Tunnel excavation encompasses all activities for creating underground voids—from ground investigation through excavation to support and final lining. In practice, geotechnical engineering, construction machinery technology, and precise manual work come together. Especially in sensitive areas, with complex cross-sections or when adjusting the excavation contour, handheld hydraulic tools come into play. These include concrete pulverizers as well as rock and concrete splitters from Darda GmbH, which are used for low-vibration and controlled removal of concrete and natural stone in tunnel construction, for example for cross passages, openings for utilities, profile corrections, or special demolition works.
Definition: What is meant by tunnel excavation
Tunnel excavation refers to the step-by-step excavation of an underground structure through loose ground or rock. The process comprises loosening the ground (mechanically, by blasting, or hydraulically), removing the muck, immediate support of the tunnel face and excavation surfaces (for example with shotcrete, anchors, and arches), and the subsequent lining (inner lining, waterproofing, installations). Common methods include drill-and-blast, mechanical excavation with roadheaders, and shield tunneling with tunnel boring machines (TBM). Selection and sequencing depend on geology, groundwater, overburden, cross-section, and construction logistics constraints. The goal is safe, economical, and dimensionally accurate advance with minimal vibrations, emissions, and risks.
Methods and technologies in tunnel excavation
The choice of excavation method is guided by ground/rock response, required excavation geometry, and environmental constraints. In practice, methods are combined to balance performance, safety, and quality.
Drill-and-blast (Conventional tunneling)
In hard rock, the ground is loosened by borehole blasting. After ventilation, mucking and immediate support with shotcrete, lattice girders, and rock anchors follow. Profile corrections, creation of niches, or preparation for cross passages can be executed low-vibration with rock and concrete splitters and concrete pulverizers—particularly in areas with strict vibration limits or where sensitive existing structures lie above the tunnel.
Mechanical excavation (Roadheaders)
Roadheaders loosen the ground with a cutting head in top heading, bench, and invert. The method is continuous, enables good profile control, and reduces vibrations. For rework at the tunnel face, removal of overbreak noses, or opening service penetrations, handheld hydraulic equipment is practical. Concrete pulverizers remove concrete in the initial support layer, while rock splitting cylinders locally induce stresses in the rock to achieve defined breaks.
Shield tunneling (TBM)
In soft ground and under groundwater, support media (earth pressure, slurry) are used and the ring lining is erected segment by segment. Adjustments at launch and reception areas, connection structures, or cross passages often take place in open cut and within existing structures. In these transition zones, controlled dismantling and cutting operations are required: rock and concrete splitters limit crack propagation, while concrete pulverizers produce openings in shotcrete or cast-in-place concrete linings with precision.
Process, sequencing, and key metrics in tunnel construction
An excavation cycle consists of recurring steps: investigation and monitoring program, setup of logistics and supplies, loosening of ground, mucking, support, surveying, and documentation. Key metrics such as advance rate (m/day), cycle time per round, downtime, failure analyses, and rework shares steer the site. Precise rework with concrete pulverizers and rock/concrete splitters shortens subsequent cycles because profile and tolerance requirements are met without large-scale overbreak. Hydraulic power units supply the tools with the required operating pressure while remaining compact—essential in confined cross-sections.
Support and lining: From the tunnel face to the inner lining
Immediately after excavation, shotcrete, anchors, and where applicable steel arches secure the excavation contour. The concrete inner lining, including waterproofing and installations, follows later. In both phases, adjustment and correction tasks arise:
- Removal of protrusions and noses along the excavation contour
- Creation of openings for cables, ventilation, and drainage
- Rework at formwork edges and joint areas
- Selective dismantling of defective or damaged sections
Concrete pulverizers work powerfully yet precisely on shotcrete and cast-in-place concrete surfaces. For natural stone and massive concrete sections, rock and concrete splitters provide a low-vibration approach: drill holes, insert split cylinders, apply load in a controlled manner—the fracture follows the plan and protects adjacent components. Steel shears and combination shears are used to cut reinforcement, structural steel, or temporary support members. Multi Cutters assist with cutting pipes and sheet-metal ducts.
