Construction Supervision

Summary

As of March 2003, total length of Main Tunnel excavation reached to Sta. 3+954.9 or 2,326.40m including 6 laybys for the Tunnel Portal.

Forty-Four (44) Niches (11 Emergency & Call Niche and 33 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 March 31, 2003, Concrete Lining construction has reached to 1,828.50 meters.

As of March 31, 2003, total length of Evacuation Tunnel excavation reached to Sta. 3+854.9.0 or 2,214.90 meters from the Tunnel Portal.

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

As of March 31, 2003, total length of Ventilation Adit Excavation reached to Sta. 0-133.2 or 1,885.71 meters from the Tunnel Portal.  Main Tunnel Excavation by the Ventilation Adit Team is now on-going at the Exhaust Tunnel and Main Tunnel connection.

Exhaust Tunnel excavation at the Ventilation Adit was completely excavated.

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

Main Tunnel 

• Excavation

For the month of March 2003, the rock encountered in the Main Tunnel was in good condition. The excavation had already passed under the curve area of the Ventilation Adit. During the excavation on the said area, although the rock condition was considerably good, the Engineer carefully monitored the NATM measurement type A under the Ventilation Adit and observed that no big deformation happened on that area.  Overall, the rock condition encountered this month was classified as Class B. Concerned that damage on the Ventilation Adit might occur, the Contractor decided to execute the excavation by controlled blasting.

This month, the top-heading excavation of the Main Tunnel from the Exhaust Shaft Section of the Ventilation Adit northward has been started by the Ventilation Adit Group to obtain more excavation progress. 

The excavation of the Main Tunnel has improved compared to the previous months. The MT full-face excavation length was extended by 146.40m (Station 3+808.5 ~ 3+954.9) and top-heading excavation from the Ventilation Adit side yielded a length of 14.50m.  Total excavation length for this month was 160.90m this month. The distance from the tunnel portal gives a total length of 2,326.40m (Progress: 60.32%).

On 22nd of March 2003, the excavation of the Electrostatic Precipitator No. 1 was completed with a total design length of 137.6m. The Evacuation Tunnel group completed the Electrostatic Precipitator No. 1 by excavating it alternately with the Evacuation Tunnel. The geological condition encountered was in good condition and was classified as class B to A.

• Niche Excavation:

Forty-two (44) Niches – Eleven (11) Emergency Call Niches and Thirty three (33) 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.

• 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+457.5 to 3+545.5 with a total length of 87.5m 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 1,848m (Station 3+512.0) 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 1,678.50 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 1,828.50m (Progress: 46.73%).

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.

Evacuation Tunnel

Since the beginning of March 2003 and for almost the entire month, the geological condition encountered was very poor. It consisted of fracture to crushing zones and slickensides, which were all under the supporting system type II and type III. Some rounds were under supporting system type I, but the rock encountered still had some joints. In addition, after those rounds, full face crushing zone appeared on two rounds before reaching the area under Ventilation Adit. On the area under the Ventilation Adit, some joints with key blocks on the crown part that caused over-breaks were observed so the Engineer gave an instruction again to change the supporting system to type III and, subsequently, to type II until the end of this month.

Generally, the rock was classified as class CI to B.

The tunnel length excavated this month was only 95.10m (station 3+762.8 ~ 3+854.9), giving a total length of 2,214.90m  (Progress: 57.43%) 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 Vehicular Cross Passageway No. 1 were also completed.

Ventilation Adit Tunnel

In the month of March 2003, the rock condition encountered was in good condition. Geologically, the rock condition was stable on class B. On some portions, it was almost classified as class A.

The excavation for the Clean Air Supply Section of the Ventilation Adit was almost completed including the 9.50m adjustment section area. The Exhaust Shaft Section was also completed and was currently used as an access for the top-heading excavation of the Main Tunnel.

This month, in Ventilation Adit, the progress was very poor due to the problem of the Contractor on the ventilation system. Previous month, the Contractor tried to modify the previous system of blowing fresh air from tunnel portal by reversing it to suction system. However, the modification made was not successful so the Contractor returned to the original system of blowing fresh air by using one (1) unit of 200kw ventilation fan from PKIB Contractor set at the portal area.  However, the temperature and humidity inside the tunnel are still high. The progress was also affected by several hours of mucking time and breakdown of equipment.      

The excavated length for the month of March 2003 was 29.4m up to the Supply Section (station 0-103.8 ~ 0-133.2), totaling to 1,885.71m (Progress: 99.90%) from the tunnel portal. A length of 9.5m was excavated for the Adjustment Section, 9.10m for the Exhaust Section, and 14.5m for the top heading excavation of Main Tunnel. Overall, the total length excavated by the Ventilation Adit group was 62.5m this month.

Major Events and Issue

Site Inspections

On March 21, 2003, Labor Department of Hue Province inspected the project in relation to safety week

On March 24, 2003, Mr. Vu Bay – Vice Deputy Director General of TQCM, together with the Employer and the Engineer visited and inspected the Project.

Monthly Meeting

Monthly Meeting No. 32 between the Employer, the Engineer and the Contractor was held last March 19, 2003 at the Employer/Engineer’s North Office.

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