Leading-edge technologies in hydropower development in China

1 Introduction

China contains abundant hydropower resources due to its vast territory,many rivers,rich runoff and fall head.The installed capacity for possible technical development is about 687 million kW,and it thus ranks first in the world.Such hydropower resources are mainly concentrated around the transboundary rivers of southwest China:the Jinsha River,the Yalong River,the Dadu River,the Wujiang River,the upper reaches of the Yangtze River,the Nanpan River-Hongshui River,the upper reaches of the Yellow River,the middle reaches of the Yellow River,and other main basins and regions in western Hunan Province.Hydropower resources are also concentrated in the Fujian-Zhejiang-Jiangxi provinces,northeast China,where fourteen large hydropower bases have been planned,with a total installed capacity accounting for about 50% of possible technical exploitation amount nationwide.

From the beginning of the last century,the history of China’s hydropower development can be roughly divided into the following major stages:formidable starting point(1900-1949),unsmooth development (1950-1979),partnerassisted development (1980-1999),and breakthrough development (2000-2018) (Fig.1).Over a period spanning from the beginning of the Western Regions Development

Fig.1 Developmental trends with regard to China's hydropower installed capacity

Strategy (1999) and the West-East Power Transmission Project’s implementation till the end of 2018,the total installed capacity of hydropower reached 352.26 million MW (including about 30,000 MW for that of pumped storage),accounting for 18.5% of the total installed capacity nationwide; furthermore,annual hydroelectric generation has reached 1,232.9 billion kWh,accounting for 17.6%of electricity generation nationwide.Thus,China’s hydropower installed capacity and generation rank first in the world.With key projects planned on the Jinsha River,the Dadu River,and other rivers,which are supported by the 13th Five-year Plan,at present,the conventional hydropower installed capacity under construction is about 510 million MW.China has achieved comprehensive leap-over in terms of installed capacity and hydroelectric generation,design and construction,equipment manufacturing,and operational management.

The breakthrough developments in hydropower generation have expedited huge hydropower station projects in China.The number of as-built hydropower station projects with an installed capacity exceeding 3,000 MW reached 13 by the end of 2018 (Table1).These large-capacity projects,which utilize hydropower engineering technologies at the world’s highest level,have accordingly accumulated abundant experience and made a series of innovation achievements with regard to construction technologies for 300-meter-high arched concrete dams,200-meter-high roller-compacted concrete(RCC) gravity dams,200-meter-high concrete face rockfill dams and 250-meter-high earth core rockfill dams,largeflow discharge and energy dissipation,huge underground cavern group construction projects,complicated treatments for the foundations of high earth and rockfill dams,and reinforcements for high and steep slopes.

Table1 China's as-built hydropower station projects with an installed capacity of over 3,000 MW

No.Project Name River Installed Capacity(MW)Capacity of Reservoir (100 million m3)Time of Completion(year)Dam Type Maximum Dam Height(m)1 Three Gorges The Yangtze River 22,500 450 2012 Gravity dam 181 2 Xiluodu The Jinsha River 13,860 129 2014 Double-curvature arch dam 285.5 3 Xiangjiaba The Jinsha River 6,400 52 2014 Gravity dam 161 4 Nuozhadu The Lancang River 5,850 237 2013 Earth core rockfill dam 261.5

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Note:1.Total capacity of the reservoir in the table refers to the capacity below the check flood level; 2.There are statistical differences between different data resources.

No.Project Name River Installed Capacity(MW)Capacity of Reservoir (100 million m3)Time of Completion(year)Dam Type Maximum Dam Height(m)5 Longtan The Hongshui River River 4,800 0.18 2012 Gate dam with a 16.7 km long tunnel 7 Xiaowan The Lancang River 4,200 150 2010 Double-curvature arch dam 294.5 8 Laxiwa The Yellow River 4,200 11 2010 Double-curvature arch dam 250 9 Pubugou The Dadu River 3,600 54 2010 Earth core wall rockfill dam 186 10 Jinping-I The Yalong River 3,600 78 2013 Double-curvature arch dam 305 11 Ertan The Yalong River 3,300 58 1996 Double-curvature arch dam 240 12 Goupitan The Wujiang River 3,000 65 2010 Double-curvature arch dam 230.5 13 Guanyinyan The Jinsha River 3,000 23 2013 Mixed dam 159(proposed) RCC gravity dam 192(216.5)6 Jinping-II The Yalong 4,900(6,300)184(298)2008

