ASTM Standards (American Society for Testing and Materials Standards) · International Standards
Shield tunnelling is a method of underground excavation in which a shield machine drives through the ground while simultaneously performing excavation, support, muck removal, and segment lining erection. Its core logic is that the shield shell (or earth pressure / slurry pressure) forms temporary support between the excavation face and the completed tunnel behind, allowing the three stages of excavation, support, and advance to overlap closely in time and space—thereby achieving safe, continuous, and rapid tunnel construction under complex conditions such as soft ground, high groundwater levels, and densely built-up urban areas. In metro projects, shield tunnelling is primarily used for running tunnel construction and is currently the mainstream method for urban rail transit running tunnels.
Historically, shield technology originated from the 19th-century Thames Tunnel project in England and was systematically developed in Japan and Europe during the 20th century. China introduced the shield concept in the 1950s, and following large-scale metro construction in Shanghai, Guangzhou, and Beijing from the 1990s onward, shield tunnelling was rapidly localized. After 2000, Chinese state-owned enterprises such as China Railway, China Railway Construction, China Communications Construction, and China State Construction undertook numerous overseas metro projects, making shield tunnelling technology a core competency that overseas general contractors must master. Meanwhile, the International Tunnelling Association (ITA), British Standards Institution (BSI), American Society for Testing and Materials (ASTM), and the European Standards (EN) system all impose requirements on shield machinery, lining, grouting, and monitoring—yet standards vary significantly between countries. Overseas projects often require a triple adaptation of "Chinese technology + international standards + local codes."
In terms of applicability, shield tunnelling is suitable for soft soil, sand layers, silty fine sand, gravel layers, soft rock, and mixed ground. It is particularly well-suited to urban environments with high groundwater levels, strict surface settlement control, and dense crossings beneath buildings and existing lines. Its limitations include: reduced efficiency in extremely hard rock, boulder clusters, and highly abrasive ground; long lead times for shield machine selection and manufacturing; large sites required for launch and reception shafts; and constraints on curve radius, gradient, and cover depth. Overseas projects must also account for non-technical factors such as local climate, logistics, labor, environmental protection, and community relations.
Shield machine selection is the foremost factor determining project success. Key criteria include: ground particle size distribution, groundwater pressure, rock uniaxial compressive strength, abrasivity index, tunnel cover depth, curve radius, and surface settlement control requirements.
| Shield Type | Applicable Ground | Core Advantages | Main Risks |
|---|---|---|---|
| Earth Pressure Balance (EPB) | Soft soil, silty fine sand, sandy gravel | Low cost, convenient muck removal | Screw conveyor blowout, cutterhead clogging |
| Slurry Shield | High water pressure sand, gravel layers | High pressure control precision | Large footprint of slurry treatment system |
| Composite Shield | Soft-hard interbedded, mixed ground | Interchangeable cutterhead, strong adaptability | Rapid cutter wear, high risk during cutter replacement |
| Hard Rock TBM | Intact hard rock | Fast advance rate | Sensitive to weak fractured zones |
For overseas projects, selection must also assess local grid voltage, spare parts supply, maintenance capability, and transport constraints. For example, some Southeast Asian projects require shield machines to be transported in sections and assembled on site due to limited port lifting capacity.
The core of shield tunnelling is maintaining face stability and controlling ground loss. Key parameters include: chamber pressure, thrust, torque, cutterhead rotation speed, advance rate, simultaneous grouting volume and pressure, and muck discharge volume.
Settlement control criteria vary by project. Overseas projects often adopt a "three-tier warning" mechanism: yellow, orange, and red, corresponding to different monitoring frequencies and response measures.
Segments are the permanent lining of a shield tunnel, and their quality directly determines tunnel service life and waterproofing performance.
Segment Erection Checklist:
Overseas projects must note differences in segment production standards. For example, European projects often require segment concrete impermeability grade and rebar cover to comply with EN 1992, which differs from Chinese standards in detail—requiring equivalence assessment in advance.
Launch and reception are the highest-risk stages of shield tunnelling. Common accidents include portal water and sand ingress, shield machine pitching, and surface collapse.
Launch Stage:
Reception Stage:
Shield tunnelling must establish a "monitor–feedback–respond" closed loop. Monitoring targets include: surface settlement, building tilt, utility deformation, tunnel convergence, and groundwater level.
