Tunnel face support is a central topic in tunnel construction and underground excavation. It links geotechnical design with practical execution and aims to keep the tunnel face stable, avoid fallouts, and enable controlled advance. In practice, it touches numerous work steps, from injections and shotcrete to reprofiling. Devices from Darda GmbH – such as hydraulic splitter or concrete pulverizer – are used in adjacent work phases, for example for controlled loosening of blockwork at the tunnel face, careful removal of shotcrete layers, or precise adjustment of the excavation profile without vibrations.
Definition: What is meant by tunnel face support
Tunnel face support comprises all temporary and advance measures that ensure the stability of the tunnel face – the excavation surface facing the tunnel cross-section. The goal is to support the rock mass or soil near the excavation front, limit deformations, control water inflow, and enable a safe construction sequence. The specific configuration depends on geology, groundwater conditions, the excavation method (e.g., blasting works, partial-face cutting, excavator excavation), as well as on the cross-section and sequence of construction phases. Typical elements are shotcrete, lattice girder beams, face bolts (spiles), pipe umbrellas, injections, and – in special cases – ground freezing.
Background: Geotechnical fundamentals and actions
The load-bearing behavior at the tunnel face is influenced by in-situ stresses, stand-up time of the material, bedding, jointing, cohesion and friction angle, as well as pore water pressure. Rock strengths, discontinuities (e.g., faults, joint sets), and crack patterns determine whether the tunnel face fails in one or multiple layers. In loose ground, settlements and flowing behavior dominate; in hard rock, wedge- and block-wise fallouts are more common. These differences shape the choice of support measures: In highly jointed rock, advance spiles improve composite action; in softer soils, pipe umbrellas and injections stabilize the face zone; under high water inflow, sealing injections and, if necessary, freezing reduce risk. For locally decoupling blockwork or low-stress profile trimming, Darda GmbH’s hydraulic rock and concrete splitters can be used to avoid vibrations and not impair the stability of the remaining tunnel face.
Overview of tunnel face support methods
The selection of methods is based on ground investigations, prediction models, and a monitoring-led construction sequence. Several methods are often combined to increase the safety of the advance.
Shotcrete, lattice girder beams, and rapid ring closure
Freshly excavated tunnel face surfaces are stabilized by prompt application of shotcrete. Lattice girder beams and reinforcement mesh distribute loads; an advance ring closure reduces deformations. During reprofiling or when exposing measuring points, the gentle removal of shotcrete layers can be carried out with concrete pulverizer from Darda GmbH to avoid damaging components or rock surfaces.
Face bolts (spiles) and spile umbrellas
Face bolts anchor loosened zones in load-bearing rock. Spiles arranged in series form an umbrella that bridges the excavation front. Drilling, installation, grouting, and fixing must be tightly coordinated. When trimming protruding reinforcement or removing local concrete protrusions at connection areas, concrete pulverizer delivers precise work.
Pipe umbrella (forepoling)
A pipe umbrella consists of steel pipes installed ahead of the face that cover the tunnel face and reduce settlements. It is particularly suitable in soft formations with groundwater. For precise fitting of cut-in areas or removal of temporary packers or shims, hydraulic splitter can be used to remove material in a controlled manner.
Injections and sealing
Grouting with cement or resin systems increases the tightness and strength of the face zone. The materials are placed via drill channels. Local adjustments at drilling start points, opening small windows in shotcrete, or relocating anchor heads can be performed with low vibration using concrete pulverizer or small rock wedge splitter.
Ground freezing and special measures
Freezing creates temporary load-bearing capacity and tightness. It is used for critical combinations of water, loose material, and low overburden. Where component adjustments are required at entry and exit areas, clean cuts in concrete and steel are necessary; in the context of support works, hydraulic shear, Multi Cutters, or steel shear from Darda GmbH may be used in adjacent steps.
Interfaces to Darda GmbH equipment
Tunnel face support itself is a system of geotechnical planning and construction execution. At numerous interfaces, tools from Darda GmbH support safe, precise, and low-vibration implementation.
- Hydraulic splitter / rock wedge splitter: Local loosening of blockwork at the tunnel face, creating relief cracks, reprofiling excavations without blasting vibrations. Relevant application areas: rock excavation and tunnel construction, special demolition, natural stone extraction.
