Main Tunnel

For the month of June, the rock condition encountered in the Main Tunnel was classified as Class B until the end of the month. The small fracture zone observed from last month continued until 26th of this month and some slickenside rock appeared, so the Engineer instructed some safety rock bolts. Geologically, the rock condition was almost good.

A total length of 128.50m (station 2+763.3 ~ 2+891.8) were excavated in the Main Tunnel this month, giving a total length of 1,238.8m (Progress: 32.12%) from the tunnel portal.

This month, the excavation of Main Tunnel was shorter compare to previous month's progress due to frequent breakdown of equipment almost every shift. The Chief Resident Engineer discussed and strongly pushed the contractor to improve and increase the equipment to catch up with the delayed progress.

Twenty-four (24) Niches - Six (6) Emergency Call Niches and Eighteen (18) Firefighting Niches - in the Main Tunnel were already excavated. Excavation of niches continued according to the design niche distribution plan.

The Layby Left No.2 in the Main Tunnel, which has a total length of thirty-two (32) meters between Sta 2+784 to 2+816, was excavated from 5th to 13th of June 2002, having the same good rock condition as the rest of the Main Tunnel length excavated this month.

In the Evacuation Tunnel, the condition of the rock encountered was generally good, although at some times we had experienced water seepage on the excavation face. Geologically, the rock condition was stable on class B ~ A. On some portions, it was almost classified as class A this month.

The performance of the blasting was still constant to more than three meters per round.
On June 21 to June 26, the excavation of the Evacuation Tunnel was stopped to give way to the excavation of the Vehicular Cross Passage No.1 at station 2+800 facing the Evacuation tunnel side.

The excavated tunnel length for the month of June 2002 was 98.8m (station 2+740.3 ~ 2+839.1), giving a total length of 1,186.1m (Progress: 30.75%) from the tunnel portal.
The Temporary Transformer Niches No. 1~6 were completely excavated as per approved plan submitted by the contractor.

The Enlarged Pedestrian Cross Passageway Nos. 1 and 2 has been completed.
The Vehicular Cross Passage No.1 was excavated from Evacuation tunnel and Main Tunnel side with a total length of 19.4m.

The ventilation system for Evacuation Tunnel has been transferred through Vehicular Cross Passage No. 1. The relocation has improved the ventilation inside the tunnel. Wasted air coming from the Main tunnel was still eliminated out through Vehicular Cross Passage No. 1 and then through the Evacuation Tunnel.

Ventilation Adit

Since the beginning of June 2002, water seepage was observed flowing out of drilling holes on almost every cutting face of the Ventilation Adit. On June 5, 2002, anomalous heavy water with a discharge of more than 1.0m3/min spouted out on a high pressure while drilling holes for blasting on the right hand part of the cutting face on Sta. 0+791.5. To observe the water condition ahead of the cutting face, the Chief Resident Engineer made an instruction to drill exploratory holes on the right side wall behind the cutting face, Sta. 0+791.5. Six (6) exploratory holes, each has a length of 10m and angled 30 degrees from the wall were drilled on Station 0+794.

When the exploratory holes were drilled, the heavy water spouting out of the cutting face on Sta. 0+791.5 suddenly vanished and reappeared on the exploratory drill holes so the Contractor was able to excavate another round with a length of 2 meter.

However, after reaching Sta. 0+789.5, water intrusion with high pressure was experienced on the cutting face again. The Engineer instructed once more to drill one (1) exploratory hole on the center part of cutting face and found out that soft rock was anticipated 1m ahead of the cutting face. Therefore, the Chief Resident Engineer immediately instructed to change the supporting system from type I to type III with the installation of IBO forepoling, wiremesh, 10cm-shotcrete and swellex-type pattern rock bolts. The soft rock, which was classified as Class CII to CI, has weathered zone many joint systems with white clay and its color was mainly gray to white.

The contractor carefully continued the excavation using backhoe breaker and not by blasting on the soft ground weathered zone. In the course of the excavation on soft ground area, big amount of water, with a total discharge of 1.2m3/min, spouted out of caves on the left part of the crown. The soft ground weathered zone was experienced until 21st of June 2002.

On the exploratory hole drilling to investigate the rock condition ahead, which was conducted on Sta. 0+769.3, it was observed that the condition of the rock ahead would become hard. Hence, the support type III was changed to type II from station 0+765, however, for one round only. The rock condition suddenly changed and became totally good so the Engineer issued an instruction to change the supporting system to type I from station 0+762 and the said supporting system was applied until the end of this month.
The soft ground weathered zone with big amount of anomalous water seepage flowing out from the cutting face had caused extreme difficulties for excavation and had affected much excavation progress of the Contractor.

Because of the several problems caused by anomalous water seepage in Ventilation Adit, the Engineer discussed and recommended to PMU 85, client representative, to do the grouting curtain on all areas that have anomalous water seepage. The Engineer anticipated that more suspension of excavation works due to water seepage could happen during the rainy season.

The PMU and MOT delegation finally schedule an inspection in Ventilation Adit and a general meeting among MOT, the Engineer and the Contractor in Hanoi on July 2002.
The excavated length for the month of June was 69.7m (station 0+809.0 ~ 0+739.3), totaling to 1,010.21m (Progress: 57.64%) from the tunnel portal.

Ventilation Adit - Outside Works

The assembling of the Sliding Form No. 2 for Standard Section of Concrete Lining in Main Tunnel was started this month.

This homepage is presented by the Consultant Team

Any further question should be forwarded to Webmaster or Consultant Team