China’s hydropower engineering construction projects have experienced rapid development and made several brilliant achievements.The Jinping-I Hydropower Station won the Hassib J.Sabbagh Outstanding Engineering Construction Prize of the World Federation of Engineering Organizations (WFEO),the Xiluodu Hydropower Station won the FIDIC Century Outstanding Significant Civil Engineering Prize,the Nuozhadu Hydropower Station won the FIDIC excellent engineering project prize; furthermore,the Ertan,Shuibuya,Nuozhadu,and Jinping-I hydropower stations along with several others won significant prizes such as the National Prize for Progress in Science and Technology,the High Quality Engineering Award,the Luban Prize,the Excellent Design Engineering award,the Tien-yow Jeme Civil Engineering Prize,the International Milestone Concrete Dam Project designation,and the International Milestone Rockfill Dam Project designation.

2 Leading-edge technologies

2.1 A series of technologies for constructing 300-meter-high concrete arch dams

China’s development of arch dam construction technology began relatively early,with the building of seven extra-high double-curvature arch dams that exceeded 200 m; these included the Ertan,Xiaowan,Jinping-I,and Xiluodu dams and several others.(Table2) Among them,the Jinping-I Arch Dam,the world’s highest as-built dam,reaches a maximum height of 305 m,and the Xiaowan Arch Dam has a body volume of almost 8 million m3 with a maximum base width of 73 m.The constructions of these extra-high double-curvature arch dams are often faced with engineering technology challenges such as complicated geological conditions,requirements for large quantities of foundation and slope treatments,the huge hydraulic thrusts against dams,high stress levels for the body,serious abutment stability problems,complicated anti-seismic problems,and large body volumes; thus,they impose very high requirements in terms of dam design and construction technique.

Chinese engineers have conducted a lot of work in the areas of reconnaissance,design,calculation,testing,and construction study with regard to these extra-high doublecurvature arch dams; they have thus developed various technologies such as static and dynamic safety evaluation,static and dynamic analysis models for system simulation,anti-seismic designs and construction techniques,temperature control and crack prevention for mass concrete structures,intelligent construction theory and system development,concrete construction techniques relying mainly on cable crane placing and grouting treatments for complicated dam foundations.

Table2 China's as-built 200 m above double-curvature arch dams

No.Dam Name River Dam Height(m)Dam Body Concrete(10,000 m3)1 Jinping-I The Yalong River 305 552 16 63 467 2 Xiaowan The Lancang River 294.5 892 12 73 761 3 Xiluodu The Jinsha River 285.5 698 14 60 558 4 Laxiwa The Yellow River 250 467 10 49 254 5 Ertan The Yalong River 240 779 11 56 382 6 Goupitan The Wujiang River 230.5 553 10 50 242 7 Dagangshan The Dadu River 210 635 10 52 298 Crest Length(m)Crest Thickness(m)Base Thickness(m)

2.2 A series of technologies for constructing 200-meter-high RCC gravity dams

In recent years,China has successively built several 200-meter-extra-high RCC gravity dams,such as the Longtan,Guangzhao,Huangdeng,and Guandi Dams (Table3).

Similar to normal concrete gravity dams,massive geological explorations and calculation analyses shall be undertaken to ensure the sliding stability of the high RCC gravity dam foundations.Several studies and engineering practices bring into comprehensive seepage control technologies including direct seepage proof for grout enriched RCC and two-graded aggregate RCC,dam body seepage proof,and drainage systems.

Table3 China's as-built 200-meter-high RCC gravity dams

No.Dam Name River Dam Height(m)RCC Volume(10,000 m3)1 Huangdeng The Lancang River 203 464 20 150 279 2 Guangzhao The Beipan River 200.5 410 20 159 251 3 Longtan The Hongshui River 192 761 35 169 390 4 Guandi The Yalong River 168 516 24 153 162 5 Jinanqiao The Jinsha River 160 640 21 242 Crest Length(m)Number of Dam Blocks Maximum Width of Dam Base (m)

The extra-high RCC gravity dam reaches almost 170 m in terms of maximum base width and has a volume of almost 4 million m3.The challenges include ensuring the continuous and rapid construction of large-section full-face poured RCC and controlling the temperature in the hydration heat of the dam body.To effectively reduce such temperature spikes,some projects have adopted full-section RCC with threegraded aggregate technology; some others have adopted new technologies involving combined construction of normal concrete and RCC.The RCC materials,grading,and proportioning are thus continuously optimized.The intelligent temperature control system has developed rapidly.Furthermore,new generation communication,Internet of Things,three-dimensional simulation,high precision locating,and early warning and decision support technologies have also been applied in high RCC gravity dam construction.

