XVI ECSMGE 2015

XVI-ECSMGE-2015.ORG.UK

EDINBURGH INTERNATIONAL CONFERENCE CENTRE, EDINBURGH

13th-17th SEPTEMBER 2015

Geotechnical Engineering forInfrastructure and Development

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Proceedings of the XVI ECSMGEGeotechnical Engineering for Infrastructure and DevelopmentISBN 978-0-7277-6067-8

© The authors and ICE Publishing: All rights reserved, 2015doi:10.1680/ecsmge.60678

Hydrotesting was undertaken upon completion of grouting to validate that the target permeability and curtain width had been achieved. The acceptance cri-terion for permeability was to achieve an average of less than 3x10-7 m/s. Lower permeabilities were also targeted to minimise leakage flows and increase the durability of the grout curtain.

Figure 6 shows a comparison of the baseline and validation hydrotest results together with the target permeability. The majority of results indicate perme-abilities well below 3x10-7m/s with an average per-meability of 2 x 10-8m/s achieved.

Figure 6. Validation hydrotest results.

Where hydrotest results showed higher permeabil-ities than targeted, the grouting characteristics and exception reporting for the adjacent grout area were reviewed. Additional grouting in three validation hole stages was undertaken to mitigate higher perme-ability zones that were identified.

7 CONCLUSION

The observational design approach adopted at Wim-bleball Dam allowed the progressive development of a preliminary grout curtain design to a detailed ar-rangement by utilisation of ground investigation and field trials in advance of production grouting.

Ground investigation comprised hydrotests and downhole geophysics, including optical and acoustic televiewers, to characterise the ground. The ground investigation was used to assign the initial GIN grouting control parameters. Trial field injections were then undertaken to provide confidence that de-sired permeability targets would be achieved.

The observational approach was continued through construction of the 135m long grout curtain by monitoring of grouting characteristics against ex-pected behaviour and evaluating borehole alignment surveys to identify areas of poorly grouted ground.

New and existing instrumentation was monitored to evaluate uplift pressures during the grouting works to ensure the safety of the dam.

Validation hydrotests undertaken following com-pletion of grouting demonstrated that the target per-meability had been achieved. The formation of the new grout curtain has reduced leakage flows in the dam drainage system to historic lows.

ACKNOWLEDGEMENTS

The authors wish to thank South West Water and Wessex Water for their permission to publish this paper.

REFERENCES

Battersby, D. Bass, K.T. Reader, R.A. & Evans, K.W. 1979. Pro-motion, design and construction of Wimbleball, Journal of the In-stitution of Water Engineers and Scientists 33, 399–428.Lombardi, G. & Deere, D. 1993. Grouting design and control us-ing the GIN principle. International Water Power and Dam Con-struction 45 (6), 15-22.Penman, J.G. Palmer, M.J. Morison, A.C. Mason, D.K. & Wel-bank, J.J. 2014. Design of a new grout curtain for Wimbleball Dam. Maintaining the Safety of our Dams and Reservoirs: Pro-ceedings, 18th Biennial BDS Conference, Queen’s University, Bel-fast (Eds: Pepper, A.), 517-529. ICE Publishing, London.

Design, construction and performance of single bore multiple anchored diaphragm wall

Conception, construction et performance d’une paroi moulée stabi-lisée par tirants a ancrage multiple avec forage unique

D. Mothersille*1, R. Duzceer2 , A. Gokalp2, S. Adatepe2 and B. Okumusoglu3 1 SBMA Ltd, Harrogate, UK

2 Kasktas AS, Istanbul, Turkey 3 Kasktas AS, Moscow, Russia

*Corresponding Author ABSTRACT: This paper presents the design, construction and performance of an anchored diaphragm wall utilizing Single Bore Multiple

Anchor (SBMA) technology to support one of the largest basement excavations in Moscow, Russia. The geotechnical challenge was to en-sure the safe and viable construction of the five-level basement, which required a 25m deep excavation within a heavily urbanized location. For this purpose a 26,500 m2 diaphragm wall, with a total depth of 45m, was designed incorporating 6-levels of temporary ground an-chors. A number of trial tests were performed prior to the commencement of the anchoring works in order to establish the in situ ultimate bond capacity in the founding stratum. The ground conditions encountered at the proposed site comprised mixed soils of mainly silt inter-spersed with sand and clay lenses/pockets. The displacement of the reinforced concrete diaphragm wall and the associated effects of these movements on the adjacent structures were analyzed using finite element methods and compared with measurements of lateral displace-ments monitored during the course of excavation. The effectiveness of the SBMA technology was demonstrated by the fact that maximum cumulative recorded wall movements were restricted to less than 65 mm for the 25m deep excavation.

