UPLIFT PRESSURES FOR SEISMIC AND POST-SEISMIC SAFETY ASSESSMENT OF GRAVITY DAMS

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D, UCB 1982-86), Ecole Polytechnique, Montreal

1 1 UPLIFT PRESSURES FOR SEISMIC AND POST-SEISMIC SAFETY ASSESSMENT OF GRAVITY DAMS Pierre Léger (Ph.D, UCB ), Ecole Polytechnique, Montreal University, Canada Pr. A.K Chopra Retirement Symposium Oct. 2-3, 2017

2 UPLIFT PRESSURES FOR SEISMIC AND POST-SEISMIC SAFETY ASSESSMENT OF GRAVITY DAMS 2 1. Computational tools to investigate seismic (postseismic) gravity dam stability and uplift pressure assumptions (Pr. Chopra) 2. Seismic uplift pressures during earthquakes 3. Post-seismic uplift pressures 4. R&D Perspectives

SEISMIC. DAMS.. Contributions 3 (21/09/2017) Seismic+Dams = 908 000 results A.K. Chopra+Dams = 336 000 results A.K. Chopra+Dam+Koyna = 153 000 results A.

3 SEISMIC. DAMS.. Contributions 3 (21/09/2017) Seismic+Dams = results A.K. Chopra+Dams = results A.K. Chopra+Dam+Koyna = results A.K. Chopra+Dam+Koyna+Seismic results A.K. Chopra+Dam+Koyna+Seismic+ 1 result Dynamic of Structures (5 th Ed).

4 «USER FRIENDLY» COMPUTATIONAL TOOLS TO STUDY MODELLING ASSUMPTIONS Fully cracked lift joint (J) 4 Resultant Pseudo-dynamic RSA - (CADAM2D) Pseudo-dynamic RSA - (CADAM3D) Rigid body dynamics (RS-DAM) Rocking-Sliding

5 KOYNA DAM 1967 Earthquake (M6.2) 5 Koyna Dam FE Seismic cracking analysis 1967 Earthquake water DAM-FOUNDATION-RESERVOIR INTERACTION MECHANISMS PRESSURISED WATER PENETRATION IN SEISMIC CRACKS (? )

6 TRANSIENT UPLIFT PRESSURES DURING EARTHQUAKES 6 (a) Opening Mode (b) Closing Mode F I F I Opening Closing Closing Decompression (Opening) Initial U Initial U U Decreases due to rapid opening Increa se in U Zero U Full U in opened crack

7 UPLIFT PRESSURES IN SEISMIC CRACKS 7 DAM SAFETY GUIDELINES CADAM SEISMIC ANALYSES 33m opening Inertia forces closing Initial uplift distribution Zero uplift pressure in crack (USBR 1995, CDSA 1997 (high seismicity)) CRACKING: 7.6% of base UPLIFT: 2237 kn SSF: 3.70 CRACKING: 21.9% of base UPLIFT: 2663 kn SSF: 3.30 Pre-earthquake uplift pressures in crack (USACE 1995, FERC 1991, CDSA 1997 (low seismicity)) Full uplift pressures in crack (ICOLD 1986) CRACKING: UPLIFT: SSF: 65.4% of base 4413 kn 1.95 NEED HYDRO MECHANICAL MODELS + VV (Experimental Data Needed)

8 Seismic Crack-Water Interaction Mechanisms + Cyclic Damage 8 (A) Water (B) Water Opening mode: Velocity of water front vs crack front Water in tension can vaporize (cavitation) Wedge effect Co sing mode: Impact and crushing of wall asperities Expulsion of water

9 EXPERIMENTAL TESTING PROCEDURE 9 CONCRETE SPECIMEN (Crack) Air compressor inlet Water tank LVDT Pressure transducer Load cell Shake table Steel frame Small water tank Reaction frame

10 10 TRANSIENT SEISMIC UPLIFT PRESSURES Dynamic amplification (reduction) of U 0 vs Crack Walls Opening / Closing Frequency Rocking F I D Seismic cracking and stability analysis U dyn / U stat U max U 0 U min Frequency (Hz) R F HD Failure plane J ü (t) J ü max Accelerogram J U Sliding Horizontal Vertical β crack (lift joint) U(t) (FRAC_DAM, RS-DAM) U U min max (CADAM)

11 SEISMIC UPLIFT PRESSURES DURING EARTHQUAKES 11 New crack in opening mode: U(t) close to zero near the propagating tip, some pressure build-up along the crack walls. Existing pressurised crack with cyclic opening / closing : U(t) oscillate around the average initial uplift pressure U 0 that remained constant. Magnitudes of pressure drops during crack opening (cavitation) and pressure increases during crack closing depend on loading frequency. If we do not recognise explicitly the dynamic variation of U(t), it appears reasonable, with our current knowledge, to assume that during the earthquake the uplift pressure remains unchanged from its pre-seismic value.

