1 Different approaches to face AAR concrete ageing Pracana and Alto Ceira Dams
2 ALTO CEIRA DAM Evaluation scenarios for renewal the hydro electrical scheme Main Characteristics of the new dam Dam Characteristics Historical Data Signs of concrete ageing Studies for diagnosis PRACANA DAM Conclusions for dam rehabilitation Rehabilitation of the dam and up rating works Monitoring system after rehab. Conclusions for Alto Ceira Dam Conclusions for Pracana Dam FINAL CONCLUSIONS
3 ALTO CEIRA DAM
4 ALTO CEIRA DAM Sta.LUZIA HYDRO ELECTRIC SCHEME Alto Ceira dam Tunnel diversion Sta.Luzia dam Penstock Powerhouse
5 ALTO CEIRA DAM CHARACTERISTICS THIN ARCH DAM - height 36 m - crest lenght 120 m - year of completion central cantilever thickness, crest - 1,5 m base - 4,5 m - reservoir capacity 1.2 x10 6 m 3
6 LOCATION AND DAM LAYOUT
7 HISTORICAL DATA Year of completion Since first impounding - Anomalous behavior detected Until the decade of 90 - Several studies carried out Since Studies concluded that the anomalous behavior was mainly by AAR reactions Improvement of the monitoring system Evaluation studies recommended a complete rehabilitation of the dam Evaluation scenarios for renewal the hydro-electrical scheme New dam design and preparation for tender construction
8 SIGNS OF CONCRETE AGEING Progressive horizontal upstream displacements Progressive upward vertical displacements Intensive cracking related with the swelling process
9 SIGNS OF CONCRETE AGEING Progressive horizontal upstream and vertical upward displacements Plumbline in ED Block and rockmeter in the GF Block 670 Alto Ceira Dam - Plumbline FPD Alto Ceira dam - Rockmeter EF ,0 4,0 Water level Air temperature ,0 Water level Air temperature ,0 0,0 Displacement (mm) -4,0-8,0-12,0-16,0-20,0-24,0 Displacement (mm) -2,0-4,0-6,0-8,0-10,0-28,0-32,0 Out-86 Radial Out-88 Out-90 Tangencial Out-92 Out-94 Out-96 Out-98 Out-00 Out-02 Out-04 Out-06-12,0-14,0 Abr-97 Abr-98 Abr-99 Abr-00 Abr-01 Abr-02 Abr-03 Abr-04 Abr-05 Abr-06 Abr-07
11 SIGNS OF CONCRETE AGEING Intensive cracking related with the swelling process
12 SIGNS OF CONCRETE AGEING Intensive cracking related with the swelling process
13 STUDIES FOR DIAGNOSIS Visual inspection 1994 and Visual inspections and ultrasonic wave test Petrography analyses and expansion tests on concrete samples 1995 and Evaluation of the structural safety Anualy since Structural behavior reports
14 STUDIES FOR DIAGNOSIS Cracking evolution by USPV measurements and visual inspections /2001 Not only the number of cracks increased but also the depth of cracking
15 STUDIES FOR DIAGNOSIS Petrographical analyses on samples of dam concrete /2001 Gel formation around aggregate particles
16 STUDIES FOR DIAGNOSIS Petrographical analyses on samples of dam concrete /2001 Cracking in the paste matrix due to AAR swelling process The aggregates constituents are mainly crypto crystalline quartz, feldspar and metapellitic rock fragments.
17 STUDIES FOR DIAGNOSIS Evaluation of the structural safety Due to: The great heterogeneity of the swelling process with estimated potential expansions until to 650x10-6 The intensive cracking special concentrated on the kidneys and on the crest; The relatively great depth of the cracks in a thin arch structure; Relative intensive leakage through the body dam: It was not possible to estimate the stresses in the structure as well as to predict the future behavior of the dam.
