Safe and reliable electromechanical system in the tunnel

5 min read

The electromechanical system in Xiang’ an Tunnel was the foundation for the tunnel’s operation after completion. It was constituted by 7 major systems, including ventilation, lighting, monitoring, communication, charge, fire and drainage. The investment reached nearly 400 million Yuan, accounting for about 10% of the total investment.

The electromechanical engineering of Xiangan Tunnel was very complex. It was constituted by the systematic engineering components such as strong current, weak current, computers, networks, etc. After the completion of the project, the traffic flow would be very heavy, so the traffic electromechanical engineering would be essential to ensure safe operation and management of the tunnel. At the very beginning of the establishment of the East Passageway on-site headquarters, the traffic electromechanical engineering project department was set up. The project department took full charge of the implementation of the whole traffic part of the electromechanical engineering in the East Passageway construction.

The electromechanical engineering of the East Passageway was located at the salt mist corrosion area below the sea level, with the characteristics of large-scale construction, high technical difficulty, and engineering interface complexity. The traffic electromechanical engineering project department was set up at the establishment of the East Passageway on-site headquarters, in order to prepare for later electromechanical engineering.

The Xiangan Tunnel electromechanical engineering involved a wide range of coordination work with aviation, navigation, Electric Power Bureau, Water Supplies Group, fire department, Bureau of Meteorology and other relevant departments. For example: in the fire engineering, the relevant information had to be submitted to the fire department for approval and acceptance during the stages of preliminary design, construction drawing design, firefighting apparatus preparation, and project acceptance.

Hu Ningxia, Manager of the Xiang’ an Tunnel electromechanical project, said,”We realized that in the stages of preliminary design and construction drawing design, we have to strengthencommunication with the related departments. Therefore, in the stages of preliminary design, construction drawing design, and construction processes during the traffic engineering, we could understand any issues in a timely manner and fully consider the latest industrial standards and adopt them in the construction process. To enhance and strengthen the interaction with various departments would greatly facilitate the implementation and acceptance of the project.”

In the design stage, the construction party invited the domestic and foreign organizations with similar tunnel construction experience to carry out the consultation work during the electromechanical preliminary design, and the developed preliminary design. The electromechanical equipment was purchased around the country, some even from foreign countries. For example, the ventilators were imported from Germany.

“The significant difference between the electromechanical engineering and the building project was that, the equipment purchases of the electromechanical engineering accounted for a larger proportion of the total project. The level of the purchased equipment will largely determine the reliability and stability of the system operation and the quality of the electromechanical engineering.”Hu Ning said,”We introduced the life cycle theory in the system settings, which means the life cycle cost of the system and the equipment=the construction cost +the operation cost.”

The preset and embed work were also carried out in the Xiang’ an Tunnel’s electromechanical engineering. After the electromechanical engineering contractors of each section entered the site, they could use the preset and embed project, and hand over the working face to the electromechanical construction units. Proven by the engineering practice, the professional implementation of preset and embed work had higher engineering accuracy, which could ensure the smooth proceeding of the electromechanical engineering.

In addition, during the Xiangan Tunnel electromechanical engineering, over ten thematic coordination meetings were held. The problems during the construction were solved in a timely manner during the meeting, which provided protection for the smooth implementation of construction.

The application of new technologies and new materials can been seen in the Xiangan Tunnel electromechanical engineering design. First, the tunnel lighting system adopted continuous fluorescent light with a continuous-variable dimming system for illumination, which can not onlyprovide a comfortable driving environment for the drivers and passengers in the tunnel, but also extend the service life of the lighting and save the electricity costs during operation.

Hu Ning said,”The fluorescent scheme adopted in the tunnel lighting would provide soft light, great coloration and higher degree of uniformity. With the continuous-variable dimming control, the lightness change in the tunnel would be very smooth, creating a similar effect to daylight. The continuous ribbon pattern lighting was set on the roof of the tunnel, which could effectively avoid the ‘ zebra effect. It was conducive to helping the driver’s sight, to ease driving fatigue in the 6 km undersea tunnel, and to ensure safety and the comfort.”

By using the continuous-variable dimming system, the long-time full power work of the tunnel lighting could be avoided. The illumination in the tunnel can be adjusted into an appropriate state according to the illumination outside the tunnel. The tunnel lighting could work at a lower power, which would not only extend the service life of the lighting, but also save on electricity costs during operation.

Second, the tunnel fire protection system not only adopted a conventional fire alarm system and fire hydrant system, but also set up the AFFF-foam water spray system on the left wall of the tunnel in the traffic direction for automatic fire extinguishing. This was China’s first time setting up this system in a large section of underwater tunnel.

Third,4 high-power axial fans were set up in the two ventilation shafts of Xiangan Tunnel.Thirty-nine 30kW jet fans were set up in the road tunnels. Twenty 15kW jet fans were set up in the service channel. If all the fans were in full operation, the tunnel would be like a huge “kitchenventilator”. These devices were connected with the vertical shafts built at the beginning of the construction. They could discharge the smell and the dust in the tunnel promptly. Therefore, when the drivers drive through the tunnel, they need not to worry about smelling the peculiar odors or inhaling dust.

In addition,3 pumping stations were set up in the Xiangan Tunnel, including two rainwater pumping stations on both the Xiamen side and the Xiang’ an side, and a wastewater pumping station in the middle of the tunnel. They could help the Xiangan Tunnel to withstand a 50-year rainstorm.

The main function of the rainwater pumping stations on the two sides is to gather the rainwaterand discharge it into the sea. The two rainwater pumping stations both have giant “stomach”. Each of them can store 1,500 cubic meters of water.

The function of the wastewater pumping station in the middle of the tunnel is to collect the seawater and wastewater. Because the tunnel was built under the sea, there would be a certain degree of water seepage. Wastewater would be produced during the cleaning of pavements andwalls and this wastewater would flow into the wastewater pumping station through the side ditches. The wastewater pumping station has a larger “stomach”. It could “swallow”over 3,000 cubic meters of water.

After the water was gathered together, another advanced instrument would be used-a water pump. The pumps in the Xiangan Tunnel were all imported high-power and high-lift stainless steel pumps, which could directly pump the water from 70 meters below the sea level into the sea.

It is finally worth mentioning that the pumping pipelines of the three pumping stations in the Xiangan Tunnel are independent, with no interference with each other.