pkw projects in vietnam - · pdf filepkw projects in vietnam m. ho ta khanh ... • weir...
TRANSCRIPT
Van Phong Dam
PKW type A
Plan View of the Van Phong DamDam with 10 radial gates in the central part and about 60 PKW units on each side
Cross-sections of a gated opening and of a PKW
The PKWs’ crest is only 5 m above the river bed, but the base is 10 to 12 m below this level to found the structure on the unweathered rock.
During the high floods, the downstreamflows are submerged.
Except during the floods, the reservoirlevel is maintained at the FSL for the irrigation and the hydropower station (12 MW) supplies.
Van Phong Dam model testsfor different discharges with free and submerged flows.
Construction of the PKW on the left bank and of the gated openingsin the central part of the dam (April 2011)
Construction of the dam in June 2013The works were delayed due to financial issues.
Submerged works during the November 2013 flood.
No damage on the PKWs.About 0.30 m between the U/S and D/S levels.
D/S view at the end of construction (October 2014)
Low overflow on the PKWs with the radial gates closed(the inflows are a bit higher than the turbined discharge and the irrigation intake was closed)
General features of some PKWs constructed in Vietnam
Van Phong Dak Rong 3 Dakmi 4B*
Dam type Barrage with a combination of PKWs and radial gates Concrete step gravity
Concrete gravity
Height of the dam on ground level Pd (m) 16 (on the bed-rock) 25 18.3
Dam’s date of construction 2009 2010 2011
PKW’s date of construction 2010 2010 2011
PKW localisation On the right and left portions of the river channel On the dam crest
On the dam crest
Dam design flood (m3/s) 14 443 6550 642.8
PKW Discharge capacity at MWL (m3/s) 8700 (with submerged flow) 6550 503.1
Head on PKW at MWL H (m) 5.20 3.50 2.0
Specific discharge at MWL q (m3/s) 28.83 32.75 13.6
Time construction (month) Not significant (several interruptions of the works due to
finance issues)24 (whole dam)
24 (whole dam)
Upstream-downstream length B (m) 12.0 18.6 9.0
Upstream overhang crest length Bo (m) 4.80 4.65 2.3
Downstream overhang crest length Bi (m) 2.70 4.65 0
Base length Bb (m) 4.50 9.3 6.7
Total height of the PKW P (m) 4.0 5.0 3.75
Total width W (m) 301.8 200 37
Inlet key width Wi (m) 2.4 5.0 1.8
Outlet key width Wo (m) 2.0 4.0 2.7
Sidewall thickness Ts (m) 0.20 0.20 to 0.80 0.20 to 0.45
Crest thickness at inlet key extremity Ti (m) 0.20 0.30 0.20
Crest thickness at outlet key extremity To (m) 0.20 0.30 0.20
Total developed length along the overflowing crest axis L (m) 1717.8 1018 180
Height of the outlet parapet wall Ppo (m) 0 0 0
Nose form Rounded Rounded Rounded
Dak Rong 3 Dam
PKW type A
Plan view of the Dak Rong 3 Dam
Figure 7: The Dak Rong 3 scheme. Plan view
U/S and D/S views of the dam at the end of construction
The breach on the left side was used for the temporary river diversion
Overflow at the end of construction
Dam overflow with the temporary cofferdam closed for the equipment tests
Combination of gated spillway and PKW
Following the incident of the Hoho gravity dam (gatesjamming with overflow on the dam crest and on the banks), →
the present tendency in Vietnam is to avoid, if possible, using only gated spillway.
A combination of gates and PKW , considered as safer, isthen adopted for several new dams.
* Note the floating debris at Hoho dam during the flood !
Dak Mi dams
Dak Mi dams location
Dak Mi 4B Dam
PKW type B
D/S view of the Dak Mi 4B Dam
Gravity dam with a combination of labyrinthand PKW weirs in place of the Creager crestof the initial design.
This original solution, with labyrinth and PKW weirs, has allowed fitting, at least cost, the project to the new constraints of the site (limitation of the MWL) during the dam construction.
