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Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack Dr Assa Mellal, Civil Engineer STUCKY SA, Switzerland NUMERICS IN GEOTECHNICS AND STRUCTURES - ZSoil Days - 1-2 September 2011, Lausanne Spitallamm Dam l =

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NUMERICS IN GEOTECHNICS AND STRUCTURES - ZSoil Days - 1-2 September 2011, Lausanne

Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Dr Aïssa Mellal, Civil Engineer STUCKY SA, Switzerland

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Spitallamm Dam

h = 114 m l = 258 m

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Objectives

  • 2. Reliable Numerical

Model of the Dam (incl. THM calibration)

  • 3. Seismic safety

assessment

  • 1. Crack Identification
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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Crack location and measurements

1800 1880 1860 1840 1820 1900

Section 3a

Cement grout Cement grout

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Crack location and measurements

Crack zone

6 4a 6a 4 5a 3a 5 3 1 2a 1a 2 0a

1900.74 m 1899.74 m

Block 3a Block 3a

1908.74 m

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Inclinometer measurements

5 10 15 20 25

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5

Borehole B1, CENTER UPSTREAM

5 10 15 20 25

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5

Borehole B2, CENTER DOWNSTREAM

5 10 15 20 25

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5

Borehole B3, RIGHT

5 10 15 20 25

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5

Borehole B4, LEFT

Depth from dam crest [m]

Upstream-Downstream Displacements

Measures with inclinometer

DS US DS US DS US DS US Depth from dam crest [m] Depth from dam crest [m] Depth from dam crest [m] Displacement [mm] Displacement [mm] Displacement [mm] Displacement [mm]

Mass concrete "Trog" concrete Face concrete 1911.24 Crest 1885.0 Borehole B1, Center Boreholes B2, B3 and B4

Initial measure: 01.10.1996 Reservoir level: 1898.90 Reference measure: 04.03.1997 Reservoir level: 1862.36 Downstream view 1 2 3 3a 4 5 6

1900 1880 1860 1840 1820 1800

LEFT BANK RIGHT BANK

B3 B4 B1& B2 1885.0 1911.24 Crest

Range 2003 Range 2001 Range 2005 Range 2004 Range 2002

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Crack location and measurements

1800 1880 1860 1840 1820 1900

Section 3a

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Numerical modelling approach

3D Model Transient Thermal analysis Thermal calibration 3D Model Mechanical analysis Displacement calibration TM Coupling Static and dynamic evaluation Stability analysis global and local Retrofit proposal 3D FE Model dam incl. crack + foundation

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Geometry and Finite element mesh (3D)

Rock: Linear elastic Concrete: Linear elastic Solid BC Pre-existing crack: Frictional contact

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Tensile (major principal stress) stress fields Full reservoir – No thermal effects

Zone of potential horizontal cracking

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Progressive crack opening Full reservoir – no thermal effects No crack model Horizontal crack model Complete crack model

S1=190 kPa S1=80 kPa S1=20 kPa S1: major principal (tensile) stress

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

0a 4a 2a 5a 6a 5 6 4 3a 1a 2 3 1

1899.74 m 1900.74 m 1830 m

Section 3a

Pre-existing crack zone

Crack configuration at the interface Face / Intermediate concrete

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Loading condition Combined effects Water level + Air-water temperature + solar radiation

Air temperature + downstream solar radiation Air temperature + upstream solar radiation

Water temperature Varying level

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Thermal evolution 2008

February May August November

UNIT [°C]

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Results of thermal analysis Comparison with the measurements

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Results of thermal analysis Comparison with the measurements

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T1 (T1)

Measured Model

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T2.2 (T3)

Measured Model

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T2.3 (T4)

Measured Model

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T2.1 (T2)

Measured Model

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T3.4 (T8)

Measured Model

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T3.3 (T7)

Measured Model

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T3.2 (T6)

Measured Model

  • 6.0
  • 4.0
  • 2.0

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Temperature (°C) Time (date)

  • Sec. 3a T3.1 (T5)

Measured Model

Results of thermal analysis Comparison with the measurements

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Thermo-mechanical analysis

Model vs. measured displacement

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Thermo-mechanical analysis

Model vs. measured displacement

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Thermo-mechanical analysis

Model vs. measured displacement

(with assumed linear deviation)

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Thermo-mechanical analysis

Crack Opening Model vs. joint meter measurements

(with assumed linear deviation)

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Crack opening

Extreme US calculated displacement: 18.65 mm (13.08.2003)

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Crack opening

Major principal stress at crack tip:

(+) Tensile / (-) Compressive stresses

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Comments on model validation

  • Thermal calibration using daily temperature measurements leads to good

agreement between calculated and measured temperatures at all dam levels

  • Displacement (daily) calibration shows good agreement between calculated

and measured diplacements below crack level

  • Calculated displacements of dam’s upper arch follow the same trend and
  • rder of magnitude as measurements, but irreversible displacements were

not reproduced. When a linear deviation is assumed, there is a close correspondance between calculated and measured top displacements

  • Calculated crack opening (max) is close to joint meter measurements (~4 mm)
  • Stresses at lower extremity of the crack (~1830 msm) are permanently

compressive under seasonal load variations (hydrostatic pressure)

Proposed finite element model reasonably simulates dam’s mechanical behaviour under transient static loads (mechanical + thermal). It is therefore considered as suitable to evaluate the dynamic response of the dam

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SLIDE 25
  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Numerical modelling approach

3D Model Transient Thermal analysis Thermal calibration 3D Model Mechanical analysis Displacement calibration TM Coupling Static and dynamic evaluation Stability analysis global and local Retrofit proposal 3D FE Model dam incl. crack + foundation

