Qilu Evening News • Qilu One Point reporter Yu Bosheng
"The Yellow River to the west to break Kunlun, roaring thousands of miles to touch the dragon gate", the Yellow River is steep, the underwater environment is more complex, Jinan City on the ground hanging river water surface 54 meters under the ultra-large diameter tunnel operation is the first time in the world. The reporter learned that the Jiluo Road through yellow tunnel project has environmental risks such as shield crossing the above-ground hanging river, bridge piles on the North Ring Expressway, as well as its own risks such as the depth of burial of shield boring and cemented sandstone formations, and the overall surrounding environment is complex and the construction is difficult.
How deep is the tunnel?
The lowest point is located 54 meters below the riverbed
It is reported that the Wanli Yellow River from Henan to the mouth of the sea gradually formed an above-ground suspension river, Jinan Luokou section of the riverbed above the south bank of the overpass area of the ground 5 meters, the maximum flood level is 11.62 meters higher than the riverbed, the lowest point of the tunnel is located under the riverbed 54 meters, Jinan Jiluo Road through the yellow tunnel shield excavation diameter of 15.76 meters, is the first time to cross the above-ground river of the super-large diameter shield tunnel, with the shield excavation section is large, the excavation distance is long, shallow cover, deep foundation pit, high water pressure, complex and changeable geological conditions, close through the existing objects and other characteristics.
"In view of the fact that the formation of the Jiluo Road Tunnel is mainly clay and silty clay, and the fine particle content is high, in order to avoid the mud cake of the shield cutterhead, the shield machine selection is mainly optimized from the cutterhead tool configuration and scouring system." The relevant staff of the Fourth Survey and Design Institute of China Railway said that the shield cutterhead adopts a large opening rate of 46% to ensure the smooth flow of slag and reduce compaction; The cutterhead center tool ladder arrangement, in the shape of a fishtail, is conducive to cutting into the soil; The center washout is individually equipped with a booster pump to increase the washout pressure and flow rate; The floodgates are individually added to the flush pump to reduce build-up. According to the above configuration, the shield boring effect is better, and there is no cutterhead mud cake phenomenon.
The reporter learned that the pipe segment, box culvert assembly quality is the final decision of the quality of tunnel molding key, in view of the characteristics of the cross-formation for the full-sectional powder clay of the lower reaches of the Yellow River, the staff through the field test, the cutterhead speed, propulsion speed, mud volume quality, grouting parameters and grouting volume to verify, to determine the suitable formation of the tunneling parameters.
"Considering that the mass of the mud volume has a greater impact on the excavation speed, the larger the mass of the mud, the smaller the excavation speed, and the excavation speed has an impact on the shield attitude, the faster the excavation speed, the more difficult the attitude is to control." The technical staff of the project department introduced to reporters that the viscosity of synchronous grouting and the initial coagulation time will also have an impact on the floating amount of the segment, and finally the project determined that the tunneling speed was controlled at 15 to 25 cm per minute.
Why does the tunnel line go this way?
Leave room for future growth
On the afternoon of September 27, the reporter came to the site of the south entrance of the Yellow Tunnel on Jiluo Road, the south entrance and exit is located in the south of Luokou South Road, with more residential areas nearby, many transit vehicles, and great pressure on commuting in the morning and evening peaks. Looking north from the south entrance, you can see the north highway around the city passing through the front, where the tunnel intersects with it, and there are several large bridge piles standing above.
It is reported that the surrounding environment of the yellow tunnel includes the north bank levee and silt area, the south bank levee and the Luokou dangerous worker, the Luokou Hydrological Station, the North Ring Road viaduct pile, the Yellow River Forest Park, the Queshan Reservoir - the underground connection canal of the sinking sand pond, etc., the surrounding environment is complex, which brings certain difficulties to the design and construction, especially the Queshan Reservoir is a first-class water source protection area, the construction can not cause an impact on the water source, and the selection of the tunnel line needs to fully consider the characteristics of the surrounding environment.
According to the project department of the Wearing Yellow Tunnel, when designing the tunnel line, it is important to consider reducing the impact on the North Ring Expressway, Luokou Hydrological Station, Queshan Reservoir, National Highway 309 and existing buildings, etc., not only to reduce the construction risk and construction difficulty, but also to take into account the upper planning and surrounding traffic relief capacity of the tunnel area.
