Recently, the double-track tunnel between Hongqi West Road Station and Nansong Road Station on Dalian Metro Line 2, excavated separately by China Railway No.3 Engineering Group and China Coal No.3 Construction Group, broke through at Shimen Mountain. A reporter descended nearly 100 meters into the tunnel by hoist bucket to visit the breakthrough point.

All descent in Dalian Metro's deepest shaft relies on hoist buckets

At the Hongnan section ventilation shaft site located halfway up the northern slope of Shimen Mountain, the reporter learned that this is the deepest shaft in Dalian Metro, constructed by China Coal No.3 Construction Group. The design elevation of the shaft on the drawings is 97 meters; during construction, the wellhead area was leveled into a platform, and the actual depth of the shaft is 85 meters. It is also the only circular shaft in Dalian Metro. To prevent accidents, the wellhead is usually covered with a steel plate cover, on which a circular steel hoist bucket is placed. The bucket is about 1.6 meters high and can hold 3 cubic meters of muck or transport 10 people.

The reporter learned that, unlike other work sites in under-construction sections of Dalian Metro, this shaft has no stairs inside; all personnel going up and down the shaft must rely on hoist buckets. Before entering the bucket, the reporter put on water boots and a safety helmet; personnel descending the shaft must also wear a relatively complex safety harness as required and hook the harness rope onto the steel cable ring above the bucket.

After the reporter jumped into the bucket, it took less than 1 minute to reach the bottom. Although the surface temperature at that time exceeded 30 degrees Celsius, the temperature underground was less than 20 degrees Celsius.

20th double-track breakthrough tunnel has too much water, draining nearly 100 tons per day

Upon reaching the bottom, the boots came in handy. The tunnel was full of water, and some sections were very muddy. It is understood that freshly blasted rock is very hard, and some weathered rock turns into mud upon contact with water. The "burial depth" of this tunnel section mostly exceeds 100 meters; the deeper into the tunnel, the more water there was. The sound of rushing water could be heard, and springs were seen gushing from the tunnel walls. The group walked close to the tunnel wall, and most people's boots filled with water multiple times. At 320 meters, they reached the breakthrough point.

The south side of the breakthrough point was constructed by China Railway No.3 Engineering Group, with a length of 900 meters, and secondary lining construction has begun. At this point, the 2,285-meter double-track tunnel between Hongqi West Road Station and Nansong Road Station on Dalian Metro Line 2 has been holed through. This is the 20th double-track tunnel section to break through on Dalian Metro. According to Wang Xiaolei, manager of the Hongnan ventilation shaft work area, the biggest difficulty in excavating the tunnel under Shimen Mountain was the large amount of water. During construction, they used two water pumps to drain nearly 100 tons per day. To drain effectively, they also built a temporary "dam" more than 1 meter high inside the tunnel for relay drainage. During initial support, to prevent shotcrete from washing away, they used dual-fluid grouting to instantly solidify the tunnel face.

Metro in numbers

Currently, Dalian Metro Lines 1 and 2 have completed nearly 9.42 million cubic meters of earth and rock excavation, nearly 330,000 tons of rebar tying, nearly 1.59 million cubic meters of concrete pouring, and over 1.02 million square meters of waterproofing. Of the 48 stations along the entire line, 26 have been capped; of the 49 sections with a total designed length of 55 kilometers, 41.85 kilometers of excavation has been completed; ventilation, water, and electricity installation projects have started sample construction at 2 stations, and track laying has completed a cumulative 6 kilometers of single track.