SANCOLD Conference 2017: “Management of and Reservoirs in Southern Africa” Centurion, Tshwane, South Africa, 15 to 17 November 2017 © SANCOLD, ISBN 978-0-620-76981-5

CONCRETE TYPES AND THE CIRCUMSTANCES AND CONDITIONS THAT FAVOUR ONE TYPE OVER ANOTHER

QHW Shaw1 1. ARQ Consulting Engineers, South Africa

PRESENTER: QUENTIN SHAW

ABSTRACT

Concrete dam types all comprise a combination of cementitious materials and processed rock, but while the rock materials are sometimes processed in different ways, different dam types can involve placement and compaction applying quite different methods. Furthermore, the different concrete dam types also include a number of quite different structure types.

Each dam project will involve a dam type selection study, during which the optimal dam type will be identified. The simpler concrete dam types are easily reviewed and compared against other dam types during this process. The more complex and less obvious concrete dam types, however, are often inadequately considered, sometimes actually unnecessarily compromising the economic feasibility of the dam site/scheme under consideration, and it is clear that a full understanding of concrete dam types does not generally exist. For example, RCC gravity dams are now often assumed to be the most competitive concrete dam type for many sites, where competing directly with embankment dam types, and consequently, the associated circumstances that might favour a conventional concrete structure are often not adequately understood.

In this paper, the author describes the various possible concrete-based dam types and discusses the particular circumstances that favour one type over another, explaining the key aspects of a site that should be reviewed to establish the respective suitability.

1. BACKGROUND & INTRODUCTION

1.1 A Brief History of Concrete Dams “Concrete” dam types can be traced right back to the origins of dam building in Mesopotamia over the period 3000 – 2750 BC, when masonry gravity structures were constructed as levees to control flood waters on the Tigris and Euphrates rivers (Yang et al, 1999).

Around 100 AD, the Romans advanced technology significantly through the use of cement and mortar in gravity dams. The dam at Ponte di San Mauro in Italy, constructed during this period, has a large block of concrete among its remains. While the dam subsequently failed in 1305, according to legend during attempts to lower the impoundment level, it would seem that the dam comprised a concrete core, with a stone masonry surfacing.

Due to the large quantities of materials required to construct gravity dams, the dam was invented, with the first known arch dam dating back to 1280 AD.

By the seventeenth century, the Spanish were leading the world in dam building and the Spaniard Don Pedro Bernado Villarreal de Berriz was the world’s first author on the subject of dam design in 1736, addressing the two dam types constructed at the time; arch and gravity dams. He also theorized on the subject of multiple arch-buttress dams, leading to a period of dam construction in favouring buttress dams. The Spanish subsequently took dam building to the Americas, constructing many small buttress dams for irrigation in the eighteenth century

However, it was in the 19th century that dam engineering technology developed to a level that allowed large-scale dam building to be initiated. With the industrial revolution, the need for water supply

79 increased, while the equipment to assist in larger-scale construction started to become available. Stress analysis was introduced from mid-century and the advent of the internal combustion engine towards the end of the century saw concrete dam construction technologies develop from dressed masonry through rubble-masonry, to concrete.

Figure 1. Vyrnwy Dam, Wales - 45 m, completed 1888

With the advent of concrete dam construction and the rapid development of infrastructure occurring at the time in many countries across the world, dam construction accelerated to a peak in the third quarter of the 20th century. Over this period, arch dam analysis and design technologies developed substantially, allowing significantly reduced concrete volumes for large dams. Conversely, labour costs started to rise and the introduction of larger plant and developments in soil mechanics reduced the costs of embankment dams. By the beginning of the 1970s, concrete dams had lost significant competitiveness and a means to reduce associated costs was sought.

Many of the arch dams constructed during the early years of the 20th century were rather conservatively designed, as analysis technologies were still in their infancy at the time (USSD, 1988). However, with the development of the constant angle arch concept, Trial Load analysis and reverse membrane theory, ambitiously proportioned arch dams were subsequently successfully implemented. While the limitations of these analysis methods were always recognized, particularly in not fully accounting for shear and temperature effects, a relatively high degree of accuracy became possible with the computer-based application of the trial-load method. A real understanding of the structural function of arch and other concrete dam types, however, realistically only became possible with the advent of finite element (FE) analysis in the late 1960s. The associated analysis systems continue to develop today and a broader availability of these design tools now allows the application of sophisticated analysis on almost all sizes of concrete dams.

