Section 2 Check of Civil Works' Condition

Article 68. (Article 68) Routine inspection and emergency inspection

1. Purpose

Article 68 stipulates requirements of routine and emergency inspections. 2. Routine inspection

A routine inspection is divided into an inspection of the external appearance of civil works and appurtenant mechanical equipment to confirm if they are in a sound condition and to prepare a repair

plan for reference.

3. Emergency inspection

An emergency inspection must be conducted in the following situation.

At earthquake events

In case a seismometer installed at the bottom of a dam recorded seismic acceleration of more than “AA” gals at an earthquake event.

Definite acceleration “AA” gals must be prepared at each power plant as the criteria for execution of emergency inspection for each major civil works.

At torrential rain or flood

In case it rained more than BB mm per day at a dam or inflow to a reservoir exceeds CC m3/s. Definite rainfall “BB” mm and inflow “CC” m3/s must be prepared as the criteria for execution of emergency inspection for each civil works for each dam and reservoir.

Others

In case civil works is damaged by any other phenomena, an emergency inspection must be conducted.

Article 69. (Article 69) Revision of monitoring program

This article stipulates that a monitoring program must be revised according to conditions and capacity of measuring devices as follows:

1.A monitoring program must be revised when it is difficult or inappropriate to continue monitoring under the same conditions with present methods or at present locations. Some examples are shown as follows.

When measurement cannot be continued in the original condition as measuring devices are buried due to progress of sediment, or damaged by earthquake or any other natural disasters.

When measuring devices are lost from the original location due to landslide, flood, change in topography or any other reasons

When measuring devices are out of order or get too old to replace them with the same ones of same specifications

When there is an event which affected some monitoring data due to change in conditions of civil works.

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2.Monitoring is not mere accumulating measurement data but it is important to analyze the observed data in view of variation in order to detect the changes in the conditions of civil works.

3.Measuring instruments must be calibrated periodically to maintain their accuracy by the supplier of measuring devices or competent authority. Frequency of calibration must be decided in consultation with their manufacturers.

Article 70. (Article 70) Investigation of monitoring data

Paragraph 1 of Article 70

This paragraph lists major monitoring items of civil works to see if they are in sound conditions. 1. Purpose

In general, monitoring of dams is conducted during construction and operation for the following purposes.

Construction supervision

Study on problems of structural analyses and design method of dams

Safety control

In general, it is judged that a dam is safe as long as values of monitoring data do not exceed those measured in the initial impoundment except in case of an earthquake. So it is practical to judge safety

of a dam by comparing monitoring data with those measured at the normal high water level in the initial impoundment stage or near the normal high water level in normal operation stage rather than comparing them with design values.

In addition, in case of a fill dam, settlement of a dam body continues after completion of embankment, so safety of a dam must be judged not only by comparing monitoring data with those measured at the normal high water level in the initial impoundment stage or near the normal high water level but also

by observing tendency in changes of settlement or deformation and also changes in seepage water level of an impervious zone in case of a zone type fill dam or seepage water level of the dam body in case of a homogeneous type fill dam.

Investigation of major monitoring items is shown in the following sections. 2. Displacement

Generally in concrete dams, displacement of a dam body fluctuates constantly according to fluctuation of air temperature, and water temperature and water level of a reservoir. A seasonal change

affects displacement of a dam body more than a change in the reservoir water level in the order of a concrete gravity dam, arch gravity dam and arch dam.

Displacement according to a change in air and reservoir water temperature is not considered in design,

so it is necessary to exclude an influence of a change in temperature from measurement records of displacement of a dam body by a graphical solution or a multiple regression analysis.

According to case studies on a dam breach, in case that a dam breach is caused by defects of bedrock, a large amount of water leakage is observed around the bedrock where destruction starts.

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Empirically, it is judged that water leakage may not affect dam safety if quantity of water leakage decreases with passing time or constant.

Water leakage is divided into the following three types.

(1)Water leakage from a reservoir to downstream of a dam by seepage through bedrock or through embankment in case of fill dams;

(2)Water leakage from a reservoir to downstream of a dam through joints and cracks of a concrete dam body or a surface diaphragm of surface diaphragm type fill dams; and

(3)Water leakage from foundations surrounding a dam.

For safety control of dams, water leakage of type (1) must be watched, especially that from a fault zone or other weak zones where there is a stratum consisting of fine particles.