Common Risks and Emergency Measures:
Overseas projects must also consider non-technical risks such as insufficient local emergency resources, language barriers, and labor union or community protests.
| Comparison Dimension | Chinese National Standards (GB Series) | International Standards (ITA/EN/ASTM) | Local Standards (Southeast Asia as Example) |
|---|---|---|---|
| Design philosophy | Emphasizes construction experience and parameter control | Emphasizes risk assessment and full life cycle | Mostly adopts British or American standards with local modifications |
| Settlement control | Generally per GB 50446, etc. | Often adopts ITA guidelines and project-specific standards | Often requires third-party monitoring and independent review |
| Segment standards | GB/T 22082, etc. | EN 1992, ASTM C series | Often requires local production and certification |
| Acceptance method | Item-by-item acceptance + government supervision | Joint acceptance by owner, engineer, and third party | Government acceptance + community disclosure |
| Environmental requirements | Gradually increasing | Strict, especially noise and slurry treatment | Highly variable, requires case-by-case confirmation |
In overseas project practice, the common approach is: use Chinese standards as the technical foundation, international standards as the communication language, and local standards as the compliance baseline. Specific projects require reference to contract technical specifications and official documents.
Scenario 1: Singapore Thomson–East Coast Line
Some sections of this project used shield tunnelling to cross urban areas and existing lines, with extremely high settlement control requirements. Public reports indicate that the project used a combination of EPB and slurry shields, coupled with real-time monitoring and automated control systems, successfully crossing multiple sensitive buildings. This case demonstrates that in developed markets, shield tunnelling must meet strict environmental, safety, and community communication requirements.
Scenario 2: Tel Aviv Light Rail Red Line, Israel
Chinese state-owned enterprises participated in this project, with shield drives crossing water-rich, interbedded sand and clay ground. Public information indicates that the project used EPB shields, optimized foam and bentonite ratios to address blowout risk, and controlled settlement through ground pre-treatment and simultaneous grouting. This case shows that the Middle East market demands high schedule and safety performance, requiring advance supplementary geological investigation and equipment adaptability modifications.
Scenario 3: Kuala Lumpur MRT Project, Malaysia
Public reports indicate that some sections of this project used shield tunnelling through limestone and soft soil mixed ground, facing risks of boulders and karst cavities. The contractor reduced tunnelling risks through advanced geological prediction, cutterhead and cutter optimization, and grouting reinforcement. This case highlights that Southeast Asian geology is complex, requiring deep integration of investigation, design, and construction.
All project information above is from public reports. For specific technical parameters and contract details, please refer to official documents.
Q1: When selecting a shield machine, how do you choose between EPB and slurry shield?
A: The key factors are ground permeability and water pressure. High water pressure sand layers favor slurry shields; soft soil and silty fine sand can use EPB. Overseas projects must also consider the footprint of the slurry treatment system and environmental permits.
Q2: How should overseas projects handle differences between Chinese and foreign standards?
A: It is recommended to create a "standards benchmarking table" listing differences between Chinese standards, international standards, and local standards item by item, with equivalent solutions confirmed by the design institute and owner's engineer. Key items such as fire protection, seismic design, and environmental protection must prioritize local requirements.
Q3: How can shield launch water and sand ingress be prevented?
A: End treatment is fundamental and requires core sampling verification; portal breaking should be done in segments; standby dewatering wells and emergency grouting equipment should be on site; air-tightness testing should be conducted after launch seal installation.
Q4: What should be done if cracks appear after segment erection?
A: First determine crack depth and width. Surface cracks can be repaired; through-cracks require structural safety assessment, with additional inner lining or grouting reinforcement if necessary. Simultaneously investigate erection stresses and segment curing issues.
Q5: How can overseas projects manage community communication and settlement complaints?
A: Establish a community liaison mechanism in advance, disclose construction schedules and monitoring data; set up a complaint hotline and rapid response team; conduct pre-construction condition surveys of sensitive buildings and commit to post-construction repairs.
1. Conduct thorough upfront site investigation: Geological data for overseas projects is often incomplete; supplementary investigation and advanced geological prediction are recommended to avoid reactive responses during tunnelling.
2. Prioritize standards benchmarking: Initiate standards benchmarking immediately after contract signing to clarify compliance pathways for design, materials, acceptance, and environmental protection.
3. Allow margin in equipment selection: Design cutterhead torque, thrust, and grouting capacity for the most unfavorable ground to avoid "a small horse pulling a big cart."
4. Establish a parameter control system: Integrate chamber pressure, muck discharge, grouting volume, and settlement monitoring into a unified platform for data linkage and early warning.
5. Dedicated launch and reception plans: Prepare separate dedicated plans, organize expert reviews, and conduct on-site emergency drills.
6. Full traceability of segment quality: Establish QR code or RFID traceability systems from production, transport, and erection through to acceptance.
7. Localization and training: Train local workers in shield operation and maintenance to reduce reliance on domestic crews while meeting local employment requirements.
8. Risk reserve and insurance: Set up risk reserves for water ingress, collapse, and equipment damage, and purchase appropriate engineering insurance.
The above recommendations are based on general industry practice. For specific projects, please execute in accordance with contracts, local regulations, and official documents.