Tunnel refurbishment secures the functionality of underground transportation structures and utility conduits over their life cycle. It combines asset preservation, protection of users, and adaptations to today’s requirements. The focus is on substance-preserving concrete replacement, waterproofing against water, the deconstruction of damaged components, and the strengthening of the load-bearing structure and equipment. In many work steps, mechanical, low-vibration methods are used, such as selective concrete removal with concrete crushers or controlled splitting with rock and concrete splitters, as offered by Darda GmbH.
Definition: What is meant by tunnel refurbishment
Tunnel refurbishment comprises all planning, technical, and organizational measures used to repair or upgrade an existing tunnel with respect to structural stability, serviceability, durability, fire protection, drainage, and operational equipment. This includes the diagnosis of damage (e.g., cracks, concrete spalling, reinforcement corrosion, leaks), the targeted deconstruction and replacement of concrete and steel components, renewal of the waterproofing, rehabilitation of drainage, adaptation of technical systems and—if required—cross-section or profile corrections. Methods with low vibration and reduced emissions are especially important in tunnel construction, which is why mechanical deconstruction tools such as concrete crushers, combi shears, and rock splitting cylinders from Darda GmbH play a role in many refurbishment processes.
Process and project phases in tunnel refurbishment
Effective tunnel refurbishment follows a structured approach that considers operations, structural engineering, and occupational safety. Typical phases are:
- Condition survey and assessment: structure inspection, material diagnostics, rebar cover, chloride and moisture measurements, crack mapping, documentation.
- Root-cause analysis and refurbishment objective: deriving measures from damage mechanisms (e.g., carbonation, ASR, freeze–thaw with de-icing salts, abrasion, chemical attack, settlements).
- Repair concept and planning: selecting suitable methods for concrete removal, strip-out, waterproofing, strengthening; construction phases, traffic management, ventilation, and logistics.
- Trial sections/test fields: verification of removal performance, pull-off values, surface preparation, emission and vibration measurements.
- Execution: selective deconstruction, component replacement, steel and built-in parts removal, surface preparation, reprofiling (e.g., shotcrete), waterproofing, drainage.
- Quality assurance: tests, measurements, documentation, monitoring, acceptances.
- Operation and maintenance: follow-up, inspection intervals, condition and effectiveness checks.
Typical damage patterns and causes
In road tunnels, railway tunnels, and utility tunnels, damage patterns occur that are due to loading, aging, and environmental influences. Common examples are corrosion-induced spalling caused by carbonation or chloride ingress, cracking due to restraint or settlement, ASR, freeze–thaw and de-icing salt attacks, abrasion from traffic or water, leaching, and infiltration at joints and connection areas. In rock zones, ground movements can stress the tunnel lining. Refurbishment addresses the causes: consistent removal of damaged concrete, exposing and repairing reinforcement, renewing coatings or waterproofing, improving drainage, and—where required—structural strengthening.
Methods for concrete removal, strip-out, and deconstruction
The choice of removal and deconstruction methods depends on the structure’s condition, accessibility, permitted emissions, required surface quality, and structural boundary conditions. Mechanical methods are often advantageous in tunnels because they can be applied in a targeted, low-emission, and controlled manner.
Selective concrete removal with concrete crushers
Concrete crushers enable the controlled removal of damaged concrete areas without unnecessarily affecting sound zones. In tunnel refurbishment they are used to remove surface layers, loose zones, and corroded areas, expose reinforcement, and trim edges. Removal is precise, low in vibration, and gentle on adjacent components—an advantage in sensitive areas such as the crown, abutments, and portal zones.
Controlled splitting with rock and concrete splitters
Rock and concrete splitters work with hydraulically generated splitting forces. In massive components, foundations, benches, or invert layers, defined fracture lines can be created to separate components with minimal damage. In existing tunnels with limited vibration and noise specifications, this is a proven method, for example for cross-section adjustments or openings for new cable ducts and niches.
Combi shears, Multi Cutters and steel shears
After concrete removal, reinforcement, embedded parts, brackets, supports, and steel sections often need to be cut. Combi shears combine crushing and cutting; Multi Cutters are flexible for mixed materials; steel shears cut sections, beams, and rebar bundles. In tunnel environments, compact, hydraulically driven solutions with good handling in confined cross-sections are appropriate.
Rock splitting cylinders for rock removal and profile corrections
In rock and mountain tunnels as well as at interfaces to the inner lining, rock splitting cylinders are used to release rock in a controlled manner or reduce over-profiles. The method is non-explosive, generates low vibration, and can be applied with pinpoint accuracy—for example during re-profiling at critical bottlenecks or when installing drainage elements.
