Guideline for QCVN xxxx : 2013/BXD

1) USACE Engineer Manual EM 1110-2-2200 Gravity Dam Design

This engineer manual regulates design of concrete gravity dams and describes major differences between conventional concrete dams and RCC dams.

2) USACE Engineer Manual EM 1110-2-2006 Roller Compacted Concrete

This engineer manual describes essential points on construction of RCC dams and allows space for mix design and quality control of concrete.

Fig 7.3-16 Installation of waterstop, joint drain, and crack initiator

3) USACE Pamphlet EP 1110-2-12 Seismic Design Provisions for Roller Compacted Concrete Dams

Earthquake resistant design of roller compacted concrete(RCC) dams are basically thesame as conventional concrete gravity dams. This engineerpamphlet summarizes essential points for seismic design of RCC dams.

4) FERC Engineering Guidelines for the Evaluation of Hydropower Projects Chapter 3 Gravity Dams This guideline summarizes points to note for design and construction of RCC dams.

2. Concrete face rockfill dams (CFRD)

This type of dam is composed of anembankment made by pervious rock and sand materials, impervious face diaphragm and cut-off or plinth. Pervious materials with particle sizedistribution suitable for

compaction are used for an embankment, and they are spread out in a thin layer and compacted to minimize settlement of an embankment. A transition zonecomposed of crushed rock or sandis prepared

on the upstream surface to transmit load from a surface diaphragm to an embankment uniformly.

A concrete diaphragm must be designed to prevent development of crack caused by nonuniform settlement of an embankment or thermal load. Empiricaldesign adopts the minimum thickness of a concrete diaphragm of 30 cm and its thickness increases in a ratio of 2 to 3 mm of increment of water depth by 1.0 m. Empirical unit amount of reinforcing bars is 0.3 to 0.5 % of the sectional area of a concrete diaphragm.

Article 7.3.1.5 describes technical requirements of a plinth.

7.4Spillways

Technical Regulation Article 7.4 describes technical requirements on spillways. Spillways for concrete dams are regarded as a part of a dam body, so details of concretestructures shall refer to Guideline for Technical Regulation Article 7.3.4 and 8.3 of QCVN 04 - 05 : 2012/BNNPTN.

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Technical requirements are described quoting provisions of Articlef QCVN8.3o 04 - 05 : 2012/BNNPTN.

8.3 Discharge works

8.3.1 Must guarantee the safety and stability working condition in the design and examined circumstances. Water should be discharged actively regarding to the managing and exploiting regulations so as to ensure that the water level in a reservoir will not excess the stipulated level.

This article stipulates that discharge facilities, form a spillway down, shall discharge design flood and check flood safely, and that thereservoir water level shall not exceed the designated level for each flood condition.

8.3.2 The general layout and structure of discharge works and continuing solutions between a construction and downstream must guarantee that the following requirements will be met in case of its operation:

a)Not influence on the safety and stability of a reservoir and its normal operating andmanaging condition;

b)The discharge of the design flood will not destroy natural characteristics of downstream channel,

not impact on socioeconomicactivities and normal operating condition of permanent hydraulic works in lower steps as well as not damage constructional works in downstream discharge works. The navigation work must guarantee that flow and velocity in downstream will not affect the normal operation of ships;

c) The operation at the examined water level allows:

- Reduction in the production of hydro-power station (if it supports safety condition of the construction);

-Abnormal working conditions of water intakes. Nevertheless, it will not lead to failures situations for water consumption sectors;

-Discharging water through close conduits with variable hydraulic states (from free flow to pressure flow and reverse) but it will not bring about the destructions of conducted lines;

-Eroded channel flow and slope in downstream head-works. However, those failures will not become hazards to the destruction of major work-items of the head-works as well as the safety condition of residential, industrial areas and infrastructures in downstream.

-Failures in the standby discharge works. However, those failures will not influence on the safety condition of major construction.

8.3.3 The computed discharge flow during the exploitation period through the permanent discharge and supply works of head-works should be determined on the ground of design flood flow, which is stipulated in the article 5.2.1 and table 4. The calculation and determination will be in accordance with the variations of the design flood flow, causedby the reregulatedactivities of current or design reservoirs, as well as the changes in the flow forming condition resulting from socio-economic activities in the basin.

