Segment ring

The term segment ring is used in construction primarily in tunneling: Several precast concrete segments (tubbings) are assembled into a ring to form the inner lining of a tunnel section. In addition, the term also appears in connection with annular cutting tools whose circumference consists of individual segments. In both meanings, the controlled processing of concrete and rock plays a central role – a field in which tools such as high-precision concrete crushers and hydraulic rock and concrete splitters from Darda GmbH are frequently integrated into planning and execution workflows, for example in concrete demolition and special demolition, rock breakout and tunnel construction, or in strip-out and cutting. In technical usage, the segment ring is also referred to as a lining ring or tubbing ring when describing the permanent inner shell of shield-driven tunnels.

Definition: What is meant by a segment ring?

A segment ring is the closed, annular unit made up of several concrete elements (segments) that is assembled in tunneling to form a mechanically load-bearing, sealing inner shell. Each segment is usually reinforced, equipped with joint tapes or gasket profiles, and connected to neighboring segments with a force-fit via alignment bolts, shear cones, or bolted connections. A complete ring is formed after installing standard, closure, and, where applicable, wedge segments. The loads from rock pressure, earth pressure, and use are transferred by the ring through the joints to adjacent rings and the surrounding ground. In mechanized tunneling with shield machines, the annular gap is typically backfilled with single- or two-component grouts to establish early ground contact and seal. In a broader sense, “segment ring” can also denote an annular cutting body with a segmented circumference (e.g., rings in sawing or drilling systems); in the construction context, however, the tubbing meaning predominates.

Design and geometry of segment rings

Segment rings typically consist of 5 to 8 individual parts. The segment geometry is tailored to the tunnel cross-section, the excavation system, and the ground conditions. Key parameters are wall thickness, width (ring length in the direction of advance), reinforcement layout, joint pattern, and the position of the closure segment. Seals (often EPDM profiles) are placed in the segment joints and compressed during clamping to ensure a durable seal of the annular gap.

• Typical detailing: dowel and shear key systems, circumferential and radial gaskets, reinforcement around lifting points, recesses for utilities, and key segments to control ring closure.
• Structural verifications: design for thrust loads from TBM jacks, ovalization, local bearing at joints, and fire or durability requirements depending on the project.
• Execution aspects: orientation markings, segment coding, and predefined staggering rules to optimize load paths and construction logistics.

Segment ring in tunneling: assembly, load transfer, and sealing

With shielded tunnel boring, the segment ring is installed directly behind the cutterhead. The erector positions the elements in a defined sequence; after placing the wedge or closure segment, the ring is aligned and clamped. Grout fills the annular gap between the outside of the segment ring and the excavation profile. The structural action derives from the ring-shaped geometry, the joint interlock, and the clamping; shear forces are transferred via shear cones or shear keys. In practice, a controlled ring build cycle with documented torque values, gasket lubrication, and staged grouting ensures dimensional accuracy and fast stabilization of the excavation.

Sealing concepts and joints

Joint profiles, joint tapes, and targeted preloading ensure tightness. The quality of the joint depends on the concrete surface, installation accuracy, and the condition of the sealing elements. If joints are damaged, remediation with injection resins, local mortar repairs, or precise removal of defects is required – often under confined conditions.

• Gasket types and tests: use of EPDM or comparable profiles with factory pressure tests, compression set checks, and on-site visual inspection before erection.
• Grouting strategy: single- or two-component grout tailored to ground permeability to avoid voids and to limit settlement.
• Quality checkpoints: verification of joint closure, alignment across ring joints, and cleanliness of sealing grooves prior to final clamping.

Repair, openings, and deconstruction on segment rings

Over a tunnel’s life cycle, segment rings are retrofitted (cable trays, cross passages), repaired (spalling, delamination, leaks), or dismantled in exceptional cases. Low-vibration, controllable methods are required to protect ring integrity and adjacent structures. Prior to interventions, reinforcement detection (e.g., ferromagnetic scanning), structural assessment of load paths, and clearly defined temporary supports minimize risks and rework.

Approaches in concrete demolition and special demolition

Typical measures around segment rings rely on a combination of separation, controlled release, and selective removal:

• Scoring and separation along defined lines (e.g., core drillings or saw cuts) to relieve the structure.
• Subsequent, low-vibration detachment of partial areas using rock and concrete splitters from Darda GmbH to create controlled crack wedges without impairing the remaining ring structure.
• Selective biting and profiling of edges, ribs, and projections with concrete crushers to produce precise openings or remove damaged areas.
• Processing of reinforcement with steel shears or multi cutters when reinforcing bars need to be exposed and cut.
• Survey-controlled marking of opening contours and installation of temporary supports to maintain ring stability during phased removal.

This sequence minimizes vibration and dust generation and is particularly suitable for rock breakout and tunnel construction as well as for work under traffic or in sensitive environments. Where necessary, surface reprofiling with repair mortars and reinstatement of joint seals restore durability and tightness.

