longitudinal joints in dams

4 weeks ago

M M Madan

Director (Hydro) - GVK

Ex Executive Director-NHPC

IntroductionNormally 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.

Longitudinal and Transverse Contraction Joints in DamsA 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

Longitudinal Joints in Dams- Some Case Studies

Longitudinal Joints in Dams- Some Case Studies | "MMM" Hydro Power http://mmmhydropower.blogspot.com/2013/08/longitudinal-joints-in-dam...

1 of 14 9/22/2013 3:32 PM

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 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

Dulhasti HE Project


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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 DamThe 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.

[http://4.bp.blogspot.com/-26XrHU7k6MA/UhogIi7OaPI

/AAAAAAAAINY/Je4LvggBAYU/s1600/X+section+dam.jpg]


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[http://2.bp.blogspot.com/-Jlel1cUs1lA/Uhofrfr63dI/AAAAAAAAINE/BvhveiE8dVA/s1600/Dulhasti+Dam.png]

Dul Dam Cross Section - Longitudinal Joint parallel to Dam Axis can be seen

[http://2.bp.blogspot.com/-pMd37LtFBZc/Uhogj6XqSMI/AAAAAAAAINg/6VIgXPGjXMc/s1600/Dul+dam+plan.jpg]

Dul Dam Foundation Plan - Longitudinal Joint parallel to Dam Axis can be seen


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[http://3.bp.blogspot.com/-GJit1zmhY5Y/UhogD-

aK2vI/AAAAAAAAINQ/QIIxFedT5j0/s1600/vertical+joints-+Dulhasti.png]

[http://2.bp.blogspot.com/-wP_1FJLEK4Q/UhojzD4kF_I

/AAAAAAAAINw/G4s-BLWbuFU/s1600/Dul+Grouting+arrangement.jpg]

Dul Dam – Grouting System Arrangement

Ravedis DamThe 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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[http://4.bp.blogspot.com/-HCz14oXuf08/UhollWb944I/AAAAAAAAIQc/Sw6gD5idfuU/s1600/Ravedis+Foundation+Plan.png]

[http://3.bp.blogspot.com/-ssXl3NvP1WI/UhollpRO4NI/AAAAAAAAIQs

/EbA0FjZB7jA/s1600/Ravedis+Dam.png]


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[http://3.bp.blogspot.com/-fU-s4D67ZPo/UhollnKmG1I

/AAAAAAAAIQo/YZQDVI51Mss/s1600/Ravedis+X+section.jpg]

Cross Section of Ravedis Dam - Longitudinal Joints parallel to Dam Axis can be seen

Les Toules Arch DamLes 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 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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[http://2.bp.blogspot.com/-TrgCHftwxKU/Uholk23tRjI/AAAAAAAAIQU/gPe-pTfDD-

k/s1600/Les+Vincas.png]

[http://1.bp.blogspot.com/-Av1Byk6Lr0U/Uholj9rGvHI

/AAAAAAAAIQE/KX3LohV0zmw/s1600/Les+Toules.jpg]


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[http://1.bp.blogspot.com/-ckGkBD6vEOE/Uholm0Xhl7I/AAAAAAAAIRA

/0liD2mkEpdA/s1600/rehabilitation+Les+Toules.jpg]

[http://3.bp.blogspot.com/-e6cqwaWbO7I/UholhN1wAiI/AAAAAAAAIPQ/QjZNrVcsUxg/s1600

/End+Block+les+toules.png]

Irabia DamIrabia Dam was heightened three times and the fourth heightening is being planned.


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[http://3.bp.blogspot.com/-pWHgZ5YG_nw/Uholikxko0I/AAAAAAAAIPw

/7w-VIc-mjEA/s1600/Irabia+Dam+stages.png]

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 DamThe 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.

[http://4.bp.blogspot.com/-5L-77kMxhSI/UholdAFmk6I

/AAAAAAAAIOg/jqLPUAHMQ0A/s1600/Bolarque+dam.png]


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[http://4.bp.blogspot.com/-XhjZ3D-ge7k/Uholj3xSIwI/AAAAAAAAIQA/bVU9mzVVm6U/s1600/Irabia+photo.jpg]


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Grand Dixence Dam285m 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.

[http://1.bp.blogspot.com/-BX8x1tX5zNk/UholhvYn1DI/AAAAAAAAIPY

/527Sejv0YUE/s1600/Grand+Dixene.png]

Figure shows the profiles for each stage. Keys were provided at each stage for better bonding.

Longitudinal joints were created in the process.


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[http://1.bp.blogspot.com/-MmlauEM3cNk/Uhoos3E3-CI/AAAAAAAAIRQ

/6h9XrDv3POk/s1600/Grand+Diexene+stages.png]

Grand Dixence Dam Cross Section – Figure shows the years in which different blocks have been

Constructed- 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 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.

[http://2.bp.blogspot.com/-psjBUnLrWzs/UhopFhvxf0I/AAAAAAAAIRY

/8pjuvOPcYfs/s1600/Bhakra+Dam.jpg]


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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.

ReferencesNew 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.

Posted 4 weeks ago by MM Madan


14 of 14 9/22/2013 3:32 PM

longitudinal joints in dams

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