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1/28/2014 Longitudinal Joints in Dams- Some Case Studies | "MMM" Hydro Power
http://mmmhydropower.blogspot.com/2013/08/longitudinal-joints-in-dams-some-case.html 1/12
Longitudinal Joints in Dams- Some Case Studies
M M Madan
Director (Hydro) - GVK
Ex Executive Director-NHPC
Introduction
Normally the provisions of longitudinal joints in Concrete Gravity Dam are made to achieve necessary
temperature control and to prevent cracks parallel to the length of the dam. This is done in case of
relatively high dams by subdividing the monolith into several blocks by Longitudinal Contraction joints.
Subsequently these Longitudinal Contraction joints are grouted to ensure monolithic action.
For consideration of Safety of the structure, the IS Code (Indian Specifications) advocates elimination of
longitudinal joints. Basically IS Code recognizes the practice of dividing a monolith block into two or more
blocks by introducing joints parallel to the axis of Dam as unsound. However if necessary, a high degree of
perfection has to be ensured by providing suitable shear keys and then properly grouting the joints to
create a monolithic block.
However, the necessity of vertical or inclined discontinuity is sometimes required due to the reasons other
than “thermal behaviour and crack control”. One such reason may be due to tight construction program and
adoption of methodology. This paper focuses on Dams where “Longitudinal Contraction Joints” have been
provided successfully and the dams are functioning properly for a long time.
Joints in Concrete StructuresCreating a construction joint in a large gravity dam is common practice and is applied on majority of dams.
Where the dam is very thick, longitudinal joints are necessary to control random cracking, to accommodate
volumetric changes and to facilitate construction. These should be able to transfer compressive and shear
stresses and must be grouted after cooling (ICOLD bulletin 107 on concrete dams).
Joints are necessary in concrete structures for a variety of reasons. All the concrete may not be placed
continuously in a structure under construction, therefore the construction joints are provided to allow for the
work to be resumed after a certain period of time.
Principally due to shrinkage and temperature changes, the concrete undergoes volume changes; therefore,
it is desirable to provide joints to relieve tensile or compressive stresses that would be induced in the
structure.
By adopting specific construction measures, the homogeneity of the dam body shall be ensured by
providing shear keys casted on the internal face of both blocks that will assure the transmission of shear
stresses if any. After concreting of the area between the two blocks, the grouting will ensure that the
structure is monolithic.
In the second stage of concreting, internal joints are an acceptable practice as far as they allow an efficient
and sound transfer of loads / stresses.
25
UGLongitudinal Joints in Dams- Some Case Studies
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Longitudinal and Transverse Contraction Joints in Dams
A contraction joint is formed by vertical or inclined surface between masses of concrete/ masonry placed at
different times. The joints divide the dam into convenient sized monoliths to permit convenient and
systematic construction and to prevent the formation of haphazard ragged cracks due to volume changes
that cannot be prevented,
Transverse Contraction joints
It is good practice for normal methods of construction to provide contraction joints in gravity dams. The
spacing of transverse contraction joints shall be such as to suit the methods of construction, materials of
the dam, the foundation conditions and the convenience of the location of control gates outlets etc. They
are usually spaced about 15m apart, experience having shown that cracks are likely to develop in monoliths
much wider than this. It is however, essential to locate the joints to best advantage relative to the shape of
the abutments. The general requirement is that each joint extends entirely through the structure.
Longitudinal Contraction Joints
For large structures the problems of cooling large masses of concrete are enormous. One of the measures
used to control cracks parallel to the length of the dam in case of relatively high dams is to subdivide the
monolith into several blocks by longitudinal contraction joints and subsequently grout these joints to ensure
monolithic action.
The spacing of joints is largely dictated by convenience of construction and foundation conditions. A
spacing of 20-30m is generally adopted.
There is also now a school of thought which believes that the longitudinal joints need to be at very close
spacing of about 15m or even omit them all, since there are doubts of the final behaviour of dams built in
such a manner.
IS Code (Indian Specifications) advocates elimination of longitudinal joints for the consideration of safety.
Basically IS Code recognises the practice of dividing a monolith block into two or more blocks by introducing
joints parallel to the axis of Dam as unsound. However if necessary, a high degree of perfection has to be
ensured by providing suitable shear keys and then properly grouting the joints to create a monolithic block.
IS Code:6512 on “Criteria for Design of Solid Gravity Dams” vide clause 7.1.1.1 states that “It is now being
increasing accepted that better alternative is to achieve necessary temperature control by pre-cooling of
concrete supplemented wherever necessary by post-cooling and avoid longitudinal joints altogether, even
in case of high dams.”