18 EVALUATION SCENARIOS FOR RENEWAL THE HIDRO-ELECTRIC SCHEME 1 Downstream strengthening of the existing dam by a new structure 2- Demolition of the dam and construction of 2 smaller dams and a system of canals 3 - Lowering the N.W.L after rehabilitation of the existing dam and construction of pumping station (no drawings) 4 - Construction of a new dam downstream of the existing one
19 EVALUATION SCENARIOS FOR RENEWAL THE HIDRO-ELECTRIC SCHEME 1 Downstream strengthening of the existing dam by a new structure Similar volume of concrete as a new dam Lower foundation Empty reservoir for construction
20 EVALUATION SCENARIOS FOR RENEWAL THE HIDRO-ELECTRIC SCHEME 2- Demolition of the existing dam and construction of 2 smaller dams whose reservoirs are connected by two canals or by one canal and a tunnel Environmental impact Total demolition of the existing dam Large amount of civil works Higher volume of concrete Existing dam
21 EVALUATION SCENARIOS FOR RENEWAL THE HIDRO-ELECTRIC SCHEME 4 - Construction of a new dam downstream of the existing one THE SELECTED SOLUTION New dam Existing dam
22 MAIN CHARACTERISTICS OF THE NEW DAM ARCH DAM - height 41 m - crest lenght 137 m - central cantilever thickness: crest - 2,0 m base - 5,5 m - reservoir capacity 1,3 x10 6 m 3
23 CONCLUSIONS - ALTO CEIRA DAM ARR was the mainly cause of the concrete deterioration Very high heterogeneity swelling process in a very thin structure causes a lack of possibilities for structure evaluation; Remedial works was not considered an adequate solution for an intensive cracked thin arch; The evaluation of different scenarios for renewal the hydro electric scheme advised (for economic, environmental and social reasons) the abandon of the existing dam and construction a new one.
24 PRACANA DAM Hydro electric scheme before 1993 Hydro electric scheme after refurbishment
25 DAM LOCATION
26 DAM CHARACTERISTICS BUTTRESS CONCRETE GRAVITY DAM - 12 buttresses with diamond shaped heads - 3 massive blocks in each bank - height 60 m and crest lenght 245 m - buttresses head span 13 m - minimal thickness of the webs 4m - reservoir capacity 112x10 6 m 3
27 HISTORICAL DATA 1948/ Construction of the scheme Since Several anomalies in the dam were detected and continuously increased Restrictions to exploitation reservoir level 1972 and 73 - Unsuccessful repair works The scheme is owned by EDP The reservoir is emptied due to: insufficient capacity of the spillway progressive deterioration of the dam low structural safety factor Conclusion of the rehabilitation studies Beginning of the works on site Conclusion of the civil engineering works and refilling of the reservoir
28 SIGNS OF CONCRETE AGEING CRACKING - Intensive cracking on the upstream face
29 SIGNS OF CONCRETE AGEING CRACKING - Important cracks on downstream face in the transition between the web and the head of the buttresses; - Significant vertical cracks in the webs, near the foundation (construction joints); - Cracks along horizontal construction joints LEAKAGE - Important seepage through horizontal cracks (concrete lift joints) with excessive carbonation
30 SIGNS OF CONCRETE AGEING DISPLACEMENTS - large displacements were measured by geodetic methods - quantitative analysis of the observation results showed non-reversible displacements with the following increasing rates: horizontal displacements (downstream): 1,2 mm/year vertical displacements (upwards) : 1,0 mm/year SWELLING - expansions were measured by no stress strainmeters
31 SIGNS OF CONCRETE AGEING CONSTRUCTION CONDITIONS THAT MAY HAVE CONTRIBUTED TO THE ANOMALIES - Deficient treatment of concrete lift joints; - Deficient concrete compaction (honeycombs); - Use of different cement types from various sources; - Heterogeneity of the aggregates (of quartzitic and metapellitic nature)
32 SIGNS OF CONCRETE AGEING CONSTRUCTION CONDITIONS THAT MAY HAVE CONTRIBUTED TO THE ANOMALIES Fairly shallow foundations along the banks (downstream) Foto Fundação Contrafortes No consolidation treatment of the foundation rock
33 CRACKING - mapping of the cracks STUDIES FOR DIAGNOSIS upstream face during a reservoir drawdown downstream face, exhaustively, in 2 buttresses - monitoring of cracks with jointmeters - inspection with boreholes - laboratory sliding tests over 150 mm diameter samples tests performed before and after grouting the samples using cement slurry, epoxy and polyester resins
