SLOVENIAN NATIONAL COMMITTEE ON LARGE DAMS MACEDONIAN COMMITTEE ON LARGE DAMS

INTERNATIONAL SYMPOSIUM

DAMS – RECENT EXPERIENCES ON RESEARCH, DESIGN, CONSTRUCTION AND SERVICE

Proceedings

Skopje, 17th–18thNovember, 2011

SYMPOSIUM ORGANIZED BY SLOVENIAN COMMITTEE ON LARGE DAMS MACEDONIAN COMMITTEE ON LARGE DAMS

HONORARY BOARD His Exc. Alain Brian Bergant, Ambassador of Republic of Slovenia Vlatko Chingovski, Ph.D., General Manager, ELEM, Skopje Matjaž Janežič, M.Sc., CEO, Holding Slovenian Powerplants (HSE) Prof. Matjaž Mikoš, Ph.D., Dean, Faculty for Civil and Geodetic Engineering (FGG), Ljubljana Prof. Milorad Jovanovski, Ph.D., Dean, Faculty of Civil Engineering, Skopje Prof. Andraž Legat, Ph.D., CEO, Slovenian National Building and Civil Engineering Institute (ZAG) Miho Janevski, Civil Engineering Institute »Makedonija«, Skopje Viljem Pozeb, M.Sc., CEO, Drava Powerplants (DEM) Jasna Ivanova-Davidovic, ELEM, Skopje Vladimir Gabrijelčič,CEO, Soča Powerplants (seng) Strasho Milkovski, GRANIT AD, Skopje Drago Polak, CEO, Sava Powerplants (SEL) Trajko Trpevski, BETON AD, Skopje Milica Slokar, Secretary, Defence Ministry, Administration for Civil Protection and Disaster Relief, Ljubljana Metodija Tomeski, Ministry of Agriculture, Forestry and Water Economy, Skopje Uroš Mikoš, M.Sc., CEO, IBE Consulting Engineers Boris Tanevski, Institute for Testing of materials »Skopje« Blagoj Donchev, ADING, Skopje Dobre Tasevski, SINTEK, Skopje Savo Janežič, Honorary Member, SLOCOLD Prof.Trifun Paskalov, Ph.D., Honorary President, MACOLD Vinko Koren, Honorary Member, SLOCOLD Ilija Andonov-Chento, Honorary Member, MACOLD

ORGANIZING BOARD Andrej Širca, president, SLOCOLD Ljubomir Tančev, president, MACOLD Andrej Križanovski, SLOCOLD Slavko Milevski, ELEM, MACOLD Mojca Ravnikar Turk, SLOCOLD Ljupcho Petkovski, MACOLD Andrej Sedej, SLOCOLD Matija Brenčič, SLOCOLD Slavcho Mihajlovski, MACOLD Stevcho Mitovski, MACOLD

PREPARED AND PUBLISHED BY MACEDONIAN COMMITTEE ON LARGE DAMS

PRINT PREPARATION AND DESIGN BY Stevcho Mitovski

PRINTED BY Institute for material testing and development of new technologies “Skopje” COVERAGE PHOTO: St. Petka dam, under final stage of construction, curtesy of Aleksandar Jovanovski

Symposium: Dams – recent experiences on research, design, construction and service

DESIGN AND CONSTRUCTION OF DAM RESERVOIR SYSTEM FOR COPPER MINE “BUCHIM” NEAR RADOVISH, MACEDONIA

Slavcho Mihajlovski, Civil Engineering Institute Makedonija, Skopje

Prof. Stanislav Milovanović, Faculty of Civil Engineering, University Ss Cyril and Methodius, Skopje

Prof. Sergey Churilov, Faculty of Civil Engineering, University Ss Cyril and Methodius, Skopje

ABSTRACT

The requirements of the technological process in the new plant for leaching copper mine and producing copper cathode in the mine “Buchim” near town of Radovish, involved design and construction of a reservoir system.

The reservoir system was created in suitable locations and barriers for safe retention and storage consisted of one concrete gravity dam and two earthfill dams with geo-composite screen. Due to the aggressive action of the solutions to be stored in the system and from functionality and ecological aspects they were fully laid with proper type of geomembrane lining.