RÉSUMÉ: L’article décrit la conception, la construction, et la performance d’une paroi moulée ancrée avec tirants construits selon une technologie appelée Ancrage Multiple Avec Forage Unique (SBMA : « Single Bore Multiple Anchorage »). La paroi moulée est exécutée dans les alluvions perméables pour construire 5 étages en sous sol dans un site fortement urbanisé à Moscou en Russie. La paroi mou-lée de superficie totale 26500m2 est d’une hauteur de totale de 45 m, ancrée sur une hauteur de 25m par 6 rangées de tirants. Des essais ont été conduits au début des travaux d’ancrage pour établir la capacité limite des ancrages dans ce type de sol. Le déplacement de la pa-roi et la conséquence de ces déplacements sur les structures adjacentes ont été analysés par l’utilisation des méthodes de calcul en élément fini. Les déplacements calculés ont été comparés avec ceux mesurés durant les travaux d’excavation. Le type d’ancrage SBMA mis en œuvre fut efficace étant donné que le mouvement latéral maximum observé fut plus petit que 65 mm pour une profondeur de fouille de 25m dans des conditions de sol difficile.

1 INTRODUCTION

Located in a south-western district of Moscow and scheduled for completion in late 2014, Kuntsevo Pla-za, is a vibrant mixed-use complex comprising offic-es, residential, retail, restaurants, leisure facilities and five levels of basement for car parks, storage and utilities.

The unique feature of the construction is the re-taining structure which supports a 25m deep excava-tion in mixed soils of mainly silt interspersed with

sand and clay lenses/pockets. In order to facilitate a safe excavation with minimal impact to surrounding structures and utilities, a 45m deep and 80 cm thick cast-in-place diaphragm wall with 6 levels of pre-stressed temporary ground anchors were constructed. This design required anchor working loads of up to 600kN, which exceeded what could be achieved by conventional anchors in the same founding stratum. For this reason the well-documented single bore mul-tiple anchor (SBMA) technology was implemented.

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2 SOIL CONDITIONS

Two separate site investigations, undertaken in Au-gust 2009 and May 2010, confirmed that the site comprised 4 to 6m of fill underlain by a mixed soil stratum of silty clays, clayey silts and sandy silts of 20 to 22m thickness. These layers were underlain by a 16 to 18m of saturated sands, and finally an imper-vious clay layer of hard consistency.

The typical soil profile together with CPT tests re-sults and soil classification are given in Figure 1. Ge-otechnical parameters of the soil layers with respect to their identification numbers on the soil profile are listed in Table 1.

Table 1. Geotechnical parameters of soil layers.

Soil ID (kN/m³)

c (kPa)

(degrees)

E (MPa)

1 19 1 28 10 10 20 32 16 11 13 21 32 15 16 16 21 56 19 25 18 20 17 27 14 21 21 75 20 29 23 20 80 19 27 24 20 20 27 14 26 20 6 38 45 30 21 11 40 33 31 21 8 39 40 33 20 56 24 25

3 GROUND WATER CONDITIONS

Soil investigation reports also indicate the presence of 3 distinct groundwater aquifers:

Upper aquifer: Free flow between varying ele-vations from 164.7 to 167.1

Middle aquifer: Located in a sand layer (ID-27) between elevations from 148.9 to 153.8. Refer-ence to piezometric measurements conducted in this layer, confirmed artesian pressure at vary-ing levels from 151.0 to 163.2.

Lower aquifer: Located between elevations from 146.5 to 150.4. Reference to piezometric measurements conducted in this layer, con-firmed artesian pressure at varying levels from 148.2 to 159.2.