However, the necessity of vertical or inclined discontinuity is sometimes required due to the reasons other
than “thermal behaviour and crack control”. One such reason may be due to tight construction programme
and adoption of methodology. The homogeneity & monolithicity of the dam body has to be ensured by
provision of shear keys cast on the internal face of both the blocks and grouting performed after the
concreting of the area between the two blocks. Further, a detailed stability analysis of the dam needs to be
carried out considering the longitudinal joints for all relevant load cases and uplift conditions.
There are examples of Bhakra Dam & Dulhasti Dam in India, Ravedis Dam in Italy, Les Toules Arch Dam in
Switzerland, Bolargue Dam, Irabia Dam & Grand Dixence Dam in Switzerland where such longitudinal joints
have been provided successfully.
The 390 MW Dulhasti Hydroelectric Project is a run of the river scheme located on river Chenab in District
Doda, J&K- India. The project consists of a diversion dam at Dul with two intakes, one to provide water for
the first stage and another to provide water for the proposed second stage. There are two underground
desilting chambers with necessary flushing conduits and two more desilting chambers has already been
Dulhasti HE Project
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constructed for the proposed second stage. The head race tunnel is 7.7 m dia and 10.6 km long. Due to
changes in alignment, it doesn't have a uniform slope from upstream to downstream and hence an air-vent
shaft of 400 m high has been provided to avoid airlock. An underground surge shaft of 18.5m diameter,
117m deep with other ancillary tunnels has been provided. Three penstocks of 4.8 m dia and 141 m depth
take-off from surge shaft. The underground power house with installed capacity of 390 MW (3x130 MW)
with all the appurtenant structures is located at Hasti.
The construction work of the project was awarded to a French consortium Dumez-Sogea-Borie SAE in
October 1989, but was abandoned in August 1992. The work remained standstill for a period of about three
years (between 1995 to 1997). The tunnelling work was carried out departmentally. Then the work was
again retendered and awarded to the Indo-Norwegian Joint venture Jaiprakash – Statkraft (JSA) during
April, 1997. The project was finally commissioned in the year 2007.
Geology of the Project Area
Geologically, the rocks of Kishtwar area are classified into two Groups viz. Older Kishtwar Group and
Younger Sinthan Group, corresponding to the metamorphic rocks and younger sedimentary and volcanic
rocks respectively. The contact of these two groups is marked by a thrust designated as Chhattru Thrust,
which is having a sinusoidal alignment. There were presence of other regional faults viz. Kishtwar Fault
(runs almost N-S) and Daddhar – Buzensheru Fault within Kishtwar Group. Structurally, the area was very
disturbed and subjected to intense folding and faulting. Kishtwar fault was a significant fault in the area and
separating schist and gneisses of Salkhala Formation and Quartzite - Phyllite sequence of Dul Formation
under the Kishtwar Group of rocks. This fault was trending in NNW – SSE direction and dipping 650 in
westerly direction. The Kishtwar plateau (fossil valley), later on, is designated as “Graben” based on
kinematic mechanism and sub-surface explorations carried out for HRT of the Project by French
Consortium.
Dulhasti Dam
The Dul dam is a mass gravity concrete dam, measuring 65 m high above foundation with a crest length of
186m. It serves the primary function of hydroelectricity.
In Dul dam longitudinal and vertical joints were provided as a construction requirement. These joints were
provided with shear keys casted on internal face of both the blocks for transmission of shear stresses.
These joints were later on grouted to ensure monolithic structure in the dam. Necessary provisions were left
during construction stage to ensure grouting after completion. The grouting was done successfully. The
dam is in operation and behaving correctly.
1/28/2014 Longitudinal Joints in Dams- Some Case Studies | "MMM" Hydro Power
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Dul Dam Cross Section - Longitudinal Joint parallel to Dam Axis can be seen
1/28/2014 Longitudinal Joints in Dams- Some Case Studies | "MMM" Hydro Power
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Dul Dam Foundation Plan - Longitudinal Joint parallel to Dam Axis can be seen
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Dul Dam – Grouting System Arrangement
Ravedis Dam
The Ravedis dam in Italy is a mass gravity concrete dam, measuring 51 m high above foundation with a
crest length of 173m and a reservoir storage volume of 25 million cum. It serves for Flood Control, irrigation
and hydroelectricity. The construction of the Dam was completed in November, 2004.
During construction of the monolithic basement of Ravedis dam, 8 (eight) different blocks were casted and
connected together by joints, parallel to the dam axis. Particular attention was given to the joint treatment of
monolithic basement blocks in order to guarantee the monolithic characteristic requested for the foundation
block.
