Borehole drilling is a central foundational topic in concrete demolition, special demolition as well as in rock excavation and tunnel construction. It defines how precisely, safely, and controllably subsequent work steps can be carried out – from hydraulic splitting to targeted removal with concrete demolition shears. Properly planned and executed boreholes guide cracks, reduce cross-sections, enable anchor points, starter openings, or wire pass-throughs, and create the basis for reliable results with the tools from Darda GmbH.
Definition: What is meant by borehole drilling
Borehole drilling refers to creating cylindrical cavities in concrete, reinforced concrete, masonry, or rock with a specified diameter, path, and depth. It serves as an upstream process to support subsequent methods such as hydraulic splitting, controlled removal with concrete demolition shears, anchor installations, wire and saw cuts, or measures for gutting and cutting. Key parameters are borehole diameter, borehole depth, drilling angle, grid pattern, and edge distances. The quality of the boreholes has a decisive influence on the splitting effect, crack guidance, force transmission from cylinders, and the efficiency and safety of the deconstruction.
Methods and equipment for borehole drilling
In practice, rotary, percussive, and diamond-supported methods are used. For concrete and rock, rotary hammer drilling (e.g., with SDS or hex shanks), pure rotary drilling, and core drilling with diamond-tipped core bits are predominant. In rock extraction and tunnel construction, high-frequency or down-the-hole methods are also common. Depending on the task, handheld hammer drills, drill stands with vacuum or dowel fastening, as well as drill carriages are used. The power supply can be electric, pneumatic, or hydraulic. For hydraulic splitting – for example with rock split cylinders and rock and concrete splitters – clean, true-to-size boreholes are crucial so that wedges and counter-wedges can operate safely and form-fit.
Borehole diameter and depth
The diameter is determined by the tool used and the desired effect. For hydraulic split cylinders, borehole diameters of a few centimeters are typically used; the depth is based on cylinder stroke and the component thickness. In core drilling, diameters from a few millimeters up to large-format openings are realized, for example for service penetrations, wire saws, or relief openings. Sufficient edge distances are important to avoid uncontrolled spalling, as is a depth that matches the planned force transmission.
Drilling angle, patterns, and grids
Straight holes perpendicular to the surface are standard. Inclined holes are used to generate shear edges or to preguide cracks. Drilling patterns can be linear (splitting line), staggered (honeycomb grid), or along edges. For splitting, closer center-to-center spacing produces more uniform crack formation; larger spacing increases the individual breakage of the material but is harder to control. For massive components, multi-row grids may be required.
Interfaces to products and application areas
Borehole drilling links planning and execution across several disciplines:
- Rock and concrete splitters as well as rock split cylinders require true-to-size boreholes to introduce wedge forces in a controlled manner. Precision in diameter and a clean hole surface minimize slip and increase process reliability.
- Concrete demolition shears crush components without boreholes. In thick or tough cross-sections, however, relief boreholes support targeted biting, reduce transverse forces, and guide cracks.
- Combi shears, steel shears, and tank cutters benefit from starter openings in plates or from core drilling through multilayer structures. This allows cuts or separations to be initiated in a controlled manner.
- Hydraulic power packs supply splitters, concrete demolition shears, and other hydraulic tools. Their performance data must match the drilling strategy so that switching between drilling, splitting, and crushing can take place without idle times.
- Multi Cutters cut lines, reinforcement, and secondary components exposed after drilling, especially during gutting and cutting.
Typical application areas are concrete demolition and special demolition (targeted crack guidance, openings), gutting and cutting (starter holes, core drilling), rock excavation and tunnel construction (drilling rows for hydraulic splitting), natural stone extraction (block release via drilling and splitting technology), as well as special applications in sensitive zones where low vibration levels are required.
Workflow: planning, execution, control
- Survey of the component/rock: Strength, structure, reinforcement position, stresses, and moisture; for rock: bedding, joints, and strength anisotropy.
- Method selection: Rotary hammer drilling for productive hole patterns, core drilling for precise diameters, dry or wet methods depending on dust and water management.
