GEOMEMBRANE SEALING SYSTEMS FOR DAMS DISPOSITIFS D ÉTANCHÉITÉ PAR GÉOMEMBRANES POUR LES BARRAGES. Design principles and review of experience

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1 2010 GEOMEMBRANE SEALING SYSTEMS FOR DAMS Design principles and review of experience DISPOSITIFS D ÉTANCHÉITÉ PAR GÉOMEMBRANES POUR LES BARRAGES Principes de conception et retour d expérience Bulletin 135

2 Cover: small photos, from left to right: Bovilla (Albania) Rouchain (France) Miel I (Colombia) Large photo: Moravka (Czech Republic) Couverture : petites photos, de gauche à droite : Bovilla (Albania) Rouchain (France) Miel I (Colombia) Grande photo : Moravka (République Tchèque) AVERTISSEMENT EXONÉRATION DE RESPONSABILITÉ : Les informations, analyses et conclusions contenues dans cet ouvrage n ont pas force de Loi et ne doivent pas être considérées comme un substitut aux réglementations officielles imposées par la Loi. Elles sont uniquement destinées à un public de Professionnels Avertis, seuls aptes à en apprécier et à en déterminer la valeur et la portée. Malgré tout le soin apporté à la rédaction de cet ouvrage, compte tenu de l évolution des techniques et de la science, nous ne pouvons en garantir l exhaustivité. Nous déclinons expressément toute responsabilité quant à l interprétation et l application éventuelles (y compris les dommages éventuels en résultant ou liés) du contenu de cet ouvrage. En poursuivant la lecture de cet ouvrage, vous acceptez de façon expresse cette condition. NOTICE DISCLAIMER: The information, analyses and conclusions in this document have no legal force and must not be considered as substituting for legally-enforceable official regulations. They are intended for the use of experienced professionals who are alone equipped to judge their pertinence and applicability. This document has been drafted with the greatest care but, in view of the pace of change in science and technology, we cannot guarantee that it covers all aspects of the topics discussed. We decline all responsibility whatsoever for how the information herein is interpreted and used and will accept no liability for any loss or damage arising therefrom. Do not read on unless you accept this disclaimer without reservation. Original text in English Layout by Nathalie Schauner Texte original en anglais Mise en page par Nathalie Schauner

3 GEOMEMBRANE SEALING SYSTEMS FOR DAMS Design principles and review of experience DISPOSITIFS D ÉTANCHÉITÉ PAR GÉOMEMBRANES POUR LES BARRAGES Principes de conception et retour d expérience International Commission on Large Dams - 61, avenue Kléber, Paris - France Tél. : (33-1) Fax : (33-1) secretaire.general@icold-cigb.org Site : 1

4 PREPARED BY THE EUROPEAN WORKING GROUP: Chairman Coordinator: A. Scuero (Italian National Committee) Secretary: G. Vaschetti (Italian National Committee) E. Aguiár González (Balsas de Tenerife, Spain), P. Bartek (Swiss National Committee), M. Blanco Fernández (Laboratorio Central De Estructuras Y Materials C.D.E.X., Spain), P. Brezina (Povodi Odry, Czech Republic), H. Brunold (Austrian National Committee), D. Cazzuffi (CESI, Italy), H. Girard (Cemagref, France), M. Lefranc (French National Committee), J. L. Machado do Vale (Portuguese National Committee), C. Massaro (Azienda Energetica Metropolitana Torino), J. Millmore (British National Committee), L. Schewe (German National Committee), P. Sembenelli (Italian National Committee), With the assistance of R. M. Koerner (GSI, USA). 2

5 TABLE OF CONTENTS 1. INTRODUCTION Scope An overview of geosynthetics Content of bulletin MATERIALS, TESTING, AGEING Materials Polymeric geomembranes Classification Composition Configurations Form of supply Bituminous geomembranes Principle and composition Configuration Form of supply Geomembranes composition and potable water Seams Polymeric geomembranes Bituminous geomembranes Comparative behaviour of geomembranes Geotextiles and related products Geomembrane Testing Type of tests by tasks Index tests and performance tests Chemical analysis and polymer identification Physical/mechanical properties and test methods Permeability to Water Tensile behaviour: uni-axial on narrow wide strips (Index Test) Tensile behaviour: axi-symmetric on large samples (Performance Test) Puncture resistance (Index/performance Test) Impact resistance (Index/performance Test) Tear resistance (Index/performance Test) Interface shear strength (Index/performance Test)