2.3 A series of technologies for constructing 200-m-high concrete face rockfill dams

Since the concept of the modern concrete face rockfill dam was introduced in 1985,China’s concrete face rockfill dam technologies have undergone continuous development based on international experiences.In recent years,China has built and put into operation a group of high concrete face rockfill dams exceeding 80 m in height; these include the Shuibuya and Houziyan dams and several others (Table4).At 233 m in height,the Shuibuya Dam is the world’s highest concrete face rockfill dam.

Table4 China's as-built 200-meter-high concrete face rockfill dams

images/BZ_56_213_413_2268_528.png1 Shuibuya The Qingjiang River 233 675 1,574 1.1 2 Houziyan The Dadu River 223.5 283 980 1.0 3 Sanbanxi The Qingshui River 185.5 424 962 0.92 4 Hongjiadu The Wujiang River 179.5 428 920 0.91 5 Tianshengqiao-I The Nanpan River 178 1,104 1,800 0.9

Extra-high concrete face rockfill dams have better adaptability with regard to geological conditions of foundation compared to concrete dams,while the key point lies in the material reconnaissance and selection.Through extensive research and practical applications,China has managed to develop safety assessment technologies related to dam body safety,stability safety,and structure safety;several tests and theoretical studies have revealed the impact of material strength,grain breakage properties,complicated stress paths,and rockfill rheological properties on rockfill stress and deformation.Thus,China has conducted extensive research to establish rheological models,constitutive models for dam materials,refined calculation analysis methods,and relevant software.

The divisional design for dam bodies has been developed based on the new concept of the coordinated deformation of the dam body.The technologies and facilities,including direct graded aggregate production,large-tonnage rolling,extruding slope stabilization,gravity drainage at a reduced pressure in the upper reaches of the dam body during the construction period,toe board slip-form construction,copper water stop one-step molding,and several other methods,have been applied in dam construction.The application of such technologies in real-time monitoring systems for dam body filling and compaction processes and the use of the additive mass method for rapid rockfill density detection is beneficial during a rapid dam body construction process.The improvement of concrete face structures,the optimization of concrete proportions,the improvement of construction techniques,and the adoption of temperature and moisture preservation methods have prevented cracking and ensured the durability of the concrete face.The joint water stop generally consists of a self-healing structure with combined top and bottom and new materials.

2.4 A series of technologies for constructing 250-meter-high earth core rockfill dams

Chinese engineers have rapidly developed technologies related to the construction of high earth core wall rockfill dams,leading to the successive construction of dams such as Xiaolangdi,Pubugou,Nuozhadu,and Changheba (Table5).

Table5 China's as-built 250-meter-high earth core rockfill dams

No.Dam Name River Dam Height (m) Crest Length (m) Core Wall Filling Volume(10,000 m3)Total Filling Volume(10,000 m3)1 Nuozhadu The Lancang River 260.5 628 475 3,268 2 Changheba The Dadu River 240 498 447 3,386 3 Pubugou The Dadu River 186 573 278 2,236 4 Xiaolangdi The Yellow River 160 1,667 779 5,185

High earth core wall rockfill dams measuring about 250 m and above impose lower requirements on the geological conditions of the foundation compared to concrete dams;however,they impose higher requirements in terms of exploration and testing for filling materials.A material yard reconnaissance method based on the P5 content isoline has been proposed,and the refined division of borrow pits has been realized,thus improving precision in reconnaissance.A series of in situ and laboratory tests have been performed;these included tests related to aggregate grading analysis,seepage deformation,consolidated quick shear,and dynamic strength for the filling materials.The controlled granular sizes of the maximum,fine aggregate,silt and cosmid for various dam construction materials were confirmed rationally.The designs of the dam body were divided as per the properties of the filling materials to control for compatible body deformation.

