The tunnel face—also called the advance face—denotes the active extraction front in tunnel or adit construction. This is where geology meets engineering: rock, loose ground, or existing concrete linings are removed in a controlled manner, secured, and hauled away. At this focal point, excavation methods, support measures, and tool technology interlock. Depending on the task, rock wedge splitter and concrete splitter, concrete demolition shear, hydraulic power pack, rock splitting cylinders, combination and steel shears, or multi cutters are used—especially for rock excavation and tunnel construction, concrete demolition and special demolition, as well as for special operations with sensitive boundary conditions.
Definition: What is meant by the tunnel face
The tunnel face is the free, immediately worked surface at the end of an underground void where the next round is excavated. It bounds the tunnel or adit in the direction of advance and is subject to high structural and geotechnical demand. Depending on the rock mass, groundwater, and excavation method, the tunnel face governs stability, work sequence, and support. The configuration of the tunnel face includes top heading, bench, and invert; for partial-face excavation also crown and steps; in existing structures, additionally the concrete and steel components of the lining, which are often selectively dismantled using concrete demolition shear or shears.
Structure and geometry of the tunnel face
The geometry of the tunnel face is determined by tunnel cross-section, excavation method, and rock mass behavior. Convex faces favor load transfer, while planar faces facilitate drilling. With partial-face excavation, top heading and bench are time-staggered, resulting in different support effects. Pipe umbrellas, spiles, or anchors engage in the face and provide pre-support. In existing structures, a distinction is made between cast-in-place concrete linings and segments; their location influences removal: localized release using splitting techniques yields controlled fracture patterns, while concrete demolition shear reprofile edges and expose reinforcement.
Geotechnical fundamentals and stability of the tunnel face
The stability of the tunnel face depends on strength, stratification, jointing systems, in-situ stress state, and water inflow. Decisive is the stand-up time until support installation. Classification systems (e.g., commonly RMR or Q) support the choice of measures but do not replace on-site observation. The goal is controlled load redistribution with minimal overbreak or underbreak.
Influence of rock mass and groundwater
Weak layers, fault zones, and anisotropic rocks promote detachment. High overburden increases the stress gradient, which can lead to squeezing or blowouts. Groundwater reduces effective stress, can cause washouts, and requires sealing or pre-injection. In loose ground, face support by pre-support and timely shotcrete application is crucial.
Support measures at the tunnel face
Typical measures include shotcrete (optionally fiber-reinforced), lattice girder beam, anchor, spiles, pipe umbrella, injection method, and temporary drift supports. Edges at the lining are neatly finished so as not to disturb load paths. For concrete components, low-vibration use of concrete demolition shear and steel shear has proven effective; in rock, rock wedge splitter and concrete splitter deliver controlled breaks with minimal edge damage.
Excavation methods at the tunnel face
The choice of method depends on geology, cross-section, environmental requirements, and accessibility. Common are conventional drill-and-blast (blasting works), mechanical excavation (roadheaders, excavators), or full-face excavation with a tunnel boring machine. In addition, splitting techniques and hydraulic shears are used—particularly where boundary conditions are sensitive.
Conventional drill-and-blast
Boreholes are drilled according to a pattern, charged, and blasted. Ventilation, support, and mucking follow. In areas with vibration limits or near existing structures, blast energy can be reduced and supplemented by splitting techniques. Scaling and edge finishing are often carried out hydraulically to improve profile accuracy and surface quality.
Mechanical excavation and cutting
Roadheaders and attachment tools remove rock continuously. In fit-out or refurbishment, concrete parts, protrusions, or embedded items must be removed precisely. concrete demolition shear and multi cutters enable targeted removal of concrete edges without unnecessary shock input. Steel shear are used on sheet pile wall elements, beams, or formwork components encountered during advance.
Low-vibration excavation with splitting techniques
hydraulic rock and concrete splitters as well as hydraulic wedge splitter transmit hydraulically generated forces via wedges into predrilled holes, utilizing the wedge principle. Crack propagation proceeds in a controlled manner along the desired lines. Advantages include low vibration levels, minimal secondary damage, and good dimensional accuracy—a plus in urban tunnels, near heritage structures, or in geologically sensitive zones. A hydraulic power pack reliably supplies the cylinders even in confined conditions.