In case significant increase in quantity of water leakage through bedrock is observed in the initial impoundment stage, it must be confirmed if water leakage is turbid. In case water leakage is turbid,

the place where water springs up must be investigated and proper measures such as additional grouting must be conducted in the periphery of the place of water leakage. In case quantity of water leakage increases and especially turbid water springs up from a weak stratum, the reservoir water level must be lowered and measures must be considered. In case water leakage does not contain silt,

mud or other small particles, and the place where water leakage springs up consists of sound rock, conditions of water leakage must be observed with the same reservoir water level as the time when water leakage is found first. In case quantity of water leakage remains constant or decreases, it is judged that a dam is safe against water leakage.

In other cases, quantity of water leakage sometimes increases immediately after a severe earthquake, however, the quantity decreases gradually and returned to its former value in most of the cases.

In case a dam meets with a severe earthquake, the dam is judged to be safe if quantity of water leakage decreases gradually though it increases suddenly just after the earthquake. In casequantity of

water leakage just after a severe earthquake increases more than the maximum value observed in the initial impoundment, it is estimated that seepage paths are made in a dam body, dam foundation or bedrock. Under these circumstances, a situationin galleries, and upstream and downstream surface of

a dam body must be investigated carefully, and places where quantity of water leakage got more than that before the earthquake must be confirmed, if any.

4. Uplift

In general, it is estimated that sudden ncreasei in uplift is caused by formation of additional seepage paths and it often occurs with sudden increase in quantity of water leakage.

In case increase in uplift and quantity of water leakage occur simultaneously, the same measures as ”3. water leakage” must be considered.

In case only uplift increases and quantity of water leakage does not increase, uplift must be measured at drain holes around the hole(s) where increase of uplift is observed and the extent of high uplift must be investigated.

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Paragraph 2 of Article 70 Investigation of monitoring data

In unusual or unexpected cases such as heavy earthquake or even aging of structure is observed, additional monitoring is required to secure the safety of structures. In this regard, this paragraph stipulates that the Owner must observe particular conditions of civil works listed above by surveys and investigations.

The background and approach of surveys and investigations works are described as follows;

Vibration of civil works;

Conditions of an intake, outlet, penstock and powerhouse must be observed to check if unusual excessive vibration which may damage their stability and function or cause fatigue fracture occurs.

Durability and waterproof of concrete;

Conditions of concrete at concrete dam and other concrete structures must be observed to check if damage or any kind of deterioration which may affect durability and watertightness of concrete such as cracks, alkali aggregate reaction, salt damage, neutralization, etc. occurs.

Behavior of structures due to thermal stress;

Conditions of structures at concrete dams and exposed penstocks must be observed to check if an extent of expansion and contraction is within a designed value and if excessive expansion and contraction cause water leakage, damage of supports or any other troubles.

Corrosion of metal and concrete;

Conditions of metal and major concrete structures must be observed to check if corrosion which may damage normal functions occurs.

Conditions of welded seams;

Conditions of welded seams at gates and exposed penstocks must be observed to check if defects which may damage stability or watertightness occur.

Paragraph 3 of Article 70 Investigation of monitoring data

This paragraph stipulates that the Owner must keep civil works in touch with requirements of the latest circumstances.)

Following changes in working conditions of civil works may severely change working conditions of civil works.

Operating rules

Change in reservoir water level: In case the normal high water level is raised, hydrostatic pressure acting on a dam increases. In case available drawdown is expanded due to change in use of reservoir water, change in seepage water level in a fill dam affects its stability.

Change in reservoir operation rule: In case maximum discharge for powerenerationg is enlarged for expansion of a powerhouse, an increase in drawdown rate becomes severer for stability of a fill dam.

Natural conditions

Change in river discharge: In case peak flood discharge increases due to climate change, flood water level may increase and hydrostatic pressure acting on a dam may increase.

Change in sediment inflow: In case sediment inflow to a reservoir increases due to change in vegetation of the surrounding area, sediment level of a reservoir may rise and sediment pressure acting on a dam body may increase.

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When the events including the above which would change the conditions of civil works severely occurred, an additional inspections and surveys are required to observe the change in the conditions and to check and confirm the stability and safety of civil works.