Figure 1. Typical soil profile.

4 DESIGN OF SHORING SYSTEM

Due to challenging ground conditions and ground water with artesian pressures, 80cm thick cast-in-place reinforced concrete diaphragm wall was select-ed as the main retaining element. The perimeter of the rectangular excavation measured approximately 638m and the overall depth of the diaphragm wall varied from 38m to 45m to provide a minimum of 1m penetration into the impervious hard clay. The plan view of the excavation and the typical retained section – namely K8 from Yarsevtskaya Street – are given in Figures 2 and 3 respectively.

The depth of the retaining structure and the close proximity of adjacent infrastructure and utilities re-quired the analysis of eight different sections for the staged excavation. Two different computer programs were adopted in the analysis; two dimensional finite element analysis software PLAXIS with HSSmall soil model (Benz 2007) to analyze both the wall and

surrounding soil and structures, and a locally imple-mented Russian computer software called Wall-3, which utilizes the classic beam on elastic soil algo-rithms to model only the wall itself.

Reinforced concrete design was undertaken ac-cording to structural forces and moments obtained from both computer programs. Since the design as-sumed diaphragm walls would act as permanent basement walls, the structural calculation included a crack check for a maximum crack width of 0.3mm in excavation side and 0.2mm in earth side.

Figure 2. Plan view of the excavation.

Figure 3. Typical retained section (K8)

Each stage of the construction process, used for the purposes of analysis, are listed on Table 2 and re-sulting force and bending moment envelopes on the wall were subsequently determined. After final exca-vation level was achieved, construction of basement slabs and decommissioning of temporary anchors was implemented within the Plaxis model, to facili-tate lateral load transfer from the diaphragm wall to the slabs.

Table 2. Construction Stages (Preliminary Design)

Stage No Construction 1 Construction of diaphragm wall 2 Cantilever excavation down to level 165.50

3 1st level anchors locked, and excavation to level 162 with lowering of GWT level to 161

4 2nd level anchors locked, and excavation to level 159 with lowering of GWT to 158

5 3rd level anchors locked, and excavation to level 156 with lowering of GWT to 155

6 4th level anchors locked, and excavation to level 153.8 with lowering of GWT to 152.8

7 5th level anchors locked, and excavation to level 150.4 with lowering of GWT to 149.4

8 6th level anchors locked, and excavation to foundation bottom level of 147.85 with low-ering of GWT to 146.85

During the preliminary design, computer modeling

was based on the assumption that the ground water would be lowered to a level of 1m below the respec-tive anchoring elevation at each construction stage. During the actual construction, with the utilization of 15 deep well water pumps, the ground water level was reduced to its final designated level, which was below the elevation of final level excavation and at the beginning of the staged excavation. Further mod-eling of this new situation, revealed a substantial dif-ference in the horizontal movement and the bending moment envelope of the diaphragm wall. The analy-sis results for each case are shown in Figures 5. The calculation results of Wall 3 are given Figure 6.

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2 SOIL CONDITIONS

Two separate site investigations, undertaken in Au-gust 2009 and May 2010, confirmed that the site comprised 4 to 6m of fill underlain by a mixed soil stratum of silty clays, clayey silts and sandy silts of 20 to 22m thickness. These layers were underlain by a 16 to 18m of saturated sands, and finally an imper-vious clay layer of hard consistency.

The typical soil profile together with CPT tests re-sults and soil classification are given in Figure 1. Ge-otechnical parameters of the soil layers with respect to their identification numbers on the soil profile are listed in Table 1.

Table 1. Geotechnical parameters of soil layers.

Soil ID (kN/m³)

c (kPa)

(degrees)

E (MPa)

1 19 1 28 10 10 20 32 16 11 13 21 32 15 16 16 21 56 19 25 18 20 17 27 14 21 21 75 20 29 23 20 80 19 27 24 20 20 27 14 26 20 6 38 45 30 21 11 40 33 31 21 8 39 40 33 20 56 24 25

3 GROUND WATER CONDITIONS

Soil investigation reports also indicate the presence of 3 distinct groundwater aquifers:

Upper aquifer: Free flow between varying ele-vations from 164.7 to 167.1

Middle aquifer: Located in a sand layer (ID-27) between elevations from 148.9 to 153.8. Refer-ence to piezometric measurements conducted in this layer, confirmed artesian pressure at vary-ing levels from 151.0 to 163.2.

