A rock crack largely governs the mechanical properties of rock. In planning, demolition, tunnel construction, and natural stone extraction, the arrangement of cracks determines stability, the drilling pattern, and the choice of suitable low-vibration methods. In practice, existing joints are often deliberately utilized: for example, when stone and concrete splitters or stone splitting cylinders from Darda GmbH controllably widen existing weakness planes to release blocks cleanly or to gently deconstruct rock. By analogy, in concrete demolition, concrete demolition shears are also used when rock is coupled with structures.
Definition: What is meant by rock crack
A rock crack is a natural or load-induced discontinuity in rock. This includes joints, shear and tensile cracks, faults, and bedding planes. They interrupt the rock fabric, reduce tensile and shear strength, and influence water flow, weathering, and the stability of rock walls, benches, and excavation pits. For demolition and extraction methods, the orientation, aperture, roughness, infill, and continuity of a rock crack are decisive because they determine splitting behavior, the required force, and the fracture pattern.
Geological formation and types of rock cracks
Rock cracks arise due to tectonic stresses, cooling, unloading, frost wedging, chemical weathering, or slope movements. The result is joint systems whose geometry dictates subsequent separation behavior.
Typical crack forms
- Tension cracks/joints: Opening cracks perpendicular to the least principal stress; often planar surfaces with limited interlocking.
- Shear planes: Offset separation surfaces with shearing; often higher roughness and interlocking.
- Bedding planes: Parallel to stratification; often low roughness and favorable separation surfaces.
- Faults: Large-scale offset surfaces with crushed zones; technically demanding due to loose material and water flow.
- Columnar/block jointing: Columnar or blocky jointing (e.g., in mafic volcanics); geometrically regular joint networks.
Importance of rock cracks for demolition, tunnel construction, and natural stone extraction
Rock cracks control the fracture pattern: Along favorable joints, rock blocks of defined size can be separated, whereas unfavorable crack orientations promote uncontrolled spalling or delayed collapses. In rock excavation and tunnel construction, taking advantage of existing discontinuities enables low-vibration methods. In natural stone extraction, cuts aligned with joint sets and subsequent splitting deliver better block quality.
Using existing cracks with splitting technology
Stone and concrete splitters as well as stone splitting cylinders act via hydraulic wedge pressure in the borehole. If the borehole axis is parallel to the desired split direction and transverse to the jointing, existing rock cracks can be controllably propagated. This creates defined separation planes without explosives and with minimized vibrations—advantageous in sensitive areas such as built-up zones, facilities, or in special operations.
Concrete–rock interfaces
Where rock cracks border structures (e.g., anchor heads, foundation seats), concrete demolition shears are used in concrete demolition and specialized deconstruction to detach concrete portions before the rock is split along natural cracks. This reduces restraint and prevents uncontrolled loading on the rock.
Identifying, mapping, and evaluating rock cracks
Surveying and evaluation of discontinuities precede any measure. Key parameters are strike and dip (orientation), spacing, continuity, infill (clay, calcite, oxides), roughness, waviness, and water ingress. From these, shear strength and resistance to splitting are derived.
Practical procedure
- Field walkover with structural mapping: determine the principal joint sets and crack spacing.
- Assessment of surface characteristics: roughness description and infills as indicators of interlocking and tightness.
- Geomechanical classification: derive the stability of the joint network for slopes, benches, and crowns.
- Definition of the separation concept: borehole diameter and spacing, splitting sequence, and stabilization measures.
From drilling pattern to controlled separation
A crack-adapted drilling pattern follows the rule: drill as perpendicular as possible to the intended split direction so that wedge forces act orthogonally on the joint family to be separated. The goal is to utilize existing joints and avoid unwanted fractures.
Step sequence for splitting operations
- Crack analysis: establish principal joint orientations and secure critical cracks.
- Drilling plan: select diameter and depth to suit stone and concrete splitters or stone splitting cylinders; drill edges and corners with reduced load.
- Control preloading: apply splitters in sequence to reduce stresses in a defined manner.
- Follow-up work: remove loose parts, re-split edges; in mixed zones near structures, deploy concrete demolition shears if required.
Tools and methods for dealing with rock cracks
The choice of tool depends on rock type, crack geometry, and constraints such as vibration limits, noise, and available space.
Stone and concrete splitters
Hydraulic wedge systems generate high, locally confined pressure in the borehole. Along suitable rock cracks, massive blocks can be released without inducing widespread microcracking. Favorable conditions are tight crack spacing, limited interlocking, and low clay infill.
Stone splitting cylinders
For precise block separation in natural stone extraction as well as for niches, benches, and portal areas in tunnel construction, stone splitting cylinders are suitable if split lines are aligned with the joint systems. Hydraulic operation via hydraulic power units enables reproducible results.
Concrete demolition shears in rock–concrete composites
For structures founded in rock, concrete demolition shears are used for strip-out and cutting, for example to remove shotcrete linings, foundations, or attachments. Rock cracks are then widened with splitting technology to produce a clean separation joint.
Interfaces to steel and hybrid constructions
Where rock cracks intersect steel components (e.g., bracing or built-ins), multi cutters or steel shears may be required before continuing rock separation along the cracks. In special operations involving tanks or vessels, special cutting tools such as tank cutters must be planned if the workflow requires it.
Influence of crack orientation on the splitting concept
Crack orientation and spacing govern the force demand, borehole spacing, and the splitting sequence.
- Cracks parallel to the desired separation joint: favorable case, lower splitting forces, clean fracture surfaces.
- Cracks oblique to the separation joint: increased risk of wedging and spalling; tighter drilling patterns and sequence splitting.
- Cracks perpendicular to the separation joint: higher wedge power required; consider pre-relief via intermediate boreholes.
- Wide, water-bearing cracks: pressure relief and glide planes; provide additional stabilization and dewatering.
Safety, vibrations, and environmental aspects
Low-vibration splitting technology is advantageous in sensitive environments such as existing buildings, near utilities, or in protected areas. Dust and noise reduction, controlled fracture propagation, water management, and rock stabilization (nets, anchors, shotcrete) must be specified project-wise. Legal requirements regarding occupational safety, noise, dust, and vibrations must be observed; permits and monitoring concepts are defined project-specifically.
Quality assurance and documentation
Consistent documentation increases process reliability and traceability:
- Crack mapping with orientation, spacing, infill, and water ingress
- Drilling and splitting logs: diameter, depth, spacing, pressure, sequence
- Stability monitoring: loosened areas, re-splitting, stabilization measures
- Results: block sizes, fracture-surface quality, rework
Typical challenges in dealing with rock cracks
In carbonate rocks, clayey infills can reduce shear strength, leading to sliding along cracks. In massive igneous rocks, large joint spacing requires higher splitting forces and tighter drilling patterns. Water-bearing cracks reduce friction and can wash out material; dewatering and stabilization are particularly important here.
Widely spaced joints
With large block spacing, the energy per splitting operation rises. Staged drilling patterns, pre-relief, and a splitting sequence from the edges toward the center help mitigate this.
Crack networks with varying orientation
Alternating joint families promote offsets. Drilling is planned in sections, adapted to the locally dominant direction; interim supports secure edge areas.
Maintenance and deployment preparation of hydraulic systems
The performance of hydraulic power units, stone and concrete splitters, and stone splitting cylinders depends on correct pressure, clean hydraulic fluid, intact seals, and well-maintained wedges. Before use, carry out a functional check, set pressure, inspect tools, and coordinate with the drilling pattern. This reduces downtime and improves the repeatability of splitting results.