Sliding formwork

Sliding formworks are mobile formwork systems for producing curved or linear cast-in-place concrete elements that can be released in sections after concreting and rolled to the next pour. They shape the construction of tunnels, shafts, circular tanks, and silos and enable reproducible geometries with high surface quality. Over the life cycle of such structures, in addition to planning and execution, repair and selective deconstruction play a central role. In these phases, as part of a controlled, low-vibration approach, Darda concrete crushers as well as hydraulic rock and concrete splitters from Darda GmbH are frequently used, especially in sensitive environments such as existing tunnels, industrial plants, or inner-city projects. Their repeatable setup supports schedule reliability, reduces interfaces, and maintains consistent joint patterns across cycles.

Definition: What is meant by sliding formwork?

A sliding formwork is a formwork unit consisting of form face, substructure, and running gear that is moved along an axis on rollers or rails. It is typically used for circular, polygonal, or curved cross-sections, for example for tunnel inner linings, circular tanks, shafts, or silos. In contrast to stationary systems, the form shape is retained, is struck once the required early strength has been reached, slightly retracted or lowered, and then moved to the next concreting section. In addition to circular formworks for tanks, formwork carriages are frequently used in tunnel construction that map the crown, bench, and invert and are hydraulically adjustable. The preserved mold geometry across cycles enables comparable surface finishes, repeatable tolerances, and coordinated joint layouts.

Design and mode of operation of sliding formwork

Sliding formworks combine a load-bearing substructure with a shaped form face. The running gear enables precise repositioning on a cycle. Hydraulic components support opening, closing, lowering, and the fine adjustment of the radius. The aim is to safely transfer fresh concrete pressure, maintain the geometry exactly, and achieve short cycle times with consistent quality. Survey control points, laser references, and adjustable stops are often integrated to verify radius, alignment, and camber during each cycle.

Components of a sliding formwork

• Form face made of steel, timber, or composite material for the required surface quality and curvature
• Substructure with ribs, girders, and deformation restraints to absorb formwork pressure
• Running gear on rollers or rails, often with track guidance for tight radii
• Hydraulics for adjustment, stripping, and pressing, including reference-point and fixing systems
• Bracing, anchorage points, and tie rods for transferring loads into the ground or the load-bearing structure

Adjustment ranges and radius adjustment

Modern systems allow adjustment of radius, taper, and camber. This makes it economical to construct conical shafts, transition zones, and variable tunnel cross-sections. Documented adjustment is essential: tolerances, joint locations, and interfaces must be defined in advance and monitored during cycling. Clearly marked witness positions, checklists for set-up values, and measured as-built radii help detect drift at an early stage.

Fields of application and typical elements

Sliding formworks are used wherever recurring geometries with high precision are required. Typical fields of application are:

• Tunnel construction: cast-in-place inner linings, service and utility adits, cross passages
• Water and wastewater engineering: circular tanks, basins, shafts, pressure-pipe shafts
• Industrial and energy facilities: silos, storage units, chimney shafts, as well as circular foundations
• Repair: supplementary concrete, fillets, strengthening rings, and collars

In these areas, during later adaptations, openings, or deconstruction steps, concrete crushers and rock and concrete splitters from Darda GmbH are often used to process components in a controlled and low-vibration manner. Constrained sites benefit from compact running gear and predictable cycle logistics, which reduce interface risks with other trades.

Planning, structural analysis, and execution

Planning covers geometry, structural analysis of the formwork, cycle lengths, and the concreting process. Fresh concrete pressure is determined by placement rate, concrete mix design, and temperature. Formwork ties, bearings, and support systems must be arranged so that deflections and deformations are minimized. Waterstops, sealing inserts, and embedded components must be integrated into the formwork plan. Applicable technical rules and project-specific requirements are authoritative.

• Design deliverables: calculation notes for formwork pressure and stiffness, stability checks, and load paths into the permanent works or temporary foundations
• Process planning: method statements for cycling, concreting sequences, emergency procedures, and contingency for temperature and mix changes
• Interface management: positioning of joints, waterstops, and penetrations with reinforcement and MEP coordination
• Survey concept: fixed benchmarks, control measurements per cycle, and acceptance criteria for alignment and radius
• Documentation: traceable adjustment logs, calibration of gauges, and verification of release agents and form liners

Concreting sections and cycle lengths

Cycle length is determined by early strength, site logistics, reinforcement density, and the structure’s geometry. Common are recurring cycles of reinforcing, placing, compacting, curing, stripping, lowering, and rolling forward. A consistent cycle chain increases quality and reduces downtime. Targeted synchronization of supply, transport routes, and compaction equipment further stabilizes cycle times and mitigates cold joints.