- Concrete pulverizer: Selective removal of shotcrete, exposing survey marks and injection ports, preparing contact faces for lattice girders, removing temporary concreting aids. Relevant application areas: concrete demolition and special demolition, strip-out and cutting, rock excavation and tunnel construction. (See Concrete Crushers.)
- Hydraulic power pack: Power supply for hydraulic attachments in the tunnel, matched to the required working pressure and flow rates in confined spaces.
- Hydraulic shear / Multi Cutters: Cutting reinforcement mesh, lattice girder beams, and small steel sections following support works; trimming rebar overhangs.
- Steel shear: Cutting rolled sections or temporary steel props during conversion phases, cross-section enlargements, or when dismantling provisional supports.
- Tank Cutter: In special situations in underground works – e.g., during dismantling of tanks, pipelines, or installations in existing drifts – clean opening of thick walls as part of special demolition scenarios.
Process in tunnel advance: From advance exploration to support
A structured process increases safety and quality. A cyclical advance with immediate follow-up support is typical.
Advance exploration and prediction
Geological models, probe drilling, seismic methods, and hydrogeological exploration provide the basis. Design assumptions for the tunnel face are derived from this.
Excavation step
Partial-face or full-face excavation, depending on cross-section. Tool selection depends on the rock mass and specifications. In sensitive areas, hydraulic splitter can minimize vibrations.
Primary support
Immediately after excavation, shotcrete, anchors, spiles, and, if needed, a pipe umbrella follow. Early ring closure is crucial.
Reprofiling and adjustments
Protrusions and local irregularities are removed. Concrete pulverizer enables controlled corrections on shotcrete and concrete members without weakening adjacent supports.
Control and monitoring
Survey bolts, convergence measurements, settlement gauges, and water levels serve assessment. The results feed into the adjustment of support parameters.
Design, quality assurance, and documentation
Design follows national and European regulations as well as project-specific requirements. The observational method and adaptive design are common: measures are planned, monitored during construction, and adjusted as needed. Complete documentation of drilling logs, injection volumes, anchor pull-out tests, shotcrete classes, and reprofiling is part of quality assurance.
Occupational safety, emissions, and construction environment
Underground work imposes high demands on safety, ventilation, and noise control. Low vibration levels – for example, hydraulic splitting of rock – can reduce vibrations, secondary cracking, and emissions. Dust suppression via spray mist, safe handling of high-pressure lines of the hydraulic power pack, and clear haul roads are essential points. Notes on legal requirements are project- and country-specific and should always be interpreted in a general and precautionary manner.
Typical challenges and practical solutions
- Blocky fallouts: Advance spiles increase composite action; local stress relief with hydraulic splitter prevents uncontrolled detachment of individual wedges.
- Water inflow at the tunnel face: Sealing injections and temporary collection lines. Openings for injection ports can be produced cleanly with concrete pulverizer.
- Shotcrete protrusions into the profile: Precise removal without damaging the substrate; the combination of concrete pulverizer and controlled splitting enables fine adjustments.
- Steel components in the way: Lattice girder beams or provisional steel beams are cut with hydraulic shear, Multi Cutters, or steel shear to avoid hindering subsequent steps.
Application areas and interfaces to advance and deconstruction works
Tunnel face support appears not only in classical tunnel construction but also in drivages of adits, caverns, cross-passages, shafts, and niches. In natural stone extraction, advance supports and targeted splitting help release rock heads in a controlled manner. In concrete demolition and special demolition – for example, when opening existing cross-sections or installing connections – clean cuts and low-vibration methods are important to avoid impairing the structural stability of adjacent components. For strip-out and cutting in existing drifts, concrete pulverizers and shears help remove installations without weakening the primary support. In special demolition scenarios, such as beneath sensitive structures or in densely built environments, low vibrations and precise work are crucial.
Logistics, power supply, and maintenance in underground construction
The spatial constraints in advance areas call for compact, reliable power sources and short setup times. Darda GmbH compact hydraulic power units deliver the required performance for hydraulic splitter, concrete pulverizer, and shears. Hose routing, couplings, pressure monitoring, and regular leak checks are central maintenance tasks. Careful equipment selection and preventive maintenance contribute to availability and support adherence to the construction schedule.