Depending on the technical context, the term earth resistance refers either to the electrical resistance of the soil against the dispersal current (grounding or soil resistance) or to the mechanical resistance of the subsoil against deformation and load. For Darda GmbH’s work in concrete demolition and special demolition, building gutting and concrete cutting, rock breakout and tunnel construction, natural stone extraction as well as special demolition, both meanings are relevant: electrical, to ensure safe power supply and equipotential bonding for Hydraulic Power Units and controls, and mechanical, to carry out splitting and shear operations in concrete and rock using rock and concrete splitters in a controlled, low-vibration and material-appropriate manner.
Definition: What is meant by earth resistance
In the electrical sense, earth resistance is the sum of all resistances that a grounding system and the surrounding soil oppose to a flowing current. Decisive factors are the specific soil resistivity (in ohm-meters) as well as the geometry and arrangement of the ground electrodes. In the mechanical sense, earth resistance describes the counter-reaction of the soil to loads and displacements, for example as modulus of subgrade reaction, passive earth pressure or as reaction force at support points. Both meanings meet on the construction site: power supply and grounding influence the safe operation of hydraulic power packs, while the soil reaction determines the effectiveness of rock and concrete splitters, concrete demolition shears or stone splitting cylinders.
Background and terminology
Electrical earth resistance is determined by soil conductivity, moisture and temperature and dictates how well currents dissipate into the ground. Mechanical earth resistance depends on density, grain structure, fines content, pore water and compaction, and governs the bearing of components as well as the bracing behavior during splitting and cutting. In practice, both perspectives should be considered together: an electrically well-conductive, moist clay can be mechanically soft; dry, mechanically load-bearing gravel can be electrically high-resistance. For Darda GmbH, this distinction matters when concrete demolition shears are used on a floor slab, or when rock and concrete splitters work in rock with alternating layers.
Influencing factors on earth resistance
Earth resistance is shaped by a variety of site and boundary conditions:
- Moisture content: High soil moisture generally lowers electrical resistance, but can mechanically lead to reduced stiffness.
- Soil type: Clays and loams conduct electrically better than dry sands and gravels; mechanically, dense gravels/crushed rock provide high reaction forces.
- Temperature: Frost significantly increases electrical earth resistance; mechanically, frozen soil can respond stiffer for a short time.
- Salt and ion content: Increases the conductivity of pore water and thus lowers electrical resistance.
- Stratification and inhomogeneity: Alternating layers of soil, fills and rock lead to strongly varying resistances and non-uniform load transfer.
- Compaction and relative density: Determine the mechanical response; re-compaction under load changes the support conditions.
- Embedded parts and reinforcement: Foundation electrodes, reinforcing steel, rails or pipelines influence current paths and mechanical load distribution.
- Groundwater level: Increases electrical conductivity, but mechanically changes the effective stress state.
Measurement and determination on the construction site
The assessment of earth resistance is carried out using established procedures, adapted to the respective purpose:
Electrical earth resistance
- Pre-investigation: Record subsoil build-up, moisture, layer boundaries and existing grounding systems.
- Four-electrode method to determine the specific soil resistivity, adapted to available measuring spans and space conditions.
- Testing the grounding resistance of existing grounding systems with suitable measurement methods; in confined conditions, clamp methods are an option.
- Evaluation: Consider seasonality (frost, dry periods); repeated measurements increase reliability.
Mechanical earth resistance
- Use geotechnical parameters from subsoil investigations; if not available, arrange simple in-situ tests (e.g., load plate test).
- Assess support conditions for slabs, foundations or blocks: identify heterogeneities, assess settlement risks.
- Define boundary conditions for splitting and shear operations: protect the substructure, add shoring, plan load paths.
Relevance for concrete demolition and special demolition
Low electrical earth resistance supports the safe dissipation of fault currents and facilitates equipotential bonding when operating electric hydraulic power packs. Sufficiently high mechanical earth resistance ensures that supports and shoring absorb the forces introduced by tools without causing unwanted deformations. This leads to practical consequences for several tools and application areas of Darda GmbH.
