MEMORANDUM

DAMS AND HYDROPOWER SECTION

36 CIVIC CENTER BLOCK M, MODEL TOWN (EXT) LAHORE
From:

Subject:

Sheikh
Shahid
Iqbal

Advisor
(Structures) ACE D&H Section, Lahore

To:

Mr. K A Ansari Excecutive

Director (CA), ACE Corporate
Office, Karachi
Date: Aug 25, 2014

ACE Manual AMD-06 (Draft) Design of Reservoir

Outlet Works, for Review
Ref:

Reference:

Given below

ED/303 dated 15-08-2014 from Executive Director (CA), ACE Corporate

Office, Karachi, to Distribution

A few items requiring some editing / attention are listed below:

1. Plain Cement Concrete and Reinforced Cement Concrete: Refer (a) Statement
Need of liningcement concrete (p I-3), (b) Statement The conveyance
structuresteel pipe (p II-2) and other locations. In ACI and other standard
references wordings are Structural Plain Concrete, and Reinforced Concrete;
which is more appropriate. [Please replace the wordings cement concrete [by
Structural Plain Concrete], and reinforced cement concrete [by Reinforced
Concrete / RC], in the whole document].
2. Use of term head: Preferably write hydrostatic head. .
3. Ref 1.4.1 General: Add after The type specific to embankment damconduit.
However, as far as practicable, outlet through embankment may be avoided
as explained later under Cut and Cover Conduit.
4. Ref 1.4.1 General: Add after Where there are alternativesgovern. The
preferred option is to avoid an outlet from within the embankment dam
body, even though this option may not be the most economical.
5. Ref 1.4.2.1 Tunnel Outlets: Edit the text (p I-4) No lining isrock formation.
While theoretically no lining is required for a flood flow diversion and
hydropower generation tunnelrock formation, concrete lining is often
provided to produce smooth flow surface to reduce hydraulic losses and
consequent cross section area, and protection of rock surface against
erosion by local cavitation / abrasion.
6. Ref 1.4.2.1 Tunnel Outlets: Edit the text (p I-4) Plain cement concretelined
fully. Structural plain concrete lining is generally provided for water supply
lining is required only on the floorlined fully.
7. Ref 1.4.2.1 Tunnel Outlets: Edit the text (p I-4) Reinforced cement concrete
internal load. Reinforced concrete liningis able to withstandto the
internal hydrostatic pressure. [This is suggestion only].
8. Ref Table 1.3 General GuideTime: It is Time in Hours or minutes?

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9. Ref 3.3.4.3 Downstream Control: Elaborate the statement addressing internal