6 Testing of anchorage by embedding (Index/performance Test) Tensile behaviour of seams (Index/performance Test) Stress-Cracking (Index/performance Test) Durability and test methods Ultraviolet radiation (Index/performance Test) Thermal aggression Biological Chemical aggression (Index / performance test) Oxidation Synergistic effects Specific testing for bituminous geomembranes CEN Standard EN Geosynthetic Barriers- Characteristics required for use in the construction of reservoirs and dams relevant Ageing of geomembranes. Field experience Lifetime prediction based on field results Plasticised Polyvinyl Chloride (PVC) Low Linear Density Polyethylene (LLDPE) and High Density Polyethylene (HDPE) Elastomeric Chlorosulphonated Polyethylene (CSPE) Polypropylene (fpp) Chlorinated Polyethylene (CPE) Bituminous geomembranes The Spanish experience Roofing experience Geotextiles and related products: properties and test methods Concluding remarks LOADS APPLIED TO GEOMEMBRANE SEALING SYSTEMS (GSS) Introduction Mechanical loads Gravity load Subgrade differential deformation Puncture load Wind load Reservoir waves Ice in the reservoir Uplift from water or air

7 3.3. Physical, chemical and biological attack Heat Ultra Violet radiation Water ingredients Biological action (micro-organisms) Vegetation Fauna Vandalism GEOMEMBRANES FOR NEW CONSTRUCTION AND REHABILITATION OF FILL DAMS General The upstream system Exposed geomembrane system Covered geomembrane system The internal system Loading The upstream system General Geomembrane sealing layer Supporting layer Drainage layer Transition zone Face anchorage General Mechanical anchorage Anchorage by loading Gluing Ballast anchorage (covered geomembrane) Anchorage at peripheries Mechanical anchorage Insert type anchorage Ballast anchorage Anchorage around pipes and penetrations The internal system Placement Supporting layer Placement of geomembrane

8 4.6. Typical examples New construction, covered bituminous membrane New construction, exposed PVC geomembrane New construction, covered PVC geomembrane New construction, covered PVC geomembrane Repair, exposed PVC geomembrane Repair, covered PVC geomembrane GEOMEMBRANES ON CONCRETE AND MASONRY DAMS Range of applications Applications in new dam construction Applications in dam rehabilitation Design principles Partial sealing system Exposed sealing system Covered sealing system Loads Geomembrane sealing system - general concepts Introduction Geomembrane Subgrade and support layer Anti-puncturing layer Anchorage Drainage and ventilation system General Design of the drainage system Construction Exposed geomembrane and anchorage system Covered geomembrane and cover layer Installation techniques In the dry Underwater Typical examples Rehabilitation of masonry dams, exposed PVC geomembrane, dry installation Rehabilitation of buttress dam subject to AAR, exposed PVC geomembrane, dry installation Rehabilitation of multiple arch dam, exposed PVC geomembrane, dry installation

9 New elastic cut-off, LLDPE geomembrane Rehabilitation of arch dam, exposed PVC geomembrane, underwater installation GEOMEMBRANES FOR ROLLER COMPACTED CONCRETE DAMS: NEW CONSTRUCTION, REHABILITATION AND INDUCED JOINTS Range of applications Applications in construction of new dams Application in rehabilitation of RCC dams Design principles General The exposed sealing system The covered sealing system Comparison of the two systems Loading Geomembrane sealing system General Geomembrane Support surface and lower protection of the waterproofing geomembrane Drainage and ventilation layer Drainage collection and discharge Anchorage system over the dam face Anchorage at top Anchorage at submerged periphery Installation techniques Exposed geomembrane system Concurrent installation Post-Installation Covered geomembrane system Typical examples Exposed PVC geomembrane installed after completion of dam, geonet on entire upstream face Exposed PVC geomembrane with different thickness depending on water head, installed during construction of dam Covered PVC geomembrane, part of prefabricated panels used as permanent formworks for construction of dam