- Define the drilling pattern: Diameter, depth, center spacing, edge distances, drilling angle, and sequence of production.
- Organize occupational safety: Dust extraction or wet drilling, noise reduction, securing of drill stands, safe support and slip resistance.
- Produce the boreholes: Centering, incremental feed, regular tool inspection, and adequate cooling or extraction.
- Cleaning and inspection: Blow-out and brush the boreholes, measure diameter and depth, visual inspection of edges.
- Documentation: Drilling plan, deviations, photos, release for the subsequent tool (e.g., splitter or concrete demolition shear).
Technical factors and quality assurance
The performance of the drilling technique is determined by aggregate size and hardness, reinforcement density, tool wear, contact pressure, rotation/impact rate, and machine stability. Stable drill stands, straight guides, and low runout are key factors for true-to-size results. Borehole cleaning – blow-out, brushing, possibly flushing – is not only important for injections but also for the form-fit force transmission of wedges in split cylinders.
Edge and center spacing
Sufficient edge distances reduce breakout and help maintain intended fracture lines. In slender components or near sensitive edges, smaller, more closely spaced holes with moderate splitting energy are often advantageous. In massive cross-sections, greater depths and, if necessary, multi-row drilling patterns are effective to define the splitting zone.
Borehole drilling in rock excavation and tunnel construction
In rock works, drilling rows are used to prepare for non-blasting removal. For natural stone extraction, boreholes are placed along geological discontinuities so that hydraulic split cylinders can gently release blocks. In tunnel headings or support areas, drilling with low vibration levels and subsequent splitting can control crack formation and protect surrounding structures.
Boreholes as predetermined breaking points in concrete demolition
Relief or predetermined breaking boreholes reduce local stiffness and guide cracks. This allows a concrete demolition shear to bite into components more easily and removal proceeds in a more controlled manner. For openings, core drilling serves as start points for wire saws or as penetrations, after which rock and concrete splitters can release the remaining areas. In gutting and cutting, boreholes support low-vibration separation – especially in occupied or sensitive buildings.
Hydraulic power supply and peripherals
Hydraulic power packs provide the necessary performance for split cylinders, concrete demolition shears, combi shears, steel shears, Multi Cutters, and tank cutters. A matched flow rate and correct pressure ensure consistent tool output. Hose routing, couplings, and protection against contamination are important, as drilling slurry and drilling dust can burden the peripherals.
Occupational safety, health, and environmental protection
Drilling generates noise, dust, vibrations, and – in wet methods – drilling slurry. Appropriate protective measures must be selected: extraction or wet drilling, hearing and respiratory protection, low vibration levels, slip-resistant supports, orderly hose and cable routing. For components with media lines or prestress, prior investigation is essential. Legal requirements may vary by project; compliance with relevant standards and permits is always project-specific.
Typical errors and how to avoid them
- Insufficient borehole depth or incorrect diameter – reduces splitting effect and tool fit accuracy.
- Misaligned holes – lead to offsets, oblique force transmission, and uncontrolled spalling.
- Poor borehole cleaning – reduces frictional engagement and can impair wedge systems.
- Edge distances too small or center spacing too large – promote breakout or irregular crack patterns.
- Missing reinforcement locating – increases tool wear and can affect structural behavior.
- Inadequate water management – causes contamination, slipping hazards, or environmental impacts.
Maintenance and tool care
Percussion and rotary tools require regular inspection of shanks, lubrication, and seals. Diamond core bits must be checked for segment wear, runout, and bond; for glazing, controlled starting with reduced feed helps. Drill stands are checked for fixation, vacuum tightness, or dowel anchorage. Well-maintained equipment increases dimensional accuracy and service life – and thereby process quality in splitting or crushing.
Documentation and verification
A documented drilling pattern with depths, diameters, grid, and deviations facilitates release for subsequent trades. Photos, measurement logs, and markings ensure traceability – an advantage, especially in special demolition and for special applications in sensitive environments.