The rock surface is the visible and workable skin of a rock mass. It determines how rock can be removed, split, stabilized, or prepared for subsequent construction stages. In application areas such as rock excavation and tunnel construction, natural stone extraction, and concrete demolition and special demolition, practice encounters very different surfaces: from fresh fracture faces and weathered joint faces to rock covered with shotcrete. For selecting and controlling the use of hydraulic rock and concrete splitters, rock wedge splitter, and concrete demolition shear by Darda GmbH, properties such as roughness, strength, joint spacing, and moisture provide the decisive framework.
Definition: What is meant by rock surface
The rock surface is the interface between intact rock and its surroundings. It consists of macroforms (e.g., bedding and joint planes, joints, veins, karst cavities) and microstructures (roughness, grain bonding, weathering crust). This surface can be fresh (fracture face), naturally formed (erosion or weathering surface), or technically modified (borehole collar, saw or shear start, shotcrete application). The rock surface governs crack propagation, splitting behavior, and force transmission in hydraulic methods, as well as the material-friendly transition between rock and overlying components.
Formation and change of the rock surface
Rock surfaces arise through tectonic separation (jointing, bedding, foliation), erosion and weathering (chemical, physical, biological), or through technical measures such as drilling, splitting, sawing, and shearing. Weathering can increase roughness, weaken mineral bonds, and open near-surface pore spaces. Moisture, freeze–thaw cycles, salt and CO2 ingress change surface strength and favor crack initiation. In a technical context, the rock surface is deliberately modified by boreholes, wedge-induced crack fronts, anchor drilling, or shotcrete overlays to control load paths or to initiate removal in a controlled way.
Geological properties and surface types
The rock type strongly shapes the rock surface. Granite often shows hard, rough fracture faces with pronounced grain interlock; limestone more frequently has smooth joint faces and karst features; sandstone shows porous, sometimes sanding surfaces; slate displays anisotropic cleavage planes. Important surface types:
- Fresh fracture face: high cohesion, distinct grain breakage, defined roughness.
- Weathered joint face: weakened edge zone, clay/oxide coatings, reduced shear strength.
- Polished joint face: smooth, undulating surfaces (low roughness, potentially low JRC).
- Carbonate or silicate crusts: brittle surface layers with different hardness than the core.
- Vein and dike faces: mineralogically heterogeneous bands with deviating splitting behavior.
For practical work this means: roughness (e.g., qualitatively analogous to JRC), joint spacing, fillings (clay, calcite), moisture, and waviness determine how well energy from hydraulic splitter is converted into directed crack propagation and how jaws or shears can be positioned.
Roughness, strength, and splitting behavior
Surface roughness influences friction and thus shear strength along existing discontinuities. Compressive strength (UCS), tensile strength (especially values relevant to splitting), and anisotropic fabrics control how cracks initiate and grow at the rock surface. Hydraulic splitting methods exploit low tensile strength: by means of borehole wedges or spreader bodies, tensile stresses parallel to the surface are generated and cracks are guided toward the free surface. Rock wedge splitter work with low vibration levels, which protects the integrity of adjacent areas when dealing with sensitive rock surfaces or in dense urban environments. Where concrete bears on rock or components sit on the rock, concrete demolition shear enable selective removal of concrete right up to the rock edge without unnecessarily weakening the rock.
Influence of the rock surface on the choice of methods and tools
Surface condition and geometry determine the choice of method in rock excavation and tunnel construction, natural stone extraction, strip-out and cutting, and in special operations (e.g., facilities in rock chambers). Typical consequences:
- Rough, compact, small joint spacing: a tight borehole pattern and higher spreading forces favor splitting methods with hydraulic splitter.
- Smooth, filled joints: first expose/relieve, exploit existing cracks; jaw work on bearing concrete becomes more predictable.
- Rock covered (shotcrete/concrete): concrete demolition shear for layer-by-layer removal down to the rock surface, then splitting or cutting along prominent discontinuities.
Method profiles at a glance
- Splitting: Borehole-based, targeted crack guidance toward the free rock surface, low vibrations.
- Jaw/shear operations: Selective removal of concrete at the rock edge, removal of edge beams, foundation elements, or shotcrete layers.
- Cutting: In combination with splitting to define geometry; near sensitive rock surfaces to limit spalling.