"The South Bank Tunnel Route selects two schemes based on the tunnel crossing the levee on the south bank of the Yellow River and the surrounding plots, and the North Bank Tunnel Route selects three schemes based on the existing roads in the surrounding area and the Queshan area control regulations." According to the designers of the Fourth Survey and Design Institute of China Railway, the main difference between the two schemes on the south bank is in the location selection of the intersection of Jiluo Road and the North Second Ring Road (North Ring Expressway Bridge) and the Luokou Pontoon Bridge; the main difference between the three schemes on the north bank is the route direction after crossing the levee and the silt area on the north bank of the Yellow River.
On the final choice of the line position, the south bank adopts a double-pipe shield machine from the main span and the east side of the intersection of Jiluo Road and the North Ring Expressway respectively, and the shield is passed by the lower procession line of the Luokou pontoon bridge, the line position is downstream of the pontoon bridge, and the pontoon bridge is anchored in its upstream position, and the two have no impact on each other. The north bank plan is to pull a straight line north to connect National Highway 309 after the line crosses the Yellow River levee, so that it can adapt to the needs of long-term connection with the Jibei region, and also reserves space for the future extension of the line to the north.
How can I be safe?
Anti-flooding doors are provided in the cut-and-cover tunnel section
On September 27, the reporter entered the inside of the tunnel, at this time the final detailing of the tunnel auxiliary settings was being processed, in the west side of the east cave wall waist line position, the reporter saw that there was an obvious escape staircase, different from the ground tunnel escape channel, the escape direction through the yellow tunnel was not upward, and downward, along the direction of the sign down the stairs into a tubular space, the bottom of the space has an exit distance display board, showing the field distance of the north and south exits, and the escape channel is only "separated by a wall" is the rail transit layer, Walking in the tunnel, it can be said that there is a hole in the sky.
Highways and tracks are jointly built, and how to do a good job in rescue work in emergencies is the top priority. "The tunnel is equipped with complete disaster prevention and rescue facilities such as fire hydrants, water sprays, fire extinguishers, broadcasts, emergency telephones, video surveillance, and equipment monitoring." The safety production personnel of the 14th Bureau of China Railway introduced to reporters that the tunnel forms an organic system through the central computer, and in case of emergency, it can be evacuated in 6 minutes on the upper road and 30 minutes in the lower subway section.
"Considering the characteristics of construction risk, structural waterproofing, and seismic safety, this project does not have a contact cross channel, and adopts the escape method of the upper and lower layers as rescue channels." Project department staff said.
The reporter saw from the engineering renderings provided by the project department that the Jiluo Road yellow tunnel is a double-pipe three-story tunnel, and the top of the tunnel is a smoke exhaust air duct; The middle of the tunnel is the lane of the urban road, and the upper part of the lane is equipped with lighting fixtures, emergency broadcasts, cameras, water mist sprinklers and other equipment, and under the lane board is the reserved rail transit space, longitudinal evacuation and rescue channel, cable channel, equipment room, etc. An evacuation and rescue channel is set up on the left side of the lower driving direction of the lane board, and a rescue staircase is set up to communicate with the evacuation and rescue channel, and there is no contact cross channel between the two tunnels.
It is reported that the terrain along the Yellow River in Jinan is mainly plain, formed by the flooding and alluvial of the Yellow River, which is an integral part of the North China Plain. The course of the Yellow River is steeper and slower than the descent, the sand transport capacity is large and small, the sediment is silted up along the way, and the riverbed is silted up year by year, forming a hanging river on the ground. Therefore, tunnel construction needs to consider the risk of river water flooding the urban area due to the damage of the tunnel structure caused by the disaster conditions.
"In addition to strengthening the structure's own disaster resistance and waterproofing ability, the design can avoid the backfilling of the river by setting up flood-proof doors in the tunnel sections on both sides of the river, which can resist the water pressure generated when the river is at its highest water level." Generally, a monitoring system is set up in the bottom section of the river, and the monitoring system receives the signal of the water level sensor in the tunnel and sends a command to allow the door to be closed to the flood prevention door. The relevant technical staff of the project department said.