34 CRACKING STUDIES FOR DIAGNOSIS 80% of the cracks show openings less than 0,5 mm only a few of them had depths about 0,5-0,6 meters Levantamento fissuras almas
35 CONCRETE SWELLING STUDIES FOR DIAGNOSIS Chemical analysis of the reservoir and leaked water Chemical analysis of the deposits in cracks and of the aggregates Mineralogical and petrographic analysis of the aggregates Standard and non-standard expansion tests
36 STUDIES FOR DIAGNOSIS Non-standard potential concrete expansion tests EXPANSION TESTS OF CONCRETE CORES SAMPLED FROM BUTTRESS P1 OF PRACANA DAM 1,6 EXPANSION (mm / m) 1,4 1,2 1 0,8 0,6 0,4 0, Age of measurements (Days) P1 I39( ) P1 I39( ) P1 I38( ) P1 R37( ) P1 I38A( ) P1 R38( )
37 STUDIES FOR DIAGNOSIS Mineralogical and petrographic analysis of aggregates and cement paste Coarse Agg. Fine Agg. Rounded particles from 5mm up to 80 mm of different rock types mainly quartz and metagreycacke fragments, also graphitous phyllite, quartzite and sandstone are also important, but less microcline, plagioclase, muscovite, biotite and dolerite fragments. Some of the coarse agg. are elongated and foliated with extensive cracks penetrating these stones. Angular grain particles, 0-5mm, mainly quartz and feldspar, but minor amounts of micas and clay lumps.
38 STUDIES FOR DIAGNOSIS Mineralogical and petrographic analysis of aggregates and cement paste Cement paste Portland-type cements with at least 1% alkalis. A lot of unhydrated cement is still left and very severe non homogeneous paste are seen. Along cracks the water/cement ratio is very high (>0,70) and is here totally carbonated. In non carbonated parts relatively coarse crystals of portlandite are seen filling microcracks along the aggregates surface.
39 STUDIES FOR DIAGNOSIS Mineralogical and petrographic analysis of aggregates and cement paste Final conclusions from the petrographic analyses Gel formation and ASR were observed in all samples of concrete which developed severe intensive cracking. The composition of the concrete, suffering of insufficient amount of fines (<0,125mm) and high w/c ratio, produced some bleeding during construction which led to high capillarity porosity and open channels along the interface with the aggregates. The presence of water in bleeding channels removed alkalis from cement and after from the feldspars reacting with SiO 2 - from quartz fragments forming a siliceous gel.
40 STUDIES FOR DIAGNOSIS Carbonation around a quartz particle. Filled crack in paste matrix by epoxi resin
41 STRUCTURAL EVALUATIONS STUDIES FOR DIAGNOSIS In-situ experimental stress evaluations, using large flat jacks Numerical structural analysis (F.E.M.) simulation of the construction stages and of the differential concrete cooling simulation of usual structural scenarios simulation of uniform and differential expansion between the head and web of buttresses simulation of concrete weakness Stresses associated to usual operation scenarios were not significant and did not justify either measured displacements or observed cracking. Calculated displacements matches quite well those observed when different expansion rates were assumed for the head and web of the buttresses.
42 STUDIES FOR DIAGNOSIS SAFETY CONDITIONS OF THE DAM Sliding along horizontal cracks was identified as the critical safety scenario. The lowest residual friction strenght obtained from sliding tests was considered, and cohesion was neglected. Considering uplift acting into the cracks, the value of the safety factor is 1,31. Without uplift into the cracks safety factor value increases to 1,81.
43 IMPROVEMENT OF THE DAM MONITORING Instrumentation of cracks STUDIES FOR DIAGNOSIS Installation of thermometers, foundation rockmeters and inverted plumblines Improvement of geodetic monitoring system
44 CONCLUSIONS FOR THE DAM REHABILITATION The expansion phenomenon in the concrete was considered the main cause of the dam deterioration. This expansion is only developed in the presence of infiltrated reservoir water. Stability conditions should be suitable if uplift effects into concrete cracks could be avoided. Integrity of dam s concrete should be achieved. A global foundation treatment should be undertaken. A careful dam monitoring program should be set up.
