Anchoring pressure describes the local pressure that an anchor, an expansion element, a gripper, or a brace introduces into a substrate. In the practice of concrete demolition, natural stone extraction, and tunnel construction, this parameter is crucial for safely and controllably introducing forces from hydraulic systems into concrete, masonry, or rock. Especially with rock and concrete splitters and with concrete demolition shears such as the Darda Combi-Shears HCS8 from Darda GmbH, anchoring pressure significantly influences efficiency, component protection, and occupational safety.
Definition: What is meant by anchoring pressure
Anchoring pressure is the area-related compressive stress (contact pressure) introduced into the substrate by an anchoring or bracing component. It arises, for example, from expansion wedges in a borehole, from the jaws of a shear, or from braces that take up reaction forces. Anchoring pressure is the decisive parameter for assessing the substrate’s load-bearing capacity against crushing, spalling, or cracking and for shaping the controlled introduction of forces from hydraulic drives.
Relevance in concrete demolition and specialized deconstruction
In concrete demolition and specialized deconstruction, high forces must often be applied to sensitive structures. Whether splitting reinforced concrete through boreholes or crushing with concrete demolition shears: anchoring pressure determines how safely loads are transferred without causing impermissible damage to the substrate. Optimally adjusted anchoring pressure increases process reliability, limits consequential damage (e.g., edge spalling), and improves the controllability of splitting or crushing operations, for example during strip-out and when cutting components.
Physical principles and influencing factors
Anchoring pressure results from the acting force and the effective contact area. It is governed by material properties and boundary conditions. Key influencing factors are:
- Strength and structure of the substrate (concrete compressive strength class, rock type, porosity)
- Contact area and shape of the anchorage (wedge angle, jaw geometry, bearing width)
- Hydraulic pressure and resulting working force of the device used
- Borehole diameter, depth, and quality in splitting operations
- Edge distances, existing cracks, reinforcement ratio, and moisture
- Coefficient of friction and surface roughness between the contact point and the substrate
Anchoring pressure for stone and concrete splitters
When splitting via boreholes, splitting cylinders generate expansion pressure that is introduced radially into the borehole wall through wedges and feathers. This local anchoring pressure initiates crack formation along preferred separation planes. An appropriate choice of borehole diameter, drilling pattern, edge distances, and splitting direction ensures that the splitting force translates into a predictable fracture path. Excessive anchoring pressure can lead to uncontrolled breakouts at edges; pressure that is too low prevents effective crack propagation. In natural stone extraction and rock excavation, a well-matched combination of machine force and drilling pattern enables reproducible splitting quality with minimized collateral damage.
Anchoring pressure with concrete demolition shears
Concrete demolition shears transfer gripping and crushing forces into the concrete via their jaws. Anchoring pressure is concentrated on line or point contacts and must therefore be managed carefully. Adapted jaw geometry, clean contact surfaces, and sufficient edge distances help avoid local over-pressurization and spalling. In strip-out and selective deconstruction, controlled placement of the shear allows steering of load-path formation so that separation cuts and fracture edges run in the desired direction. Where required, interlayers (e.g., hardwood pads) can enlarge the contact area and reduce anchoring pressure.
Design and assessment fundamentals
For a basic assessment: anchoring pressure p = force F divided by the effective contact area A. In practice, A for wedges and jaws is not the entire component area but the actually load-bearing contact zone. For borehole splitting, the wedge angle is decisive, as it influences the expansion force and thus the hoop pressure in the borehole. For concrete demolition shears, local pressure depends on jaw shape and the concrete structure.
Conceptual steps for design
- Determine the maximum working force from the hydraulic system (e.g., from pressure gauge readings of the hydraulic power pack and the areas of the hydraulic cylinders).
- Estimate the effective contact area (borehole circumference × load-bearing length; jaw seating × effective width).
- Compare the resulting anchoring pressure with permissible contact pressures of the substrate (material-dependent; adopt conservative values).
- Adjust the drilling pattern, contact points, interlayers, or hydraulic pressure until a safe margin is achieved.
Note: Numerical values and verifications depend on standards and project-specific boundary conditions. A project-specific assessment should always be performed with appropriate safety factors.
Measurement, control, and documentation
Direct measurements of anchoring pressure are rare; indirect control is common:
- Monitoring hydraulic pressure at the hydraulic power units as an indicator of the acting force
- Visual inspection for microcracks and edge spalling during load build-up
- Trial cuts or trial splits to calibrate the settings
- Documentation of drilling patterns, contact points, and pressure stages for reproducibility
Material dependence: concrete, masonry, natural stone, rock
Concrete of higher strength class tolerates higher contact pressures than weak masonry; heterogeneous natural stones behave anisotropically. In tunnel construction, bedding and joint systems influence the optimal load path. Therefore, drilling pattern and shear placement must be adjusted to the material structure and moisture. For reinforcement in reinforced concrete, select shear forces and splitting direction so that reinforcement is cut in a controlled manner without causing unwanted crack propagation.
Edge distances, crack risk, and stabilization
Small edge distances increase the risk of spalling due to high local pressures. In practice, with stone and concrete splitters, boreholes are positioned so that the crack front propagates in a defined manner and edge areas are preserved. With concrete demolition shears, larger bearing areas and suitable gripping angles reduce anchoring pressure at edges. In special operations, temporary bracing or load relief may be required to safely transfer reaction forces.
Practical guide: setup and application
- Assess the substrate: strength, structure, edges, reinforcement, moisture.
- Select the method: splitting via borehole or crushing with shears—define suitable contact points in each case.
- Optimize contact areas: ensure borehole quality; position jaws cleanly; use interlayers if necessary.
- Increase hydraulic pressure step by step, observe the response, reposition if necessary.
- Choose edge distances and splitting direction so that components fracture in a controlled manner and load-bearing parts are not overloaded.
- Document results; carry over settings for similar components.
Typical failure patterns and countermeasures
- Edge spalling: enlarge the contact area, adjust the approach angle, build up pressure more slowly.
- Uncontrolled crack formation: adapt the drilling pattern, increase edge distances, align splitting direction with the material structure.
- Slip instead of force transfer: clean surfaces, improve friction, check jaw/wedge geometry.
- Insufficient effect: optimize hydraulic pressure, wedge stroke, or gripping point; consider material heterogeneity.
Safety and organizational aspects
Safe handling of anchoring pressure requires forward-looking planning. This includes clear load paths, sufficiently dimensioned reaction areas, and incremental load increases. Personal protective equipment, exclusion zones, and continuous team communication are essential. Legal and normative requirements are context-dependent and should be checked on a project-specific basis; occupational safety and structural stability requirements must be observed in principle.
Application in Darda GmbH’s fields of use
In natural stone extraction and rock excavation, the anchoring pressure of splitting cylinders is used to create fracture surfaces along predefined lines. In concrete demolition and specialized deconstruction, controlled shear forces support the precise release of components, for example during strip-out and cutting. In tunnel construction, controlled load transfer helps protect existing structures and increases process stability. In special operations, for example with tight boundary conditions, mastering anchoring pressure and selecting suitable contact points are key success factors.