and external hydrostatic head For penstocks through the embankmentsin this
case the entirereservoir head. External hydrostatic pressure is also a
consideration, when the penstock is depressurized.
10. Ref 4.1 Introduction: Please check / edit the text of paragraph 3 Outlet
componentsfour types after outlet appurtenances. .
11. Refer 4.2.1 Approach Channel: (a) Refer text For an excavatedinto
consideration. Add when deciding the channel side excavation slopes. (b)
Please check the next paragraph To retain upstreamare provided. [where?]
12. Refer 4.3.2 Stability of the Control Structure: Edit statement When the
Controlsafe against flotation, overturningsafety in the applicable load
conditions. Besidescapacity. Add a paragraph after Case VI (f) All
bulkheadsstructure In partly submerged structures, when uplift is not
separately accounted, submerged weight of concrete and steel
components to be considered and buoyancy of the hollow spaces, in
structure portion below water level.
13. Refer 4.3.3.2 Gate Structure near Dam axis: Add after may be neglected in the
stability analysis but duly considered for reinforcement design.
14. Refer 4.3.4 Gate Frames and Conduit Liners: Edit second paragraph.
Adjacent to thestage II concrete should be tied with stage I concrete by
means of dowels provided in stage I concrete.
15. Refer 4.3.5 Air Vent: (a) Briefly address the requirement of Air Vent. (b)
Please write after operation of the gate, Suitable mesh / grill may be provided
at the inlet, to forestall entry of birds / unwanted objects.
16. Refer 4.4 Tunnels: (a) In first sub-paragraph, add few words after imbalanced
pressure head to elaborate (cause of imbalance). (b) Edit the text Thickness
of lining variesreinforcement is required WRT constructability and concrete
cover. Note that Thickness of concrete lining is determined by constructability
rather than structural requirement. Minimum practical lining thickness is about
225mm, Clear concrete cover is taken as 75 to 100mm, which is greater than
normal, to allow for misalignment during concrete placement, abrasion, and long
term exposure to water [Ref EM 1110-2-2901 Tunnels and Shafts in Rocks].
17. Refer 4.4 Tunnels: (a) Please edit paragraph In a free flowdepth of flow.
The quite categorical statement in support of use of structural plain concrete and
provision of lining only up to flow depth may be reviewed. (b) Please use the
term Consolidation Grouting rather than grouted.
18. Consolidation Grouting: Refer 4.4 Tunnels. Consolidation Grouting of the
rock around the lining of a pressure tunnel and the filling of all voids is a
necessity if the rock is to take part of the radial loads. In tunnels excavated
by drilling and blasting, a weak rock (plastic) zone is formed around the
excavation. Consolidation Grouting also stabilizes the plastic zone.
19. Contact Grouting: Refer 4.4 Tunnels: Add few lines. Contact grouting is
provided for improved contact at the interface of rock and concrete lining
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of the constructed section where small gap may form between concrete
and rock surfaces due to concrete placing against gravity or shrinkage.
Contact grouting refers to the filling of voids between concrete and rock
surface with grout. The grouting pressure is 300 to 500 KPa. Extent of this
grouting is generally limited to about 120 o to 180o arc in the crown region
performed through grout-holes that have been either pre-placed or drilled
in the concrete lining for this purpose.
20. Refer 4.4 Tunnels: Rock mass stabilization based on method of excavation, may
be briefly addressed
21. Joints in Tunnel: Ref 4.4 Tunnels : (a) Time lapse in concrete pouring in
adjacent panels, shall be about 5 to 10 days. (b) Resistance to shrinkage and
expansion offered by rock excavated by drill and blasting method is important, as
the tendency is partly resisted at the interface of tunnel and rock. (c) Expansion
joints are avoided in pressurized tunnels. If expansion joints are not provided, it
may be more feasible to limit the concrete pour length to lesser than about 15m
adopted for (massive) hydraulic structures in open. (d) Vertical joints in tunnels
may be contraction type with no reinforcement crossing the joint.
22. Drawings: Refer 4.4 Tunnels: Structural detail drawings shall address probable
method of excavation, and show (a) Components of rock mass stabilization
(Shotcrete, Rock Bolts, Steel Supports etc), Theoretical Excavation and Actual
(Payment) Lines, (b) Concrete lining thickness and reinforcement details, (c)
Contact and Consolidation Grouting, (d) Joints and waterstop; etc i.e. all
features and/or items of BOQ, to facilitate the bidder in preparing realistic bid. .
23. Hydraulic Factor for Reinforcement Design: Following may be added.
Hydraulic Factor: Outlet works structures are categorized as hydraulic structures.
The reinforcement design considers factored moment and tension multiplied by
an additional factor called hydraulic factor. Recommended value in ACI 350R-01
Environment Engineering Structures and USACE document EM 1110-2-2104
Strength Design for Reinforced Concrete Hydraulic Structures, given below:
Force
Factor Remarks
Flexure / BM
1.30
BM in beams, slabs, walls
Shear Force
1.30
Only on shear to be taken by steel
Direct Tension
1.65
Tension tie / components in direct tension
Hydraulic Factor is not applicable to combinations governed by seismic loading
Thank you and assuring you of my best services.
(SSI)

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