A design and check flood discharge for each class shall refer to Table 4 of Article 5.2.1of QCVN 04 - 05 : 2012/BNNPTN and shall be reviewed properly considering changes in surrounding circumstances.

Examples of regulations on flood discharge criteria in the foreign countries are shown below for reference.

1. Example of Japan

1)Concrete dams

The design flood is the largest value selected among the following methods: 1) A flood estimated to occur at a rate of once in 200 years

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2)The maximum flood that has occurred at the dam site

3)The flood which is obtained by Creager’s formula, i.e. q = C×A×(A-0.05-1).

q: specific yield (m3/s/km2), A: catchment area(km2), C: regional factor (given in the guideline)

2)Fill dams

The design flood is 1.2 times of the value estimated by the above method for a concrete dam

Source: Governmental Ordinance for Structural Standard for River Administration Facilities, Ministry of Land, Infrastructure, Transport and Tourism, Japan, July 20, 1976.

2.Example of P.R. China

Table 7.4-1 Criteria for Project Ranking

Note MCM : Million Cubic Meters

Source:Unified Design Standard for Reliability of Hydraulic Engineering Structures, GB-50199-94, P.R. China, Nov. 01, 1994.

Table 7.4-2 Criteria of Design and Check Flood (Return Period to be Applied)

Source: Flood Control Standards, GB-50201-94, P.R. China, Jan. 01, 1995.

3.Example of U.S. Army Corps of Engineers

Table 7.4-3 Size Classification

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Source of Table 7.4-3 to 7.4-5: Engineering Regulation ER-1110-2-106, Recommended Guidelines for Safety Inspection of Dams, Appendix D, U.S. Army Corps of Engineers, Sept. 26, 1979.

4.Example of Norway

Norway adopts a double design criterion:

The 1,000 year probable inflow flood is prescribed as design flood for normal operation of dam spillway system, while the stability of the dam is subject to the PMF.

5.Example of Canada

Note 1) Incremental to the impacts which would occur under the same natural conditions(flood, earthquake or other event) but without failure of the dam. The consequence(i.e. loss of life,or economic losses) with the higher rating determines which category is assigned to the structure. In the case of tailings dams, consequence categories should be assigned for each stage in the life cycle of the dam.

2) The criteria which define the Consequence Categories should be established betweenthe Owner and regulatory authorities, consistent with societal expectations. Where regulatory authorities do not exist, or do not provide guidance, the criteria should be

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set by the Owner to be consistent withsocietal expectations. The criteria may bebased on levels of risk which are acceptable or tolerable to society.

3)The Owner may wish to establish separate corporate financial criteria which reflect their ability to absorb or otherwise manage the direct financial loss to their business and their liability for damage to others.

4)An appropriate level of conservatism shall be applied to loads from this event, toreduce the risks of dam failure to tolerable values. Thus, the probability of dam failure could be much lower than the probability of extreme event loading.

5)Within the High Consequence category, the IDF is based on the consequences failureof. For example, if one incremental fatality would result from failure, an AEP of 1/1,000 could be acceptable, but for consequences approaching those of a Very High Consequence dam, design floods approaching the PMF would be required.

6)If a Low Consequence structure cannot withstand the minimum criteria, the levelupgradingof may be determined by economic risk analysis, with consideration of environmental and social impacts.

Source of Table 7.4-6: Water Act, Alberta Province, Canada, January 1, 1999.

A design and check flood discharge in a cascade exploitation shall follow Article 4.2.5.

8.3.5 Reservoirs of class I and above, apart from the major flood spillway, the standby spillway (overflow the checked floods) should be placed. Reservoirs of class II and below will be arranged with the standby spillway in case of adequate arguments and acceptance from the investor:

a)The major spillway must obtain adequate capacity in order to discharge design and checked floods;

b)The standby spillway in accordance with the major spillway must evacuate a flood that exceeds the checked flood and guarantee that water in a reservoir will not overflow through the dam crest. The frequency of a flood, that exceeds the checked flood, refers below stipulations:

-Works of special grade: flood with frequency of0.01% (in accordance with the returned period of 1000 years) or extreme flood;

-Works of grade 1 and below: equal frequency of checked flood regarding to works of grade being increased one class (referring to the Table 4);

c)A class of a standby spillway can be lower than that of the major flood spillway;

d)If there are not adequate conditions for the arrangement of individual standby spillways, the major spillway will be studied to extend or the dam height will be increased so as to improve the regulated volume of a reservoir. The two above approaches can be applied individually or in a combination solution in order to evacuate a flood exceeding the checked flood;

e) The determination of a model for a flood exceeding the checked flood as well as a ofclass standby spillway is proposed by the design consultation and accepted by the decision authority for the investment.