Article 71. (Article 71) Location and geometrical features

Displacement of civil structures are measured by survey works. To measure accurate dimensions of the structure and a long term tendency of change in location and dimensions, it is desirable that the same reference points must be used as long as possible.

Base marks and mediate ones of civil works such as dams, headworks and powerhouses These marks are used as reference points of the structures.

Location and elevation of anchor blocks of exposed penstocks; These data are used to measure displacement of anchor blocks.

Geometrical features such as length, starting points, terminal points, radius of curves, and location of submerged and embedded equipment for dykes, dams, inlets, canals, and tunnels.

These features are used to record initial conditions of the structures.

Article 72. (Article 72) Protection of measuring devices

This article stipulates that the Owner must keep measuring instruments in good conditions to conduct the monitoring accurately.

Important measuring instruments and relevant appurtenances must be installed in such a place that may not be damaged by natural hazards, i.e. torrential rain, inundation, debris avalanche, etc. The site

of the instruments and relevant appurtenances must be protected by a fence and those doors and covers must be locked to prevent them from artificial obstruction.

Article 73. (Article 73) Board on flood control

Article 73 was prepared based on the requirements in Decree No.72/2007/ND-CP and Circular No.34/2010/TT-BCT. Relevant articles of decrees and circulars are as follows:

Decree No.72/2007/ND-CP:

Article 18. Protection boundary of dam

1.Dam protection boundary includes dam and surrounding protection area

2.The dam Owner shall be responsible for defining, making benchmarks of the boundary of dam

province to issue concrete regulation and implementation of making benchmarks; responsible for management of project protection areas as specified in the Regulation.

Article 20. Ensuring dam safety in flood seasons

1. Dams belonged to flood control projects: each year, prior to the flood, raining season, the dam Owner shall prepare or update, supplement the alternative for protection against floods, typhoons, submit the alternative to the State competent organization for approval.

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2.The contents of the alternative for protection against floods, typhoons shall include:

a)Summary of features, conditions of water reservoir relating to the works for protection against floods, typhoons;

b)Progress of situation and features of rains and floods at the upstream of the reservoir;

c)Assessment of dam quality and equipment operating on the dam;

d)Anticipating the dam unsafe circumstances which could happen and technical solutions for forecast, finding, copping with and warning on flood, typhoon.

e) Preparation works on personnel, materials, back-up materials, equipment, transport means, communication, lighting etc.;

f)List of members of steering committee on prevention and protection against flood, typhoon.

3.After the alternative has been approved, the preparatory works shall be performed; materials, tools shall be gathered and protected at the specified points; the technical staffs, rescuing team, rescuing facilities shall be managed in compliance with regulation in order to be ready for operation in when necessary. The Steering Committee on prevention and protection against flood, typhoon shall organize meeting for endorsement of the regulation on working and being on duty.

4.Throughout the flood, rainy season, the dam Owner shall maintain communication system in good working conditions and report the situation to the higher level of The Steering Committee

on prevention and protection against flood, typhoon and State competent organization, as specified in the Regulation.

Circular No.34/2010/TT-BCT:

Article 13. Flood protection for downstream areas caused by flood discharge or dam failure

1.Plans preparation a) The dam’s owner shall collaborate with local authority in preparing flood protection plan for downstream areas when discharge flood or dam failure occurs, then submit to the Provincial People's Committee for approval; b) The plan shallist outl the affected

subjects, the influence degree and countermeasures in appropriateness with different flood situations.

2.Dam owner shall announce (by phone or fax) to the local meteorological & hydrological forecasting organization, Local Flood Control Steering Committee in downstream area the following content:

a) The operation of flood discharge gate according to regulations; b) The flood discharge in

3.Dam owner shall install alarm and notice system to notify the upstream / downstream dam’s owner, report immediately to the Provincial People's Committee, Local Flood Control Steering Committee for coming dangerous cases caused by dam damage or failure.

Article 14. Organization of implementation

1.Department of Safety Engineering and Industrial Environment– MOIT is head organization to carry out the inspection and approval for flood protection plans for dams cases as mentioned in Paragraph 2 of Article 12 of this Circular andinspect national wide the implementation of the regulations on dam safety management of hydropower structures.

2. DOIT takes a lead and collaborates with local competent authorities to inspect the implementation of the regulations on dam safety management of hydropower structures in the

province.

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