Lower aquifer: Located between elevations from 146.5 to 150.4. Reference to piezometric measurements conducted in this layer, con-firmed artesian pressure at varying levels from 148.2 to 159.2.

Figure 1. Typical soil profile.

4 DESIGN OF SHORING SYSTEM

Due to challenging ground conditions and ground water with artesian pressures, 80cm thick cast-in-place reinforced concrete diaphragm wall was select-ed as the main retaining element. The perimeter of the rectangular excavation measured approximately 638m and the overall depth of the diaphragm wall varied from 38m to 45m to provide a minimum of 1m penetration into the impervious hard clay. The plan view of the excavation and the typical retained section – namely K8 from Yarsevtskaya Street – are given in Figures 2 and 3 respectively.

The depth of the retaining structure and the close proximity of adjacent infrastructure and utilities re-quired the analysis of eight different sections for the staged excavation. Two different computer programs were adopted in the analysis; two dimensional finite element analysis software PLAXIS with HSSmall soil model (Benz 2007) to analyze both the wall and

surrounding soil and structures, and a locally imple-mented Russian computer software called Wall-3, which utilizes the classic beam on elastic soil algo-rithms to model only the wall itself.

Reinforced concrete design was undertaken ac-cording to structural forces and moments obtained from both computer programs. Since the design as-sumed diaphragm walls would act as permanent basement walls, the structural calculation included a crack check for a maximum crack width of 0.3mm in excavation side and 0.2mm in earth side.

Figure 2. Plan view of the excavation.

Figure 3. Typical retained section (K8)

Each stage of the construction process, used for the purposes of analysis, are listed on Table 2 and re-sulting force and bending moment envelopes on the wall were subsequently determined. After final exca-vation level was achieved, construction of basement slabs and decommissioning of temporary anchors was implemented within the Plaxis model, to facili-tate lateral load transfer from the diaphragm wall to the slabs.

Table 2. Construction Stages (Preliminary Design)

Stage No Construction 1 Construction of diaphragm wall 2 Cantilever excavation down to level 165.50

3 1st level anchors locked, and excavation to level 162 with lowering of GWT level to 161

4 2nd level anchors locked, and excavation to level 159 with lowering of GWT to 158

5 3rd level anchors locked, and excavation to level 156 with lowering of GWT to 155

6 4th level anchors locked, and excavation to level 153.8 with lowering of GWT to 152.8

7 5th level anchors locked, and excavation to level 150.4 with lowering of GWT to 149.4

8 6th level anchors locked, and excavation to foundation bottom level of 147.85 with low-ering of GWT to 146.85

During the preliminary design, computer modeling

was based on the assumption that the ground water would be lowered to a level of 1m below the respec-tive anchoring elevation at each construction stage. During the actual construction, with the utilization of 15 deep well water pumps, the ground water level was reduced to its final designated level, which was below the elevation of final level excavation and at the beginning of the staged excavation. Further mod-eling of this new situation, revealed a substantial dif-ference in the horizontal movement and the bending moment envelope of the diaphragm wall. The analy-sis results for each case are shown in Figures 5. The calculation results of Wall 3 are given Figure 6.

Mothersille et al.

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Figure 5. PLAXIS Modeling results for horizontal displacement and bending moment envelope of the diaphragm wall, with prelim-inary design and actual construction (with respect to lowering of groundwater level at the beginning of the staged excavation).

Figure 6. Horizontal movement (X) and bending moment (M) en-velopes of the diaphragm wall (Wall- 3).