A standby spillway shall be surely placed in a dam of Special and Class I, and placed after due discussion with an investor of Class IIand below against inflow exceeding a check flood. A design consultantshall estimate flood for a standby spillway and design structures for approval of the decision authority.

8.3.6 A reservoir, which has flood discharge work such as flood relief welltunnelor -type discharge carrier, must place the discharge construction for a flood exceeding the design flood (emergency spillway).

A dam equipped with a tunnel type spillway shall have an emergency spillway against inflow exceeding a design flood.

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8.3.7Apart from a major flood spillway, researches on the application ability of other

Fig.7.4-1 Classification of reservoir sediment management

8.3.8 The flood discharge work is permitted to arrange on the dam crest and inside the body of a concrete barrage or on the compacted rock-fill dam with concrete face. However it must guarantee

the safety condition for a dam during the constructional and exploitation periods. Regarding to barrages using locally natural materials such as earth dam, rock-fill dam or earth and rock-fill dam,

the flood discharge work will be placed separately from the barrage.

A spillway may beequipped with a dam body of a concrete dam butitshall not damage safety and stability of the dam body. A spillway shall not be equipped on a dam body of an earth dam, rockfill dam or earth and rockfill dam except a concrete faced rockfill dam.

8.3.9 The flood discharge for constructions from class I and above or class II in accordance with complex hydraulic states, model experiments will be implemented in order to obtain adequate evaluations about the reasonability of hydraulic arrangement and design.

A shape, arrangement and capacity of spillway shall be confirmed by a hydraulic model test for a dam of Special and Class I.

8.3.10Structures of the flood discharge and release constructions as well as its continuing

work-items should be computed regarding to the basic exploiting situations -andexaminedre

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regarding to the extra-ordinary circumstances to guarantee the safety condition for a construction. It also ensures that water is not allowed to excavate through the crest pressurealignment. Computing circumstances are:

a) Working with the maximum design water level in upstream of the head-work: fully opened water discharge works in case of design flood, operating turbines and normal working condition of other discharge and supply works. The operation pursue that circumstance, work-items in the head-work including the continuing parts in up and downstream must be in normal working condition and are not broken. Load and influence in coherence with this situation will be computed based on the basic loads compounds. If there are adequate arguments, there will be the considerations about the ability of blocked discharge gates;

b) Working with the maximum examined water level in upstream of the head-work: All of discharging and supplying works, which are mentioned in the item a, in accordance with standby spillways will be fully opened in case of the checked flood. The ability of blocked discharge gate will not be considered. Loads and influences in this case are in coherence with the special load compound;

c) Other gate-opening-combinations will be considered in order to meet the design targets and ensure the safety condition of a construction in case of the flood regulation or emergency situations;

d) Consideration about the occurring ability of a flood that exceeds the checked flood.

NOTE: Regarding to the computed circumstance, mentioning in the item ‘a’ of the article8.3.10, if there is a blocked situation in a major discharge gate, it will be calculated in accordance with the special load compound.

Discharge of a design flood shall not obstruct a normal operation of a hydropower plant or damage river facilities in the downstream area.Partial blockage of discharge gates is allowed in case ofdesign flood but not allowed in case of a check flood because discharge capacity of a spillway is designed to be able to discharge a check flood with a whole ability of spillway gates.

8.3.11 The determination of the unit discharge rate (specific discharge), downstream channel velocity, continuing state for downstream flow, structure of major constructions as well as methods for energy dissipation and consolidation in downstream area should base on the comparison among economic and engineering criteria of options.

Table 3 and 4 in Article 1.44 of 14TCN56-88 provide with guidance for allowable specific discharge of a spillway to prevent erosion in the downstream area.

Table 3 – Allowable specific discharge of different soils corresponding to different flow depth (*)

(*): M.Grisin, Design of hydraulic works on non-rock bases, page 114, 1966.

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