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Cross Section of Ravedis Dam - Longitudinal Joints parallel to Dam Axis can be seen
Les Toules Arch Dam
Les Toules Dam in Switzerland is a 86m high double curvature Arch dam with a crest length of 460m. The
first dam was built as single curvature arch dam in 1958. The heightening of this dam was carried out in
1960-1964 and converted to Double curvature Arch dam. Particular design was very slender shape without
abutment thickening, high vertical curvature towards valley and no shear keys.
The dam foundation lies on gneiss and mica schist rocks forming alternate subvertical strips almost parallel
to the valley. In 2003, upgraded seismic regulations and recommendations of Swiss Federal Office of
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Energy required the dam owners to reassess the safety of their structures. In this context comprehensive
studies of the existing dam structure and its behaviour were carried out, and dam strengthening was
required.
This arch dam was rehabilitated by adding buttresses on the downstream face of the dam, creating a
longitudinal curved joint between the existing structure and the new concrete structure transferring the load
from the overloaded cantilevers to the thickened arches, creation of shear keys in the vertical joints, local
foundation treatment and some other secondary rehabilitation works. To strengthen the dam, abutment
thickening was done in both abutments, shear columns were provided, for seismic purpose downstream
face was provided with 30,000cum of concrete. The bonding between old and new concrete was done with
proper joint treatment by hydro-demolition with high pressure rotating water jets. The contact between the
existing dam and the new concrete was not grouted to prevent any jacking effect because of grout
pressure. After rehabilitation, the final monolithic structure behaved satisfactorily along expected lines.
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Irabia Dam
Irabia Dam was heightened three
times and the fourth heightening is being planned.
The figure above shows the original profile over which three other profiles of the extended
portion. The profile of the fourth extension being planned can be seen.
Bolarque Dam
The Bolarque Dam was heightened & the base width was increased. Galleries were also provided at the
foundation & at the top of the existing dam to take care of the uplift forces.
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Grand Dixence Dam
285m tall Grand Dixence Dam is located in Switzerland in Canton of Valais on the Dixence River. The river
supplies water to the Rhône Valley. It is the highest Gravity Dam in the world. It is 695m long with a base
width of 200m. It was carefully planned to be built in successive stages. The hydroelectric power plant has a
capacity of 2000 MW. It holds back Lac des Dix which is 3.65 Sq. km (902 acres) in area. It holds 400 million
cum of water and is 284m deep. It is the 5th tallest dam in the world & highest gravity dam in the world.
The Grout curtain extends 200 m deep and 100 m outward in each direction. First Dixence dam was built in
1929 and construction on the new dam started in 1950. The New dam submerged the old dam.
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Figure shows the profiles for each stage. Keys were provided at each stage for better bonding.
Longitudinal joints were created in the process.
Grand Dixence Dam Cross Section – Figure shows the years in which different blocks have beenConstructed- Longitudinal Joints created during successive stages can be seen
Bhakra DamBhakra dam in India is a mass concrete gravity dam of 225.55m height located on Satluj River
corresponding to a total volume of 3.82 million cum of concrete. It is located in an area with large seasonal
temperature variation. The dam construction was started in 1955 and completed in 1963. Several remedial
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measures were taken to avoid cracks in this large massive structure. The dam body was segmented in a
series of blocks by traverse and longitudinal joints. Without longitudinal joints for such a large concrete
structure, stoppages or delays in the construction during the winter time would have involved cracking of
the dam body. Cross section of the dam body shows the joints provided during construction in Bhakra Dam.
Cross- section of Bhakra Dam
ConclusionThe various examples cited above where Longitudinal Contraction joints have been provided due to varying
reasons. Concrete Gravity Dams with Longitudinal Contraction joints can be planned when necessitated
due to reasons such as construction programme and ultimately the viability of the project itself. However,
utmost care has to be taken so that a high degree of perfection is accomplished in ensuring monolithicity by
providing suitable shear keys and successfully grouting all the joints. These examples demonstrate that with
proper planning, adopting strict quality control measures and maintaining all necessary design
requirements, there is no reason as to why Longitudinal Contraction Joints cannot be adopted in large
concrete dams.
References
New York, VI Congress of ICOLD 1958
Rome, VII Congress of ICOLD 1961
New Delhi, XIII Congress of ICOLD 1979
Florence, XIX Congress of ICOLD 1997
Muller, O., Wohnlich, A., Safety Enhancement and Strengthening of Les Toules arch Dam.