5 DESIGN OF MULTI UNIT ANCHORS

SBMA technology is a contemporary method for ef-fective mobilization of bond strength of a ground an-chor in soils and weak rocks. Barley (1995) and Os-termayer & Barley (2003) explained that as the bonded length of a conventional anchor increases, its efficiency decreases due to the progressive debond-ing phenomenon. At the ultimate load only a residual bond stress is mobilized along the majority of the bonded length with the peak bond stress mobilized at the distal end of the fixed anchor as illustrated in Figure 7.

Figure 7. Progressive debonding in conventional anchors.

The ultimate load in the anchor, Pult, is a function

of the ultimate in situ bond stress and the fixed an-chor dimensions corrected by a factor that accounts for the non-linearity of the bond stress distribution and progress debonding within the tendon bond length.

Where: D: Anchor drilling diameter Lk: Anchor fixed length fult: Ultimate bond stress feff : Factor of efficiency

The ratio of the total mobilized capacity of the

fixed anchor (area A in Figure 7) to a fully efficient bond strength mobilization (area B in Figure 7) has been studied by the aforementioned authors, and a re-

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lationship established for the efficiency factor (ratio of Area A to Area B) vs. the respective fixed length as shown in Figure 8.

Figure 8. Fixed bond length vs. its respective factor of efficiency.

In a multi-unit anchor with shorter efficient bond lengths, the total capacity is increased substantially due to the reduced effect of progressive debonding. At the Kuntsevo project, three units comprising 3m bond lengths with 86% of efficiency (Figures 8 and 9), was designed to increase the total anchor capaci-ty.

Figure 9. SBMA design for Kuntsevo Project.

The differences in free lengths between the units

warranted the use of a hydraulically synchronized a multiple jack setup for testing and stressing of SBMAs, which successfully sustained test loads up to 1200 kN. To reduce creep displacements to magni-tudes stipulated in the governing standards for the project (VSN 506-88 and Appendix M of BS 8081:1989), post-grouting and end-of-casing grout-

ing were also been implemented during testing (Mothersille et al. 2012).

Figure 10. Investigation testing of SBMAs with multiple jacks.

6 CONSTRUCTION

During the staged excavation, a total of 3,512 an-chors were installed. 3,442 of these were subjected to an acceptance testing using a proof load factor of 1.25 and the remainder (~10 anchors at each level) to a proof load factor of 1.5 due to requirement VSN 506-88. All anchors were locked-off to 1.1 times the specified working load of 600 kN.

The displacement of the diaphragm wall, at its highest location, was optically measured continuous-ly during the excavation using prisms socked on to the capping beam of the diaphragm wall. The final displacements of the capping beam are presented in the plan view in Figure 11. At the corner of Partizan-skaya and Yartsevskaya streets, the movement is rec-orded to be in excess of the average recorded throughout the site. The reason for this was that at this location a 2m high reinforced concrete cantile-vered wall was constructed by the general contractor and connected to the diaphragm wall. This was sub-sequently back filled to grade and incorporated a

569

Figure 5. PLAXIS Modeling results for horizontal displacement and bending moment envelope of the diaphragm wall, with prelim-inary design and actual construction (with respect to lowering of groundwater level at the beginning of the staged excavation).

Figure 6. Horizontal movement (X) and bending moment (M) en-velopes of the diaphragm wall (Wall- 3).

5 DESIGN OF MULTI UNIT ANCHORS

SBMA technology is a contemporary method for ef-fective mobilization of bond strength of a ground an-chor in soils and weak rocks. Barley (1995) and Os-termayer & Barley (2003) explained that as the bonded length of a conventional anchor increases, its efficiency decreases due to the progressive debond-ing phenomenon. At the ultimate load only a residual bond stress is mobilized along the majority of the bonded length with the peak bond stress mobilized at the distal end of the fixed anchor as illustrated in Figure 7.

Figure 7. Progressive debonding in conventional anchors.

The ultimate load in the anchor, Pult, is a function

of the ultimate in situ bond stress and the fixed an-chor dimensions corrected by a factor that accounts for the non-linearity of the bond stress distribution and progress debonding within the tendon bond length.