Generally,both the Duncan-Chang EB model and Shen Zhujiang’s double-yield surface elastoplastic model were adopted for conducting calculation analysis of the dam body deformation.The large-tonnage compacting machinery and the GPS-based digitalized dam filling monitoring system were adopted to monitor the types,weights,locations,speeds and rolling tracks,number of passes,and the status of construction machinery throughout the whole course and all day long.

2.5 Technologies for facilitating large-flow discharge and energy dissipation

The challenge of the large-flow discharge of high dams in China calls for complex discharge structures,energy dissipation technologies,and scour prevention methods(Table6).

Table6 China's as-built hydropower stations with a discharge power exceeding 40,000 MW

No.Project name River Discharge Power(MW)Discharge Flow(m3/s) Dam Type Height (m)1 Three Gorges The Yangtze River 97,833 102,500 Gravity dam 181 2 Xiluodu The Jinsha River 95,094 50,153 Double-curvature arch dam 285.5 3 Nuozhadu The Lancang River 67,084 37,532 Earth core rockfill dam 260.5 4 Xiaowan The Lancang River 45,948 20,688 Double-curvature arch dam 295 5 Goupitan The Wujiang River 41,999 28,902 Double-curvature arch dam 230.5 6 Xiangjiaba The Jinsha River 40,730 48,680 Gravity dam 161

An ultra-high or extra-high dam will inevitably face difficulties in terms of discharging large-flow flood waters with high head and dissipating energy.Gravity dams usually discharge water and dissipate energy through orifices in the dam body.Arch dams generally use dam orifices and bank tunnels to split the flood waters and dissipate the energy to different areas.All earth-rock dams adopt bank channels to discharge the flood waters.These dams’ designs are determined after a large number of discharge and energy dissipation schemes have been compared in combination with the project characteristics.Large-scale hydraulic model tests,decompression model tests,hydroelastic tests,and numerical simulation calculations give technical support to prevent cavitation and ensure the effectiveness of energy dissipation.With carefully designed concrete materials and optimized mix proportion,temperature rises of in terms of hydration heat,ultimate tensile value,volumetric deformation,and the drying shrinkage of the anti-scour concrete can be maintained within a reasonable range.Leveling and crack prevention methods are carried out on the concrete surface during construction.

2.6 Construction technologies of huge underground cavern groups

According to incomplete statistics,by the end of 2017,China had built more than 120 underground hydropower stations,and the total length of the underground headrace tunnel had reached about 1,100 km.Details about some of the huge underground powerhouses and super-long headrace tunnels of these hydropower stations are shown in Tables 7 and 8.

Table7 Some of the as-built huge underground powerhouses (excavation volume＞1 million m3)

No.Name of the Underground Powerhouse River Main Powerhouse(length×width×height/m)Main Transformer Cavern(length×width×height/m)Tailrace Surge Chamber(length×width×height/m)Excavation Volume (m3)1 Xiluodu (left bank) The Jinsha River 439.7×31.9×75.6 349.3×33.3×19.8 317×25×95 204 2 Xiluodu (left bank) 443.3×31.9×75.6 205 3 Nuozhadu The Lancang River 418×31×81.6 348×19×38.6 3-φ28～30×92 149.67 4 Longtan The Hongshui River 311.8×30×74.9 311.8×30×22.5 93.5×21.6×89.7 123.23 5 Laxiwa The Yellow River 388.5×30.3×74.5 397×19.5×22.5 2-φ29.6×69 114 6 Xiaowan The Lancang River 298.4×30.6×79.4 257×22×32 2-φ38×91 111 7 Jinping Ⅱ The Yalong River 352.4×28.3×72.2 374.6×19.8×34.1 192.3×26.3×23.9 109

Table8 Some of the as-built underground headrace tunnels＞16 km

No.Tunnel Maximum Buried Depth (m)1 Futang The Minjiang River 19.3 9.0 120 700 2 Yaoji The Baoxing River 18.7 4.5 166 1,300 3 Jinping Ⅱ The Yalong River 16.7 11.2 - 11.8 125 2,525 4 Jinkang The Jintang River 16.3 4.1 565 1,140 5 Maoergai The Heishui River 16.2 8.6 118 1,060 Name River Tunnel Length (km) Diameter (m) Maximum Internal Water Pressure (m)

These underground caverns are of mega scale,they have deeply buried depths,and they are also facing large ground stresses and complicated geological conditions.The superlong underground headrace tunnels have deep buried depths,long lengths,and large diameters; furthermore,they are characterized by large ground stresses and rich groundwater.Therefore,the construction of the underground cavern group has faced technical problems related to the stability of surrounding rocks,excavation and reinforcement,ventilation and smoke extraction,groundwater treatment,and large ground stresses.

