and carbonation at the downstream face were observed. Unsatisfactory performance of local repairs required lowering the reservoir level. In 1997 EDP, Electricidade de Portugal, became the owner of the dam, and put the dam out of operation to thoroughly investigate its behaviour, its conditions, the causes of deterioration, and to develop a rehabilitation plan. Investigations ascertained that among concurrent causes of cracking (deficiency in construction techniques, thermal variations of concrete during construction, differential settlements of not-consolidated foundations) were also expansive phenomena of concrete. A major concern was related to the critical scenario relevant to sliding conditions along horizontal cracks, especially considering the uplifts. Expansion of concrete was further investigated and ascertained the presence of alkali-aggregate reactions, which further activated by infiltration of water from the reservoir. Restoring and granting long-term imperviousness to the upstream face, and reducing the uplifts, were mandatory. The large rehabilitation and refurbishment works at the dam included an upstream drained waterproofing geomembrane, to stop water infiltration, to avoid that water in pressure could act on the horizontal cracks, and to deprive the dam of its water content; construction of a new grouting plinth and of two sets of struts between buttresses at the downstream face, to improve stability; treatment of foundations, including execution of a new grout curtain; construction of a new auxiliary spillway, to improve behaviour and safety in respect to extreme floods, and of a new water intake, and concrete treatment, consisting of individual cement grouting for larger cracks and mass grouting with epoxy resin for smaller cracks. The exposed drained PVC geomembrane system was installed in the dry season of 1992, concurrent with the huge civil works. To enhance drainage capability a drainage geonet was placed on the entire surface then covered by the waterproofing geocomposite (Fig. 12 on left). The drainage system was divided in 10 separate compartments

11 Innov. Infrastruct. Solut. (2017) 2:29 Page 11 of Fig. 12 Pracana buttress dam, Portugal The upstream face during rehabilitation and refurbishment works: from left to right, the new intake, the black geonet covering the face, and the PVC geocomposite installed over the geonet. At right, the tensioning profiles for the water drained from the upstream face of the dam, and a separate compartment for the water coming from foundations. At bottom, the perimeter seal was installed on the new foundation plinth, achieving connection of the liner with the new grout curtain, so that the water barrier is continuous from crest down to deep impermeable foundations. Watertight perimeter seals were placed also around intake and outlets, and at the rails for operation of the gates. The PVC geocomposite SIBELON Ò CNT 3750, consisting of a 2.5 mm thick PVC geomembrane, heat-bonded during manufacturing to a 500 g/m 2 non-woven geotextile, is anchored by Carpi patented tensioning profiles (Fig. 12 on right, an excerpt of ICOLD Bulletin 135), placed at 1.8 m spacing, and by a watertight perimeter seal of the tiedown type already discussed. The regularising resin, rubber gaskets and stainless steel splice plates allow achieving the even compression that grants the watertightness. The tensioning system is designed to maintain the liner in a stable position, to tension it, avoiding formation of slack areas and folds, and to keep it independent from the dam face, allowing and facilitating drainage of water between the dam and the geocomposite by creating an air space between the upstream face of the dam and the geocomposite. The waterproofing system was installed in 5 months, for a total of 7900 m 2. Reported total leaks, from upstream face and from foundations, are less than 0.34 l/s. Since 1992, in addition to monitoring the performance of the geocomposite system and its effectiveness in respect to leakage control, EDP has been monitoring the behaviour of the dam, to ascertain the capability of the system to dehydrate the dam body, reducing the water content feeding the AAR. LNEC, the National Laboratory for Civil Engineering, is in charge of studying the swelling reactions through various measuring systems. The details of the monitoring systems and of the findings of the study can be found in the exhaustive paper presented by EDP at the 21st Congress of ICOLD in Montréal (Liberal et al. [5]. In the final conclusions of the paper, EDP reports that A significant gradual reduction of the swelling rate was observed [omissis] and the concrete dam waterproofing may be assumed to contribute for the reduction of the swelling process (Fig. 13). In 2017, during the oral presentation made by EDP (S. Domingo Matos) at CFBR (French Committee for Dams and Reservoirs) it was announced that the installation of the geomembrane has definitely almost stopped the reaction. In masonry dams, the waterproofing system is similar to the one adopted on concrete dams; the roughness of the masonry generally requires installing a thick anti-puncture geotextile under the geocomposite, and regularising with mortar the surface where the perimeter seals are placed. Kadamparai dam, owned by the Tamil Nadu Electricity Board (TNEB), is an example. The dam is 67 m high and 478 m long, was completed in 1983, and is used as a forebay reservoir to the 400 MW Kadamparai pumped-storage scheme. From around 1995, seepage gradually began to increase. Main seepage sources were deteriorated joints between the stones of the masonry, cavities that had formed in the masonry, joints between monoliths, and seepage through the foundation rock. Over time seepage rates increased dramatically, with a peak seepage of 38,000 l/min. Since the conventional methods already adopted had failed