Surface quality, tolerances, and curing

For water-retaining structures, watertightness, burr-free edges, and a homogeneous surface are paramount. The choice of form face, the use of suitable release agents, and uniform compaction determine the result. Tolerances and joint patterns must be defined in advance; additional requirements apply for architectural concrete. Curing (moisture retention, temperature management) protects against early shrinkage cracks and ensures final strength.

• Define acceptance criteria for blowholes, color variation, and joint offsets before production
• Use consistent release agents and application rates, recorded per cycle
• Plan curing continuity across joints to avoid differential drying and edge curling
• Monitor early-age temperature and humidity to control heat of hydration and shrinkage

Assembly, stripping, and repositioning

Sliding formworks are preassembled on assembly areas, lifted in, aligned, and moved cyclically in the course of concreting. Clear responsibilities, free spaces for moving, and safe access routes on the construction site are decisive. Commissioning includes functional checks of hydraulics, locking devices, brakes, and emergency stops, as well as a documented trial cycle.

1. Preassembly and functional testing of the hydraulics and the locking devices
2. Lifting in, alignment, and control measurement of the geometry
3. Concreting with a coordinated placement and compaction strategy
4. Stripping, lowering, and releasing without damaging the edges
5. Rolling forward, fine adjustment, and preparation of the next cycle

Where appropriate, a small-scale mock-up validates surface quality, joint detailing, and curing measures before the first production cycle.

Repair and deconstruction of components made with sliding formwork

Components produced with sliding formwork frequently need adapting during their life cycle: openings for services, recesses, cross-section enlargements, or selective strengthening. In existing structures, low vibration, reduced dust and noise emissions, and precise material removal are advantageous. Here, concrete crushers as well as rock and concrete splitters from Darda GmbH have proven effective, as they introduce forces locally and in a controlled manner and thus protect adjacent structures. Hydraulic power packs ensure the power supply; steel shears, combination shears, and multi cutters assist in cutting reinforcement, embedded components, and secondary steel. For circular steel tanks or linings, tank cutters can be a useful addition, provided the work area has been cleared, measured, and secured. Prior to intervention, surveys, utility detection, vibration thresholds, and dust control measures should be defined and monitored.

Selective deconstruction in tunnels and shafts

For tunnel inner linings or shaft structures, the combination of rock and concrete splitters and concrete crushers enables incremental opening of the concrete skin. Load redistribution is planned in advance, the work area is secured, and the demolition is executed in cycles. Steel shears are used for reinforcement and brackets; at the rock interface, rock splitting cylinders provide support, especially in the context of rock breakout and tunnel construction. Temporary supports, sequence plans, and monitoring points help maintain stability and document the progress of removal.

Creating openings and recesses

For cable and pipe penetrations, boreholes are drilled, splitting cylinders are inserted, and the concrete is released in a controlled manner. Concrete crushers break remaining webs; combination shears or multi cutters cut reinforcement. This approach is advantageous in enclosed spaces and for strip-out and cutting when vibrations must be avoided. A cutting plan with defined edge distances, rebar handling, and reinstatement detailing minimizes rework and preserves watertightness.

Occupational safety, environmental protection, and permits

Formwork operations require safe workplaces, load paths, and regular visual and functional inspections. During deconstruction, dust and noise reduction, extraction, and wetting must be taken into account. Interventions in load-bearing structures must be assessed structurally in advance. Legal requirements and authority permits must be clarified on a project-specific basis; binding commitments cannot be given here.

• Risk assessments and method statements for each cycle and deconstruction step
• Defined exclusion zones, lifting plans, and certified attachment points
• Vibration, dust, and noise management with measurement logs and trigger levels
• Emergency procedures, communication routes, and access/egress concepts
• Training and competence records for hydraulic equipment and survey tasks

Quality assurance and documentation

Good practice includes control plans for geometry, surfaces, and joints, checks of early strength, and documented curing. During deconstruction, locating reinforcement and embedded parts, clearance measurement of utilities, and complete documentation of the work steps are advisable. This facilitates later inspections and serves traceability.

• Pre-pour checks: form face cleanliness, release agent application, reinforcement clearances
• In-process control: compaction records, temperature and maturity data, and cycle timestamps
• As-built verification: survey reports on radius, alignment, and joint offsets per cycle
• Deconstruction logs: sequence, tools used, measurements of removed sections, and reinstatement notes

Terminological classification and distinction

Sliding formworks differ from climbing systems through their movement on rollers or rails and from continuous slip formwork through their cyclic mode of operation. In tunnel construction, sliding formworks are often executed as formwork carriages with crown, bench, and invert; for circular tanks, segmented circular formworks are used. This classification helps select suitable processes, equipment, and safety measures – both in production and in repair, concrete demolition, and special deconstruction, special operations, or strip-out and cutting. Clear terminology also supports coordination with structural design, surveying, and site logistics.