The vent borehole is an inconspicuous yet highly effective detail in the practice of concrete demolition, special demolition, rock excavation and natural stone extraction. When properly planned and executed, it supports controlled crack guidance, reduces pressure peaks in closed or semi-closed cavities, and improves occupational safety. In combination with tools from Darda GmbH such as hydraulic rock and concrete splitters, concrete demolition shears, and other hydraulic equipment, a deliberately placed vent borehole helps separate components with lower emissions, greater precision, and fewer collateral damages.
Definition: What is meant by vent borehole
A vent borehole is a targeted, usually small-diameter borehole that allows air, gases, or liquids to escape from a structural component or rock mass. In demolition and extraction technology, it often serves as a relief borehole or vent borehole to absorb and dissipate pressure during mechanical separation processes, influence crack propagation, and avoid uncontrolled spalling. In interplay with main boreholes for split cylinders or with the cutting edges of concrete demolition shears, it contributes to predictable load redistribution and improved process stability.
Function and purpose of the vent borehole in demolition
The central function of the vent borehole is pressure relief. During splitting, cutting, or shear-based deconstruction, entrapped media (air, water, residual gases) can be locally compressed. This creates undesired energy that may discharge as sudden spalling or ejected material. A correctly positioned vent borehole creates a defined discharge path, reduces stress concentrations, and supports directed crack formation along the intended split or cut line. This makes the separation process more controllable, produces cleaner edges, and better protects adjacent components or rock sections.
Vent borehole with stone and concrete splitters
When used with Darda GmbH stone and concrete splitters, a main borehole for the split cylinder is drilled first. Additionally, a vent borehole can be provided where trapped air or water hinders the splitting process or uncontrolled spalling is imminent. In massive concrete cross-sections, in dense natural stone, or with wet drill slurry, the vent borehole acts as a pressure vent along the planned split line. It helps load the splitting wedges more evenly and guides the crack front in a controlled manner toward the free edge or a helper joint.
Positioning along the split line
The vent borehole is preferably placed to support energy dissipation toward a free surface or into a defined cavity. With series boreholes for multiple split cylinders, it may be located between two main boreholes to stabilize crack coupling. In reinforced concrete, the position must also be coordinated with the reinforcement layout to avoid undesired crack deflection at steel bars.
Process advantages
- More uniform splitting action of the cylinder
- Reduced spalling and less edge damage
- Better control of crack propagation in dense or damp materials
- Less rework on edges and contact surfaces
The role of the vent borehole when using concrete demolition shears
Concrete demolition shears separate concrete and may engage reinforcement. When they encounter voids, chambers, or shells, local pressure build-ups can occur. A prior vent borehole provides a safe equalization path and reduces the risk of sudden ejection of material. It is also helpful when concrete demolition shears are to open components step by step, for example during strip-out: small vent boreholes mark the separation line, release water and air, and facilitate subsequent cuts or shear bites.
Practical added value
In addition to pressure relief, the vent borehole enables targeted flushing of drill fines and residual moisture, which improves visibility to the component edge and enhances edge quality in the next work step.
Use in rock excavation and tunnel construction
In compact rock, pore spaces and joints are often unevenly distributed. When inserting split cylinders or cutting with heavy hydraulic tools, the vent borehole prevents local pressure congestion, especially when water is present in drill holes. It makes an important contribution to controlled crack guidance toward the break-out edge or an access shaft and reduces the risk of unwanted rock throws and shell delamination. In tunnel headings, the additional vent borehole promotes regulated relief toward a safe cavity, improving work in confined spaces.
Planning and execution: From idea to borehole
The quality of a vent borehole is decided in planning. The goal is a borehole small enough not to weaken the component uneconomically, but large and favorably positioned enough to reliably discharge the intended media and to steer the crack line.
Step-by-step approach
- Component analysis: Clarify material, moisture, reinforcement layout, voids, load transfer, and free edges.
- Align separation strategy: Define the sequence of splitting, shearing, or cutting; integrate the vent borehole into the workflow.
- Set sizing: Choose diameter and depth to provide sufficient relief without unnecessarily reducing the main load-bearing action.
