Third National Dam Safety Conference COMPREHENSIVE ...Drycrete, M-60 grade concrete was used....

Er. SANDEEP SINGHALDirector (Projects) UJVN Limited, Dehradun, (UK)

[email protected]

Third National Dam Safety Conference18-19 February 2017, Roorkee

COMPREHENSIVE REHABILITATION / REPAIR OF MANERI DAM IN DIST. UTTARKASHI

MANERI DAM D/S VIEW

ABSTRACT

Severe floods in the rivers of Uttarakhnad in August 2012 andJune 2013 badly damaged some hydro-electric power projectsmainly in Bhagirathi and Alaknanda river valleys. Spillway ofManeri Bhali Stage –I dam was damaged severely due to rollingboulders which resulted in heavy leakages downstream. In orderto arrest leakages, temporary arrangements such as caulking ofgates were undertaken. After the monsoon of 2014,comprehensive rehabilitation/repair of Maneri Dam wasplanned after studying damages of similar nature and treatmentmeasures at other hydro electric projects. The spillway no-01 &02 were extremely damaged, therefore the repair works of thesespillways were planned on priority basis in two phases:



• Repair work from the sill beam of stop log gates to the 2.00 mtsdownstream of sill beam of radial gates were planned by takingminimum shutdown of Power House.

• Repair work in entire spillway glacis from 2.00 mts downstreamof sill beam of radial gate were planned in running power housecondition.Repair of entire roller bucket and realignment of thedownstream training wall were also planned subsequently.PROJECT BRIEF

• Maneri Bhali Stage-I (90 MW) Hydro electric scheme wasplanned in 1960s to harnesses the potential energy of waterflowing down river Bhagirathi between Maneri and Uttarkashi.The power house of this project is generating approx. 455 MUenergy annually (average generation from 2004-05 to 2014-15)since October, 1984.

This Scheme comprises of:-

• A 39 m high and 127 m long Concrete Gravity Dam acrossriver Bhagirathi near Maneri with four numbers spillwaysgates of size 13 m width & 14.55 m high separated by 2mthick piers. The spillway gates are radial type fitted withelectrically operated hoists. The energy dissipation is allowedby providing slotted roller bucket.

• Intake structure comprises of three bays 9.00 m. wide with allweather channel on the left flank. A sedimentation tank with08 hoppers 15.00m wide x 15.70 m length X 5.75 m deep, in 2rows is provided to remove silt particles which are passed backto the river downstream of the dam through silt flushingtunnel.


• A 8.631 km long and 4.75 m diameter circular concrete linedpower tunnel.

• A 69 m high and 11 m diameter underground surge shaft ofrestricted office type along with 316 m long and 6m diameterupper expansion chamber, 89.5 m long and 6m diameter lowerexpansion chamber.

• About 456 m long single steel lined penstock of 3.8 m diameterhaving three branches of 2.5 m diameter just upstream of thepower house

• A surface power station near Uttarkashi, housing three Francisturbines of 30 MW capacity each, i.e. total installed capacity of90 MW. The firm power is 38.23 MW.


• The design discharge of the power station is 71.4m3/s. Thedifference in elevation between the barrage and the powerstation affords a design head of 147.5 metres and gross head of180 metres.

• Open tailrace channel about 120 m long joins river Bhagirathi at Uttarkashi

EXTENT OF DAMAGESi ) Damages observed in Spillway gate no. 01 & 02:-• The sill beam of stop log gate and radial gate were washed out

in approximately 6.00 m & 8.00 m length (out of 13 m)respectively. The flange of the remaining sill beams wascompletely damaged.


• As both the sill beam were washed out in some length,therefore a cavity of about 6 m-7 m in length (along the piers)having a depth upto 2.00 m was created in between radial gateand stop log gate. The flood also damaged the spillway glacison the right side and in the d/s of radial gate beam throughoutits length & upto roller bucket in 3.00 m width with a varyingdepth of maximum 13.00 m.

ii ) Damages observed in Spillway gate no. 03 & 04:-• The concrete in between stop log gate and radial gate was

eroded due to high flood. The maximum depth of the erosionwas in range of 0.25 m to 0.70 m.

• The profile of spillway glacis was also damaged from 0.25 mto 0.80 m in depth.


Photograph 01 (Damages in gate no-1)


STUDY OF DAMAGESConsidering the past history of damages in Maneri Bhali Stage-Idam following were the major reasons of damages:i. There is no check dam or hydro power project dam upstream

of Maneri Dam, due to these rolling boulders in monsoonperiod hit the Maneri dam directly.

ii. In the upstream side there is a turn in the river and shortestradius of the turn is towards the gate no.1. Due to this rollingboulders in monsoon season pass more through bay no. 1 incomparison to other spillways bays.

iii. The width of roller bucket is converging towardsdownstream, therefore the training walls obstruct thedesirable flow pattern and consequently damages occurred inthe spillway structure and roller bucket.


REHABILITATION/REPAIR WORKS EXECUTED IN GATE NO. 01&02

• The damaged sill beams of bay no 01, 02 & 03 were removedand replaced with the new ones of the same size. The spillwayglacis were repaired with M60 grade concrete and 20 mmthick MS steel plate was fixed over the repaired surface.Activities Performed During Closure Period

• Detailed planning of execution of repair works of threespillway bays from sill beam of stoplog gate to 2m d/s of sillbeam of radial gate within minimum possible time was done.A period 36 days starting from 02/12/2014 to 07/01/2015 wasfinalized for closing the Power House of MB-I HEP located atTiloth in District Uttarkashi. Following activities wereperformed in sequential order to complete the works:

• Creation of bund in front of spillway bay 1, 2 & 3 to divertwater through spillway no. 4.