1.2 Introduction

The author has been exposed to dam engineering and construction in 20 countries around the world. He has also worked with, and been exposed to, consulting engineers and contractors from many countries and he has been disappointed by the generally low level of understanding of the factors that favour one concrete dam type over another and the designer’s role in ensuring efficient, rapid and low cost construction.

In this paper, the author discusses the factors that favour one concrete dam type at a particular site over another and illustrates the consequential requirements to allow and ensure maximum constructional efficiency.

80 2. MODERN CONCRETE DAMS

2.1 Concrete Dam Types

The primary modern forms of the concrete dam are conventional mass concrete (CVC) gravity, buttress and arch dams and roller compacted concrete (RCC) gravity and arch dams.

While dressed stone masonry will no longer represent an economical solution in any environment, rubble masonry concrete (RMC) can represent a very economical alternative on a small and even medium- scale, in an environment where low-cost labour is available, founding conditions are good and alluvial sand is abundant.

In conventional mass concrete, many variations of the arch and buttress dam types exist, including a combination of both. Buttress dam types include slab-and-buttress, arch-buttress, massive arch- buttress, diamond head buttress and dome-buttress. Arch types include arch/gravity, single-curvature arch, double-curvature arch and multiple-arch buttress.

RCC does not offer the same flexibility as CVC and associated dam types are limited to gravity, gravity arch and arch. While less than 10% of all RCC dams in the world are , the vast majority of these structures are located in China, where over 20% of all RCC dams are arch dams. It is something of a paradox that China, the country with by far the highest number of RCC dams, constructs RCC arches at all sites with some potential, while the rest of the world seems very nervous to adopt this dam type.

A variation of RCC than can only realistically be applied for broad-sectioned gravity structures is Hardfill. Hardfill is a low strength roller compacted concrete, which is generally applied in a trapezoidal section, with equal up- and downstream face slopes and an impermeable element, or membrane attached to, or constructed on the upstream face.

RMC was an evolution of masonry that was used in dam construction in between the introduction of the commercial availability of cement and the general development of concrete, which occurred with the internal combustion engine allowing the crushing of rock for aggregates. A similar technology was used in China and until the advent of RCC late in the 20th century, but this was limited to the construction of gravity dams. The key success of modern RMC dams lies in the combination of modern analysis techniques with a historical form of labour-based construction, to apply a dam type that history missed; RMC arch and multiple arch buttress dams.

2.2 Materials

All concrete dam types comprise cementitious materials, water and rock aggregates, which combine to form a composite material with elastic properties within the applicable normal stress range, a relatively high compressive strength and limited tensile strength. Even a Hardfill will typically indicate an elastic modulus exceeding that of the foundation on which it is constructed. It is considered that a rolled fill with some level of plasticity, as suited to poorer foundations, would probably now be classified as a cemented materials dam (CMD) and not as a concrete dam.

Generally, aggregates for a concrete dam will be crushed, or at least processed, although natural gravels can certainly be used for Hardfill and lower strength RCCs.

Otherwise, cementitious materials can include a variety of cement types and pozzolans, with total cementitious materials contents typically varying from 60 to 250 kg/m3. In the early days of RCC dam construction, lower cementitious materials contents were used, compared to equivalent mass concrete. In recent years, this is no longer generally the case, although the cementitious materials used in RCCs tend to comprise a substantially higher proportion of pozzolans.

It seems that a good deal of knowledge on mass concrete for dams has been lost in the past 3 decades of RCC development and it is worthwhile to remember that it is not at all uncommon to find an RCC with a cementitious content exceeding 200 kg/m3, while the bulk mass concrete used for the 240 m Deriner double curvature arch dam in Turkey comprised 117 kg/m3 OPC + 63 kg/m3 fly ash. To compact this CVC mix with just 110 litres/m3 of water, powerful banks of excavator-mounted compactors are used and although a lower fly ash content was applied, compared to equivalent RCCs, some economy is

81 regained in a substantially lower fine aggregate content. For the 275 m Yusufeli double curvature arch, a similar bulk concrete mix is being tested, but with 45% fly ash.

2.3 Roller Compacted Concrete Dams

The roller compacted concrete dam is viewed as the most modern form of concrete dam construction and RCC has essentially replaced CVC as the conventional approach for the construction of gravity dams. While this situation is not the same for arch dams, it is apparent that it has become a convenient assumption that RCC is now always the lowest cost form of concrete dam, which is not always, necessarily true.

