Construction Supervision

Summary

As of April 30, 2003, total length of Main Tunnel excavation reached to 2,469.7m (including 6 Laybys) from the Tunnel Portal.

Forty seven (47) niches (12 emergency & call niches and 35 Firefighting Niches) were completely excavated inside the Main Tunnel.

Concreting of the Foundation Beam and concrete Lining Works at the Main Tunnel were carried out. As of April 30, 2003, concrete lining construction reached to 1,862.5 meters.

As of April 30, 2003, total length of Evacuation Tunnel excavation reached to Sta.

As of April 25, 2003, total length of Evacuation Tunnel excavation reached to Sta. 3+983.2 or 2,340.20 meters from the Tunnel Portal.

Five (5) Cross Passageways were completely excavated across the Evacuation and Main Tunnels. 

Ventilation Adit excavation is almost completed. As of March 31, 2003, total length of Ventilation Adit Excavation reached to Sta. 0-133.2 or 1,885.71 meters (99.90% of total progress) from the Tunnel Portal. Excavation of the remaining unexcavated portion or breakthrough to the Main Tunnel will be done once the excavation from the Exhaust Tunnel passes through this connection point.

Preparations are now ongoing for the construction Ventilation Adit Portal Cut and Cover Section.

Exhaust Tunnel at the Ventilation Adit was completely excavated on March 21, 2003.

Electrostatic Precipitator No. 1 was completely excavated last March 22, 2003.

Main Tunnel 

• Excavation

In the month of April 2003, the rock encountered in the Main Tunnel was stable on Class B, although one major fractured joint with soft filling and water seepage parallel to tunnel axis was observed continuing from last month to end of this month.

This month, the top-heading excavation of the Main Tunnel from the Ventilation Adit stopped due to the problem of ventilation system of the contractor. 

Total excavation length for this month was 143.30m. The distance from the tunnel portal gives a total length of 2,469.70m (Progress: 64.03%).

• Niche Excavation:

Forty-seven (47) Niches – Twelve (12) Emergency Call Niches and Thirty-five (35) Firefighting Niches – in the Main Tunnel were already excavated. Excavation of niches continues according to the designed niche distribution plan.

• Lay-by Left No.1, 2, 3 and Right No.1, 2, 3

The Lay-by Left Nos. 1, 2, 3 and Lay-by Right Nos. 1, 2, 3 in the Main Tunnel, which has a total length of thirty-two (32) meters each, were completed as per original plan. Excavation of Lay-by Left No. 4, which is connected to Vehicular Cross Passage No. 2 at station 4+100, is currently going on.

• Behind Works (Behind Tunnel Excavation)

The pouring of Class D concrete for the Foundation Beam of the Lining Concrete continued this month from Station 3+545.5 to 3+588.5 with a total length of 43.0m on each side.

Installation of Mole Drain Pipes, together with filter cement aggregate, on both sides of the tunnel continued simultaneous with the foundation beams.

Cutting of Rock bolt heads and installation of geo-textile covers were done on areas with rock bolts.

Installation of EVA Waterproofing Membrane was also continued following the covering of rock bolts. Until the end of this month, a total length of 1,897.7m (Station 3+561.50) was completely covered with waterproofing membrane. The Engineer continued to require testing of the welded joint sheets using air pressure test, as per procedure stated on the method statement, before continuation of the installation.

Pouring of Concrete Lining was also carried out as per approved design segment. The Engineer carefully checked, during the joint survey with the contractor, the setting of the form for both bulkhead sides and the thickness as per design requirements.

The Concrete Lining for Standard Section of the Main Tunnel completed until the end of this month totaled to 1,738.50 meters. The Concrete Lining works for Lay-by Left Nos. 1, 2 and Lay-by Right No.1, 2 in Main Tunnel, totaling a length of 124m were also completed.

The Main Tunnel Concrete Lining completed up to the end of this month totaled to 1,862.50m (Progress: 48.29%).

For cross passages, only the concrete lining for the blocks connected to the Main Tunnel are being executed. Concrete lining completed until the end of this month includes the Pedestrian Cross Passage No. 1 (station 2+000), No. 2 (station 2+400) and Vehicular Cross Passage No.1 (station 2+800), and Pedestrian Cross Passage No. 3 (station 3+190), totaling a length of 15.10m.

Cable Duct Bank Concreting:

This month of April 2003, the concreting of the duct bank on the eastern side of the Main Tunnel started with two (2) lines of embedded conduit pipe from station 1+699.0 to 2+093.5, giving a total length of 320m. 

EP No. 1 Concreting Works:

The pouring of Class D concrete for the Foundation Beam of the Lining Concrete started this month with a total length of 94.6m on right side and 107.9m on the left side.

Installation of Mole Drain Pipes, together with filter cement aggregate, on both sides of the tunnel continued simultaneous with the foundation beams.

The assembling of Sliding Form for Lining Concrete of the Electrostatic Precipitator No.1 was also started and continuing inside this tunnel.

Evacuation Tunnel

In the beginning of April 2003, fracture zones and good rock alternately appeared on the cutting face of the Evacuation Tunnel. Generally, the rock was classified as class CI to B, which was under the supporting system type I.

The Contractor excavated a Temporary Cross Passage No. 2 at station 3+910 simultaneous with the excavation of ET in order to reduce the mucking time for ET and to make good the ventilation system between Main Tunnel and ET. 

The tunnel length excavated this month was 125.30m (station 3+857.9 ~ 3+983.2), giving a total length of 2,340.20m  (Progress: 60.67%) from the tunnel portal.

The Temporary Transformer Niches No. 1~11 were completely excavated as per approved plan submitted by the Contractor.

The Enlarged Pedestrian Cross Passageway Nos. 1, 2, 3 and 4 and the Vehicular Cross Passageway No. 1 were also completed.

Ventilation Adit Tunnel

In the month of March 2003, the excavation of the Ventilation Adit was almost completed, reaching up to Supply Clean Air Section at station 0-133.2. The excavation of Exhaust Waste Air Section has also been completed.

This month of April 2003, in Ventilation Adit, due to the problem of the Contractor on the ventilation system, the top heading excavation for MT was stopped.

The Contractor proposed a Temporary Connection Tunnel that will connect the Ventilation Adit to MT at station 0+090 VA side. As a countermeasure for the suspended top heading excavation of MT, the Consultant agrees to execute the excavation of the temporary connection tunnel in order to resume and improve the advance for MT. The contractor has already started excavating the connection tunnel this month.

Concreting Works:

Cut and Cover Section / Connection Lining Concrete at Portal:

Class D concrete for the Foundation Beam of the Lining Concrete started and a total length of 17.1m, from station 1+752.51 to 1+735.5, on both sides was completed this month.

Installation of Mole Drain Pipes, together with filter cement aggregate, on both sides was also completed.

Cutting of Rock Bolt Heads and installation of geo-textile cover were also completed this month.

The assembling of Standard Sliding Form for Lining Concrete and of the Staging Form for the waterproofing works were completed this month.

Major Events and Issue

Site Inspections

On April 26, 2003, a delegation headed by Mr. Nguyen Ngoc Tran – General Director of PMU 85 visited and inspected the project.

Monthly Meeting

On April 16, 2003, a Monthly meeting was held at the Employers/Engineer’s Office between the Employer, the Engineer and the Contractor.

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