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Input for dynamic analyses

  • Accelerograms: Friuli Sept. 15, 1976 earthquake, San Rocco station
  • Peak ground acceleration: 0.17 g (OBE)
  • Dynamic elastic modulus: Edyn = 1.25 Estat
  • Damping: 5%
  • Water level: full reservoir level (1908.74 msm)
  • Temperature gradient:

– Winter: T(15.11.2007) - T(30.04.2007)

  • Concrete strength: fDyn = 1.5 x fStat

fc (Stat/Dyn), MPa ft (Stat/Dyn), MPa Mass concrete 25 / 37.5 3 / 4.5 Face concrete 49 / 73.5 3 / 4.5 « Trog » concrete 36 / 54 3 / 4.5 Source: Stucky Report no. 4400/4013, July 2003

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

log ah = 0.26 IMSK + 0.19 ah = 0.17 g

Spitallamm

IMSK = 7.8

Return Period 1’000 years (OBE)

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Seismic safety assessment

Accelerograms and corresponding response spectra

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Temperature field 30.04.2007 (reference)

T

air = 6.7°C, Twater = 2.6°C, Water level: ~1860 m

DS view US view

LB RB RB LB

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Temperature field 15.11.2007 (Winter)

T

air = -11.2°C, Twater = 3.5°C, Water level: 1901.4 m

DS view US view

LB RB RB LB

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Temperature gradient

Winter thermal gradient DS view US view

LB RB RB LB

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Principal stresses

Self-weight

smin = -0.2 MPa smax = 0.1 MPa smin = -1.4 MPa smax = 0.0 MPa

DS view US view

LB RB RB LB

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Principal stresses

Hydrostatic pressure: full reservoir level (1908.74 msm) DS view US view

LB RB RB LB smin = -1.3 MPa smax = -0.1 MPa smin = -0.8 MPa smax = 0.2 MPa

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SLIDE 34
  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Principal stresses

Temperature gradient: DT Winter DS view US view

LB RB RB LB smin = -0.1 MPa smax = 1.3 MPa smin = -0.3 MPa smax = 0.0 MPa

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SLIDE 35
  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Principal stresses

Self-weight + Full reservoir level (1908.74 msm) DS view US view

LB RB RB LB smin = -1.2 MPa smax = -0.1 MPa smin = -1.3 MPa smax = -0.8 MPa

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SLIDE 36
  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Principal stresses

Self-weight + Full reservoir level (1908.74 msm) + DT Winter DS view US view

LB RB RB LB smin = -0.8 MPa smax = 0.9 MPa smin = -1.4 MPa smax = -0.8 MPa

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Absolute displacement Major principal stress

Dynamic analysis

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

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10 20 30 40 50 5 10 15 20 25 30

Displacement (mm) - DS / + US Time (sec)

Dynamic upstream-downstream displacement

Full reservoir level (1908.74 msm) – OBE – 5% damping - Winter

(a) (b) (c) (e) (+) (-) (d)

(a) Construction stages (b) Hydrostatic load (1908.74 masl) (c) Temperature gradient (d) Dynamic properties (e) Dynamic load

5.6 mm @13.22 s

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

5 10 15 20 25 5 10 15 20 25 30

Absolute crack opening (mm) Time (sec)

Dynamic absolute crack opening

Full reservoir level (1908.74 msm) – OBE – 5% damping - Winter 12.5 mm @13.24 s

(a) (b) (e) (d) (c)

(a) Construction stages (b) Hydrostatic load (1908.74 masl) (c) Temperature gradient (d) Dynamic properties (e) Dynamic load

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Stress evaluation locations

A B C D

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

  • 2
  • 1

1 2 3 4 5 6 5 10 15 20 25 30

Stress (MPa) - Compression / + Tension Time (sec)

A (1830 m) B (1850 m) C (1880 m) D (1900 m)

Dynamic major principal stresses S1

Full reservoir level (1908.74 msm) – OBE – 5% damping - Winter

(a) (b) (c) (e) (d)

A B C D

3.7 MPa @13.33 s

(a) Construction stages (b) Hydrostatic load (1908.74 masl) (c) Temperature gradient (d) Dynamic properties (e) Dynamic load

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Dynamic principal stresses at time of extreme S1 (t = 13.33 s)

Self-weight + Full reservoir level (1908.74 msm) + Earthquake (OBE)

smin = -0.7 MPa smax = 3.7 MPa smin = -1.2 MPa smax = -0.7 MPa

DS view US view

LB RB RB LB

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Stability analysis of a detaching bloc

1899.74 m 1900.74 m 1830 m

Lift joint opening Tensile vertical stresses Overturning Sliding

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Stability analysis of a detaching bloc

Wh Qh Qv G U 1908.74 msm Wv 1899.74 msm 1911.24 msm

SSF = 5.25 (sliding) OSF = 1.43 (overturning)

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Comments on stability analysis – Both sliding and overturning stability are satisfied for OBE earthquake, with full reservoir level (1908.74 msm) – Water pressure has a stabilizing effect against sliding towards upstream (hydrostatic) but a destabilizing effect on overturning (hydrodynamic)

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  • A. Mellal

Numerics in Geotechnics and Structures 2011 - Z_Soil Days - 1-2 September 2011, Lausanne, Switzerland Evaluation of the behaviour of an arch-gravity dam featuring a pre-existing crack

Conclusion – 3D finite element of an arch-dam including a crack – Combined effects of thermal, static and dynamic mechanical loads – Successful evaluation of main dam’s behaviour characteristics including crack evolution in time – Dynamic analyses show that seismic safety of the dam is guaranteed regarding both concrete strength and stability against sliding and

  • verturning