Konar cwc

Numerical Modeling of Konar Dam

Mr Bikram Patra, CWC Mr Ankur Agarwal, Dassault Systemes Mr Abhishek Shukla, DVC

Over View Konar Dam DVC • Konar dam is situated on river Konar amidst the picturesque surroundings of the forests of Hazaribagh district at about 30 km above its confluence with the river Damodar.

• It is the second of the four dams, included in the first phase programme of unified development of the Damodar Valley corporation.

• The total length of the dam comprising earth dam, concrete dam and dykes is 3825.0 m. The concrete dam is located in the river portion. It is 277.37 m long with a spillway section of 107.9 m length between blocks 6 & 16. Hollow spaces have been left at block joints.

• The dam was constructed in stages. In first stage the upstream side of the dam was brought up and used for partial storage. The downstream part was later added and dam raised to full height No reinforcement has been provided in the galleries.

Location Over View of Konar Dam

Downstream View Of Konar Dam

Upstream View Of Konar Dam

Unique features of Konar Dam Design of the concrete dam is unique (Technical Completion Report of Konar dam 1966) in planning. Hollow spaces are left inside it between blocks in spillway and abutments, which accounted a saving in concrete to the extent of about 6% and also facilitated curing of concrete during construction. M/s Gruner S.A,Basel Switzerland were the designer & Consulting Engineer.

A concrete roadway 5.8 m. wide runs at the top of the dam at EL. 431.3 m. Inspection gallery (1.2 m x 2.1 m), operating gallery (1.5 m x 2.7 m) and drainage gallery (2.4 m x 3.1 m) are provided at EL. 408.4 m, 394.7 m. and 383.7 m respectively where river bed level is at EL. 382.2 m. Inspection shafts (0.9 m x 0.9 m) between blocks are also provided at different levels.

Dam Blocks incorporating galleries ,Hollow spaces, Gates

Typical Dam Blocks Inspection shafts (0.9 m x 0.9 m) Inspection gallery EL. 408.4 m (1.2 m x 2.1 m)

Hollow spaces

Operating gallery EL. 394.7 m (1.5 m x 2.7 m)

Drainage gallery EL. 383.7 m (2.4 m x 3.1 m)

Hollow spaces

Distress- Sequences-Rehabilitations • The dam was constructed during 1950-1955.The initial filling was carried out in 1954, first full impoundment was on 7/1/1956.

• After about eight years of construction in 1963 the cracks were first observed on the walls of the inspection gallery. The cracks were also simultaneously observed in other two galleries, but they were comparatively less dominant than those in the inspection gallery.

• Following which tell-tales were fixed across the cracks in different places in different years.

The tell-tales shows started cracking which shows the cracks were progressive.

• The cracks appeared on both downstream and upstream faces of the galleries and seen in almost all the blocks.

• No remedial measures or treatments were taken before 1970, except for restricting the reservoir level.

Distress- Sequences-Rehabilitaions • CWPRS, Pune Govt. of India, investigated the cracks by Sonic Tests.

On the basis of this report, in 1970-71, the cracks were grouted with epoxy in consultation with the Central Water Commission (then CW&PC), CWPRS, Pune and Shri. P. M. Mane, Ex. Member, CWC. At some places the grouting was done with cement.

• In the concrete dam no instrumentation for observation of internal stress or strain, uplift pressure, temperature, etc. was provided.

However, a number of dial gauges were installed across the cracks for continuous observation after grouting. Monitoring by dial gauges indicated considerable seasonal fluctuations in the crack openings.

• After grouting, re-appearance of cracks was observed in 1973. These cracks appeared somewhere little above the grouted cracks and at other places they appeared right along the grouted portion.

Distress- Sequences-Rehabilitaions • Although cracks were found to develop on the upstream and downstream faces of the inspection gallery, no seepage was observed in the inspection gallery. However, in some blocks seepage at the floor level of access gallery coinciding with the lift (construction) joint was observed. Some leaching was also noticed through the cracks near the block joints in the drainage gallery. • An expert committee was formed by DVC on the advice of the CWC in 1979. The committee consisted of Dr. K. C. Thomas, Ex. Chairman, CWC, New Delhi, as Chairman and other members. As per the suggestion of the Expert Committee, Finite Element Studies of the typical section of the dam (block-13) was conducted by WRDTC, Roorkee under the guidance of Dr. B. Pant.

Leaching, Seepage, Water pool in drainage galleries

Cracks in galleries

Distress- Sequences-Rehabilitations • Dr. Pant Professor WRTDC, visited the site in June 1982 and studied the behavior and submitted his report to expert committee in June 1984. However, no substantial action seems to have been taken by DVC on the observations of the studies carried out by Dr. Pant.

• In 1989 Expert committee headed by Dr. K.C Thomas , learnt that in 1965 during partial operation of the under sluices heavy vibration were felt, Since 1979 no partial opening permitted. Data pertaining to 1965-1979 was not available. Also reported that the uplift pressure considered was not inline with Is 6512-1972.

• Tell-tales installed over the cracks at many locations indicate that crack formation was active up to 2009. However, tell-tales installed in 2009 or onwards, are appeared to be still intact indicating that perhaps cracks are stabilised.

Distress- Sequences-Rehabilitations • NHPC ( October, 2010) recommended that owing to the quantum, nature and severity of longitudinal cracks in Dam blocks and galleries, rehabilitation measures should be taken up as per recommendations of safety review panel. The same may be planned in consultation with DSO under CWC for considering the Dam for its rehabilitation under DRIP(Dam Rehabilitation and Improvement Project).

• On the request of the Chief Engineer (Civil), DVC, Maithon, the DSRP visited Konar Dam from 12th to 17th November 2013.

• Following the recommendation of DSRP chief engineer DVC requested CSMRS for evaluation of quality of concrete with regards to its strength and other associated properties.

Distress- Sequences-Rehabilitations • Initially in the month of March-2015 CSMRS preliminary visited to Konar dam, following in the month of June 2015 with drilling crew, submitted its report in the month of September 2015 • In the month of October 2015 a team comprising members from DSR dte. and along with consultant i.e. Egis and Dassault system visited dam site prior to take up the Numerical modeling work. • Then the work for numerical modelling stared in November 2015. A collaborative Approach adopted , staff from CWC, DVC, Egis, Dassault engaged for smooth progress.

Few Observation Of Dr. Pants Report.

Cracks were found mostly horizontal and running continuous throughout all the galleries particularly in the inspection gallery.

Numbers of cracks and their width sizes in the upstream face of the galleries were lesser than that of the cracks in downstream face which were more in numbers and also wider in size.

Further, cracks were found wider in the central blocks of the dam (blocks 13 & 14) and narrower near the abutment ends. maximum width of the crack was found 54.36 mm in the central portion at downstream face.

Vertical cracks were also visible in the inspection gallery in block 3 to 5 and in block 19 to 20.

Among the various method as suggested by the expert committee i.e. photo elastic method Trial loading method and Finite element analysis method .

So

Top View Layout of Konar Dam

Sectional view of Konar Dam

CWC Team site visit to Konar Dam during October 2015 as a part of DRIP

Objective Of 3D FEM Study of Konar dam A detailed Three dimensional FEM analysis of the konar dam under taken in order to understand the complex behavior of the Dam Under various mechanical and thermal loads and to suggest the most pragmatic rehabilitation to the ongoing problem.