This paper presents an overview of the research, design and construction of the three dams outlining certain specific issues for their realization.

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1. Introduction

Copper mine “Buchim” is located near town of Radovish, Macedonia, on a distance of about 14 km from the town. A new technological process for production of copper cathode by copper leaching was implemented. Copper leaching is performed from two disposal sites. With a help of a watering system leaching solutions with uniform distribution are added to the surface of the disposal sites.

Solutions which are drained through the disposal site are stored in small reservoirs and from there transported to the plant for the needs of the technological process. There, by using circular system, solutions are being transported back to disposal sites.

Presently, there is small a reservoir with a dam, denoted as D2, on the site which stores polluted drainage waters. Solutions from this reservoir are collected in a receiving chamber of the pump station 1, and therefrom with pumping they are transported into the hydro tailing pond.

The construction of the watering system for copper leaching in the disposal sites imposed construction of three small reservoirs. Their disposition was determined with the preliminary design in relation with the topographic terms on the site and provisions of the technological process, as shown in Fig. 1. Dam types (D3, D4 and D5) were classified according to topographical, morphological, geological and geomehanical conditions on the site.

Figure 1. Disposition of the dams and reservoirs system

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2. Bases for design

The design was assisted by existing topographic maps in scale 1:50,000 and 1:25,000 that served as geodetic bases, as well as by purposely made detailed situation plans for dam and reservoir locations.

From hydrological point of view, hydrological analyses from the report “Basic design project for water protection measures in copper mine ‘Buchim’, drainage water management and management of mine waste disposal” were used. According to the results obtained from this report, characteristic parameters used in the project were: Q10%=1.6 m3/s, Q2%=3.7 m3/s, Q1%=4.5 m3/s и Q0.1%=9.0m3/s.

Required geological and geomechanical data was acquired from purposely made site location testing, conducted by “Civil Engineering Institute Macedonia”, Skopje. For each barrier profile programmed engineering and geological tests were performed and written in separate reports, as illustrated in Fig. 2.

Figure 2. Geological testing on the profile of dam D5

According to previous geological mapping of the wider region around the construction site, several lithological elements with different geological properties were discovered.

Alluvial various-grained sands - These sediments with depth of 0.5 m were detected along the stream paths running in the inspected area. Their total volume and way of appearance have almost no important geological influence when determining the rock masses as working environment. They were defined as incoherent, small sized, mealy and clastic sediments.

Talus sand clays and clayey sands - These sediments have great influence in the definition of the overall geological properties of the rock mass within the inspected area. They are present along the left confluent running from the north-east direction of the examined location. Their maximal depth is about 10 m in the region where two streams are aggregated, whereas in the far north-east parts of the area their depth is shallower and reaches 1 - 2 m. The mixed sand and clay content of the soil contributes in definition of the shallow parts of the sediments as clayey sands, while the deeper can be identified as sandy clays. There is increased presence of fragment from dilapidated rocks in the faraway edges of this sediments right in the contact with surrounding rocks. These sediments were classified as coherent, non rock-solid, soft clastic sediments.

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Two-daze gneisses - Basically these rocks represent the lithological base of the location. They are solid metamorphic rocks which lay over sediments described previously. According to their geological properties they were classified as coherent, solid rocks, with large-sized slates. There was degradation present in many parts and they were covered with thin dust layer with thickness of 0.5 m. Their main structural, tectonic, mineralogical and petrographic properties are clearly visible in the regions where large amount of this material are present. Several jointed rock segments were discovered coupled with secondary transformation of the primary minerals into rocks. Significant representative appearance of this transformation was the process of conversion of some primary sulphide minerals into secondary sulphate, oxide, carbonated and hydroxide minerals. Moreover, the most remarkable was the process of limonitization discovered along the joints filled with such secondary materials.

As a result from performed laboratory analysis, the parameters in Eq. 1 were suggested for this lithological element.

kPac 300450 ==ϕ (1)

Geomechanical investigations to define possible deposits of local building materials were performed in a wide location around the construction site and borrow pit for homogeneous earth material for body of the earthfill dams was established.