Furthermore, successes have demonstrated the achievable level of efficiency of RCC dam construction, but in reality, this level of efficiency is rarely achieved; partly due to poor design and partly due to a low level of understanding on the part of contractors. The generic rules of thumb in RCC construction consider an efficient RCC construction when the ratio of the peak month’s RCC placement/the average monthly placement is less than 2 and the ratio of peak month placement/peak day exceeds 20. If the peak day of placement represents the RCC production capacity, the average monthly placement will equate approximately to 10 days placement at full capacity. With typically 26 to 27 construction days per month, what is considered as efficient construction consequently achieves a little over 35% plant utilisation. Consequently, it can be stated that most contractors do not even achieve a 35% plant utilisation on RCC dam construction. In fact, the figure of De Hoop Dam was less than 10%.

Considering that the De Hoop Dam RCC contained more cementitious materials than would be typically used in the bulk CVC for a high arch dam, the question must be asked as to whether an RCC dam type, or the applied arrangement of an RCC dam type, was the optimal solution in the case of De Hoop Dam. Despite the best intentions, the primary benefits of RCC construction, speed and lower cementitious materials costs, were not realised at De Hoop Dam.

De Hoop Dam can be compared with Melen Dam in Turkey, where the 2 million m3 of RCC comprising the 120 m high structure was placed in 22 months, averaging 90 000 m3 per month with the construction staff peaking at a little over 500. At De Hoop Dam, an average RCC placement rate of less than 25 000 m3 was achieved with a peak construction staff complement of 1200.

3. FACTORS THAT INFLUENCE THE OPTIMAL CONCRETE DAM TYPE

3.1 General

A dam type selection study will typically consider geology, available materials, hydrology, spillway requirements and site topography to identify the most economical and appropriate solution. In some instances, particularly for hydropower schemes, a shorter construction period for a dam can substantially influence the project economics and consequently, certain dam types can offer increased related benefits.

3.2 Geology & Founding Conditions In terms of geology and geotechnical conditions, there are various rules of thumb for concrete dams and concrete dam types. In this regard, South Africa has been somewhat conservative in its development of dams, perhaps as a result of the frequent incidence of relatively favourable geotechnical conditions.

As a starting point, the relationship between the elastic modulus of the dam concrete and the foundation rock mass (Ec/Em) is generally considered, with a ratio of 4 being considered a maximum that should not ideally be exceeded for arch and other concrete dams (Rocha, 1964). Rocha also provided the following guidance on the impacts of a range of ratios of concrete elastic modulus (Ec) and rock mass elastic modulus (Em).

Table 1. Structural influence of Ec/Em ratio for Arch Dams, Rocha (1964)

Ec/Em Influence on Dam Problems < 1 Negligible None

82 1 – 4 Low Importance None 4 – 8 Important Some 8 - 16 Very Important Serious > 16 Special Measures Very Dangerous

In addition, two further systems for reviewing suitability were proposed by Romana (2003), as indicated in Table 2 and

Table 3.

Table 2: Deformability problems according to foundation Rock Mass Rating (RMR) value

Dam Type Height RMR Value (m) Normal Problems Serious Problems Gravity < 50 > 40 25 - 40 < 25 50 - 100 > 50 40 - 50 < 40 100 - 150 > 60 60 - 60 < 50 Arch < 10 > 45 35 - 45 < 35 100 - 150 > 60 45 - 55 < 45 150 - 200 > 70 55 - 70 < 55

Table 3: The influence of joint orientation on dam stability (Romana, 2003)

Dam Type Very Favourable Fair Unfavourable Very Favourable Unfavourable Fill 10 – 30 DS 0 – 10 A - - Gravity 10 – 60 DS 30 – 60 US & 10 – 30 US 0 – 10 A - 60 – 90 A Arch 30 – 60 DS 10 – 30 DS 30 – 60 US & 10 – 30 US 0 – 10 A 60 -90 A Rating 0 -2 -7 -15 -25 DS dip downstream US dip upstream A any dip

The above represent useful rules of thumb to establish appropriate dam types and related limitations during the planning and early project design stages. In the later stages of design, greater levels of investigation and in situ testing can allow some variation.

Additionally, on more deformable foundations and/or foundations of variable stiffness, a distinct disadvantage exists in the horizontal construction associated with RCC, particularly when induced joints are not specifically designed to accommodate differential vertical movement. In such conditions, mass concrete construction, with separate monoliths, separated with joints incorporating 1-dimensional shear keys, will typically be more appropriate.