Applications: tunnel face in rock and tunnel construction
Whether a new line in mountainous terrain, an urban utility tunnel, or the rehabilitation of an existing adit: the tunnel face demands material- and method-appropriate work. Tools and support are coordinated to balance stability, profile accuracy, and construction time.
Urban/near-city tunneling projects
Strict requirements on noise and vibration favor mechanical methods and splitting techniques (Rock Splitters). rock wedge splitter and concrete splitter reduce harmful effects on adjacent buildings. concrete demolition shear take over precise reprofiling of concrete or shotcrete areas, such as at niches, inserts, and cross passages.
Underpinning, cross passages, and enlargements
When opening cross passages or enlarging cross-sections, controlled cut edges are required. Splitting cylinders create predetermined fracture lines, concrete demolition shear remove residual fins and expose reinforcement. Steel shear cut profiles, rails, or temporary support frames.
Rehabilitation and deconstruction in existing structures
When renewing internal linings, joint elements, or support structures at the face, the combination of splitting and shear techniques enables low-vibration deconstruction. This is particularly relevant in special demolition and building gutting, when operational influences or adjacent infrastructure must be considered.
Planning and occupational safety at the tunnel face
A systematic plan defines excavation steps, support cycles, instrumentation, and logistics. Safety concepts consider geohazards, compressive and shear stresses, water inflows, and the handling of hydraulic systems. All information must be verified for the specific project and does not replace a detailed hazard assessment.
Process organization and logistics
Short cycle times require reliable power supply and material flows. Hydraulic power pack are positioned so that hose runs are short and protected. Tools for removal, downsizing, and profile finishing are kept ready directly at the tunnel face to avoid waiting times.
Occupational safety and health protection
Personal protective equipment, safe setup of units, hose management, and exclusion zones are mandatory. Accumulator and hydraulic components are depressurized before changing tools. Dust suppression and noise reduction measures, sufficient ventilation, and clear communication pathways enhance the safety of all involved.
Tool selection at the tunnel face: criteria and trade-offs
Selection is based on material, boundary conditions, and target quality. Decisive factors include strength, reinforcement ratio, water ingress, space constraints, and permissible emissions (vibration, noise emission, dust).
Concrete at the tunnel face
For cast-in-place concrete, shotcrete, or segments, accurate edges and minimal spalling are important. concrete demolition shear enable controlled removal even in confined cross-sections. Steel shear cut reinforcement and profiles, multi cutters handle versatile separation tasks. Splitting cylinders create predefined fracture edges that are then neatly finished.
Rock at the tunnel face
In competent rocks, splitting techniques offer a low-vibration alternative or complement to impact tools. rock wedge splitter and concrete splitter and hydraulic wedge splitter improve profile accuracy, minimize overbreak, and facilitate support. In jointed rock, drilling patterns and wedge forces are adapted to joint orientations.
Quality control and documentation at the tunnel face
Documented are advance rate, profile accuracy, support condition, and measurements (settlements, convergences, water levels). Overbreak and underbreak are assessed and, if necessary, reworked—often with concrete demolition shear or shears to ensure lining quality. Tool and hydraulic parameters are recorded to guarantee reproducibility and traceability.
Environmental aspects and emissions at the tunnel face
Vibration, noise, and dust are key influencing factors. Hydraulic splitting and shear techniques generally operate more quietly and cause fewer secondary damages than percussive methods. Proper water management, dust binding, and the right tool choice support environmentally responsible excavation.
Practical sequence: typical work steps at the tunnel face
A structured sequence increases safety and efficiency.
- Expose and assess geology; secure water inflows.
- Install pre-support and temporary support (e.g., spiles, shotcrete).
- Drill according to pattern; adjust hole diameter and depth for splitting techniques.
- Excavation by blasting works, mechanical cutting, or hydraulic splitting.
- Reprofiling and downsizing: concrete demolition shear, steel shear, or multi cutters for edges, reinforcement, and embedded items.
- Muck removal, cleaning, completion of support.
- Documentation, measurement, and preparation of the next cycle.