Dak Mi 4B: Former and new alternatives for the spillway
Former design : Creager weir
• Design Flood (500 years) = 641 m3/s
• Weir level (FSL) = 106.00 m
• MWL = 109.11 m
• Crest level of the dam = 110.50 m
• Length of the weir = 55 m
Features of the PKW with
Pm = 2.50 m
* When the construction of the first block of the spillway was at the level 100.50 m, it was decided to lower the MWL at 107.30 m.
Final design*: Labyrinth + PKW type B*
• Design Flood (500 years) = 641 m3/s
• Weir Level (FSL) = 105.30 m
• MWL = 107.30 m
• Crest level of the dam = 110.50 m
• Labyrinth length = 17 m
• Labyrinth width at the base = 4 m
• Labyrinth height = 1 m
• Capacity of the labyrinth at MWL= 139.70 m3/s
• PKW length = 38 m
• PKW width at the base = 6.60 m
• PKW height = 3.75 m
• Capacity of the PKW at the MWL = 503.10 m3/s
U/S view of the Dak Mi 4B Dam
Dak Mi 4B Dam
D/S views of the PKW
Dak Mi 4B Dam
U/S details of the PKW
Dak Mi 4B Dam
View of the labyrinth weirwith a floating log
Dak Mi 4B Dam: a combination of free overflow and bottom outlet
D/S view of the bottom outlet
Dak Mi 4B Dam (end of construction)
Overflow during the construction of the footbridge
Dak Mi 4C Dam
PKW type B
Dak Mi 4C Dam
Gravity dam with 2 gates and a PKW on the left side
Dak Mi 4C Dam
U/S views of the PKW on the left side and the 2 gated openings on the right side
Dak Mi 4C DamDetails of the PKW
For this scheme (small HPP), the sizing of the PKW was carried out only with the utilization of the «standard model type A» provided by Hydrocoop in order to reduce the cost and the delay of the study.
Dak Mi 4C Dam
D/S views of the PKW with the stepped outlets.
Construction of the PKWs in Vietnam and in FranceVietnam ↓ France ↓
Except the Van Phong Dam, note the very badquality of the concrete of the Vietnamese PKWscompared with the PKWs constructed in France : sofar these PKWs are generally constructed by Independent Power Producers at low cost and by incompetent contractors !
The development of PKW can be hindered by these bad examples !
Dams under design
The Dak Mi 2 DamPKW type B
RCC dam with H = 38 m and L =144 m
• The peak discharge of the check flood (1000-year) is 6 500 m3/s.
• The spillway includes a 2 gates-surfacespillway in the central part and two P.K weirs onthe two sides, with steps on the downstreamface and on the left bank.
• This alternative was selected as it allows:
– with the gates, to evacuate 3000 m3/sduring the design flood and to control thewater level during the first filling of thereservoir and in operation.
–with the P.K weirs, to evacuate 3500m3/s during the design flood with a shortspillway length (W=75 m), minimizing theexcavation on the left bank. Thecombination of the P.K weirs and thestepped spillway permits to reduce thesize of the stilling basin.
• The tests confirm that, even in the case the 2 gates are jammed during frequent floods (inf. to the 100-year flood), there is no overflow on the dam crest.
F.E.M analysis of the dam and the PKW
Vinh Son 3
Dam under design with 2 new alternatives:
- PKW, with one or two surface gatesin the central part of the dam.
- PKW, with a large orifice spillway on the right side.
Spillway of the Ngan Truoi Dam
PKW type A
.
This design was cancelled following a modification of the general scheme.
Proposal for the Xuân Minh Dam
Preliminary study of a barrage according to the Van Phongmodel.
Proposal for the use of a PKW type D in place of the type A.
Proposal for the Xuân Minh Dam
New alternative Type D (outlet)
Đá Hàn Spillway - Hà Tình
If the 2 linear weirs on each side of the central
gate were replaced by 2 Piano Key weirs, it will
be possible to keep the same total width for the
weir, the chute and the plunging pool with the
following advantages:
- Improvement of the flow downstream the weir
(no contraction).
- Cost savings for the weir and the piles in
foundation (reduction of the weir width).
Thank you for your attention !
Note the betterintegration in the environment of the PKWscompared withthe gates and the pillars.