While a “concrete” material with a lower modulus of elasticity, such as Hardfill, may sometimes be appropriate for construction on lower strength foundations, in fact, the above constraints imply that such an approach is not really applicable for foundation rock mass materials with elastic moduli below approximately 1 GPa.

83 3.3 Topography & Geometry

Site topography and structure geometry can significantly influence the optimal, or appropriate dam types. While a low crest length/height ratio is essential for an arch dam, higher ratios specifically favour construction by roller compaction. The greatest efficiencies of RCC construction have been achieved on long, straight gravity dams, typically with constant sections and steep abutments and typically with an RCC placement volume exceeding 1 million m3.

On narrower sites with steep abutments, particularly with a V shape, access and materials delivery will often favour vertical, rather than horizontal construction. In this regard, a delicate balance exists between the CVC and the RCC arch dam. While constraints related to double curvature and tensile strength capacity effectively limit the height of RCC arches, these structure types are in fact much more suited to heavy-section and arch/gravity configurations, when simplicity and rapidity of construction can be easily maintained. Conversely, when topography and geology allow efficient double curvature and a thin arch, vertical construction and a significant reduction in total concrete volume will substantially favour a CVC arch.

A useful comparison can be made between the 171 m Cahora Bassa CVC arch, completed in 1974, and the 133 m Gomal Zam RCC arch/gravity dam, completed in 2011. In the former case, the 520 000 m3 of CVC was placed in 26 months. In the latter case, the 390 000 m3 of RCC was placed in 28 months at an average rate of just 14 000 m3 per month, with the construction complicated to the point that it is considered unlikely that an RCC arch was actually the optimal solution.

Figure 2. Cahora Bassa Dam (171 m), Mozambique & Gomal Zam Dam, Pakistan (133 m)

It should be noted that very large CVC arch dams are often constructed at similar rates as achieved at the larger RCC dams, i.e. > 100 000 m3 per month.

3.4 Structural Requirements, Height & Loading

Rubble masonry concrete dams have height limitations due to strength and stress capacity, as well as practical construction limitations. While a high RMC arch would require the inclusion of groutable joints and thicker sections, an inability to construct RMC to any significant double curvature implies that such a dam type will lose cost competitiveness with height. Similarly, the inability to slope the arches of a multiple arch-buttress dam configuration in RMC also imposes a height limitation on this dam type.

All but the smallest buttress dams require a sloped upstream face to gain the benefit of water loading for sliding stability. With increasing height, however, the vertical load requirements to achieve typical factors of safety progressively erode the reduced concrete quantities, compared to a gravity dam, while cross-canyon stability can necessitate bracing under seismic loading. The advent of the RCC gravity dam further compromised the competitiveness of buttress dams, which will now rarely represent the optimal solution for heights above 30 m.

The height of an RCC dam is realistically limited by an achievable inter-layer tensile strength of approximately 1,5 MPa. Depending on the applicable seismic loading, this limitation implies that RCC

84 dams significantly higher than 200 m will require zones of high-tensile strength mass concrete at the upstream face, at least for the lower part of the dam height. On the other hand, very substantially higher tensile strengths can be assured with conventional mass concrete.

3.5 Design

Dam design and the associated constructability can incur a significant impact on the comparative competitiveness and appropriateness of one dam type compared to another. For example, simplicity is an absolute for RCC dams, with complex appurtenant works and conduits through the structure incurring a very significantly greater impact on an RCC dam than is the case for all variants of the conventional concrete dam. Furthermore, in the case of RCC dams, the design and construction of all appurtenant and associated works must be carefully planned to incur minimum impact on the overall construction programme.

An example in this regard can be made comparing the highest dam raise in the world to date using RCC, at San Vicente, and the proposed Clanwilliam Dam raise. While the former was raised from 68 m to 103 m at an equivalent cost of approximately R 1,8 billion, with the RCC placed in 11 months, it is intended to raise the latter from 41 to 56 m at a budgeted cost of approximately R 3 billion.

Similarly, the requirement for simplicity implies that RCC construction cannot be applied to achieve the complex double curvature, cupola, or dome shapes inherent to the most efficient and thinnest concrete arch structures.