12 29 Page 12 of 17 Innov. Infrastruct. Solut. (2017) 2:29 Fig. 13 At left waterproofing works completed at Pracana dam. At right, the dam pictured in 2003, when the owner reports: waterproofing may be assumed to contribute for the reduction of the swelling process at Kadamparai, the final decision was to adopt an upstream geomembrane; an international tender was floated, and the waterproofing works started at site on January The Carpi system at Kadamparai consists of an impermeable PVC geocomposite liner, mechanically fastened to the dam body, tensioned and drained, according to the patented solution with tensioning profiles. To mitigate the roughness of the masonry, a 2000 g/m 2 needle-punched nonwoven anti-puncture geotextile was placed over the masonry. The waterproofing liner is the same geocomposite installed at Pracana. As at Pracana, adjoining sheets were vertically joined by heat welding. A double mechanical 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, implemented by piezometers detecting if water is standing behind the geocomposite, and by an optical fibre cable system that allows locating the area of a leak if any (Fig. 14). The whole system covering more than 17,300 m 2 including the monitoring system was completed in 4 months, 6 weeks ahead of schedule. Total seepage has been reduced from 38,000 l/m to about 100 l/m. It is more than 10 years now still the measured leakage rate stands around 100 l/m. Rehabilitation in this type of dams is generally made on the entire upstream face, but partial sealing systems have been used to seal specific joints at heel or cut off wall (Kölnbrein 200 m high arch dam and Schlegeis 131 m high arch dam, both in Austria), or joints with failed joint sealant (Vale do Rossim, Portugal). In recent times rehabilitation limited to most leaking areas, to meet budget constraints or to stage construction according to available funding, is also experienced. Among the various design and installation aspects addressed, the possibility of reducing uplift with a drained system, and recent developments allowing underwater repair of the entire upstream face. Fig. 14 Kadamparai masonry dam, India 2005, pumped storage. The installation of [17,000 m 2 geomembrane system involved the use of thick geotextile to cover the rough masonry face. Prior to installation, the dam was leaking more than 38,000 l/m, after Carpi completed the geomembrane installation leakage dropped to 100 l/m

13 Innov. Infrastruct. Solut. (2017) 2:29 Page 13 of Chapter 6: RCC dams Extensive construction of RCC dams started at the beginning of the 1980s. The use of geomembranes in RCC dams followed closely, in Since 2000, the use of geomembranes has been extended from new construction also to rehabilitation of RCC dams (entire face, leaking sections, cracks, holes). Rehabilitation has been carried out also underwater and is described in Chapter 7: special cases. In RCC dams, geomembranes are used to waterproof the entire upstream face, or as external waterstop for contraction joints or repair of cracks. Basically all dams have been waterproofed with one of two available options: exposed geomembrane or covered geomembrane, both patented. The exposed system is an evolution of the system used for rehabilitation, and it was first adopted at Riou France, in Outstanding examples reported in Bulletin 135 were Miel I (Colombia 2002), at 188 m then the highest RCC dam in the world, and Olivenhain, 97 m high, 1,036,736 m 3, and highest RCC dam in USA, Miel I is a straight gravity dam constructed in a narrow gorge in Colombia. To meet contractual schedule, the original design of an upstream face made of slip formed reinforced concrete was changed to a drained exposed PVC geomembrane system, placed on a 0.4 m thick zone of grout enriched vibrated RCC. This double water shield was considered necessary due to the height of the dam. The use of grout enriched RCC allowed good compaction at the dam face, assuring a good finishing of the upstream concrete surface. The waterproofing liner is a geocomposite, consisting of a PVC geomembrane laminated to a 500 g/m 2 non-woven polypropylene geotextile. In the lowest part of the dam, from elevation 268 m to elevation 330 m, the PVC geomembrane is 3 mm thick, from elevation 330 m to elevation 450 m it is 2.5 mm thick. The entire upstream face is 31,500 m 2. The geocomposite face anchorage is made by parallel vertical tensioning profiles, placed at 3.70 m spacing. Where the water head is higher, i.e. from elevation 268 to 358 m, the stainless steel profiles have a central reinforcement. The configuration was slightly different from the one shown in Fig. 12 because, according to the state-ofthe-art at the beginning of the 2000s, the U-shaped component of the tensioning profile assembly was attached to the formwork and embedded in the 0.3 m high RCC lifts, while in current projects this component is placed after the RCC is completed, like in rehabilitation of concrete dams. The second component of the tensioning profile assembly, placed over the installed PVC geocomposite and connected to the first component, secures and tensions the PVC liner