• Dismantling damaged mild steel sheets previously placed overspillway concrete profile.

• Damaged & remaining sill beams of stop log gate and radialgate were removed.

• Dismantling of concrete so as to get a minimum thickness of250 mm of new concrete and a cover of 200 mm over thereinforcement.

• Drilling hole of 600 mm depth and 32 mm dia in staggeredmanner in parent concrete for fixing anchors.

• Fixing 25 mm dia Fe 500 TMT bars in drill hole with groutingmaterial for anchorage of reinforcement as well as dowel barsfor fixing of MS plates.

• The reinforcement was laid with 20 mm dia bars @ 150 c/ckeeping the top cover of 200 mm. Where the cavity was morethan 80 cm deep, reinforcement was provided in intermediatelayers also keeping the top cover & bottom cover of 200 mm.


• Applying bonding coat (BASF make) between old and newconcrete.

• Laying of concrete (ACC make Drycrete of M80 grade) incavity between sill beam of stoplog gate and radial gate.

• Fixing sill beams i.e. ISMB 300 (300 X 140) confirming to IS:2062 (E250) with 20mm SS plate for Stop Log gates andRadial gates.

• Laying concrete (ACC make Drycrete of M80 grade) up to final level as per the profile.

• Fixing MS sheet (20mm thick with yield strength of 450 MPA) over the prepared concrete surface.

• Grouting between steel plate and concrete by cutting notes through the steel plate & fixing the cut plate after grouting.


To complete the repair works of spillway no 01 & 02 withinstipulated period, all the pre-requisites such as manpower,material etc. were arranged before start of work. The workswere taken up in 3 shifts continuously. The works werecompleted within 36days and Power House was restartedthereafter.

Repair Works in Spillway Glacis• Repair works in spillway glacis is carried out from 2m d/s of

radial gates during power house running condition. Allactivities were same as stated above only instead of M80Drycrete, M-60 grade concrete was used.

Concrete Mix Design Adopted For Works• Based on IS: 10262-2009 and IS: 456-2000 mix design for

concrete is derived as below:a) Cement = 450 kg/m3 b) Water = 157 kg/m3c) Silica fume = 25 kg/m3 d) Fine Aggregate = 598 kg/m3


e) Coarse Aggregate = 1269 kg/m3f) Chemical Admixture = 7.125 kg/m3

• The 28 days crushing strength of trial mix proportions for target M-60 grade of concrete was achieved as 68.9 N/mm2.


Photograph 02 (Temporary Bund for channelization of river)

Photograph 03 (Laying concrete in gate no-02)

Photograph 04 (Grouting of MS Plate of gate no-2)


REHABILITATION/REPAIR WORKS PROPOSED IN SPILLWAYS NO 03 & 04; ENTIRE ROLLER BUCKET AND TRAINING WALLS:-During execution of repair work of spillway no.1&2, the entireslotted type roller bucket and training walls were alsoexamined and it was found that the slots of roller buckets arecompletely damaged. Both side training wall were also founddamaged very badly (Photograph no.05).

Photograph 05 (Training wall)


Photograph 06 (Cavity in Roller Bucket)

Deep cavities ranging between 1.00 m to 4.00 m in front of allthe four bays of roller bucket were also found, Photograph no. 6


Proposed Repair of Spillway Glacis No 03 & 04• It has been proposed by CWC and World Bank to repair one

spillway glacis with M90 grade concrete and the other withM90 grade concrete along with steel fibres. The remainingprocedure of repairing will be same as executed in spillway no.1&2. Mix design for M90 grade concrete will be provided byNational Council for Cement and Building Materials(NCCBM), Ballahabgargh (Haryana).Proposed Repair of Roller Bucket

• It has been proposed by CWC and World Bank to repair theentire roller bucket with M90 grade concrete along with steelfibres as per the actual profile. The repair work will be startedas soon as mix design is available from NCCBM.


CONCLUSIONS AND DISCUSSION• Repairing works of spillway glacis no. 1&2 were carried out by

using M-60 grade concrete and fixing MS steel plate overprepared profile followed by cement grouting. The MS platesof spillway glacis no.1&2 are found intact after passing themonsoon of 2015 & 2016

• The repair works of spillway glacis no 03 & 04 as proposedabove are in progress and the performance of M 90 gradeconcrete with and without steel fibres will be examined afterthe monsoon of 2017. On examination of these three differenttypes of repair works conclusion can be drawn as to whichmethod is the most suitable for repairing of spillway glacis andfor roller bucket.


• The repair work of training wall is also in progress and theobstruction in water paths will be removed to get the desirableflow conditions so as to reduce the impact of rolling boulder.REFRENCES

i. Indian Standard code 10262-2009.ii. Indian Standard code 456-2000.iii. Indian Standard code 383-2016.iv. Indian Standard code 269-2015.v. Indian Standard code 2386-1963.


Thank You

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Third National Dam Safety Conference COMPREHENSIVE ...Drycrete, M-60 grade concrete was used....

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