【Domestic News】Introduction of Key Technology and Innovation of Shantou Bay Tunnel
Key Technical Characteristics
TBM
1. "Shallow" means that super-large diameter TBM can drive through shallow overburden under water with pressure up to 5bar.
2. "Intensive" means that the mechanical properties of stratum is of big diversity and the uncertain distribution: the strength of subsea bedrock is high and the bedrock surface changes dramatically, extremely heterogeneous strength of compound stratum is changing intensively from soft to hard.
3. "Long" means that the long distance of excavation with high-risk and operation of cutterhead intervention subsea probably.
4. "High" means that it is the first subsea TBM tunnel with design seismic intensity of 9 degree in China. Related new challenges should be fully considered in terms of structure performance of anti-earthquake, waterproof and the joints performance of anti-earthquake (including materials).
The project set up an Academician Studio and National Key Laboratory of TBM which can guarantee the TBM work smoothly and well organized by means of scientific research and on-site simulation experiment etc.
Open-Excavation
1. "Various" means that the line covers a number of important main roads and structures such as such as Longhu Ditch, Haibin Park, container wharf, sewage lines etc.
2. "Water" means that the open tunnel is located in Longhu Ditch and close to the inland sea. The underground water is abundant and the formation is covered by silt.
3. "Deep" means that the foundation pit of open tunnel is deep and the excavation depth of working shaft is 32.5m on the north bank. The thickness of muck and mucky soil is up to 24m within the foundation pit and which need to give attention to the slope failure, pit deformation and collapse during excavation.
4. "Near" means that the nearest distance from building No.45 of Hai Bin Park Residential Community to foundation pit is 9m where the depth of excavation is 18m. In the process of excavation, it is necessary to take measure to prevent soil erosion, building deformation, cracking, and sedimentation.
The project pursues a new mode of cooperation that integrated " Consulting Expert Team and Experienced Design Team", which can promote the safety control of excavation work by the means of organizing on-site expert meeting and design discussion.
Equipment Technology and Innovation
The diameter of the TBM (Herrenknecht) is 15.01m on the eastern line and the diameter of the TBM(CREG) is 15.03m on the western line. The total weight of the TBM is about 4800t. The TBM cutter design is integrated with both "soft" and "hard" conditions and cutter can be changed freely under normal pressure between “soft” and “hard”. The main drive and the spherical bearing can minimize the impact on the cutter head and main bearing as well as reduce the cutter changing times. Cutter plate wear-resistant and verification system can provide convenience to information based construction.
Chart1 Design details for TBM
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Serial No. |
Name |
Function |
Mark |
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1 |
Pressure Cutter |
During the tunneling, the cutter can be changed at any time according to the detection device, which can reduce the times of operations and improve the efficiency of cutter change. |
Pressure cutter weight is about 560t |
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2 |
Elastic and waggle drive |
After the cutter stucked in the boulder, the main drive can be expanded and adjust the position of cutter disc. In addition, which can reduce eccentric load for main drive under the boulder excavation. |
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3 |
Detection for Cutter Disk Abrasion |
Six monitoring belts with different heights and a circular point-type contact are installed on the TBM cutter disk, which will be warning when the disk abraded. |
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4 |
Monitor Measurement for Cutter Disk and Tools |
The TBM cutter is equipped with a rotation, temperature and abrasion monitoring system, which can detect the abnormal status and feedback the information to the operator. |
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5 |
Waterproof By Tailskin Brush |
The design of five tailskin brushes and four sealing grease can well seal the TBM and segment by the means of injecting the high quality grease under pressure, which can prevent the external soil from flowing into the tunnel. |
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6 |
Design of Reserved Pass Entrance |
Diving can be required if necessary. |
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7 |
High strength Stone Crusher |
During the boulder excavation, the crusher can break the small boulders to prevent air cushion from clogging |
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8 |
SSP Detection Device |
To estimate the position, the size, and the shape of boulders to adjust the excavation parameters based on the data from SSP Detection Device |
Herrenknecht |
|
9 |
3D Seismic Wave Detection Device |
To estimate the position, the size, and the shape of boulders to adjust the excavation parameters based on the data from SSP Detection Device |
CREG |
Key Technology and Innovation
Design of Segment Waterproof
High-performance and corrosion-resistant concrete C60 is applied and impervious grade is P12. Two layers of EPDM elastic gasket are pasted outside while joint waterproof is inside. Each circumferential joint is connected with 56 pieces of M42 bolt and longitudinal joint is connected with 30 pieces of M36 bolt. Under normal condition, the water pressure resistance capacity shall not be less than 0.4mpa in a long-term (100 years), and the water pressure resistance capacity shall not be less than 0.8mpa at the present time. Under seismic conditions, the water pressure resistance capacity is not less than 0.4Mpa in a long-term (100 years), and the water pressure resistance capacity is not less than 0.65Mpa at the present time.
Energy Dissipation Technology
Shantou Bay Tunnel is the first subsea tunnel located in the 8-degree seismic intensity area in China and measurement should be taken according to seismic intensity of 9-degree.
Anti-Earthquake: The reinforcement design of segments and the reinforcement of longitudinal bolts design at the joint of rock and soil layers. Mechanical performance grade of bolt in ordinary section is 6.8 degree while that in reinforced section is 8.8 degree.
Vibration Absorption: Flexible energy absorption node is installed at the larger deformation area; 6 energy absorption nodes are installed at each East and West line and with a total of 24 rings of special segments.
Vibration Isolation: The external isolation layer is set by the means of synchronous grouting.
Choosing the suitable cutters according to different geological condition.
Stratum reinforcement technology of large-diameter TBM
In order to drive TBM through the backfilling sections of boulder and bedrock, a reinforcement zone was set at the foot of the slope of the cofferdam with a length of 22.5m and a width of 25m and which is divided into 4 zones according to the design. The zone1, 2 and 3 are reinforced by triaxial mixing pile of 850@600mm and zone 4 by double pipes jet grouting pile of 800@600mm. Finally, it fulfilled the aims of checking the cutter tools, verifying the welding effect of protection carrier and catching the stones at the bottom of chamber.
Slurry parameters matching technology:To calculate the maximum and minimum pressure of slurry ring by ring in advance
Process of Information Based Construction: During the construction, we can adjust and optimize the pressure of slurry according to the comparison of liquid level of chamber, subsidence monitoring and muck quantity
The optimum parameters were determined by the study of the proportion of slurry and synchronous grouting in marine environment.
Scientific Management on TBM Tunnelling
Geological Research: in the launching section, the stratum on top of the shield section is mainly composed of silt and sand. In main drive section, excavation part is composed of silt, soil, clay, coarse sand and weathered granite. The stratum beneath the tunnel is mainly composed of weathered granite and moderately weathered granite and boulders.
Analysis of muck Sample: Collecting the muck samples during excavation to classify and mark them ring by ring, counting the proportions of different samples to compare with the geological drawings and renew them, which can provide the base to control the subsequent drive parameters.
Parameter Research and Judgment: Shield and Tunnelling Key Laboratory has established an information big-data platform to synchronously transmit and display the TBM parameters on site. Analyzing the cutter torque, penetration, cutter Extrusion force as well as other key parameters to handle the abnormal data timely.
Acoustic Wave Identification: The center cone of the TBM is equipped with an acoustic acquisition and monitoring device, which can filter the frequency of acoustic wave generated from cutter disk when contacting with anterior different media, which can accurately judge abnormal data and control the tunneling parameter to avoid damage of cutter tools.
Index control: Through model test to analyze and research drive parameters (penetration、rotation etc.) and stress of cutter, which obtain better parameter index of TBM drive.