on the upstream face. The profiles are then waterproofed with PVC cover strips, as shown at right in Fig. 15. The integrated face drainage system behind the geocomposite consists of the gap between the liner and the dam face, of the geotextile laminated to the PVC geomembrane, of the vertical conduits formed by the tensioning profiles, of a peripheral collector embedded in the RCC, of the transverse discharge pipes discharging into the gallery, and of ventilation pipes assuring water flow at ambient pressure. The drainage system is divided into 4 horizontal sections (compartments), each discharging in the gallery located at its lower point. Each horizontal compartment is in turn divided into vertical compartments with separate discharge. In total there are 45 separate compartments that allow accurate monitoring of the behaviour of the waterproofing system. Construction of the grouting plinth was made following placement of the RCC. A PVC geocomposite, placed over the completed RCC lifts and over the natural excavation rock, waterproofs the plinth. The liner waterproofing the Fig. 15 Miel I RCC dam. Left: U-shaped profiles and drainage collector attached to the formworks are embedded in the RCC. Middle: U-shaped profiles after embedment appear as vertical drainage grooves in the face of the dam. Right: tensioning profiles are waterproofed with PVC cover strips

14 29 Page 14 of 17 Innov. Infrastruct. Solut. (2017) 2:29 Fig. 16 Left: installing the geocomposite in horizontal phases concurrent with RCC placement reduced times for completion at Miel I. Right: the geocomposite already installed in the lower sections allowed impounding the reservoir and testing the machinery while construction was still ongoing plinth is watertight connected to the liner waterproofing the upstream face by a tie-down seal. This type of seal, tested at 2.4 MPa, is placed also at crest, to resist water overtopping. In correspondence of the contraction joints, two layers of sacrificial geocomposite provide support to the liner on the joint. The PVC geocomposite was installed in 6 horizontal sections. A movable railing system was used to install the PVC waterproofing system concurrent and independent of RCC activities. The railing system was attached to the dam face at first at approximately 90 m above foundation, and then moved to some 140 m above foundation. The travelling platforms, from which all activities were carried out, were suspended at the railing system. Installation of the PVC geocomposite could thus be carried out from the platforms while RCC placement was ongoing above the railing system. Staged installation allowed early impounding while the dam was still under construction (Fig. 16). Construction of the dam started in April 2000 and ended in June 2002, in total 26 months. The change in design allowed meeting the schedule, and saving several 10 millions US dollars, because of reduced content of cement, faster completion, earlier power generation. Olivenhain RCC dam in California is a conventional gravity dam 788 m long and 97 m high. The dam, the highest RCC dam in USA and first RCC dam built in the highly seismic state of California, is a key element of the Emergency Storage Project (ESP) of the San Diego County Water Authority, owner of the dam. About 90% of water is brought to San Diego from hundreds of miles away, and the aqueducts cross several large active faults, including the San Andreas Fault. The ESP will provide water to the San Diego region in case of an interruption in water delivery deriving from an earthquake or drought. Evaluation of the alternatives for the upstream face, considering the magnitude of design earthquake and the critical function of the dam to provide water during an emergency, placed emphasis on seismic stability and seepage control. In a range of 1 3, these features were assigned the maximum weighting factor of 3 (Kline et al. [4]). Special consideration was also given to construction sequence because the dam had to be fully operational within a certain date. In the stability analysis, the exposed geomembrane liner and its face drainage system were considered two features that would tend to reduce the uplift pressure. Furthermore, if this uplift reduction features were to be damaged and rendered inoperable during a large earthquake which would damage the geomembrane, the effects of uplift pressures would not be as critical, because it would take some time for the pore pressure to increase, and by then the water level would have been lowered according to the rules of the California Division of Safety of Dams. The external geomembrane system received the highest score among the 11 considered alternatives. Shaping blocks and plinth are waterproofed with the same geocomposite used for the upstream face, watertight connected to the geocomposite of the upstream face with the same seal used at Miel I. Also the face drainage system is similar to the one adopted at Miel I, with the addition of a drainage geonet installed on the RCC (Fig. 17 on left), to enhance discharge capabilities should accidental damage occur to the impervious geomembrane. Under the pressure of the hydrostatic load the geonet will maintain high transmissivity, no water will be able to migrate through lift joints in the body of the dam, thus saturation levels and pore pressures in the dam will be lowered, with beneficial effects on the stability safety factors, and on the appearance at the downstream face. The PVC geocomposite, the same adopted in the higher part of Miel I dam, is fastened by vertical tensioning profiles at 3.70 m spacing. The embedded profiles have been designed larger than standard, to create larger vertical

