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Around the loosen soil problem at Hai Van Pass Tunnel

Date: April 04, 2002

At 10 am on April 2, 2002 we are at South Portal of Hai Van Pass Tunnel. It is such a blazing hot day that the area where the machines and equipment located in front of the portal is scorching and shining aching the eyes. Many grass squares turn yellow.

Discussing with Mr. Thai Son, Deputy Project Manager of Package 1B Hai Van Tunnel Construction Project (Joint Venture of Dong Ah -Korea and Song Da Incorporation), we are informed that inside main tunnel the construction unit reach loosen mud on drilling to meter 29. Because groundwater ejects so hard, loosen mud streams out, which is easy to cause cave-ins, that's why it is a must to tighten the tunnel width from 12m to 3.8m and height from 7.8m to 4.2m, to lead loosen mud and groundwater outside. This conducting tunnel has been 48m long. Mr. Thai Son also discloses that after the cave-in during the construction in rainy season September 2001, the construction team used wire mesh and shotcrete lining to cover the hole; at the same time used a big quantity of rocks and soil to lean on the tunnel face preventing rock and soil from coming out through groundwater, making the subsidence area stable for excavation continue. But after that when they reached loosen mud, a conducting tunnel was required. The loosen mud out-of-plan trouble takes the construction company lot of .labor to overcome. Joint Venture of Dong Ah and Song Da is going to hire contractors of international experience to proceed the construction of expanding the conducting tunnel to main tunnel. The joint venture has recommended three prestigious tunnel companies from Japan, Taiwan, and Hong Kong; and they are waiting for the approval from their superior...

Right on site of South Portal, contacting with us. Engineer Le Van Khang - Manager of Technology and Design Department of PK1B Management Unit, adds some more information: Because of the loosen mud in main tunnel, they concentrate on excavating evacuation tunnel (4.2m long and 4.7m high), up to now, reaching 622 meter deep. At Station 0+180, they make a cross passage to main tunnel and find all rock and soil with no loosen mud, therefore they excavate open to the main tunnel compliant with the design to the North for 312 meters. So, excluding weak soil part of 48 meters of conducting tunnel already excavated, and 25 meters of not yet excavated, the main tunnel excavation is 341 meters (29 meters from the portal and 312 meters inside). The loosen mud during excavation slows down the work progress by 4 months; but after overcoming with cross passages to main tunnel at the area of no loosen mud, there will be a delay of only 2.5 months compared with the overall schedule. At this time of sunny and hot weather. Joint Venture of Dong Ah - Song Da mobilizes more than 600 workers in three shifts for 24/24 hours on site, pushing the progress, to get through with North Tunnel on October 1, 2004 as planned.

At the office of Project Management Unit 85 (PMU85), we are informed by Mr. Nguyen Ngoc Canh - Project Manager: In North Tunnel through Hai Van Pass, the excavation length is 790 meters for main tunnel and 780 meters for evacuation tunnel. Currently 168 meters of main tunnel lining was already concreted waiting to be installed lighting equipments. The length of Ventilation Adit is 720 meters. To South Tunnel, after the overcome of loosen mud by making cross passage from Evacuation Tunnel to Main Tunnel from inside, 6 meters is excavated per day and there is a tendency to catch the progress to finish in time. We raise a question "Government has agreed for PMU85 to change one part of Hai Van Pass Tunnel Project, means the enlargement of Evacuation Tunnel to Main Tunnel, why has there been no commotion so far?". Mr. Canh answers that the enlargement of Evacuation Tunnel to Main Tunnel can be considered as a new project, therefore it is waiting for the passing of Japan Bank for International Cooperation (JBIC), because the investment capital of USD 251.042 million mainly comes from this unit loan.

(Source: Cong An Danang)

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