The Cumbidanovu dam is located on the main course of the Cedrino river, about 250 m downstream from the confluence of the Rio Sorasi, in the municipality of Orgosolo, province of Nuoro. The section of the dam is situated in the locality of Cumbidanovu, about 1.5 km linear distance from the center of the town of Orgosolo.
The purpose of the dam is to realize a reservoir with a total capacity of 13.3 hm³ of water for the irrigation of approximately 2’810 hectares of land in the territory of the Municipalities of Orgosolo, Oliena Nuoro, Lula and Dorgali.
The works started in May 2011, but in November 2013, the central-eastern part of Sardinia was hit by an unprecedentedly intense weather event (cyclone “Cleopatra”) with very heavy rainfall affecting in particular the Cedrino catchment area, and the site was inundated by an exceptional flood event that caused extensive damage to the structure and the complete destruction of site facilities.
The services now contracted by the dam operator include the reconstruction of the previously built structures and the design of a 73 m high concrete gravity dam (V=303.297 m3) with an inclined axis with a radius of 330 m, divided into 18 segments of 13 m width plus a 19th segment with a length of 10.50 m and a spillway capable of handling the exceptional flow of 1’200 m3/s.
The project also includes the construction of a bottom outlet in a metal tunnel incorporated in the structure with a maximum flow rate of 165 m3/s and a first section of the future irrigation pipeline, which will also be used as a penstock for a future HPP (not included in the contract) with a capacity of about 700 kW and an average annual production of 1.9 Wh/year during the autumn-winter period.
The Belesar arch dam, owned by Gas Natural Fenosa SLU, was built between 1957 and 1963 on the Miño River, north-west of Spain. The dam is 129 m high and impounds a reservoir of 655 hm³, used mainly for power generation. It is equipped with a bottom outlet (160 m³/s) at the central part of the dam body and two gated spillways, located at both gravity abutments (total capacity 4’000 m³/s). The total length of the dam crest is about 500 m, considering the arch (268 m) plus both abutments.
During the 1970’s, shortly after construction, permanent displacement towards upstream as well as vertical deformation of the dam body were noticed. In addition, a peripheral crack near to the foundation appeared at the downstream face. This phenomenon has been caused by and ARR reaction, producing an expansion of the dam body and a concrete swelling. The irreversible deformations have been increasing up to now with values of 10 cm in the radial direction at the dam crest, without reaching an equilibrium state so far.
After 50 years in service, Lombardi Ltd has been commissioned by Gas Natural Fenosa SLU to carry out a safety assessment of the dam, focussing on the expansive phenomenon due to the concrete alkali-silicate reactions. The expertise includes the evaluation for the medium-long term of the safety and operation conditions and the proposal of potential restauration measures, consisting probably of vertical slots using diamond wires to release the compressive stresses induced by the ARR reaction.
|Nenskra Dam - Dynamic analysis by means of numerical modelling||References_4939|
Lombardi Ltd was commissioned by Salini-Impregilo SpA to perform the Basic Design of the Nenskra HPP (installed capacity = 280 MW), which will be built on the Nenskra river in the Svaneti region (Georgia), some 260 km north-west of Tbilisi.
The HPP foresees the construction of a 130 m high Asphaltic Face Rockfill Dam (AFRD) which has a crest length of 940 m and rests completely on alluvial soils at the valley floor (max. depth = 140 m) and alluvial fan deposits at both abutments (max. depth = 60 m).
Due to the seismicity of the Caucasian region, the stability of the dam has been analysed in dynamic conditions. The behaviour of the dam body and its foundation, the asphaltic face, the dam crest and the cut-off wall has been evaluated performing fully nonlinear dynamic simulations, by means of FLAC2D and FLAC3D software. The execution of large scale laboratory tests and in-situ measurements allowed the proper definition of the mechanical parameters for the modelled materials.
The dynamic behaviour of the dam was checked for both MCE and OBE earthquakes. The maximum permanent displacements at the dam crest have been evaluated (below 1% of the height of the dam for a MCE earthquake). The permanent displacements under an OBE event have been analysed to verify the serviceability conditions.
A detailed analysis of the bituminous facing was also performed by means of the 3D model, to evaluate if the maximum asphalt deformation was concentrated either close to dam abutments or within the dam body. The maximum tensile strain of the asphalt allowed evaluating the potential of cracks onset and the consequent risk of saturation of the dam body. The behaviour of the jointed connection between the head of the cut-off wall and the inspection gallery at the upstream toe of the dam embankment has been verified during both the quasi-static phase (dam construction) and the dynamic loading.
|Pavana dam rehabilitation||References_8082|
The Pavana mixed type dam was built in the years 1923-1925.
The central part consists of a multiple arch dam on buttresses, the left part is a caisson type and the right is a concrete gravity structure.
The spillway is an independent structure, located upstream of the dam on the right bank and consist of two vanes, one with a sector gate and the other with an automatic flap gate. The spilled discharge is collected in a basin, and by means of a vertical vortex shaft is evacuated into the outlet tunnel. The same outlet tunnel receives the discharge from the intermediate outlet.
The bottom outlet is located between the dam and the spillway structure. Its inlet is regulated by two hydraulic gates and the water is released downstream by an independent tunnel.
