Fig.7.9-2 Relationship of h and h0

b) Infiltration and water leakage

Infiltration of water into penstock may deteriorate water quality, and water leakage out ofpenstock may loosen surrounding bedrock, so these phenomena shall be controlled.

Detail structures are described in Technical Regulation Article 8. c) Penstock route

As stipulated in Technical Regulation Article 7.5.1 e). d) Expose d type penstock

As stipulated in Technical Regulation Article 8.

7.10Tailraces

Technical Regulation Article 7.10 describes technical requirements on tailraces. a) Safety and stability

As stipulated in Guideline for Technical Regulation Article 7.5.1 a). b) Prevention of leakage

Leakage from a tailrace may loosensurrounding bedrock in case of a tunnel type tailrace and erode the slope in case of an open channel type tailrace. Followings are typical measures to prevent damage by leakage from a tailrace:

Sealing of construction joint, effective for tunnel lining and open channel; and

Tunnel grouting

c)Prevention of damage to downstream waterways

To prevent damage to the downstream waterways due to collapse of a tailrace,regulation pond to absorb spilt water, installation ofsensors to detect collapse of a tailrace and to stop operation of a hydropower plant.

106

Guideline for QCVN xxxx : 2013/BXD

7.11Outlets

Technical Regulation Article 7.11 describes technical requirements on outlets.

a)Stable and safe operation in all working conditions of hydropower plant A location of an outlet shall be selected considering the following conditions:

Structure is based on firm foundation;

Structure is not damaged by flood flow;

Outlet is not blocked by sediment; and

Outflow does not collide with river flow.

b)Stable and favorable connection with downstream channel flow

In case an outlet is connected to an intake of anotherhydropower plant, it is desirable that structures to absorb fluctuation of outflow be prepared in front of an intake of another hydropower plant.

c)Solutions to guaranteestable and safe operation of structures located downstream of hydropower plant

Outflow from an outlet shall not affectstable and safe operation of structures located downstream of hydropower plant. Fluctuation in the river water level does not affect turbine efficiency.

7.12Hydropower plants (Powerhouse)

7.12.1. Technical Regulation Article 7.12.1 describes technical requirements on powerhouses. a) Safe, stable and effective operation

A hydropower plant shall give full scope to its capacity under every condition estimated in the design stage.

b) Appropriate layout

A hydropower plant shall be connected with headworks and a waterwappropriately and harmonize with surroundings. A process for harmonized design shall refer to Article 7.1.4 of this Guideline .

c) Head as calculated in design stage

Water pressure acting on structures and hydropower equipment measured at the site fits design value. d) Appropriate geological conditions

A powerhouse shall be constructed on firm foundation with sufficitbearing capacity tosupport structures.

e) Prevention of inundation

A location, elevation and structures of a powerhouse shall be decided to prevent it from being inundated by flood, water leakage, or any other causes.

f) Drainage system

A powerhouse shall be equipped with a drain pit, water collecting well andadequate pumping system to prevent it from being inundated and keep it in a conditiondry. The number,arrangement, type and capacity of drainage shall be decidedconsidering groundwater level, estimated flood water level, water leakage from penstock and foundation, and any other causes.

g) Erection bay

A location and dimensions of an erection bay shall be selected considering transport from an access road, work schedule of installation and maintenance.

107

Guideline for QCVN xxxx : 2013/BXD

h) Ventilation and lighting

Capacity of ventilation shall be decided considering air temperature and humidity of the project site, and generation of heat from equipment installed in a powerhouse.

Specification of lighting shall be decided considerelevanting laws and ordinances, safety and convenience of installation and maintenance works.

i) Layout of galleries

As stipulated in Guideline for Technical Regulation Article 7.12.3. j) Appropriate transport of machines

A location and layout of a powerhouse shall dbecided considering convenience of machines to an erection bay and connection with an access road and access tunnel.

k) Stable connection with downstream channel flow

In case a powerhouse faces towards a river directly, layout and structure shall refer to Guidelinefor Technical Regulation Article 7.11.

7.12.2. Technical Regulation Article 7.12.2 describes technical requirements onseparation of structures below the turbine floor level.

A part of a powerhouse where is located below the groundwater level or normalverri water level shall provide for unexpected inundation.

7.12.3. Technical Regulation Article 7.12.3 describes technical requirements on galleriesand wells in powerhouses.

a)Minimum dimensions of a gallery shall be decided considering convenience of inspection. A gallery shall be equipped with two gates considering watertightnessand a stairway as an evacuation route in case of inundation.

b)The crest level ofan entrance to an underground powerhouse shall be at least 0.5m higher than the

maximum water level ni downstream to prevent intrusion of water into a well. A well shall be equipped with a watertight cap to prevent it from being submerged by inundation in a gallery.

7.12.4. Technical Regulation Article 7.12.4describes technical requirements onrock support including lining concrete of a powerhouse.

A basic development process of an underground powerhouse cavern is as shown in Fig. 7.12-1. Fig.7.12- 2 shows construction of underground caverns.

108

Guideline for QCVN xxxx : 2013/BXD

Fig.7.12-1 Development process of underground cavern

109