10 7. SPECIAL CASES General System as repair of joints and cracks General Support Anchorage Sealing at periphery Cover layer System on induced contraction joints (RCC dams) General Design Subgrade preparation Type of geomembrane Underwater applications Typical examples Exposed PVC geomembrane for repair of failing joints/cracks Exposed PVC geomembrane on contraction joints where major movements are expected Exposed PVC geomembrane on leaking joints Exposed PVC geomembrane on contraction joints since construction Dry and underwater installation: exposed PVC geomembrane on joints and crack CONTROL OF QUALITY OF A GEOMEMBRANE SEALING SYSTEM Foreword Quality control and quality assurance MQC items Procedures to assure survival CQC items Acceptance of materials at site Acceptance of surface Installation of geotextile Installation of geomembrane sheets/panels Installation of fastening system on upstream face Assembling of geomembrane sheets/panels (field joints) Watertightness of perimeter seals

11 Final concluding inspection of geomembrane Placement of cover layer Final concluding inspection of geomembrane sealing system Documentation GUIDANCE ON TECHNICAL CONTENT OF CONTRACTS General considerations Technical specifications Materials Synthetic materials Fixation materials Drainage materials Other materials Sealing system Description of constituents Surface preparation Joining of sheets/rolls Perimeter seal Drainage system Fixation Experience of proposed material Experience of the proposed fastening system Ballasting layer Installation plan and schedule QC plan Acceptance criteria of performed works Liner Fixations Seams Leakage Warranty Bill of quantities and conditions Concluding remarks Annexes Check list Compliance to tender requirements Example of warranty

12 Technical solutions/geomembranes adopted in the cited examples Appendix 1 (data base for the 290 dams in which geomembranes have been used) is available at ICOLD. Appendix 2 (list of geomembrane technology terms and definitions). Appendix 3 (the leading references on testing standards and on the use of geomembranes and their application on various dams). 10

13 FOREWORD 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. Lastly, 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 (*) 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). (**) 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). 11

14 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 12

15 1. INTRODUCTION 1.1. SCOPE According to IGS, the International Geosynthetics Society established in 1983, a geomembrane is a planar, relatively impermeable, polymeric (synthetic or natural) sheet used in contact with soil/rock and/or any other geotechnical material in civil engineering applications. Geomembranes are made from relatively thin continuous polymeric sheets, but they can also be made from the impregnation of geotextiles with asphalt or elastomer sprays or as multilayered bitumen geocomposites. These sheets are prefabricated in a factory and transported to the job sites, where placement and field-seaming are performed to complete the job. For more than 45 years geomembranes have been successfully used to provide a watertight facing on new RCC dams up to 188 m high, they have been employed for repair of old masonry and concrete dams up to 174 m high, and as impervious components on fill dams up to 198 m high. They have been installed in the dry and underwater. Table 1 Total dams with geomembranes* Type of dam Number of dams % on total Fill Concrete RCC Unknown Total *The cut line for the database which is the source of tables and figures is December 31, The full database up to publication of the Bulletin is available from ICOLD. Based on the successful experience gained and on the expected expansion in the future of use of geomembranes in dams, this Bulletin will focus on factory-made continuous polymeric and bituminous sheet geomembranes and their application in dam construction. The following information and guidelines aim to give a thorough understanding of the characteristics and potential advantages of a geomembrane facing, to achieve a solution that is adequately specified, designed, constructed and controlled. The synthetic product Geomembrane is part of the Geomembrane Sealing System, abbreviated as GSS, a system of superposed layers necessary for the construction, placement and the preservation of the sealing of a structure or, in accordance with the aim of this Bulletin, a dam. A geomembrane sealing system is generally a composition of more than one layer of geosynthetic material or natural material, which provides protection, strengthening or downstream drainage. 13