45 THE REHABILITATION OF THE DAM AND UPRATING WORKS DAM REHABILITATION Foundation struts between buttresses webs Upstream foundation plinth Foundation treatment Concrete regeneration Upstream watertight system Improvement of monitoring system CONSTRUCTION OF AN AUXILLIARY FRONTAL SPILLWAY POWER HOUSE UPRATING (construction, in the dam body, of the in the intake for the new generation unit)
46 THE CONCRETE TREATMENT A Scaffolding enabled Individualized Crack Treatment Mass Treatment The cleaning of all faces of the dam by high pressure sand and water jets. The mapping and classification of all the cracks. Stabilized Cement Grouting of the cracks with openings larger than 0.5 mm (about 20% of the total length of the mapped cracks). Injection of epoxy resins based on systematic drilling pattern.
47 THE CONCRETE TREATMENT SCAFFOLDING
48 THE CONCRETE TREATMENT INDIVIDUALISED TREATMENT OF CRACKS BY INJECTION OF CEMENT STABILIZED GROUT
49 THE CONCRETE TREATMENT MASS TREATMENT BY INJECTION OF EXPOXI RESIN EXECUTED FORESEEN The lower part of the buttresses webs were systematically injected with a cement grout
50 THE UPSTREAM IMPERVIOUS SYSTEM MAIN AIMS Prevent the contact between the concrete and the reservoir water (chemical protection). Prevent the action of uplift into the cracks (safety condition). MAIN CHARACTERISTICS FOR THE GEOMEMBRANE PVC membrane, 2,5 mm thick, with a heat bounded geotextile (applied over a HDPE geogrid for drainage purposes). Mechanical fastening system composed by stainless steel vertical profiles (Sibelon/Carpi System). Mechanical connections of the membrane around the intakes and bottom openings, and around the supports of the trash racks rails.
51 THE UPSTREAM IMPERVIOUS SYSTEM PVC GEOMEMBRANE GEOMEMBRANE DRAINAGE UPSTREAM FACE DRAINAGE PIPE CONSOLIDATIONG GROUTING PLINTH DRAINAGE PIPE ORIGINAL CURTAIN CURTAIN IMPROVEMENT W/ CHEMICAL GROUTING NEW DEEP CURTAIN
52 THE UPSTREAM IMPERVIOUS SYSTEM
53 UPSTREAM PLINTH
54 CONSTRUCTION OF THE NEW AUXILLIARY FRONTAL SPILLWAY CONSTRUCTION OF THE NEW INTAKE AND THE NEW POWERHOUSE
55 MONITORING SYSTEM
56 MONITORING SYSTEM Vertical displacements on the crest (levelling) (+ upwards) (*) Vertical displacements between levels 54.0 m and m (borehole extensometer) (+ upwards) (*) (*) a) Observed values; b) Calculated values; c) Time effect component of the calculated values;
57 FIRST PERIOD OF OBSERVATION (LNEC, ) Quantitative analysis of plumblines results give indications of a non-reversible horizontal displacements towards downstream with a maximum rate of 0,7 mm/year Rockmeters along the head of buttresses accuses upwards displacements increasing about 0,3 mm/year The multiple rockmeters pointed out that 50% of the expansion is verified in the upper part of the buttresses Dam crest leveling seems to confirm the results given by the rockmeters
58 CREST DISPLACEMENTS ON BUTTRESSES P2, P6 AND P11 (Since first filling-1952)
59 CONCLUSIONS - PRACANA DAM Results of Pracana dam observation show evidences that the expansion phenomenon in the concrete is yet present, but it was rather attenuated by the rehabilitation works. Continuous monitoring of the expansion phenomenon evolution is advisable. The upstream membrane seems to be effective to the concrete protection of the dam
60 FINAL CONCLUSIONS TWO DAMS AFEECTED BY AAR LED TO DIFFERENTE APPROACHES FOR RENEWAL THE RESPECTIVE HYDRO ELECTRICAL SCHEME WAS CARRIED OUT IN THESE TWO CASES INTENSIVE MONITORING AND STRUCTURAL EVALUATION ARE THE MAINLY CONDITIONS FOR THE REHABILITATION STUDIES THE DIAGNOSIS AND RESEARCH THROUGH THE MATERIALS REPRESENTS VERY IMPORTANT INPUTS FOR ANY DECISIONS ABOUT REMEDIAL WORKS AND LONGEVITY OF THE STRUCTURES
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