12 POST-SEISMIC CRACKS EFFECTIVE STRESSES 12 PRE-SEISMIC SEISMIC POST-SEISMIC (a) (b) (c) F I F = 0 I F = 0 I Te n sion 0 Compression Compression σ eff (A) Crack L c Crack Compression Te n sion 0 Compression Tension (B) Uplift pressures in cracks (?) No compression

13 13 POST-SEISMIC UPLIFT PRESSURES Post-Seismic Uplift Pressures Depend on: Post-seismic stress and displacement conditions along the crack plane (compression or tension) Post-Seismic seepage path; (crack hydraulic conductivity, aperture boundary conditions) Presence of drains, pressure relief at crack boundaries (water stops damaged or not ) Post-earthquake drain efficiency

14 Historical Evidences : Post-Seismic Uplift Pressures 14 Kobe M7.2 EQ Japan 1995 Several dams affected Yuzuruha Gravity Dam (42m high) 43 km from epicentre (minor damage) «Drainage water and uplift both slightly increased after the quake, but stabilized later» (Matsumoto et al. 1996) Sefid Rud Buttress Dam, Iran (106m high), M7.3 EQ in 1990, very close «Uplift water pressures were found to have strongly decrease after the earthquakes, perhaps as a result of the closure of joints or of increased compressive forces across the seepage paths» (ICOLD 2001) Koyna Dam, India (103m high), M6.2 EQ in 1967, 3km from epicentre

15 KOYNA DAM POST-SEISMIC UPLIFT PRESSURES (Pant 1990) 15 Before Earthquake After Eq. 664 m 658 m 652 m 646 m 640 m 634 m 628 m 622 m 616 m 610 m 604 m 604 m 597 m 591 m 585 m 579 m 573 m 567 m 561 m 555 m Drain Monolith 22 Piezometers (P - P ) 1 12 P 1P2 P 3P4 P 5 P 6 P 7 P 8 P 9 P 10 P 11 P 12 Reservoir water level (m) 655 m 640 m 625 m 610 m Uplift head (m) 99 m 76 m 61 m 46 m Reservoir water level P 1 P 2 P 1 Drains P 1, P2 upstream of drains Monolith 22 Gallery P 4 P 1 P 2 P 3 P 5 P 6 P 10 P 3 to P12 downstream of drains P 1 P m P m m Designed R. L m 07/12/1967 (before earthquake) R. L m 16/12/1967 (after earthquake) 579 m 15 m 564 m P P 3 P 4 P 5 P 6 P 6 P 6 June P 9 P, P, P July Aug Sept Oct Nov Dec 1967

16 POST-SEISMIC UPLIFT PRESSURES UNDRAINED (COMPRESSED) CRACK 16 γhu/s K Uniform γhd/s K 1 K 2 K 3 γhd/s K > K > K γhd/s γhu/s Linear U γhu/s Nonlinear U (a) Uniform Aperture (b) Tapered Aperture

POST-SEISMIC UPLIFT PRESSURES DRAINED (COMPRESSED) CRACK 17 Drain K 1 K 2 Crack beyond drain γhd /s γhu /s Pre-seismic condition Reduced post-seismic

17 POST-SEISMIC UPLIFT PRESSURES DRAINED (COMPRESSED) CRACK 17 Drain K 1 K 2 Crack beyond drain γhd /s γhu /s Pre-seismic condition Reduced post-seismic drain efficiency Upper bound (d) Drained Crack HYDRO-MECHANICAL MODELS NL Analyses R&D Perspectives static/seismic loads Computational - Experimental

18 POST-SEISMIC UPLIFT PRESSURES 18 Undrained complete compressed crack: full uplift pressures (too (?) conservative, hydraulic conductivity, Boundary Cond.) Drained Compressed cracks drains minimal disruption by sliding Maintain some drain efficiency Possibility (1) : return to pre-seismic uplift pressures Possibility (2) : full headwater pressures up to line of drains, significant reduction past the line of drains (e.g. tailwater pressures + 50% of the difference between headwater and tailwater).

19 CONCLUSIONS 19 Analytical/Num. models Computational tools Validation/Verification Applications Anagram Pr. CHOPRA - THANK YOU ANIL K. CHOPRA ---> KOYNA VisionarY ANIL K. CHOPRA ---> ARCH DAM

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