Where: D: Anchor drilling diameter Lk: Anchor fixed length fult: Ultimate bond stress feff : Factor of efficiency

The ratio of the total mobilized capacity of the

fixed anchor (area A in Figure 7) to a fully efficient bond strength mobilization (area B in Figure 7) has been studied by the aforementioned authors, and a re-

0

5

10

15

20

25

30

35

40

45

-6 -4 -2 0 2 4 6 8

Dept

h (m

)

Horizontal Displacement (cm)

Preliminary Design Actual Construction

0

5

10

15

20

25

30

35

40

45

-1500 -1000 -500 0 500 1000 1500 2000

Dept

h (m

)

Bending Moment (kNm)

Preliminary Design Actual Construction

lationship established for the efficiency factor (ratio of Area A to Area B) vs. the respective fixed length as shown in Figure 8.

Figure 8. Fixed bond length vs. its respective factor of efficiency.

In a multi-unit anchor with shorter efficient bond lengths, the total capacity is increased substantially due to the reduced effect of progressive debonding. At the Kuntsevo project, three units comprising 3m bond lengths with 86% of efficiency (Figures 8 and 9), was designed to increase the total anchor capaci-ty.

Figure 9. SBMA design for Kuntsevo Project.

The differences in free lengths between the units

warranted the use of a hydraulically synchronized a multiple jack setup for testing and stressing of SBMAs, which successfully sustained test loads up to 1200 kN. To reduce creep displacements to magni-tudes stipulated in the governing standards for the project (VSN 506-88 and Appendix M of BS 8081:1989), post-grouting and end-of-casing grout-

ing were also been implemented during testing (Mothersille et al. 2012).

Figure 10. Investigation testing of SBMAs with multiple jacks.

6 CONSTRUCTION

During the staged excavation, a total of 3,512 an-chors were installed. 3,442 of these were subjected to an acceptance testing using a proof load factor of 1.25 and the remainder (~10 anchors at each level) to a proof load factor of 1.5 due to requirement VSN 506-88. All anchors were locked-off to 1.1 times the specified working load of 600 kN.

The displacement of the diaphragm wall, at its highest location, was optically measured continuous-ly during the excavation using prisms socked on to the capping beam of the diaphragm wall. The final displacements of the capping beam are presented in the plan view in Figure 11. At the corner of Partizan-skaya and Yartsevskaya streets, the movement is rec-orded to be in excess of the average recorded throughout the site. The reason for this was that at this location a 2m high reinforced concrete cantile-vered wall was constructed by the general contractor and connected to the diaphragm wall. This was sub-sequently back filled to grade and incorporated a

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slope at this location. The original anchored dia-phragm wall was checked to ensure that accommo-dated this additional surcharge loading.

Figure 11. Measured horizontal displacements at capping beam.

The lateral movement of the diaphragm wall was also monitored by 12 no. of inclinometers; placed within the wall. It should be noted that the inclinome-ter readings were taken immediately after the stress-ing of first row anchors. Therefore the lateral dis-placements recorded at the capping beam, given in Figure 11, should be added to inclinometer readings to provide an indication of the total displacement. A comparison of predicted and measured lateral dis-placements of the wall for Section K8 is presented in Figure 12.

Figure 12. Predicted vs. measured displacements for Section K8.

7 CLOSING REMARKS

One of the deepest excavations recorded in the histo-ry of the capital city of Russian Federation, Moscow was undertaken ahead of programme in 13 months from July of 2011 to August of 2012. This included construction, in difficult ground conditions, of ap-proximately 28,000 m² of diaphragm wall and ap-proximately 90,000 linear metres of SBMAs.

Originally envisioned to be a lengthy and difficult top-down excavation project, which is a common construction methodology for Moscow, the project was executed successfully with detailed QA/QC pro-cedures for installation of SBMAs and continuous monitoring of wall displacements as the excavation progressed to 25m. As apparent in Figure 12, after the locking off the first row of ground anchors, to reaching the final excavation level, the horizontal displacement of the wall was restricted to less that 10mm.

On completion, the open excavation, delivered to the general contractor, comprised a safe working en-vironment for the construction of the large basement levels forming the Kuntsevo complex.