Borehole planning and wedge orientation at the rock surface
Drillings are oriented so that the crack front induced by spreaders runs toward the rock surface and along favorable discontinuities. Key points:
- Distance to the free rock edge: choose so that cracks run out cleanly without uncontrolled spalls.
- Orientation to bedding/joint systems: set wedges parallel to the preferred splitting direction.
- Borehole diameter/depth: matched to the rock wedge splitter and rock strength.
- Pattern: tighter in hard, isotropic rock; wider where distinct discontinuities are present.
Careful marking of the rock surface and checks for voids, moisture, and loose areas reduce risks such as wedge kickback or uncontrolled edge breakouts.
Work preparation and safety on exposed rock faces
Before starting, remove loose blocks, identify water inflows, and secure potentially unstable overhangs. The rock surface is cleaned to reveal drill starting points, joint traces, and bedding. In areas with bearing concrete or attachments, exposure often begins with concrete demolition shear before proceeding in the rock itself with hydraulic splitter. Safety measures (safety nets, exclusion zones, dust suppression and noise reduction measures) must be adapted to the location and geology.
Rock surfaces in tunnel construction and underground
Underground, rock surfaces are often temporarily secured with shotcrete. During removal or reprofiling, a gentle transition between concrete and rock is essential: concrete demolition shear enable stepwise removal of shotcrete down to exposed rock; subsequent excavation or trimming is often done with rock wedge splitter to minimize vibrations and disturbance of the rock mass. Where installations (pipelines, steel section) lie on the rock surface, supplementary cutting or shearing processes are used to avoid damaging the rock.
Rock surface in natural stone extraction
In quarries, the rock surface serves as extraction face, berm, or block edge. Splitting along bedding and joint planes creates block geometries with high dimensional accuracy. The combination of borehole planning, hydraulic splitter, and controlled approach to the free surface enables low-vibration extraction. Careful surface guidance reduces microcracks in the remaining mass and improves the quality of raw blocks.
Surface treatment for subsequent measures
After removal, the rock surface often forms the basis for waterproofing, shotcrete, anchors, or concrete foundation. Depending on the purpose, it is cleaned, locally roughened, or smoothed. Where concrete adjoins rock, precise deconstruction with concrete demolition shear supports a defined contact area. Splitting methods provide clean run-outs at the free edge, which can favor the bonding behavior of shotcrete.
Environmental and emission aspects on rock surfaces
Dust, noise, and vibrations must be minimized around sensitive rock surfaces. Hydraulic splitting works with low vibration levels and preserves adjacent structures. On open rock surfaces, water runoff must be controlled to avoid washouts. The choice of methods also influences the preservation of protected surface forms or biotopes on natural rock faces.
Quality assurance and documentation
Capturing the rock surface with photos, sketches, or scanning methods supports planning and evaluation. Metrics such as roughness characterization, joint orientation, moisture, and visible weathering are recorded. In practice, comparing planned and actual crack paths, borehole positions, and the rock’s response during splitting and shear removal proves valuable. This feedback improves future parameter selection (borehole spacing, wedge orientations, starting points).
Typical risks and their mitigation
- Spalling at the free rock surface: limit by matching borehole offset and moderate spreading.
- Wedge jamming or kickback: ensure borehole cleanliness, correct alignment, and controlled pressure build-up.
- Uncontrolled crack deflection along weak layers: survey geology in advance, plan crack guidance toward the intended exit surface.
- Edge loosening at concrete–rock transitions: first remove concrete layer-by-layer with concrete demolition shear down to exposed rock, then split.
Practice-oriented scenarios on the rock surface
Removal of a foundation beam on exposed rock
The overlay concrete is removed layer by layer with concrete demolition shear until the rock surface is exposed. Boreholes and rock wedge splitter then define removal along existing joints to avoid weakening the rock mass.
Reprofiling a tunnel contour
Shotcrete is carefully removed, installations are released, then splitting proceeds toward the free rock surface. This keeps the rock mass as unaffected as possible while achieving the target contour.
Extraction of a limestone block
Bedding planes are mapped, drill rows are set parallel to the face, hydraulic splitter guide cracks to the rock surface. The result is dimensionally accurate blocks with minimal edge damage.