Underpasses are central structures of transport infrastructure. They enable grade-separated crossing of roads, rail lines, waterways, or utility bundles, thus contributing to safety, capacity, and noise reduction. In the planning, construction, maintenance, and deconstruction of an underpass, structural requirements, concrete technology issues, and the constraints of ongoing traffic converge. Especially for works on existing structures, precise, low-vibration methods are required—such as the selective removal of reinforced concrete with concrete pulverizers or the controlled opening of massive components using hydraulic rock and concrete splitters from Darda GmbH.
Definition: What is meant by underpass
An underpass is a structure that disentangles traffic flow on two levels by routing one trafficway or a watercourse underneath another. Typical forms include road and rail underpasses, culverts, pedestrian and bicycle underpasses, and agricultural crossings. Structurally, reinforced concrete frames, cast-in-place tunnels, precast frames, vaults, or combined construction methods are predominant. Functional aspects such as drainage, waterproofing, frost resistance, structure gauge clearance, lighting, and fire protection are integral components. Over the lifecycle of an underpass, structure inspection, condition assessment, repair, strengthening, and, where necessary, partial or complete deconstruction play a key role.
Types, components, and materials of underpasses
Underpasses are usually executed as closed frames (abutments, walls, deck, floor slab) in reinforced concrete. Alternatively, open frames with elevated roadway slabs, half-frames, or vaults made of precast concrete elements are used. Depending on subsoil and groundwater conditions, impermeable base slabs, underwater concrete, pile foundations, or ground improvement may be required. Key components include: abutments and wing walls, roadway slab/deck, foundations/floor slab, edge beams, caps, drainage channels, joint and waterproofing systems as well as noise control and lighting elements. The high reinforcement ratio and often limited structural depth influence both construction methods and subsequent demolition and repair strategies.
Planning and construction methods
The choice of construction method depends on traffic situation, subsoil, groundwater, available space, and schedule. Common methods include open-cut with pit shoring, top-down method while maintaining traffic, and jacking and sliding for short closure windows, for example under rail lines. In urban environments, low vibration, dust suppression, and noise reduction are crucial. This favors selective concrete removal with hydraulic attachments and hand-held systems. compact hydraulic power units from Darda GmbH supply tools with high performance under controlled operation.
Open-cut method
After constructing the excavation pit using sheet pile walls, bored piles, or shotcrete, the frame is built as cast-in-place or with precast elements. Waterproofing, drainage, and backfilling follow. In confined conditions, sectional concrete removal with concrete pulverizers reduces interventions in shoring elements.
Top-down method
The deck is constructed first and serves as a temporary traffic surface. Excavation then proceeds beneath the deck. This restricts free space: equipment with a slim build and precise point force application—e.g., rock and concrete splitters—is advantageous for local openings and intentional fracture lines.
Jacking and sliding
Precast frames or closed boxes are jacked or slid beneath traffic routes. During the insertion window, precise concrete and earthworks are required. For adjustments at interference edges, transitions, and pile heads, concrete pulverizers are useful, while splitter cylinders release massive blocks with low induced stress.
Repair and strengthening in existing structures
Underpasses are exposed to freeze–thaw and de-icing salt loads, chloride contamination, and fatigue. Typical measures include concrete repair on edges and caps, crack repair, joint renewal, waterproofing and drainage upgrades, and cross-section strengthening. To minimize traffic impacts, components are processed selectively and with low vibration:
- Concrete pulverizers for removing deteriorated zones (caps, edge beams, soffits) with controlled exposure of reinforcement.
- Rock and concrete splitters for crack-controlled opening of massive areas (abutments, footing enlargements) to define fracture lines and minimize vibrations.
- Combination shears, Multi Cutters, and steel shears for cutting exposed reinforcing steel, embedded parts, and beams.
Partial demolition, deconstruction, and replacement
When usage requirements increase or damage is advanced, selective deconstruction of key components or full deconstruction with replacement becomes necessary. Under rail and road facilities, closure windows are tight; the method must be repeatable, fast, and controlled:
- Cutting and decoupling components in sections.