- Determine position/angle: Guide toward the free edge or into a safe cavity; avoid reinforcement and utilities.
- Select drilling technique: Clean core drilling or hammer drilling, depending on the material; plan flushing or dust extraction for low-emission execution.
- Control: Flush the bore channel, check for continuity; trigger a test discharge of media.
- Follow-through in execution: During splitting or shear-based deconstruction, observe discharge and crack path; add boreholes if needed.
Diameter, depth, and angle
The diameter is determined by the expected flow rate of the media to be relieved and the component thickness. Depth and angle should create the shortest safe path for relief. A slight inclination toward the free edge facilitates discharge. Where the crack line needs active steering, the vent borehole can be deliberately terminated at points of higher stress density to initiate controlled relief there.
Work safety and cautious legal notes
The vent borehole is one element of the safety concept. It does not replace a hazard analysis. Particular care is required with unknown void distribution, suspected residual gases, or in tank areas. Appropriate measurement and ventilation measures, approved equipment, and qualified personnel are fundamental. The statements in this text are general in nature and do not replace project-specific planning or regulatory requirements.
Practical protective measures
- Prior locating of reinforcement, utilities, and voids
- Dust extraction/flushing to reduce dust and aerosols
- Shields and defined safety zones at discharge openings
- Personal protective equipment, especially when pressure relief is directed toward the operator
Interaction with hydraulic power packs and other tools
Dedicated hydraulic power units for demolition supply stone and concrete splitters, concrete demolition shears, combination shears, steel shears, multi cutters, and tank cutters with the required energy. The vent borehole complements these tools on the process side: it reduces friction and pressing forces on the component, shortens the duration of critical work steps, and facilitates smooth work in tight sequence. Especially in demolition sequences where splitting and shear-based deconstruction alternate, a well-planned vent borehole stabilizes the transitions between methods.
Vent borehole in the context of strip-out and cutting
During strip-out, different layers meet: screed, lean concrete underlayment, service conduits, hollow-core slabs. Vent boreholes allow controlled pressure relief when sawing or cracking these layers and reduce the risk of hidden voids suddenly blowing out. They also serve as markers for guiding cuts and make it easier to flush fine particles before sensitive work steps.
Special cases: tanks, hollow sections, and special operations
For work on tanks, hollow sections, and closed systems—such as in special operations or with tank cutters—a vent borehole can be part of a comprehensive degassing and clearance measurement concept. It must be embedded in a safe procedure that includes appropriate measurements, ventilation, and releases. The goal is a defined, controlled discharge path for gases or liquids before mechanical separation forces are applied. This helps avoid pressure surges and uncontrolled splashing.
Influence on crack control, edge quality, and emissions
A well-placed vent borehole acts like a small regulator in the system: it limits local stresses, stabilizes the crack front, and contributes to smoother tool loads. This favors smoother edges, fewer secondary damages, and—combined with suitable dust extraction—lower dust and aerosol emissions. In natural stone extraction, it facilitates the planned release of raw blocks along existing textures without unnecessarily damaging the raw material.
Common mistakes and how to avoid them
- Borehole too small or unfavorably located: media back up, crack runs uncontrollably.
- Lack of a decoupling path to the free edge: relief does not reach where it is needed.
- Oversizing: unnecessary cross-section weakening and extra effort.
- No flushing: drill slurry blocks discharge, effect is lost.
- Reinforcement not considered: crack is deflected, leading to breakout in the wrong place.
Quality assurance and documentation
For reproducible results, simple but consistent documentation pays off: location, depth, diameter, and angle of the vent boreholes, the observed discharge direction, and the resulting crack path. This information improves planning of subsequent work steps, especially for serial tasks in concrete demolition and special deconstruction or for longer splitting sequences in tunnel and rock work.
Practical relevance: Integration with Darda GmbH workflows
In combined methods—splitting with stone and concrete splitters, reworking with concrete demolition shears, localized separation with multi cutters or steel shears—the vent borehole is inserted as a small, defining step between the main cycles. The hydraulic splitting process benefits from pressure relief, the shears grip more smoothly, and subsequent cuts require fewer corrections. The result is a coherent workflow that brings together material properties, emissions control, and operational safety into a balanced outcome.