Additional detailed investigations performed on this material at the location of the dams helped in definition of the representative properties for dam slope design as well as to estimate the available material reserves. This material was classified as sandy clay with following properties, as in Eq. 2.

kPacWmkNmkN optd 28;20%;13;/7.18;/20 03max

3 ===== ϕγγ (2)

Estimated material reserves from this material were app. 90,000 m3 which indicated that beside supplying the required quantities for earth dams D4 and D5 the location of the borrow pit could be used for overlaying the reservoir basins of all dams.

3. Design documentation

The preliminary design was done by Bulgarian company “Ionteh-Engineering” from Sofia. The general design and detailed design was made by companies “Yord” LLC from Skopje and “Jonteh-Engineering” from Sofia. The review of the design documentation was obtained from “Institute for testing materials” from Skopje.

The conceptual situation of the reservoir system was suggested in the preliminary design. This documentation proposed dam types to be used as barriers, so that D3 and D4 were suggested to be concrete gravity dams and D5 was suggested as earthfill dam. After geological and geomechanical investigations of the building site, the suggested dam types were changed according to real geological, geotechnical and geomechanical provisions. D4 and D5 were selected to be earthfill dams constructed from selected homogeneous earth material, while D3 concrete gravity dam with appropriate rationalization of the cross-section.

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4. Basic technical properties of selected dam types

4.1 Concrete gravity dam D3

The profile of the dam for live storage reservoir for failures D3 is designed as massive concrete gravity cross-section with the following properties of the cross-section (Fig. 3):

Dam crest width of 1 m for movement of people and transporting materials without vehicles;

The upstream face of the dam is vertical, while the part embedded in rock is with 10% sloping at upstream face;

The slope of the downstream face is 1:0.8 which satisfies stability conditions for the body of the dam;

All blocks are designed with additional enlargement in the foundations. This intervention provides the required width in the layout, app. 75% from the dam height and allows safe working platform for fixing the upstream formwork.

The cross-section of the dam in contact with the rock is sloped, and the upstream part is deeply buried. This structural measure provides sloped contact surface which increases the stability against sliding.

Figure 3. Typical cross-section of concrete gravity dam D3

In the longitudinal direction the dam is designed according to the topographical profile provided by the company “Ionteh-Engineering” and contains the geological profile, i.e. the level of the underground rock.

Transversely, dam D3 was separated in 5 blocks with vertical joints. In the lowermost part of the river-bed one spillway block was located (block 2), with a length of 5.8 m. It contains one spillway with clear length of 5 m and 1 m wide reinforced concrete slab bridge with slab thickness of 0.4 m passing over. The bridge over the spillway is supported by two end columns with thickness of 0.4 m. These columns stretch along the slope of the spillway block until the spillway pool. On the right of the spillway, a block 1 with length of 13 m was designed, while on the other side of the spillway other three blocks were designed with the following lengths: block 3; L=10 m, block 4; L=7.1 m, block 5; L=8 m.

The contact of the dam blocks with the rock in longitudinal direction is cascade between the block joints. Having in mind the construction sequence for each block, the contact was designed and constructed with continuous slopes, except in the areas of

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vertical joints. Vertical joints were constructed as trapezoid toothed planes. The toothed indentation provides mutual work of the concrete blocks and this makes simple construction of the joints. In the upstream face rubber seals with minimum width of 20 cm were fitted to secure impermeability of the joints. During the exploitation the separation of the joints can be neglected and depends on the temperature changes at the site. The filling of the joints in the downstream face was by elastic sealants.

The body of the dam was constructed with hydraulic concrete class MB 30, impermeability class V 60 and freezing class M 100. Standard concrete mixture was designed with 4 fraction parts and stiff consistency (low water-cement ratio). Sulphate resistant concrete was provided in the upstream face with a thickness of 0.4 m. The concreting of the blocks was in layers with thickness of 0.4-0.5 m and height up to 2 m. The contractor made a design for the concrete and dynamic plans for concreting. Particular attention was paid in the time for casting and vibration of the concrete layers before lower layers could harden. The vibration of the concrete layers allows compact concrete body along the height of the layer. After concreting of one layer and after concrete hardening, cement milk was washed away from the horizontal planes. This measure enables unreinforced concrete to reach its designed tensile strength. Reinforced concrete elements (side walls of the spillway, bridge slab and columns, spillway and etc) were constructed with standard pumped concrete class MB 30.