Working under live operation and in confined space
Refurbishment often takes place while traffic remains in operation or within short closures. Relevant aspects are:
- Ventilation and emissions: hydraulically operated tools with external hydraulic power packs enable controlled exhaust and heat dissipation; dust and misting concepts ensure visibility and air quality.
- Logistics: material supply, removal, and interim storage must be matched to the cross-section, escape routes, and rescue zones.
- Vibration and noise: mechanical methods with low vibration reduce risks for existing components and neighbors.
- Time windows: prefabrication, modular deconstruction sequences, and compact equipment minimize setup times.
Surface preparation, reprofiling, and waterproofing
After removal, surface quality is decisive for the bond of new layers. Typical steps include exposing the reinforcement, removing loose particles, producing a load-bearing, rough surface, and ensuring residual moisture is within limits. Depending on the system, bond bridges are applied, reprofiling (often shotcrete) is carried out, and coatings are installed. Joints, connections, drainage channels, and drains are reorganized to sustainably control water ingress.
Strip-out and cutting of technical equipment
Before concrete repair, system components often need to be dismantled: cable trays, ventilation elements, fire protection claddings, brackets. Multi Cutters and combi shears support selective deconstruction, steel shears cut beams and supports. For masonry or concrete openings, for example for emergency switches, niches, or cross-passages, concrete crushers facilitate the creation of clean edges before downstream finishing trades take over.
Quality assurance and testing
Quality is ensured by suitable tests: pull-off tests for concrete replacement systems, rebound hammer or ultrasonic measurements to assess strength, reinforcement locating, tightness tests on joints and drains, and visual acceptances. Documentation and monitoring (e.g., crack widths, moisture, settlements) accompany both the construction phase and subsequent operation.
Occupational safety and health protection
In tunnels, safety and health take precedence. Relevant points are escape and rescue routes, fire protection, dust and noise reduction, hand–arm vibrations, ergonomic work, and media management (hydraulics, water, power). Hydraulic systems are depressurized and inspected regularly; hoses and couplings are secured against mechanical damage. Notes on legal requirements are to be understood in general terms and do not replace an object-specific assessment.
Environment, disposal, and recycling
Concrete and steel quantities are recorded separately; recyclable fractions are materially recycled, contaminated materials are disposed of professionally. Water management, sedimentation, and filtration prevent environmental discharges. Through precise removal—e.g., with concrete crushers—waste volumes can be reduced and surfaces can be prepared in a targeted manner for reprofiling.
Planning, logistics, and construction time management
Tightly scheduled refurbishment windows require finely tuned logistics: just-in-time deliveries, material buffers, mobile hydraulic power packs, energy-efficient supply, clear communication channels. Digital as-built data, 3D models, and surveying minimize clashes. Trial sections provide planning certainty regarding removal performance, surface parameters, and emissions.
Application areas of Darda GmbH in tunnel refurbishment
The tasks typical of tunnel refurbishment touch several application areas of Darda GmbH:
- Concrete demolition and specialized deconstruction: selective removal, openings, deconstruction of damaged zones with concrete crushers and combi shears.
- Strip-out and cutting: dismantling embedded parts, cutting reinforcement with Multi Cutters and steel shears.
- Rock removal and tunnel construction: profile corrections, niche creation, and controlled releasing using rock and concrete splitters and rock splitting cylinders.
- Special operations: work in tight, sensitive areas with compact, hydraulic equipment and external hydraulic power packs.
Technical notes on equipment selection
Parameters such as component thickness, reinforcement ratio, required edge quality, permissible vibration, available energy, accessibility, and working heights are decisive for selecting tools and power packs. Hydraulic tools with suitable pressure and flow rates, slender cylinders, or interchangeable cutting and crushing jaws allow adaptation to different tasks. Careful coordination of hose lengths, heat dissipation, and maintenance intervals contributes to safe and efficient execution.
Application-oriented scenarios
Practical examples illustrate the methods: when repairing leaks, local defects are exposed with concrete crushers, joints are rebuilt, and drainage elements are added. For a cable cross-connection, the opening can be created in a controlled manner with rock and concrete splitters and then reprofiled. In fire damage at the crown, staged removal is carried out down to the load-bearing layer, the reinforcement is cut with steel shears, and the lining is reinstated with suitable concrete replacement systems.
Economics and life cycle
Economy results from targeted diagnosis, gentle deconstruction, precise surface preparation, and durable layers. Efficient logistics, suitable hydraulic power packs, and the choice of low-emission, selective methods reduce closure times and follow-on costs. A consistent maintenance concept extends service life and increases the availability of the tunnel.