Figure 3. RCC Arch/Gravity Dam

3.6 Spillways

Spillway requirements will often favour one concrete dam type over another, with the practical requirements to accommodate very large flood discharges often representing a significant cost component of a dam. When relatively low specific discharges can be applied and the dam is not paricularly high, a chute on the stepped downstream face of an RCC dam can represent a very efficient solution, for which only a short toe apron might be required. On the other hand, when a long Roberts crest splitter arrangement is applied on an RCC dam, the associated construction period can be significantly extended. Substantial and complex works on a dam crest will often be more suited to vertical construction, with the provision of crane access being necessary that will anyway be present for vertically constructed CVC, but is not required for horizontally-placed RCC.

Chutes and flip-buckets have been very efficiently constructed on RCC dams, with the reinforced concrete construction of the chute lagging the RCC placement by as little as 2 weeks.

3.7 River Diversion

All variants of the concrete dam obviously offer advantages over earth and rock fill dam types in respect of river diversion and river management during construction. While the ability to overtop concrete dam

85 types during construction allows diversion works to be designed for a lower capacity, or a higher risk of capacity exceedance, diversions can often be integrated into, or through the dam, often reducing the construction period and cost associated with a tunnel diversion.

On rivers subject to monsoon seasons, it is often simply uneconomical to provide a diversion with a year-round capacity and spilling over a partly constructed dam is a frequently applied solution. In such situations, variations of the concrete dam type are obviously most suitable and when RCC is applied in such circumstances, the structure is often constructed in blocks, with one, or more blocks remaining low and without formwork for the wet season (see Figure 4). While this arrangement allows construction to continue on other adjacent blocks, it substantially compromises the speed and economy of continuous horizontal construction.

Figure 4. Inanda Dam (CVC) and Bui Dam (RCC) overtopping during construction

When concrete placement must be interrupted for an extended wet season and the particular dam arrangement implies that construction cannot continue at full capacity on other sections, the advantages of vertical construction will significantly increase the time and cost competitiveness of a CVC dam type.

3.8 Construction Time

The 2,5 million m3 of CVC in was placed in just 24 months in the 1930s, while several of the super-high CVC arch dams constructed in China in the last decade realised average monthly concrete placements exceeding 100 000 m3. By comparison, only seven of the 600 completed RCC dams worldwide have so far achieved average rates of RCC placement exceeding 100 000 m3/month.

Rapid construction is undoubtedly a particular advantage of the RCC dam, but it is important to understand the requirements necessary to realise this advantage and to actually achieve rapid construction in RCC.

Again, De Hoop Dam provides us with a useful comparison with Changuinola 1 Dam in Panama. Both dams were constructed in high-workability RCC, started at around the same time and comprised almost 1 million m3 of concrete. Changuinola 1 Dam is an arch/gravity structure for which cement and fly ash had to be imported by sea, while 4,1 m of rain fell on site during the 15 month RCC placement.

Despite these difficulties, Changuinola 1 Dam plots towards the top of the envelope of rates of RCC placement achieved to date (see Figure 5), while De Hoop Dam lies at the bottom. The primary difference was that every aspect of Changuinola 1 Dam was designed to be constructed rapidly.

3.9 Economy

Comparisons on the basis of construction economy are often country-specific, with cement prices, materials availability, contractor competition and risk all influencing costs. For example, a comparison can be made between the 1 million m3 De Hoop RCC gravity dam in South Africa, with a completed price exceeding R 3 billion, and the 2 million m3 Melen RCC gravity dam in Turkey, with a contract price equivalent to R 750 million.

86

Figure 5. Comparative RCC dam placement rates (Dunstan)

As discussed above, the comparison between San Vicente Dam and Clanwilliam Dam is considered important and in this instance, construction in California should generally be much costlier than construction in South Africa. However, it is quite likely that the final complexity of the proposed construction for Clanwilliam was not fully, or adequately accommodated in the dam type selection study, illustrating clearly that we need to understand that such decisions sometimes need to be revisited. This example also serves as a reminder that all concrete dam types must be designed understanding the associated construction and giving economy of construction highest priority.

It is undoubtedly true that the full economy of RCC dam construction only becomes apparent with scale. In the early days of RCC construction, it was sometimes suggested that RCC was only suitable for dams with concrete volumes exceeding 100 000 m3 and while this has since been frequently disproved, the full cost benefit is probably not realised for RCC volumes less than 750 000 to 1 million m3.