Low-vibration removal and protection of sensitive environments
In urban settings, with small overburden or near sensitive facilities, strict limits for vibration, noise, and dust apply. Blasting bans and restricted operating windows are common. Rock and concrete splitters minimize vibrations because the energy is introduced into the borehole and the fracture is triggered in a controlled way. Concrete pulverizers reduce secondary damage because they work by mechanical gripping and crushing. As a result, installations, waterproofing, and adjacent structures remain protected. Low-dust working methods, targeted water misting, and matched hydraulic output from the power unit support environmental protection.
Geology, material, and tool selection
Rock mass behavior varies widely depending on grain fabric, layering, joint systems, and groundwater conditions. In hard, brittle rock, stress cracks can be initiated purposefully using split cylinders; in tough, ductile rocks, greater split widths and higher pressure are expected. For concrete, cover depth, reinforcement content, strength class, and any prestressing are crucial. For reinforced concrete, a combination of a concrete pulverizer (concrete removal) and steel shears (cutting reinforcement) is appropriate. Power units must deliver operating pressure stably while being lightweight and mobile so they can be relocated efficiently within the tunnel cross-section.
Typical applications of handheld hydraulics in tunnel excavation
- Profile corrections on top heading, bench, and invert
- Creation of cross passages, emergency bays, and equipment rooms
- Openings in shotcrete and inner linings for cable and drainage runs
- Selective dismantling at defects, voids, or flatness deviations
- Dismantling temporary supports, beams, and installations
- Rework at portal areas and connection structures
In these situations, concrete pulverizers are ideal for precise concrete removal, and rock and concrete splitters are ideal for controlled separations in rock and mass concrete. Additionally, combination shears, steel shears, and Multi Cutters are used for cutting steel, sheet metal, and reinforcement.
Planning, occupational safety, and operations
Equipment selection follows a coordinated concept based on geology, construction method, cross-section, and accessibility. Criteria include performance data (pressure, flow rate), tool weight, handling in confined cross-sections, emissions, energy supply, maintenance access, and transport routes. Safe operation is governed by applicable regulations on blasting and demolition, hydraulic systems, dust and noise mitigation, and handling of reinforcement and prestressing systems. Notes are general and do not replace case-by-case assessments. Careful instruction, regular function checks, and clear barricading of the work area are mandatory.
Quality assurance, dimensional accuracy, and documentation
Surveying, digital checks, and continuous documentation of excavation, support, and lining ensure dimensional accuracy. Tolerances for excavation cross-section, flatness, and joint geometry influence the subsequent inner lining and its durability. Targeted, small-area rework with concrete pulverizers limits overbreak and achieves the design contour. Rock and concrete splitters help create defined edges without weakening the load-bearing structure. This reduces rework quantities and keeps construction sequences on schedule.
Dismantling, modifications, and special operations in tunnels
Selective methods are required for special demolition and repurposing: concrete pulverizers for dismantling inner lining sections, rock splitting cylinders for opening natural-stone masonry, steel shears and combination shears for beams, lattice girders, and installations. Multi Cutters support trimming of technical installations. Tank cutters are considered in special cases where steel tanks or thick-walled steel components in plant systems around the tunnel site must be dismantled. The goal is a plannable, low-emission workflow with high control over fracture lines and component separation.
Sustainability and resource efficiency in excavation
Selective removal, minimal overbreak, and precise openings reduce spoil, transport, and energy demand. Hydraulically powered handheld tools work locally and on demand, lowering noise and dust emissions. Through the controlled use of concrete pulverizers and rock and concrete splitters, components can be separated so they can subsequently be sorted for recycling or require only minimal rework.
Application areas and practical relevance
The methods described cover several application areas: rock excavation and tunnel excavation in the advance itself, including rock demolition in tunnel construction, concrete demolition and special demolition at inner linings and structural connections, gutting and cutting for technical fit-outs, natural stone extraction in the vicinity of quartzites or limestones for portal structures, as well as special operations in plant and existing facilities. Products from Darda GmbH, such as concrete pulverizers and rock and concrete splitters, combine the requirements of these application areas with the necessary precision and low vibration in tunnel construction.