In a huge underground cavern group,the layout of the main and auxiliary powerhouse caverns,main transformer caverns,and tailrace surge chambers should be reasonable.The thickness of the rock columns between caverns should suit the geological conditions; this will help to ensure the stability of the surrounding rock masses.Appropriate timing and the parameters for reinforcement design are adopted by analyzing the deformation and mechanical characteristics of the surrounding rock based on a reasonable assumption of failure law for the surrounding rocks and the anchoring mechanism of the reinforcement measures.

The stability of the cavern mainly depends on the self-stability ability of the surrounding rock masses and reinforcement measures,such as steel ribs,shotcrete anchoring and high-pressure consolidation grouting,and cavern reinforcement,which are dynamically adjusted according to the deformation and the stability of the surrounding rock masses during construction.Some countermeasures have been devised for dealing with geological problems such as large ground stress,rock burst,high-pressure large-flow water inrush,and karst development strata.Auxiliary adits should be properly arranged in accordance with the excavation and construction methods of the “multi processes in one plane and multi layers in the complex.” Ventilation and smoke extraction should be strengthened to keep construction safe.For these reasons,an advanced geological prediction system,composed of macro,both long-term and near-term,has been established.

2.7 Complicated treatments for the foundation for high dams

High dam projects have always been characterized by complicated foundation treatments,which are represented by construction on the overburden.Some typical earth rockfill dams built on thick overburden foundations are shown in Table9.

Table9 Some of the typical earth rockfill dams built on thick overburden foundations

No.Project Depth (m) Cutoff Structure Maximum Depth of Cutoff Wall (m)1 Changheba The Dadu Name River Height(m)Overburden River 240 79 Earth-core wall+foundation gallery+fully enclosed cutoff wall 51 2 Pubugou The Dadu River 186 75 Earth-core wall+foundation gallery+fully enclosed cutoff wall 78 3 Xiaolangdi The Yellow River 160 80 Earth-core wall+cutoff wall+horizontal clay blanket 82 4 Yele The Nanya River 125.5 ＞420 Asphalt-core wall+cutoff wall+gallery in the overburden+curtain 84

The key to successfully building a dam on a thick overburden is to figure out the distribution and main characteristics of the overburden; furthermore,it is important to evaluate the stability,including aspects such as sliding resistance,the seepage and deformation features of the embankment,and the foundation,through a series of static and dynamic tests and calculations.Treatments for thick overburden foundations include removal or reinforcement of the shallow-buried sand,construction of cutoff walls,and curtain grouting.After the long-term accumulations of practice and research,the fully enclosed treatment of high earth rockfill dams’ thick overburdens can be accomplished based on 200 m ultra-deep cutoff walls technology.Furthermore,a construction system for ultradeep cutoff walls by building orifices to form grooves under complicated and adverse geological conditions has been established,a technology to reinforce walls by using orifices and grooves has been developed,and innovations have been introduced into the concrete-casting walling technology.The maximum depth of these orifices and grooves can reach about 220 m in tests and 158 m in actual construction,and the maximum height of a dam built on a thick overburden foundation can reach 240 m.

2.8 Reinforcing high and steep slopes

The difficulty of excavating and reinforcing high and steep slopes is a prominent problem that challenges hydropower station construction in west China.Natural slopes with heights reaching up to 1,000 m and artificial slopes that rise hundreds of meters in height are distributed with large ground stresses and high seismic loads.Among the hydropower projects in China,the largest artificial slope is nearly 700 m in height,the largest ground stress is 34 MPa,and the maximum design for horizontal earthquake acceleration is 557.5 gal;such conditions pose extreme difficulties for the design and construction of projects in this region.