- Preparing intentional fracture joints via drilling and controlled splitting with rock splitter cylinders.
- Incremental crushing and reduction of concrete volume with concrete pulverizers down to manageable piece sizes.
- Cutting reinforcing steel and embedded parts with steel shears or combination shears.
- Material logistics in confined conditions with clear lifting and transport routes.
Special boundary conditions
In existing structures, utilities, cable trays, drainage, and temporary shoring must be protected. Low-vibration methods—splitting instead of percussion—reduce risks to sensitive systems and lessen disturbance for residents.
Application areas and practical relevance
Work on underpasses touches several application areas of Darda GmbH:
- Concrete demolition and special deconstruction: selective opening and removal of heavily reinforced components without damaging adjacent areas.
- Strip-out and cutting: targeted openings for utility penetrations, cross-section adjustments, and embedded parts in existing frames.
- Rock breakout and tunnel construction: in underpasses through rocky terrain or at interfaces, controlled splitting serves as a low-vibration alternative.
- Special deployment: short-notice damage remediation after impact events or acute water ingress within tight closure windows.
Equipment and method selection in detail
The combination of hydraulic power pack, concrete pulverizer, splitter cylinder, and cutting tools is selected project-specifically. Decisive factors are element thickness, reinforcement ratio, accessibility, permissible vibrations, and environmental requirements.
Concrete pulverizers
They are suitable for slab-like and beam-like components. Advantages include controlled edge quality, metered fracture formation, and simultaneous exposure of reinforcement. In underpasses with low structural depth, handling compact pulverizers beneath auxiliary shoring is a plus.
Rock and concrete splitters
Defined drilling patterns create crack planes precisely where they are needed structurally and logistically. The method is low-vibration and quiet—important for work under traffic or during closure windows at rail underpasses.
Hydraulic power packs and complementary tools
Hydraulic power packs provide the required energy for the tools. Combination shears, multi cutters, and steel shears cut reinforcement, beams, railings, and attachments. Selection depends on steel grade, cross-section, and accessibility.
Drainage, waterproofing, and durability
Underpasses require functional drainage to safely discharge splash water and groundwater. Waterproofing and waterstops protect the concrete against chlorides. During rehabilitation, transitions between existing and new construction must be executed with particular care; removal down to sound, low-chloride concrete is achieved precisely with concrete pulverizers without unnecessarily removing substance.
Occupational safety, environmental and neighborhood protection
Construction sites at underpasses are often close to traffic and buildings. This results in requirements for dust suppression, noise reduction measures, utilities management, and vibration control. Controlled splitting and stepwise crushing of concrete minimize emissions. Safety measures include adequate shoring, clear exclusion zones, safe lifting, and utility shut-offs. Legal requirements and regulatory conditions must always be generally observed; project-specific requirements are coordinated on site with the competent authorities.
Quality assurance and documentation
For planning, construction, and deconstruction, accompanying controls are essential: inspection plans, component approvals, measurements of vibrations and noise, evidence of material separation and disposal, and documentation of rebar exposure and concrete repair areas. Visual and dimensional checks on cut and fracture edges provide the basis for waterproofing, joints, and subsequent fit-out trades.
Typical challenges and solutions
- Confined access: sectional work, small tool geometries, modular hydraulic power packs.
- High reinforcement ratio: combination of concrete pulverizer and shears for efficient separation.
- Groundwater: waterproofing concepts, temporary impermeable slabs; selective removal with minimal vibration.
- Short closure windows: preplanned splitting and cutting patterns, logistics chains for rapid haulage.
Practical procedure for removing an abutment
First, the reinforcement layout is surveyed and the work area shored. Drilling then follows along the planned separation joints. Splitter cylinders create defined cracks, components are broken down into transportable segments with concrete pulverizers, and reinforcement is cut with steel shears. This reduces vibrations, protects adjacent components, and accelerates subsequent activities.