REFERENCES

Barley, A.D. 1995. Theory and Practice of the Single Bore Multi-ple Anchor System. International Symposium on Anchors in Theo-ry and Practice,. Saltzburg, Austria. pp 293-301 BSI, 1989. BS8081:1989. British Standard Code of practice for Ground Anchorages, BSI, London, UK. Mothersille, D.K.V. Bayur, A.O. & Okumusoglu, B. 2012. The performance of Single Bore Multiple Anchor trials installed in mixed Moscow soils. Proceedings of the Road Construction Con-ference, 461–470. Penza, Russia. Ostermayer, H. & Barley, A.D. 2003. Fixed anchor design guide-lines, Geotechnical Engineering Handbook Volume 2, 189-205. Pub Ernst and Sohn, Berlin, Germany. VSN 506-88 1989. Design of Arrangement and Installation of Ground Anchors, USSR Ministry of Assembly and Special Con-structions, Moscow, Russia. Benz, Thomas 2007. Small-Strain Stiffness of Soil and Its Numeri-cal Consequences, PhD Dissertation. The Institute of Geotechnical Engineering, University of Stuttgart, Germany.

Probabilistic numerical modelling of an RCC dam during construction

Modélisation numérique probabiliste de la construction d’un barrage en BCR

A.Gaspar*1,2, A. Gomes Correia1 , F. Lopez-Caballero2 and A. Modaressi2 1 Universidade do Minho, Escola de Engenharia, ISISE, Guimarães, Portugal

2 Ecole Centrale Paris, MSSMat, Châtenay-Malabry, France * Corresponding Author

ABSTRACT A probabilistic numerical modelling of a roller compacted concrete (RCC) dam construction is proposed by accounting for some uncertainties related to material properties. Probabilistic tools are applied in order to propagate uncertainties and perform a sensitivity analysis with the aim to improve the understanding of how input uncertainties will affect the output variability. A thermo-chemo-mechanical model is used in order to simulate the RCC behaviour The model couples the chemical hydration reaction at early ages with the mechanical properties evolution by introducing an ageing parameter. The sensitivity analysis is carried out using the RBD-FAST test. Temperature, hydration degree, ageing degree and cracking index outputs are assessed.

RÉSUMÉ Une modélisation numérique probabiliste de la construction d’un barrage en béton compacté au rouleau (BCR) est proposée. Quelques incertitudes liées aux propriétés du matériau sont prises en compte. Des méthodes probabilistes sont utilisés pour propager les in-certitudes et une analyse de sensibilité globale est effectuée de façon à comprendre quelles variables aléatoires vont influencer le plus la sortie du modèle. Un modèle thermo-chemo-mécanique est utilisé pour simuler le comportement du BCR. Ce modèle fait un couplage entre la réaction d’hydratation chimique au jeune âge et l’évolution des propriétés mécaniques à travers un paramètre de vieillissement. L’analyse de sensibilité est réalisée avec la méthode RBD-FAST. Les résultats de température, degré d’hydratation, degré de vieillissement et indice de fissuration sont évalués.

1 INTRODUCTION

The safety evaluation of dams has been mostly done under a deterministic basis. However, it is known that the safety of dams is a concept of probabilistic nature. That evaluation should therefore take into ac-count uncertain parameters by means of probabilistic tools as a complement to the deterministic classical tools. This work aims to be a contribution in this do-main by applying some probabilistic tools to propa-gate uncertainties and assess how those uncertainties will influence the behaviour of a roller compacted concrete (RCC) dam during its construction phase. To do so, a layer-by-layer construction of the RCC dam is simulated using a thermo-chemo-mechanical model to describe the material behaviour. That model is based on the one presented by (Cervera et al. 1999)

and enables the account for the mechanical properties dependence on the hydration reaction evolution that occurs in RCC at early ages. A global sensitivity analysis using the Random Balanced Design Fourier Amplitude Sensitivity Test (RBD-FAST) method is performed over the thermo-chemo-mechanical model in order to understand the influence of the input vari-ability of each random parameter on the model out-put. In this sense, a random character is given to some RCC properties such as the water-to-cement ra-tio or the cement content.

2 NUMERICAL MODEL

The RCC is a concrete which is placed and compact-ed by successive layers and is widely applied in dam