Rock and concrete splitters
During splitting, the tool generates a concentrated tensile stress in the material between the spreading elements. The quality of the crack path also depends on the reaction of the surroundings. If a floor slab rests on a compliant subsoil, the crack may deflect or propagate unevenly. On a load-bearing, uniformly responding subsoil, the split proceeds more controllably. In rock, stratification, joint spacing and lateral resistance (rock pressure, restraint) influence the required splitting pressure and the positioning of wedge holes. Careful selection of borehole spacing and securing supports improves result quality.
Concrete demolition shears
When crushing components with tools such as Concrete Crushers, local compressive and shear forces act. On soft bedding, the component can yield; as a result, the tool stroke increases and the fracture becomes less targeted. A hard, level bearing with sufficient mechanical earth resistance reduces these effects. At the same time, for electrically powered units, the electrical earth resistance on the construction site must be considered to establish discharge paths and equipotential bonding correctly and to safely integrate conductive components (e.g., reinforcing steel).
Rock breakout and tunnel construction
In massive rock, lateral restraint significantly affects splitting success: high lateral resistance promotes crack propagation along the borehole line, whereas open joint systems “relieve” the energy input. Electrically, in underground areas, continuous effectiveness of grounding and equipotential bonding systems must be ensured, since closed metallic structures can carry large-area currents.
Planning: power supply, grounding and supports
For a robust process chain from the unit to the material, a coordinated approach is recommended:
- Assessment: Record subsoil, component build-up, reinforcement, existing grounding elements, supply lines and potential sources of interference.
- Measurements: Determine electrical earth resistance and essential mechanical parameters, or assume conservatively; consider seasonal influences.
- Design: Define supply lines, protective measures, equipotential bonding and grounding; define mechanical shoring, bearing pads and load distribution plates.
- Execution: Route lines short, protected and clearly; prepare contact points cleanly; construct bearings flat and slip-resistant.
- Control: Functional test of grounding and equipotential bonding; visual and functional check of shoring before and during the works.
Typical values and practical interpretation
As a guide, specific electrical soil resistivities are often lower in moist, clayey soils and significantly higher in dry sands and gravels. Rock can vary greatly depending on jointing and moisture. Mechanically, dense gravels and crushed rock provide high reaction forces, while soft fills, peats or organic layers respond compliantly. For practice this means: on high-resistance, dry subsoils, additional ground electrodes or larger extents of the grounding system are sensible; on soft subsoils, load-distributing pads or temporary shoring help to deploy concrete demolition shears or rock and concrete splitters accurately.
Risk management and sources of error
- Underestimated seasonality: dry or frozen soils change electrical earth resistance and can weaken protection concepts.
- Inhomogeneous subsoil: local settlements shift components and alter reaction forces during splitting or shearing.
- Unsuitable contact points: contaminated, painted or corroded surfaces increase contact resistances in the grounding path.
- Overlooked embedded parts: concealed reinforcement, lines or ground electrodes influence current paths and mechanical load distribution.
- Missing equipotential bonding: different metallic parts can exhibit hazardous touch voltages.
Reference to recognized rules of technology
Planning, execution and testing of grounding systems as well as the assessment of mechanical soil parameters should follow the generally recognized rules of technology. Limit and guideline values depend on the use case, the network type and local conditions. The information in this article is general and does not replace project-specific design.
Practical guide for the areas of application
Concrete demolition and special demolition
- Electrical: measure grounding resistance, establish equipotential bonding, keep cable routing short and protected.
- Mechanical: plan bearing areas, ensure a load-bearing subsoil, install shoring to prevent lateral yielding.
Building gutting and concrete cutting
- Electrical: document temporary grounding points, integrate conductive components.
- Mechanical: for ceiling cuts, consider load distribution to avoid crack formation due to non-uniform earth resistance.
Rock breakout and tunnel construction
- Electrical: ensure continuity of grounding and equipotential bonding in metallic structures.
- Mechanical: account for joint systems and rock pressure, adjust drilling patterns and splitting spacings accordingly.
Natural stone extraction
- Electrical: operate mobile units with adequately sized ground electrodes under changing soil moisture.
- Mechanical: use stratification and bedding joints, employ lateral restraint purposefully to produce clean separation joints.
Special demolition
- Electrical: in confined, temporary setups, check and document earth resistance at close intervals.
- Mechanical: use load distribution plates, wedges and spacer layers to introduce reaction forces into the subsoil in a controlled manner.