The concrete of the structure is subject to expansive alteration phenomena due to alcal aggregate reaction (AAR), with visible cracks on the arches and buttresses.
Lombardi has been awarded with the revision of the final design and the construction design of the rehabilitation works. After completion, the historical arch-buttress static scheme will be converted in a gravity dam, preserving part of the original concrete. Structural joints will be realized to avoid adverse transmission of loads between existing and new parts. A new drainage scheme will be implemented.
The design activities include the verification and seismic enhancement of the dam and its appurtenant structures.
Lombardi Ltd. is also in charge of environmental assessments, support for authorizations, site supervision and related technical assistance.
|Frankonedou and Kogbedou Dams||References_6122|
The Frankonédou and Kogbédou hydropower complex on the Milo river in Upper Guinea involves the construction of two cascade dams with the following characteristics:
Frankonédou dam: composite dam with concrete core, height 40 m and length 305 m, provided with outlet structures and power house equipped with two Francis groups with installed capacity of 18 MW and two side rockfill dams with clay core, 403 respectively 242 m long.
Kogbédou dam: composite dam with free concrete threshold in the central part, maximum height 11 m and total length 216 m, and two rockfill dams with clay core on the sides, 267 respectively 324 m long.
|Arenal RCC gravity arch dam||References_6401|
The hydroelectric project Arenal, which uses the water of the Yaguala River, is located at the districts of Arenal and Olanchito, department of Yoro, in northern Honduras.
The project comprises the construction of a RCC arch-gravity dam with a height of 93.5 m from the foundation to the spillway crest (H=100 m to the dam crest). The dam has a RCC volume of 270’000 m³ and impounds a reservoir with a volume of 72’000’000 m³.
The works also include the construction of an upstream intake structure, a diversion tunnel of 4.52 km length with a cross section of 28.5 m², an external steel penstock consisting of two tubes with D = 2.40 m each and L = 110 m, a powerhouse with two Francis turbines with vertical axis and two bypass tunnels for the Yaguala river during construction, one of them to be used as the bottom outlet after construction. The central spillway of the dam has a capacity of more than 6’000 m³/s.
The average annual production will reach 230 GWh with an installed power of approximately 60 MW for an available net head of 129 m and a design discharge of 51 m³/s. In addition a dotation turbine with a design capacity of 1 MW will be installed.
|Les Marécottes - Rehabilitation of the Regulating Basin||References_4804|
The compensation reservoir Les Marécottes, which holds the turbined water of the Châtelard hydroelectric plant for further power generation at the Vernayaz hydroelectric plant, is owned by the Swiss Federal Railways. The downstream multiple arch dam is the characteristic element of the compensation reservoir, which was designed in 1926 by the engineer A. Sarrasin. The multiple arch dam consists in 43 thin, inclined reinforced concrete arches supported by buttresses. The total length of the structure reaches 200 m. Although no unusual behavior of the dam has been detected since commissioning, a general rehabilitation of the plant aims to increase the service life of the fairly sensitive structure.
In close collaboration with the expert Prof. E. Brühwiler (EPFL), the feasibility study was completed and optimized in order to cautiously preserve the historic monument. The first intended step is the removal by high-pressure water jetting of the pore sealing layer currently covering the surface of the buttresses. This water vapor impermeable layer caused various spalling phenomena in concrete and corrosion on the original steel reinforcement. After local treatment of the damaged zones and reprofiling with a color-matched repair mortar, the entire concrete surface is saturated with a deep impregnation. The purpose of the depth impregnation is to ensure the corrosion protection of the existing reinforcement. The upstream surface of the buttress dam is sealed by an application of synthetic PUR-based layers. The damaged zones of the ground slab of the basin and on the upstream retaining walls are restructured locally.
The rehabilitation is planned for 2019 and 2020 and includes the motorization of the vertical gates at the intake of the compensation reservoir as well as the reconstruction of the bottom outlet.
|La Punilla multipurpose scheme||References_4258|
The Punilla multipurpose project will be built on the Ñuble river, about 70 km East of Chillán in the Ñuble region (Central-South of Chile).
The main purpose of the scheme is to secure and improve the irrigation in the valley. Additionally, the scheme is equipped with a powerhouse which uses the irrigation water releases to produce power (approx. 500 GWh/yr).
The project main features are:
- a 32 m high upstream rockfill cofferdam;
- two diversion tunnels (D=10 m, L=850 m and 1'015 m) designed for an AEP
1:30 return period flood discharge of 1’800 m³/s;
- a 137 m high CFRD (Concrete Face Rockfill Dam) which impounds a
625 Mm³ reservoir;
- a gated spillway located on the left bank equipped with three radial gates
(BxH=11,0 x 17,5 m) and a chute ending with a ski jump, designed for a
discharge of 4'800 m³/s (AEP 1:1’000);
- a bottom outlet (B=2.5 m, H=3.5 m, radial gate) located in a diversion tunnel;
- a 410 m long penstock in tunnel and buried (D=5.2 to 2.2 m);
- an external powerhouse equipped with two 47 MW Francis turbines
- a bottom outlet with two Howell Bunger dissipating valves (D=1.55 m)
installed in dissipation chambers;
- a substation of 220 kV.