Tunnel lamella

In German-speaking engineering, the term tunnel lamella is used as a practice-oriented umbrella term for lamella-shaped components and sectionally constructed elements in tunnel construction. Depending on the context, this may refer to individual lamellae of a diaphragm wall in cut-and-cover and diaphragm-wall construction, lamella-like sections in shotcrete construction (NATM/SEM), or lamellae in the area of portals and ventilation structures. In planning, construction, maintenance, and deconstruction, the tunnel lamella is particularly important because it directly influences excavation pit and tunnel statics, construction sequencing, and topics such as sealing, ventilation, and maintenance. For modifications, controlled concrete demolition, and special demolition, low-vibration methods are often used; in combination with hydraulic power packs, this includes the use of a concrete pulverizer as well as a hydraulic wedge splitter. In both temporary and permanent works, lamella-wise approaches enable targeted interventions with minimal impact on adjacent structures and operations.

Definition: What is meant by a tunnel lamella?

A tunnel lamella is a lamella-shaped, self-contained partial structure or a sectionally constructed component area that fulfills structural, sealing, guiding, or ventilation functions in tunnel construction. Typical examples are diaphragm wall lamellae of excavation pits and tunnel exterior walls, lamella-wise applied shotcrete panels for face stabilization, lamellae for noise and light control at portals, and ventilation lamellae in shafts and cross passages. The term does not describe a single standardized component type, but rather the lamella-like execution: as a panel, field, segment section, or air-guiding lamella. For maintenance or deconstruction of such lamellae, controlled methods with low vibration, low dust, and high precision are required, such as splitting massive concrete areas or clamp-like removal of reinforced concrete components. In engineering usage, distinctions are made between load-bearing lamellae with structural interaction and purely functional lamellae for airflow and light control, with tolerances and joint control determining durability and serviceability.

• Core functions: structural load transfer, groundwater sealing, guidance of air and light, as well as controlled construction sequencing
• Execution formats: single panels, fields, sectional segments, and aerodynamically shaped slats

Construction types, materials, and installation locations of tunnel lamellae

Tunnel lamellae occur in several practical variants. They differ in material, thickness, dimensions, and connection details, but always fulfill a clearly assigned function in the construction sequence and later operation. The following outlines the most important construction types, explains their typical applications, and shows the impacts on production, inspection, maintenance, and deconstruction. Interface design to adjacent slabs, base slabs, and interior linings is decisive for watertightness and long-term performance.

Diaphragm wall lamellae in cut-and-cover and diaphragm-wall methods

Diaphragm walls are constructed in lamella-wise separated sections. Each lamella is excavated in a support fluid, fitted with reinforcement cages, and concreted. In tunnel construction (especially in cut-and-cover), these lamellae take significant earth and traffic loads, provide groundwater protection, and often form the future exterior wall of the structure. Waterstops, swelling profiles, and interlocking solutions ensure sealing between lamellae. Integrity checks and joint testing are part of quality assurance. When opening, retrofitting, or deconstructing individual lamella fields, controlled removal of heavily reinforced concrete is required; here, a concrete pulverizer and-for massive zones-a hydraulic wedge splitter are preferred to minimize vibrations.

Shotcrete lamellae in NATM/SEM

In conventional tunneling, the tunnel face and top heading are secured section by section with shotcrete. These panels are often installed alternately in a lamella-like pattern to limit settlements and control load behavior. The lamellae consist of shotcrete with reinforcement meshes, anchors, and possibly fibers. Lattice girders, lattice arches, and drainage layers may be integrated depending on the ground. For local reinforcements, openings, or repairs: thinner shotcrete lamellae can be removed precisely with a concrete pulverizer; for thicker areas or rock-laden zones, a hydraulic wedge splitter as well as a rock wedge splitter have proven effective to release the rock-concrete bond without impact.

Ventilation and portal lamellae

At tunnel portals and in ventilation structures, lamellae made of steel, aluminum, or GFRP are used for air guidance, weather and noise protection, and light control. These ventilation lamellae are corrosion-protected and designed for flow performance, including pressure loss, aeroacoustics, and icing risk. For replacement and deconstruction, separation of metal sections and disassembly of frames are key. For mechanical cutting, a steel shear can be used; load-bearing concrete frames of lamella fields are reduced in a controlled manner with a concrete pulverizer. Smaller metal profiles or installations can be cut with an attachment shear.

Materials and typical dimensions

• Concrete lamellae: shotcrete 80-300 mm, reinforced concrete (diaphragm wall lamellae) 600-1500 mm and more
• Metal lamellae: steel or aluminum profiles, profile heights 100-400 mm, wall thicknesses according to structural requirements
• Composite lamellae: GFRP or CFRP slats for ventilation and portal areas, typical panel thicknesses 2-8 mm depending on span and stiffness
• Connection details: waterstops, swelling profiles, reinforcement lap splices, sealing joints

Planning, design, and construction sequence

The planning of tunnel lamellae depends on geology, groundwater, construction method, and operational requirements. For diaphragm wall lamellae, structural stability, deflection, filter stability, and joint sealing are paramount; for shotcrete lamellae, deformation limits, anchor spacing, and early strength are decisive. Ventilation lamellae are designed aerodynamically and verified for corrosion and fire protection. A careful construction sequence-lamella-wise production, adequate curing times, defined joints-ensures load-bearing and sealing performance. Digital coordination with model-based planning and as-built updates supports clash-free execution and traceable documentation.