To prevent filtration of the solutions from the reservoir, the upstream face of the dam and the whole reservoir basin were overlaid with geo-composite material (geomembrane with thickness 1.5 mm + geotextile with weight 300 gr/m2).

4.2 Earthfill dam D4

Earthfill dam D4 was erected from homogeneous earth material (sandy clay) from the borrow pit located at dam D5. Dam faces were sloped symmetrically with slopes 1:2. Dam crest width is 4 m. The foundation of the dam in the centre part of the profile was on the existing sandy clay material with previous washing of the surface layer in thickness of 1.5-2.0 m. The total height of the dam is 12 m. The total volume of the earthfilling material was calculated with sufficient number of cross-sections and was about 11,213 m3.

As illustrated in Fig. 4, the upstream face was overlaid with geo-composite material (geomembrane with thickness 1.5 mm + geotextile with weight 300 gr/m2) to prevent solution penetration through the dam.

The dam barrier D4 creates reservoir basin with volume of 16,000 m3. The whole reservoir basin was also protected from solution penetration by using geo-composite material.

To evacuate the floods, a side-channel spillway was constructed. It is located on the right side of dam profile. The spill-crest was established at water normal level of 478 m above sea level. Authoritative water for spillway design was 100 year’s flood with flow rate of 4.5 m3/s. Because retention of the reservoir was not performed for this flood, from practical design aspects it could be considered that the spillway was designed for greater flood volumes, but with retention it could be reduced to 100 year’s flood.

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Figure 4. Typical cross-section of the earthfill dam D4

Designed overflow height of the dam is 0.56 m. The side-channel spillway consists of 5 m long side channel with slope of 5%, 25 m passage with slope of 5 ‰, two-way chute with rectangular bed with lengths 31.7 m with slope of 15.17% and 14.97 m with slope of 38.2 %, and spillway pool with length 8.5 m. Restrained water flows into the river bed over spill-weir at one side of the spillway. The downstream part of the river bed is protected by 12 m long riseberm. It was constructed from stone block paving embedded in concrete with total thickness of 0.45 m. The construction of the side-channel spillway was with reinforced concrete class MB 30.

To supply the technological process with materials from reservoir D4, a collector intervention was constructed and designed for authoritative water quantity of 200 m3/h (0.075 m3/s). The intake system is pressurized and has total length of 250 m and pipe diameter of 250 mm. The height difference of about 19.5 m was overcome with pumps which distribute the water from the failure reservoir D4 to the sedimentation pond in the geo-technological plant.

4.3 Earthfill dam D5

Earthfill dam D5 was erected from homogeneous earth material (sandy clay) from the borrow pit located at the site. Dam faces were sloped symmetrically with slopes 1:2. Dam crest width is 4 m. The foundation of the dam in the centre part of the profile was on the existing sandy clay material with previous washing of the surface layer in thickness of 1.5-2.0 m. The total height of the dam is 11.5 m. The total volume of the earthfilling material was calculated with sufficient number of cross-sections and was about 16,500 m3. As illustrated in Fig. 5, the upstream face was overlaid with geo-composite material (geomembrane with thickness 1.5 mm + geotextile with weight 300 gr/m2) to prevent solution penetration through the dam.

The dam D4 creates reservoir basin with volume of 7,500 m3. It should be noted that this volume was increased with the additional excavations of the materials needed for construction of the dam body. The whole reservoir basin was also protected from solution penetration by using geo-composite material.

To evacuate the floods, a side-channel spillway was constructed located on the right side of dam profile. The spill-crest was established at water normal level of 513 m above sea level. Authoritative water for spillway design was 100 year’s flood with flow rate of 4.5 m3/s. Because retention of the reservoir was not performed for this flood, from

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practical design aspects it could be considered that the spillway was designed for greater flood volumes, but with retention it could be reduced to 100 year’s flood.

Figure 5. Typical cross-section of the earthfill dam D5.

