Night falls, another day of March gradually ends, the destination of traffic opening is less than 3 days away. Halfway up Than Vu Mountain, the sound of machinery became more intense. The groups of workers who changed shifts from 50:18 p.m. have not yet rested, even though they are somewhat tired.
From the northern tunnel door, returning to the corrugated iron room of less than 10 square meters nestled at the end of the worker shack, engineer Bui Van Toan, Construction Commander of Than Vu Tunnel under Cienco2 Group, took off his dusty protective jacket. quietly walked towards the drinking table in the yard so as not to disturb the sleep of the colleague in the bed next to him.
“Many difficulties. But what I thought I couldn't do was close to the finish line," Mr. Toan said.
Engineer Bui Van Toan disseminates the plan to workers before starting their shift
Participating in the construction of the 567m northern left tunnel branch, he said, while in most other tunnel projects, the tunnel door is usually opened at the foot of the mountain, the starting point of Than Vu tunnel door is halfway up the mountain.
Geology is constantly changing, survey assessments are not accurate, there are segments that are assessed as hard rocks, but in reality the rocks are easy to fall.
The most stressful time was when digging into the middle of the tunnel (around June 6), many psychologically weak workers refused to reinforce the tunnel vault when they saw some cases of falling rocks even though there were no serious incidents. happen.
Colonel Le Minh Duc checks reinforcement construction techniques before pouring concrete on the Than Vu bridge deck.
“They are right to demand enough safety before working. But what is absolutely safe? How to explain to them? With the highest position at the scene, I made a written commitment that if any problem occurred, I would be fully responsible before the law," Mr. Toan said, thanks to which the workers gradually became back to construction sites.
The digging steps are also more careful and meticulous. According to the original plan, if things go well, the contractor can dig 3m per day, but the geology is difficult, the average speed is only about 1m/day. On October 5, 10, the last mine exploded safely. It was as if a burden had been lifted from everyone, ending the days of hardship, not knowing when the risk would strike.
Mr. Vo Son Hai, Commander of Hoa Hiep Co., Ltd. also admitted that working through soft ground areas is the most nerve-wracking time: "There are cases where you are making an arch, and just take a few steps back and the rock falls." Big rocks fell, luckily everyone was okay, but it is estimated that about 10% of the workforce asked for leave after that because they were too scared."
Weak geology is also a bottleneck that caused the construction of the Nui Vung tunnel on the Cam Lam - Vinh Hao expressway (the longest tunnel among the 6 cross-mountain tunnels of the North-South East expressway project phase 1) to have to be completed. continuously stop construction during the period from December 12 - June 2022.
The construction process of Nui Vung tunnel encountered weak geology. For 4 consecutive months, construction had to be paused many times to optimize construction solutions and ensure safety.
Mr. Dang Tien Thang, Deputy General Director of Cam Lam - Vinh Hao Joint Stock Company, said that the geology in the southern tunnel is so complex that at the end of the excavation step, there are places where water spurts out like "waterspouts", barrels. 18 liters of paint filled with water in just a split second.
“That difficulty forced us to choose: stop construction, delay progress, continue digging or accept risks. While working and searching for solutions, the progress of digging the southern tunnel slowed down. If the northern tunnel can be dug 3m per day, the southern tunnel can only dig 3m every 1 days," Mr. Thang said, adding that Deo Ca Group has increased resources and accelerated the progress of the northern tunnel.
The digging step is calculated to be longer, the execution cycle is optimized. If the normal steps of drilling, blasting, loading, reinforcing, and transporting out take about 24 hours, then all must be accelerated to 20 hours. Previously, one cycle of drilling and blasting could only cover 100m3. When accelerating, we had to calculate an increase of several dozen blocks.
When joining Long, the south side can dig about 350m while the north side can dig about 1.800m instead of each construction end digging half the length of the tunnel as in the original plan. Thanks to that solution, by August 8, the Nui Vung tunnel will be opened.
"If I were to write a memoir, it would probably take me about 6 months to tell about the construction journey at the Cam Lam - Vinh Hao expressway," said Mr. Nguyen Van Ngoi, slowly walking on the road leading to the executive board headquarters. , Deputy General Director of Construction Investment Corporation 194 Joint Stock Company (Company 194) just confided.
Approaching the project from the early days, Mr. Ngoi was impressed with the time it took to construct the project's two largest terrain-crossing bridges. "This is Km55+982 bridge", pointing to the middle pillar of the bridge, Mr. Ngoi said, bored pile construction is an extremely stressful project.
In this area, all the rocks are hard. During the initial construction period, conventional drilling methods only worked for a while before the drill bit broke. No less than 5 units can be drilled for one pile and then abandoned. Even if the investor pays more money, they will not continue. It took up to 3 months of struggling with all the solutions, but success came with the solution of using a larger drill, higher rpm, and a more special drill bit.
For Mr. Tran Nam Trung, General Director of Company 194, the most memorable memory is the Km60 bridge. The bridge is located in the middle of a valley between two high mountains. According to the approved construction method (longitudinal beam thrusting), it takes 1 month to complete 1 span, which means it will take up to 22 months to construct 22 bridge spans and by around June 6, the new bridge will be built. finished.
To optimize progress, Company 194 changed the solution from vertical to horizontal. The contractor expanded the service road, brought beams of 60 - 70 tons to the bridge pier area, used two cranes of 350 and 450 tons to lift them, at an average speed of 3 days/span. Thanks to that, in less than 18 months, the bridge reached its destination, meeting the opening date of April 30, 4.
The Km 60+552 overpass has the highest pillar (more than 47m) on the Cam Lam - Vinh Hao highway, designed with a length of 883m, 21 pillars, 22 spans and has now been completed.
Being bold in converting construction solutions is also the direction to help Truong Son Construction Corporation optimize the construction time of 2/4 of the largest terrain overpasses of the North - South expressway project, Dien Chau - Bai Vot section.
Standing on Than Vu 2 Bridge - the project's longest terrain-crossing bridge (1.300m), Colonel Le Minh Duc, Managing Director of XL2 package, said that according to the original plan, the construction of beams and bridge deck will be deployed from the middle to both ends.
During the construction process, realizing that the end of Than Vu tunnel had a longer construction length, the contractor improved the method, doubling the construction line instead of just one line.
Than Vu 2 Bridge is the longest terrain-crossing bridge (nearly 1.3000m) on the Dien Chau - Bai Vot highway section, including 31 pillars, 2 abutments with 32 spans, 224 beams.
The 70 - 80 ton beams are not transported on the road but are lifted from the casting yard below and moved on the bridge deck. Working capacity increased by 5 beats/month compared to 2,5 beats/month compared to the original measure.
“If not calculated early, the construction time could be extended by at least another 1,5 months, meaning it will be completed by May or June 5. With the characteristics of a high, long, and large bridge, initially, Than Vu 6 bridge was a project that many units did not dare to accept," Colonel Duc said.
At Than Vu 2 Bridge, 346 bored piles with a total length of about 6.000m constructed on rocky geology is a huge challenge. There are 7m long piles that take 7 days to complete. That's why the target of completing bored piles in 6 months is something no one dares to believe.