Tools and methods in connection with segment rings

Depending on the work objective, different hydraulic tools are used, powered by compact hydraulic power units. Selection and sequence depend on concrete strength, reinforcement content, and the structure’s boundary conditions. Remote or tethered operation enhances control in confined or high-sensitivity zones.

• Rock and concrete splitters: Generate controlled splitting forces in predrilled holes. Suitable for releasing parts of a segment ring for retrofit openings or for removing deteriorated concrete – particularly helpful in special demolition and in strip-out.
• Concrete crushers: Precise removal of concrete, creation of defined edges, biting off cover concrete. Indispensable in concrete demolition to shape openings in segment rings to exact dimensions.
• Combination shears and steel shears: Cutting of reinforcement, anchors, and embedded parts that are often located in segment joints or connections.
• Multi cutters: Versatile cutting tools for thin-walled components, sheets, and installations around segment rings, for example during the deconstruction of technical equipment.
• Tank cutters: For special assignments with high safety requirements when cutting closed hollow bodies in tunnel operations facilities, if present in the project.
• Core drilling and ring sawing: Predefine separation lines and reduce stresses before controlled splitting and crushing, improving accuracy and reducing emissions.

Terminological classification in the area of strip-out and cutting

Outside tunneling, “segment ring” is sometimes used for annular cutting bodies with a segmented circumference (e.g., in special ring saws). In strip-out and cutting, such tools can pre-cut openings in reinforced concrete with precision. Afterwards, concrete crushers handle clean reprofiling, while rock and concrete splitters detach larger components with low vibration. The result is a coordinated process with high dimensional accuracy and minimal impact on adjacent components. In contrast, the segment ring in tunneling denotes the permanent or primary lining element assembled from precast segments.

Safety, emissions, and environmental protection

Work on segment rings requires particular care: structural capacity, tightness, and operational requirements must be observed. Low-vibration methods reduce the risk of crack formation and minimize noise and dust. Hydraulic tools, as operated with Darda power units, enable controlled interventions with low vibration – an advantage in sensitive areas and during ongoing operations. Water suppression, extraction, and waste segregation for grout and slurry contribute to low-emission workflows and regulatory compliance.

Occupational safety and workflows

Confined space conditions, ventilation, dust and water management, load handling during component removal, as well as emergency and escape routes must be defined before starting. Extraction, water management, and coverings improve working conditions. Interventions in load-bearing elements must be monitored and stabilized section by section. Method statements, task-specific risk assessments, and lifting plans ensure coherent coordination with operations and emergency services.

Quality assurance, tolerances, and documentation

For the fit of segment rings, tolerances in roundness, offset, joint width, and ring position are decisive. In repairs, processed edges should be produced plumb and aligned, and joint profiles kept undamaged or replaced. Comprehensive documentation (measurement logs, photos, material certificates) supports verification to the client and inspection bodies. Laser-based as-built checks, pressure or leak tests at joints, and recorded torque values for connectors increase traceability and acceptance quality.

Typical problems and practical solutions

• Spalling at edges: Gentle biting with concrete crushers, followed by reprofiling with repair mortar.
• Cracks emanating from drill holes: Reorder load transfer, check drilling spacings, controlled re-splitting with splitters instead of impact methods.
• Binding during ring closure: Rework segment edges, remove material locally, verify the geometry of the closure segment.
• Leakage in joints: Open the defect, clean, inject, and rebuild to be watertight; low-vibration processing protects joint profiles.
• Void zones behind the ring: Identify by sounding or radar, then perform targeted backfilling or re-injection to restore contact and reduce deformation.

Planning and interface management

Successful work on the segment ring requires coordinated steps between excavation, lining, MEP, surveying, and deconstruction trades. Early definition of opening sizes, tolerances, and installation sequences shortens downtimes. The choice of demolition and separation technology is based on material properties, reinforcement drawings, and accessibility. Clear hold points, inspection and test plans, and digital coordination models streamline approvals and reduce clashes at interfaces.

Special operations and confined spaces

In special operations, such as emergency repairs or in shafts with restricted access, compact hand-held systems are in demand. Here, hydraulic rock and concrete splitters and concrete crushers excel, working precisely and with low emissions even under difficult conditions. For natural stone extraction near structures – such as at portal areas – similar, controlled splitting methods can be applied to avoid vibrations and uncontrolled fractures. Modular tooling and quick-change setups reduce set-up times where work windows are short.

Legal and technical framework

The planning, execution, and testing of segment rings are governed by the applicable technical rules and contractual specifications. Interventions in load-bearing or sealing components must be designed, approved, and supervised. The information in project documents and test certificates is authoritative; the selection of methods and tools is project-specific and should be based on expert assessment. Permit procedures, structural approvals, and environmental requirements need to be aligned with construction sequencing to ensure safe and compliant delivery.