TOR Geophysical Investigation-V-04

TERMS OF REFERENCE FOR GEOPHYSICAL INVESTIGATION

Contents

1.      Statement of Requirement. 2

2.      Scope of Work and Technical Specifications. 2

3.      Contractor’s Requirement. 3

4.      The Bidder. 3

5.      Reports’ Submittal 4

6.      Estimated Cost of the scope of Work: 4

7.      Time Schedules. 5

1.Statement of Requirement 

Darunta Dam is constructed on Kabul River approximately 15 Km north of the city of Jalalabad. Approximate coordinates of the dam axis are 34° 29' 06 " N and 70° 21' 49" E.  Height of the dam is about 22 m.

The dam crest is approximately 8 meters wide and is concrete paved and is used a functional road link across the river. Upstream face of the dam pitched with stone and cement and downstream face is stone pitched a stone pitched wall, topped by a wide concrete capping. The Dam has a number of gated spillways. The dam has two spillways one each on both sides of the Embankment dam. A schematic diagram of the dam showing two spillways, top road and mid level bench on the downstream face is attached for reference.

Currently some seepage is apprehended in the dam body as some water is entering into the dam along the contact between the concrete wall of spillway and the embankment dam as highlighted on the sketch with arrow mark. The survey is aimed to detect the seepage path and its effect on the rock fill material beneath and possible piping or cracking.

2.Scope of Work and Technical Specifications

Primary objective of the work is to conduct geophysical surveys to identify:

• Identify the embankment materials.
• Identify internal erosion/ leakage in the dam.
• Identify any Cracks in the dam body.
• Identify various layers of dam.
• Identify the foundation condition and depth to bed rock and type of bed rock.
• Show 3D Model of Darunta Dam.
• Interpret the results in a format that will facilitate design of the grouting measures which should stop the leakage.

The geophysical surveys should include resistivity imaging/ resistivity surveys, suitable for a rockfill dam with clay screen.

Possible methods to be applied for the investigations include:

• Ground penetrating radar;
• 3D electrical resistivity imaging;
• Streaming potential;
• Sonic/ultrasonic impact echo.

It is Client’s requirement that the testing method used is of a non-destructive nature (NDT), given the state of the embankment.

However, the bidder can choose a method or combination of methods, in which case it will be limited maximum to three methods, to achieve the above objective.

Two lines A-A’ and B-B’ are anticipated on road above dam and mid level bench respectively as shown in the enclosed sketch.

Finally, the investigations will be done in two phases:

• Immediately, showing the profile and seepage at present; and
• After the grouting works, showing the impact of the seepage treatment.

3.Contractor’s Requirement

The bidder will submit detail of method or methods (limited to maximum tow methods) that it proposes to be use in achieving the above objective. The agency will also submit limitations it foresees in application of the methods. However, selected methods should be able to provided information as mentioned the scope of work.

4.The Bidder

The selected bidder should have an adequate knowledge of geophysical methods and past experience in undertaking geophysical surveys and works of above. Information in this regard will be provided by the bidder. The bidder will provide statement with similar work experience and CVs of the key technical staff.

5.Reports’ Submittal

The bidder will submit two reports: an interim report after one month from the beginning of the works, showing the state of the dam and seepage at present as well as a final report at end of the assignment. The latter will be done after the grouting works.

It is estimated that the grouting works will take four months, so the time period between the two geophysical investigations will be maximum six months.

The reports amongst other things should incorporate the following:

1. Layout of profile or profiles of each method and on each of the profiles (which are maximum 100m in length);
2. Summary of results in respect of above findings, describing:
   1. Leak path/s detection;
   2. Internal erosion, if any;
   3. Identification of zones of water accumulation, if any;
   4. Cavities/sinkholes, if any;
   5. Degradation, if detected;
3. Conclusion and recommendations, resulting from the interpretation of the geophysical investigations.

6.Estimated Cost of the scope of Work:

The bidder is requested to break the costs into:

• Mobilization/demobilization;
• Travel and Investigations;
• Reports’ production;
• Findings presentation of one day workshop (inception and final).

7.Time Schedules

The time duration for field work, report preparation and submission of report shall be 30 days for each of the two phases (inception and after grouting), separated by the grouting works, which will take maximum six months.

        Layout Map Showing Project Area and Proposed Lines and Observed Seepage