Table10 Typical high slope (＞300 m) in hydropower stations in China

No.Project Name Position Slope Height (m)1 Xiaowan High slope on the dam abutment on the right bank 700 m 2 Jinping-Ⅰ High slope on the dam abutment on the left bank 530 m 3 Longtan High slope at intake 420 m 4 Dagangshan Slope on the dam abutment on the right bank 420 m 5 Tianshengqiao-Ⅱ High slope behind the powerhouse 380 m 6 Hongjiadu High slope on the dam abutment on the left bank 310 m

Based on the geomechanical model test,numerical analyses,and the development of construction techniques,China has accumulated a wealth of practical experience in the investigation,design,excavation,and reinforcement of high and steep slopes.It has adopted technical systems with regard to the deformation and stability analysis of high slopes,excavation and construction control,and system safety monitoring.The principle of “clearance on high elevation,the lowering of excavation lines,excavation to steep gradient,reinforcement with strengthened measures,and drainage from the deep” is summed up to ensure the stability of high slopes.

3 Outlook

With the progress of the West-East Power Transmission Project,more mega- and large-scale hydropower projects are under construction or have been proposed in west China,including the regions surrounding the Jinsha River and the Yalong River (Table11).

Table11 Some of the large-scale hydropower stations under construction (installed capacity＞2,000 MW)

No.Project Name River Installed Capacity (MW)Storage Capacity(100 million m3)Commencement Date(year) Type 1 Baihetan The Jinsha River 16,000 206 2015 Double-curvature arch dam,289 m high 2 Dongwude The Jinsha River 10,200 74 2014 Double-curvature arch dam,265 m high 3 Lianghekou The Yalong River 3,000 108 2015 Earth core rockfill dam,295 m high 4 Shuangjiangkou The Dadu River 2,000 29 2015 Earth core rockfill dam,312 m high 5 Lawa The Jinsha River 2,000 25 2018 Concrete face rockfill dam,245 m high

With the support of the Belt and Road Initiative,China will become more involved in the development of water resources worldwide,particularly in terms of high dam construction.Under-construction or proposed dams that are higher than 200 m are listed in Table12.

Table12 Some of the under-construction or proposed high dam projects (＞200 m) (worldwide)

No.Dam Name Country Installed Capacity(MW)Storage Capacity(100 million m3)Height(m)1 Bhasha Pakistan 4,500 79 270 2 Bakhtiari Iran 1,500 48 315 3 Nam Ngum III Laos 440 13.16 220 4 Abula Philippine 360 39.3 234 5 Morro de Arica Peru 270 2.44 221

These domestic and international projects are to be built under severe natural conditions including high altitudes,low temperatures and anoxia,high temperatures and low pressures,and complicated topographical and geological backgrounds.There are also some technical difficulties in the construction of structures such as 300-meter-high concrete arch dams,200-meter-high RCC gravity dams,300-meter-high earth core rockfill dams,250-meter-high concrete face rockfill dams,large-flow discharge and energy dissipation,huge underground cavern groups,complicated foundation treatments,and reinforcements for high and steep slopes.These projects will provide China with opportunities to widely apply and further develop its leading technologies for hydropower development.

4 Conclusions

(1) Since the implementation of the Reform and Opening-up Policy,especially the implementation of the West-East Power Transmission Project,numerous high dams and mega-scale hydropower stations have been built on the Yangtze River,the Jinsha River,the Lancang River,the Yalong River,the Dadu River,the Hongshui River,the Wujiang River,and several other rivers; these projects have greatly propelled the development of hydropower resources in China.

(2) After extensive efforts dedicated to learning advanced foreign technologies,building up experiences,and increasing long-term research and practice,China has finally found a new view with regard to independent intellectual property rights in the field of hydropower development.China now owns a series of construction technologies for 300-meter-high concrete arch dams,200-meter-high RCC gravity dams,200-meter-high concrete face rockfill dams,and 250-meter-high earth core rockfill dams; the country also owns leading technologies for facilitating large-flow discharge and energy dissipation,construction of huge underground cavern groups,complicated treatments for dam foundations,and reinforcements for high and steep slopes.

(3) Moreover,China plans to further develop hydropower resources in the high-altitude areas of west China,including the upper reaches of the Jinsha River and the Lancang River.At the same time,the country will be more involved in hydropower developments all over the world.It is expected that China’s leading-edge technologies will be widely used and further developed in these domestic and international hydropower projects and that these projects will provide the country with the opportunity to make even greater contributions toward global development.