This document summarizes the history and rehabilitation of the Nalanda Dam in Sri Lanka. Some key points: 1) Nalanda Dam, built in 1954, was Sri Lanka's first concrete dam and showed deterioration over time due to cracking from alkali-aggregate reaction and lift joint issues. 2) By the 2000s, concerns over stability and increased leakage prompted lowering the reservoir. Engineering assessments determined a continuous buttress was needed to strengthen the dam. 3) From 2012-2015, a buttress was constructed along the upstream face to improve stability under seismic and flood loading scenarios. The project upgraded the dam to modern design standards.

1. Ailments of the First Concrete
dam in Sri Lanka and the
Remedial Works
Susantha Mediwaka (Irrigation Department of Sri Lanka)
Nihal Vitharana (Arup)
Badra Kamaladasa (Irrigation Department of Sri Lanka)

2. 22
Some statistics on Sri Lanka
• 50% of Island’s energy is from “hydropower”
• Land area = 65,000 km2
• Population = 20 million
=> Population density = 320 people/km2
• (it has 6000 wild elephants too !)
• Let us compare this with Tasmania ?
• Land area = 90,750 km2
• Population = 500,000
Population density =5 people /km2

3. 3
There is a large
stock of dams in
Sri Lanka, mostly
in the central zone

4. 44
Present Dam Stock in Sri Lanka
• Medium and Large = 355
Earth dams = 343
Concrete gravity = 07
Concrete arch = 01
Rockfill = 04
(out of above 110 are “large” dams according to ICOLD)
• Small = 12,000

5. 55
“Ancient” Major Irrigation
Systems in Sri Lanka
5th BC – 12th AD
(2500 – 800 years ago)

6. 66
Nuwarawewa
Nachchaduwa
Kalawewa
Parakrama
Samudraya
Minneriya
Kaudulla
Kanthale
Girithale
Giants Tank
Padaviya
Balaluwewa
Basawakkulama
Thisawew
a
Elehera
Diversion

7. 77
Abhaya Wewa
King Pandhukabhaya
437 -366 BC
First reservoir - with written evidence

8. 88
King Parakramabahu
1164 - 1196 AD
“Let not a single drop of water drain to sea
without making maximum use of it.”
Parakrama Samudraya

9. 99
Built 1500 years ago
Original riprap at Giritale dam

10. 1010
Nalanda Dam: First Concrete Dam built on the Island
• First earth dam built 2500 years ago => still in good shape
• Rip rap on 900-yr old dam => still intact and in place
• First concrete dam was built in 1954 (Nalanda Dam)
• Nalanda dam has some similar features to those in Australian
dams built around that time:
- Lift joints with cement:sand mortar
- No drainage gallery
- No Uplift allowed in the design
- Alkali-Aggregate Reaction (AAR)

11. 1111
Key features of Nalanda dam
• Type= Concrete gravity dam
• Hazard category = “extreme”
• Catchment Area = 124 km2
• Storage capacity = 15 GL
• Maximum height = 36 m
• Length at crest level = 125 m (dam + 2 spillways)
• Crest width = 2.13 m
• Maximum width at base =25 m
• Down stream slope = 350 to vertical

12. 1212
Typical Cross Section of Nalanda dam

13. 1313
Role Played by Nalanda dam
• Provides irrigation water to local farmers
- Small/medium scale farming
(Famous for vegetables => egg plants or brinjal)
• Serves a key role in hydropower in droughts
(located upstream of old and important HP plant feeding the
national grid)
• Failure of Nalanda could affect safety of HP dam/plant
=> Nalanda dam is an “extreme’ hazard dam.

14. 1414
Spillway and hydrology
• Two spillways:
- Low-level horse-shoe section (1.53m below DCL)
- High-level broad-crested (1.22m below DCL)
- (in an emergency flood situation in 2010, military was deployed to blast
off 2m off the horse-shoe section)
• Catchment response is said to be very fast as observed during
previous floods.