Designed overflow height of the dam is 0.56 m. The side-channel spillway consists of 5 m long side channel with slope of 5%, 20 m passage with slope of 5 ‰, two-way chute with rectangular bed with lengths 33.21 m with slope of 25% and 38.46 m with slope of 11.86 %, and spillway pool with length 8.5 m. Restrained water flows into the river bed over 1.5 m high spill-weir at one side of the spillway. The downstream part of the river bed is protected by 12 m long riseberm. It was constructed from stone block paving embedded in concrete with total thickness of 0.45 m. The construction of the side-channel spillway was with reinforced concrete class MB 30.

To supply the technological process with materials from reservoir D5, a collector intervention was constructed and designed for authoritative water quantity of 0.075 m3/s. The level of the intake system in the reservoir is 509.85 m above sea level. The intake system is gravitational and has total length of 262 m and pipe diameter of 250 mm. In combination with the intake, bottom outlet for empting the reservoir was constructed. From the intake to the distributing pit, the pipeline is 62 m long and has diameter of 250 mm. It has double function. The distribution pit is separated from the bottom outlet with drain pipe with diameter 250 mm which flows into the chute channel. The distribution pit is equipped with necessary shutters and additional companion equipment for normal operation in exploitation.

Considering the height of the dams, the reservoir capacity, their remote location and geomembrane lining in the basins, a set of minimum required measures for dam monitoring, and monitoring of additional structures and the reservoir were prescribed. Visual observation of the dam and the additional structures was prescribed on daily basis coupled with control and verification of the operating equipment in the intake and bottom outlet.

5. Construction of the dams

The construction of the dams was performed by company “Mashinokop” and “Gradba Promet” from Kavadarci with several subcontractors. The supply and application of the geomembrane with the geo-textile material was carried out by a specialised company from Bulgaria. The inspection during execution works of all dams was maintained by “Geocontrol” company from Skopje. For quality control and verification of the built-in materials “Civil Engineering Institute Macedonia” was appointed for earth and concrete works, while verification of the

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geomembrane quality was performed in a specialized laboratory “IRIK” - Department for quality control at factory “Ohis” from Skopje. The effective construction time for all dams was over 6 months and started on April 1st, 2011 and ended on September 30th, 2011. At the beginning of the construction works executive designs were modified according to real excavation levels. During the construction, few alterations of the design documentations were made that match real geological and engineering conditions in addition to readjustments and amendments in the technical solutions for all dams and accompanying structures. Pictures 6, 7 and 8 illustrate some of the important aspects during the process of building the dams and reservoir system.

Picture 6. Building of dam D3

Picture 7. Building of dam D4

Picture 8. Building of dam D5

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6. Conclusions

A brief overview of the most important technological aspects from the design and construction of the reservoir system with three dams for leaching copper for production of copper cathode was presented. All necessary geological, technological and other characteristic phases were pointed out.

In the end, in addition to the successful, well-timed and economical construction of the reservoir system with three dams, the authors emphasise the following facts:

The investigation, design and construction of small dams requires the same amount of time and involvement as well as for medium or large dams;

During design and construction of small dams the local positive code provisions and practice together with worldwide knowledge for such type of structures should be followed;

At the time of construction, several alterations of the technical solutions can be made to match the real on-site conditions, as illustrated with this case study, and design of dams ends together with construction of the whole system;

The presence of the design engineers for the whole time during the construction period turned out to be the right and essential decision to be made.

The appropriate selection of the parties to execute the in-situ investigations, the designers, the contractors and the inspection, together with the successful cooperation with the Investor, resulted with on-time and economically stable construction of the whole system.

7. Resources

[1] “Hydro Energo Engineering“, Skopje (2009), Basic design for measurement for protection water on Mine “Buchim”-Radovish.

[2] “Ionteh-Engineering”, Sofija (2010), Preliminary design for dams D3,D4 and D5. [3] “Civil Engineering Institute Macedonia”, Skopje (2010) , Geological and geomechanical reports

for dams D3,D4 and D5. [4] “Yord” LLC ,Skopje and “Ionteh-Engineering”, Sofia (2010) , Basic design for dams D3,D4 and

D5. [5] “Yord” LLC ,Skopje and “Ionteh-Engineering”, Sofia (2011) , Final design for dams D3,D4

and D5. [6] ICOLD-Bulletin 135 (2010), Geomembrane sealing system for dams-Design principles and

review of experience.