16 Therefore, the design of a geomembrane sealing system implies the global study of the composed sealing system and is not limited to the geomembrane. Most of the present recommendations of course also apply to dams less than 15 m high, to linings for embankments, canals, hydraulic tunnels, ponds and reservoirs of all kinds AN OVERVIEW OF GEOSYNTHETICS All soil-, rock-, and groundwater-related activities fall within the general scope of the various applications of geosynthetics. Geo, of course, refers to the earth. Therefore, the term geosynthetics seems to be appropriate in the combination with synthetics, since the materials used are almost exclusively from human-made products. With synthetics an exciting new chapter in engineered construction materials has emerged for the civil engineering community -and the rapidity with which the related products are being developed and used is nothing short of amazing. The reasons for this explosion of geosynthetics are numerous and include the following: They are quality controlled manufactured in a factory environment with constant parameters, They generally replace short or missing natural material resources, They generally replace natural construction materials in designs which are difficult if using natural materials, They have made previously impossible designs and applications possible, Their use is required by regulations in some environmental protective cases, They are (generally) cost competitive against natural soil materials and concrete that they replace, They can be installed rapidly, As of December 2009, they have a 50 years performance history (first application in 1959) that makes engineers increasingly inclined to use them, They are being actively marketed and are widely available, They can easily be transported over great distances at relatively low costs. The use of geosynthetics instead of natural (soil) or man-made materials (concrete, steel) has basically the objectives: To replace natural material where either short in availability or missing or of inadequate quality, To provide better structural quality (e.g., without deterioration of material or water tightness), To do the job more economically (either through lower initial cost or/and through greater durability and longer life, thus reducing maintenance costs). The family of geosynthetics which are commonly used in dams are grouped in accordance with their characteristics and field of application. 14

17 Diagram for geosynthetics and their application Geosynthetics(GSY) (definition includes both synthetic and natural polymeric materials) PERMEABLE ESSENTIALLY IMPERMEABLE Geotextiles (GTX) Geotextile-related products (GTP) Geosynthetic clay liners (GCL) Geomembranes (GMB) WovenNonwoven (GTX-W)(GTX-N) Knitted (GTX-K) Geogrids (GCR) Geonets (GNE) Geocells (GCE) Geostrips (GST) Geomats (GMA) Geospacers (GSP) Polymeric (TE-GMB) Elastomeric Thermoplastic Bituminous (B-GMB) GEOCOMPOSITES(GCO) Fig. 1 Diagram for geosynthestics and their application Separation Filtration Drainage Table 2 Geocomposites (GCO): Some examples by function Reinforcement Surface Protection Barrier erosion control GTX + yarns GTX + GTX GSP + GTX + GTX GTX + GTX GMB + GTX + GCE GTX GTX (+ GBR*-P) GTX + GTX GTX + GTN + GTX + GGR GTX + soil GTX + GGR+ GMA GTX soil GMA (+ GBR-P) (bentonite) etc. etc. etc. etc. GMA + soil GBR-P + GTX + soil seeds (bentonite) GTX + GMA GTN + soil etc. GTX + GGR etc. NOTE: All geosynthetics may have multiple functions. *GBR: Geosynthetics Barriers. etc. 15

18 Because of their open fabric, the main application of geotextiles, geonets, geospacers and geogrids is the separation, drainage, filtration and reinforcement of soils in earthworks such as fill dams. They are also used in combination with geomembranes mainly as protective layers. A geocomposite is a combination of at least two geosynthetics: geotextile and geonet, geotextile and geomembrane, or any other combination of these materials with other materials (e.g., deformed plastic sheets, steel cables, or steel anchors). This is the most creative area of geosynthetics, and application areas are numerous, covering all functions previously discussed. A major topic area of polymeric and bituminous geomembranes is that of providing a leak-proof low permeability barrier for sealing purpose in order to prevent liquid movement from one point to another. Geomembranes retain their watertight properties even under service strains and are connected by strong and durable bonding. Another category of impermeable barrier are the geosynthetic clay liners (GCL): a mainly bentonite layer in between two geotextile layers for stabilisation. GCL do not provide strong permanent bonding of the layers and they have never been used in dams and they are not considered in this Bulletin. Consistent with current engineering practice, the term geomembrane is used here mainly for polymeric geomembranes and for bituminous geomembranes. Geomembranes are made from relatively thin factory-made continuous sheets, but can also be made on site from the impregnation of geotextiles with bitumen or elastomers. Polymeric geomembranes have been used in 240 dams of which 9 geomembranes are made by in situ impregnation, bituminous geomembranes in 23 dams of which 3 geomembranes are made by in situ impregnation. Last application of in-situ bitumen impregnated geotextile was in 1988 at Humenize (CZ). In general this technology did not provide satisfactory behaviour and these days it is disregarded. In 1990, the ICOLD Bulletin 78 made a short reference to in-situ geomembranes, impregnated geotextiles and sprayed liners based on polyurethane and polypropylene resins, which are produced on site instead of being factory manufactured. This type of product relies on constant thickness and perfect bonding to the support, which entails extensive surface preparation. Its application requires weather conditions which are difficult to obtain constantly on a job site. This is one of the reasons of the failures incurred by this type of membrane. Since they are close to the family of the resins as a coating layer and their use is less and less frequent, this type of membrane is not subject of this Bulletin CONTENT OF BULLETIN The Bulletin is divided in the following chapters: Chapter 1 provides an introduction to geosynthetics and to their classification in several distinct families and in general their field of application. It provides the content and scope of this Bulletin. Chapter 2 describes the classification and characteristics of geomembranes; it further discusses materials specifications and testing. 16