Design aspects

• Load assumptions: earth and water pressure, traffic loads, temperature effects, fire
• Verifications: load-bearing capacity, serviceability, fatigue under recurring loads
• Joints: watertightness, allowances for displacements, differential settlements
• Durability: exposure classes, cover depth, reinforcement protection, resistance to freeze-thaw and chemical attack
• Constructability: access, segmenting, temporary support, and logistics under confined conditions

Maintenance, modification, and deconstruction of tunnel lamellae

In existing structures, inspections and repurposing often require interventions in individual lamella fields: openings for cable routes, shaft connections, portal modifications, or selective deconstruction. The goal is a precise, low-vibration, and dust-minimized process to avoid affecting adjacent structures, railway operations, or traffic. Time windows and permit requirements necessitate efficient sequencing and reliable emission control.

Method selection and equipment reference

• concrete pulverizer: for targeted removal of reinforced lamella areas, good control of break lines, low vibration
• hydraulic wedge splitter and rock wedge splitter: for massive concrete sections and rock inclusions, particularly suitable in sensitive areas with vibration restrictions
• steel shear: cutting of reinforcement cages, steel frames, and metallic ventilation lamellae
• hydraulic demolition shear: when both concrete and steel must be handled in the same work sequence
• attachment shear: for conduits, smaller profiles, and auxiliary structures
• hydraulic power units: energy supply for hydraulic attachment with the appropriate drive power class

Application areas and boundary conditions

• concrete demolition and special demolition: selective, controlled, and with a defined sequence
• building gutting and concrete cutting: preparations for splitting and clamp-like removal, e.g., core drilling as predetermined breaking points
• rock breakout and tunnel excavation: loosening excavation in heterogeneous zones
• natural stone extraction: comparable splitting techniques for lamellar rock strata
• special demolition: work under restricted headroom, in ventilation-sensitive areas, or during operations in existing facilities
• works under traffic: possession times and strict vibration, noise, and dust limits in rail and road environments

Typical damage patterns and maintenance of lamellae

Common occurrences include crack formation, spalling, efflorescence, leaking joints, and corrosion of reinforcement or metal lamellae. Alkali-silica reaction, freeze-thaw damage, and biogenic corrosion may occur depending on exposure. Diagnosis and measures proceed step by step, from monitoring to intervention.

Procedure

1. Inspection and testing (visual, rebound hammer index, potential measurement, if necessary non-destructive methods)
2. Root cause analysis (water, load redistribution, material fatigue)
3. Repair: crack injection, local renewal of lamella fields, joint upgrading, replacement of ventilation lamellae
4. Controlled removal of defective areas with a concrete pulverizer, cutting reinforcement with a steel shear, splitting massive zones with a hydraulic wedge splitter

Occupational safety, emissions, and environmental protection

Work on tunnel lamellae often takes place in confined spaces with demanding ventilation conditions. Priority is given to safe access, orderly load transfer, and emission reduction. Low-vibration methods such as splitting or clamp-like removal reduce vibrations, dust, and noise. dust extraction, water mist, low-spark cutting, and a coordinated ventilation concept are recommended. Requirements for fire protection, escape route, and hazardous substance handling must be observed. A task-specific risk assessment with rescue planning and continuous gas monitoring is essential.

Practice-oriented approach: selective deconstruction of a concrete tunnel lamella

The following example shows a practical sequence for the selective deconstruction of a lamella-like concrete field, e.g., on a diaphragm wall in the tunnel area:

1. Existing-conditions analysis: clarify drawings, reinforcement layout, joint locations, utilities, and adjacent loads
2. Stabilization: shoring, load transfer, protective wall, ventilation, and dust suppression measures
3. Preparation: mark cutting and break lines, execute core drilling as predetermined breaking points
4. Pre-weakening: introduce a grid of relief boreholes
5. Splitting: controlled release of massive areas with a hydraulic wedge splitter and-or a rock wedge splitter
6. Clamp-like removal: stepwise removal with a concrete pulverizer, exposing the reinforcement
7. Steel separation: cut reinforcement and embedded parts with a steel shear and-or a hydraulic demolition shear
8. Fine removal: rework edges, carefully expose joint areas
9. Disposal-logistics: separate collection of concrete, steel, and auxiliary materials, transport under operating constraints, organize waste disposal logistics
10. Documentation: as-planned vs. as-built comparison, release for subsequent trades

Quality assurance and interfaces

Lamellae directly affect adjacent components. Therefore, interfaces-such as between lamella joints, intermediate supports, cover slabs, base slabs, and interior works-must be coordinated early. Measurement concepts (control measurement of settlement, crack widths, moisture), load test, and functional checks (e.g., for ventilation lamellae) ensure serviceability. For adaptations in existing structures, step-by-step methods with a concrete pulverizer and a hydraulic wedge splitter help reveal the existing structure in a controlled manner without damaging edge zones. Acceptance criteria and handover records provide traceability and facilitate maintenance planning.

• Typical checks: joint tightness tests, reinforcement cover measurements, alignment and level surveys, airflow and pressure drop verification for ventilation lamellae

Terminology distinctions in tunnel construction

The term tunnel lamella is used flexibly in practice. Diaphragm wall components are clearly executed as lamellae; shotcrete panels are often constructed sectionally in a lamella-like fashion. Prefabricated inner linings of shield tunnels consist of segments (segment ring in a segment tunnel); they are generally not referred to as lamellae. Ventilation lamellae and portal lamellae are function-related components with air-handling tasks. This classification facilitates the choice of suitable construction and deconstruction methods and supports precise specification in planning documents, tendering, and site execution.