3.10 Local Conditions & Available Skills

Local conditions must always be considered when selecting a dam type, particularly a concrete dam type. With the majority of the construction materials located close to the dam site, the construction of an embankment dam type is typically a relatively isolated exercise, once all the plant has been established on site. In the case of a large concrete dam type, on the other hand, the importation to site of cementitious materials and sometimes aggregates will continue for the period of concrete placement and this requirement must be considered against local conditions. For example, the railway system of the southern Cape needed to be scheduled around the 1000 tonne fly ash delivery trains for Wolwedans Dam, while environmental restrictions limited the number of daily aggregate deliveries to the Spring Grove Dam, environmental requirements limited construction times at the Olivenhain Dam in the USA, sea transportation of cementitious materials to Changuinola 1 Dam in Panama required the establishment of a port terminal and transfer facility, roads constructed primarily for motorbike traffic had to be used for cementitious materials delivery to Trung Son Dam in Vietnam and procurement problems impeded the construction of De Hoop Dam.

The realisation of the full benefits of RCC construction simply comes down to the involvement of people with the right skills and experience. Evidently, this requirement is frequently not acknowledged, or understood and while the involvement of adequately skilled and experienced people should be specified in all stages of all RCC projects, a risk review may be appropriate during the dam type selection study, assuming lower levels of construction efficiency and higher costs for RCC when related risks are considered significant.

While the above constraints essentially favour design optimisation, with a consequential objective of reducing concrete volumes, they, and all other local conditions that could impact construction, must be addressed during the dam type selection study and carefully evaluated during all subsequent stages of project development.

87 4. DESIGN FOR CONSTRUCTION & ENGINEERING EXPERIENCE

While construction must be given comprehensive consideration in the design of all concrete dam types, this is particularly true for RCC dams. Simplicity is the key element of successful RCC dam construction and achievable placement rates can quickly be impacted by complexities that can be relatively easily accommodated in other concrete dam types. To achieve an optimal dam, all concrete dam types should be designed for simplicity of construction, as speed comes with simplicity.

The decline in dam construction worldwide (outside China) over the past few decades and the reduction in the use of expatriate expertise in developing countries has resulted in a situation in which opportunities to gain and develop experience have significantly diminished. In a generation in which young engineers are reluctant to be away from cities and to spend extended periods on remote dam sites, a troubling situation has developed in which decisions on dams are being made by inadequately qualified people. Dam engineering is not a skill that is learned in a couple of years and our industry is powerless to enforce changes and systems that would ensure sustainability.

Historically, dam projects worldwide had a reputation for costs spiralling out of control. This situation had changed significantly by the 1990s and dam projects were more and more frequently being implemented in time and on budget. The lack of experience currently within the industry is now reversing this trend, with poor design and inadequate understanding of construction increasingly seeing poor results on dam projects.

5. SUMMARY

While this paper may seem to deride the benefits of RCC dams, that is not its intention. Rather the intention of the paper is to contextualise the requirements necessary to realise an optimal solution for all concrete dam types and to foster an understanding of when each type might become more, or less favourable, as well as to try to dispel the apparent perception that RCC is the best solution in all cases. As a general rule, the concept of simplicity needs to be understood as a pivotal requirement of both the design and construction of an RCC dam. When simplicity is not possible, other solutions should always be considered and when vertical construction is required as a result of access, or other constraints, CVC solutions should always be compared with RCC solutions.

Many concrete dam projects do not succeed to the level that they should due to a lack of understanding on the part of the designers and the contractors and, unfortunately, this situation continues to become more commonplace. A combination of reduced opportunity as a consequence of fewer projects being implemented and a generation of engineers reluctant to gain the necessary construction experience has resulted in a lack of knowledge of the requirements of concrete dams. The focus on RCC dams over the past 3 decades has also given rise to a perception that RCC is a universal solution and a consequential loss in understanding of all of the other types and forms of the concrete dam.

6. REFERENCES

Rocha, M. Statement of the physical problem of the arch dam. Proceedings. Symposium on the Theory of Arch Dams. Southampton. 1964.

Romana, M. DMR (Dam Mass Rating). An adaptation of RMR classification for use in dam foundations. Technology roadmap for rock mechanics, South African Institute of Mining and Metallurgy, 2003.

USSD. The Development of Dam Engineering in the United States. The United States Committee of the International Commission of Large Dams. Pergamon Press. New York.1988

Yang, H, Haynes, M, Winzenread, S & Okada, K. The History of Dams. Center for Watershed Sciences. University of California, Davis. 1999.

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