19 Chapter 3 describes the loads and stresses to which geomembranes are exposed, criteria and recommendations for design, construction and operation. Chapter 4 deals with the application of geomembranes as the sealing element in construction of new fill dams. The chapter also illustrates application of geomembranes to repair of asphalt-concrete sealing facings, bituminous geomembrane facings, and concrete facing in CFRD. Chapter 5 provides the application of geomembranes to repair of concrete, shotcrete and masonry facings of gravity and arch dams. The chapter addresses repair in the dry and underwater. Chapter 6 deals with the application of geomembranes to RCC dams as a watertight upstream facing in new construction, and as a repair on existing RCC dams. Chapter 7 deals with special applications: as a watertight element at joints and cracks and as an underwater repair measure. Chapter 8 deals with QCA. Chapter 9 gives recommendations for specification for design, supply and construction of geomembrane sealing systems. Appendix 1 contains a data base for the 250 dams in which geomembranes have been used. The cut line for the statistics of the database is December 31, This appendix, and the updated database, are available from ICOLD. Appendix 2 contains a list of geomembrane technology terms and definitions. Appendix 3 contains the leading references on testing standards and on the use of geomembranes and their application on various dams. As many information given are common to different types of dams, in order to keep the size of the Bulletin reasonable, they have been listed only one time and not repeated. Therefore the various Chapters of this Bulletin cannot be used as a self standing document but shall be read in conjunction with all the other parts. 17

20 2. MATERIALS, TESTING, AGEING 2.1. MATERIALS The geomembranes reported in this Bulletin (more than 260 dams) are made from synthetic polymers (more than 91%) and from bitumen (more than 8%). This section aims to afford (a) an appreciation of the wealth of information that is available (b) basic understanding of geomembranes, and (c) the tests that are available to assess the characteristics and behaviour of geomembranes Polymeric geomembranes This section refers to polymeric geomembranes only, which have been used in 240 dams. Polymeric geomembranes consist of one or more layers of polymeric materials, manufactured in a plant by one of the three processes: calendering, extrusion, and spread coating Classification A polymeric material consists of many units (monomers) linked together. A monomer is the molecular compound used to produce the polymer. Different type and lengths of the polymeric chain result in materials with different characteristics. The most common polymers used as base products in the manufacture of geomembranes can be classified in three types: I. Thermoplastics: they can be repeatedly heated to their softening point, shaped or worked as desired, and then cooled to preserve that remoulded shape. Table 3 Synthetic materials more frequently employed as geomembranes Type Basic Material Abbreviation Chlorinated polyethylene CPE Ethylene-vinyl acetate copolymer EVA/C Thermoplastic Polyethylene PE* Polypropylene PP Polyvinyl chloride PVC Thermoplastic rubbers Chlorosulfonated polyethylene CSPE Ethylene-propylene copolymer E/P Polyisobutylene PIB Chloroprene rubber CR Thermoset Ethylene-propylene diene monomer EPDM Butyl rubber IIR Nytrile rubber NBR *Within the group shown, polyethylene and polypropylene are collectively called polyolefins. 18