15. 1515
Inflow and outflow PMF-hydrographs
• Hardy any attenuation => outflow/inflow ratio =0.99
• Dam overtops by 0.9m under PMF

16. 1616
Original construction: concrete placement
• 1. Via a chute => free falling
• 2. Heavy-duty bucket hanged from a cable-way
• Targeted concrete strength was 20MPa (1:3:6 by volume)

17. 1717
Dams performance over 60 years
1. Dam crest was overtopped in 1957 by 3m (anecdotal evidence)
=> no immediate adverse effect on the dam.
2. In late 1980s, hair-line cracks appeared on u/s & d/s faces
3. In 1987, dam was emptied =>showed extensive cracking u/s +
opening up of lift joints.
4. Noticed over time increased leakage at d/s lift joints.
5. Petrograpic tests on concrete => extensive AAR
6. In 1991, fiber-glass coating was applied on u/s face to reduce
AAR-activity (=> reduced rate of water ingress)

18. 1818
Cont...
7. In 1999, storage was emptied => showed delimitated fiber-glass
coating (just after 8 years).
8. Since 2003, increased leakage and stability concerns => storage
level was lowered to 3m below FSL (most of the time).
9. In 2011, Stability calculations showed that dam was deficient in
this regard for water levels up to PMF-levels.
<In 2012, decided to “strengthen” the dam according to
international design practices >

19. 1919
Cracking and leakage on d/s and u/s faces
• Leakage and calcification on d/s face + cracks on u/s:

20. 20
AAR-cracking on the intake tower

21. 2121
Upgrading options considered
1. Covering u/s with pvc: rejected due to poor past
performance
2. Post-tensioning of the dam: rejected due to lack of
local expertise
3. Permanent lowering of FSL: rejected due to farming
demands
4. Construction of a continuous buttress: accepted

22. 2222
Stability Assessments
• Assume unbonded lift joints with residual strength
parameters (FERC, ANCOLD)
• Various uplift pressure scenarios
• Storage drawdown levels (for load sharing): refer ANCOLD-
2013 paper N Anderson and N Vitharana
• Limit equilibrium calculations
• Simple finite element modelling
• => buttress with widths of 1.5m at the crest and 3.5m at the
base

23. 23
Uplift Pressures – dam body
Uplift
Toe
Uplift in the dam body
Lift joints
Existing Dam

24. 24
Uplift Pressures – dam body with buttress
Uplift
Toe
Drainage path blocked:
Uplift approaches a near
rectangular distribution
New Buttress

25. 2525
Concrete Mix Design
• Strength testing (tensile/compressive strengths): 30MPa
• Heat of hydration (hot box) tests; 0.9m cube
• Use of fly ash with 20% replacement ratio to limit temperature
rise
• Cement content = 350 kg/m3
• 20kgs of ice added for 1 m3 of concrete

26. 2626
Interface Design Details
• Scabbled to roughen the interface and to remove
degraded concrete
• Anchor bars at 1.5m spacing
• Seepage-collection at existing d/s face with half-round
pipes at all lift joints

27. 2727
Seepage-collector pipes on existing d/s
Close up view

28. 2828
Construction Aspects
• In 1.2m lifts
• The time gap between the lifts was 5 days on average
• Joints were cleaned with water-jetting only
• Temperature was monitored against acceptable limits
• Concreting typically between 4pm to 8am at night

29. 2929
Construction photo (Jan 2014)
Foundation and dam’s interface prepared

30. 3030
Concluding Remarks
• Earth dams have survived in excess of 2000 years.
• Concrete dams can degrade rapidly => spend $ and time on
concrete mix designs (AAR, heat of hydration).
• Appropriate technology was adopted to upgrade Nalanda dam
with modern design criteria.
• Project was successfully completed in May 2015
If you have any questions please email:
Nihal.Vitharana@arup.com