15 Innov. Infrastruct. Solut. (2017) 2:29 Page 15 of Fig. 17 Olivenhain RCC dam, USA At left, drainage geonet is placed on the RCC to enhance drainage collection and discharge; at middle, the PVC geocomposite is placed over the geonet; at right, the tensioning profile is connected to the profile embedded in the RCC Fig. 18 The exposed PVC geocomposite system completed at Olivenhain RCC dam, USA At right, in 2004 Olivenhain, 97 m high, sustained a magnitude 5.2 earthquake conduits and further enhance drainage transmission. Stainless steel plates, mm, placed every 40 cm inside the profiles, avoid that the profiles deform under the hydrostatic load. Each line of profiles discharges separately into the gallery, and can be individually monitored. Theoretically there is one compartment for each line, in practice since the area of influence of the vertical lines is not watertight confined, some water of pertinence of one line may still travel to the adjacent lines. The upstream face has, therefore, been divided into 12 compartments, separated by a vertical watertight seal, to allow defining the area of the leak in case of damage. The peripheral seals are made by compressing the geocomposite with mm flat stainless steel batten strips. The seal is of the same type adopted at Miel I. Waterproofing works were completed in 5 months. The reservoir started filling on August 7, Concerning resistance to seismic events: Olivenhain on June 16, 2004, experienced a magnitude 5.2 earthquake, with reservoir almost at full supply level. The event was centred about 60 miles SW of the dam site. Inspection was performed, seepage rates were compared to those of the previous inspection of June 1, 2004, and seepage was found to be about the same, or smaller (Fig. 18). RCC dams lined with PVC geomembranes typically show insignificant seepage as compared to RCC dams with conventional concrete facing. At Miel I, total leakage at fully impounded reservoir is 2.0 l/s, mostly from abutments [5]; Balambano 95 m high RCC dam, Indonesia, exposed PVC system installed in 1999, has a total water flow for all 6 box drains of the 15,490 m 2 upstream face varying from l/s to a maximum of l/s at full supply level. The covered PVC system was developed in USA, and the first installation was made in The bulletin analyses pros and cons of the two solutions, and critical aspects of design and of installation techniques. Chapter 7: special cases Special applications are basically related to an external waterstop system that can be installed since construction (on contraction joints of RCC dams, or to allow partial application at crucial locations). The system can also be used to rehabilitate failing joints and cracks in concrete facings (CFRDs, concrete and RCC dams), in the dry and underwater.

16 29 Page 16 of 17 Innov. Infrastruct. Solut. (2017) 2:29 The external waterstop system shown in Fig. 19, which is patented, consists of: A support layer, installed over the completed RCC lifts, which impedes the waterproofing liner from intruding in the active joint at maximum opening of the joint under the maximum water head. This component is generally composed of one or more independent layers, in function of the water head and anticipated movements of the joints The waterproofing liner, a PVC geocomposite watertight anchored along the perimeter. With [230% tri-dimensional elongation at break of the PVC geomembrane, the external waterstop is more efficient than a conventional embedded waterstop, elongation is free over a larger width, bridging movements in the order of several cm. Installation does not interfere with RCC placement. Examples of new construction are Platanovryssi RCC dam, Greece 1998, at 95 m the highest RCC dam in Europe, and Porce II 118 m high RCC dam, Colombia An outstanding example of special application is the installation of a PVC geomembrane on the horizontal joint between phase 1 and phase 2 face slabs at Karahnjukar 198 m high CFRD, where the same PVC geomembrane had been installed on the toe wall in The PVC geomembrane has the objective of waterproofing the horizontal joint in case of potential cracking (Fig. 20). Examples of repair are Dona Francisca RCC dam (63 m high, Brazil, 2000, failing joints and cracks), Platanovryssi RCC dam (the same system installed on contraction joints during construction was used in 2002 to repair underwater a crack) and Strawberry CFRD (50 m high, USA, failing joints). In the last few years, the same system has been adopted for underwater repair of cracks and failing joints in concrete and RCC dams. Chapters 8 and 9: quality control and guidance on technical contents of contracts Chapter 8 includes recommendations on Quality Control and Quality Assurance at manufacturing, transport, and installation. It discusses items to be addressed, type and frequency of controls, and testing procedures. Chapter 9 on technical contents of contracts provides some guidelines on how procurement of geomembrane Fig. 19 Scheme and example of external PVC waterstop installed during construction: Porce II RCC dam, Colombia 2000, 118 m high Fig. 20 Example of special application: Karahnjukar, Iceland. In 2005 PVC geomembrane to waterproof the toe wall (left), in 2006 PVC geomembrane to waterproof the horizontal joint of the 198 m high CFRD in case of potential cracking