Subsoil investigation

Subsoil investigation is the technical foundation for plannable, safe, and efficient work in concrete demolition, special demolition, strip-out, rock excavation and tunnel construction, as well as in natural stone extraction. It provides clarity on material composition, strength, reinforcement, embedded items, and risks – and delivers the key parameters needed for the proper selection and parameterization of concrete demolition shears, hydraulic rock and concrete splitters, hydraulic power packs, combination shears, steel shears, multi cutters, rock splitting cylinders, or tank cutters from Darda GmbH. When applied correctly, subsoil investigation reduces vibrations, avoids uncontrolled crack formation, protects prestressing tendons and utility lines, and increases precision for selective interventions.

• Typical deliverables: investigation plan and scope, risk register, mapping of embedded items, drilling and cutting plan, method statement, monitoring concept, and acceptance criteria.

Definition: What is meant by subsoil investigation?

Subsoil investigation refers to the systematic exploration, measurement, and evaluation of properties and boundary conditions of the substrate to be processed – such as concrete, reinforced concrete, masonry, natural stone, or rock. The goal is to assess the load-bearing capacity, strength, structure, layer build-ups, discontinuities (joints, fractures, cracks), moisture, reinforcement, or prestressing in order to establish a suitable, low-risk method. The results determine, for example, whether concrete demolition shears or rock and concrete splitters are used, which drilling pattern is chosen, what hydraulic performance is required, and which protective measures are appropriate. In practice, this spans desk study, non-destructive testing, targeted probing, laboratory testing where necessary, and a consolidated evaluation with actionable recommendations.

Objectives, scope, and typical key parameters

Subsoil investigation pursues three main objectives: risk minimization, method selection, and parameterization. To this end, key parameters are recorded that represent the mechanical properties (e.g., compressive strength, tensile strength, modulus of elasticity), the geometric boundary conditions (member thickness, layer sequence, voids), and embedded items (reinforcement, tendons, lines, inserts). In rock and natural stone, joint spacing, joint orientations, degree of weathering, and block sizes are added. This information is crucial for reliably predicting splitting behavior, the crushing pattern from concrete demolition shears, or the required pre-drilling for splitting cylinders. In sensitive or protected structures, additional boundary conditions such as heritage protection, vibration limits, and access restrictions must be integrated into the scope.

Procedure: Sequence of a subsoil investigation in concrete and rock demolition

A proven practical sequence is divided into clearly structured steps:

1. Document review: plans, sections, as-built records, structural verifications; in case of uncertainties, adopt conservative assumptions and record gaps.
2. Site visit and visual inspection: crack mapping, spalling, areas of re-compaction, moisture; identify constraints and the vibration sensitivity of the surroundings.
3. Non-destructive testing: rebar location, material homogeneity, layer boundaries, member thickness.
4. Probing and sampling: core drilling, endoscopy, and, where appropriate, mortar and rock samples for laboratory testing.
5. Evaluation and method selection: derivation of measures, tool and parameter definition, drilling patterns, cut sequences.
6. Release and protective measures: cordoning, shoring structures, stabilization against instabilities, utility isolation.
7. Monitoring: control of vibrations, crack widths, and removal progress; adjust the approach if deviations occur.
8. Reporting and handover: structured documentation of findings, updated method statement, and sign-off of the defined measures.

Methods and measurement techniques: from screening to detailed testing

Rapid reconnaissance (screening)

• Rebound hammer: rough assessment of concrete surface strength and homogeneity.
• Tapping/sounding: localization of voided areas, delaminations, and honeycombing.
• Moisture measurements: influences splitting behavior, dust development, and electrical measurement methods.
• Infrared thermography: qualitative mapping of moisture and delaminations where boundary conditions allow.

Locating and geometry

• Rebar locators and radar (GPR): position, diameter, and cover of reinforcing bars; detection of inserts and empty conduits.
• Ferroscan/eddy current: detailed reinforcement mapping, especially in areas of planned cuts or splitting boreholes.
• Wall thickness measurement/ultrasonic: determination of member thicknesses and detection of layer boundaries.
• 3D laser scanning/photogrammetry: as-built geometry, deformations, and clash detection for precise drilling and cutting plans.

Material properties and structure

• Ultrasonic pulse velocity: statements on structural quality and absence of cracks.
• Core drilling with lab testing: compressive strength, density, porosity, carbonation; in rock, additionally petrographic classification and point load index.
• Endoscopy: insights into cavities, bedding joints, drill channels, and pipelines.
• Pull-off or pull-out tests: near-surface tensile strength for cut guidance and attachment points.
• Carbonation depth testing: influences reinforcement corrosion risk and local strength gradients.

Influence of subsoil investigation on the selection of concrete demolition shears and rock and concrete splitters

The test results indicate whether the intervention should be splitting, cutting, or crushing, and with which parameters. A combination is often useful: pre-splitting to initiate cracks and reduce stresses, followed by selective severing of reinforcement with concrete demolition shears or a steel shear. Coordinating these methods based on measured properties reduces rework, shortens cycle times, and increases predictability in confined or vibration-limited environments.

Concrete demolition shears: requirements for the substrate

• Reinforcement density: High reinforcement contents favor the use of concrete demolition shears because steel can be grasped and cut separately.
• Member accessibility: Cantilevers, edges, and nodes allow targeted gripping; subsoil investigation clarifies clearances and collision risks.
• Structure and crack pattern: Existing cracks facilitate breakage; brittle, high-strength concrete entails increased reaction forces.
• Vibrations: Crushing methods are low-vibration; this can be decisive in sensitive surroundings.
• Carrier class and reach: Tool weight and kinematics must match access conditions and allowable surface loads.

Rock and concrete splitters: requirements for drilling pattern and material

• Boreholes: The subsoil investigation defines diameter, depth, and spacing of pre-drilling for splitting cylinders; layer boundaries and reinforcement layers are avoided.
• Strength and anisotropy: Bedding joints, fractures, and layering favor defined fracture planes; in isotropic, high-strength areas, tighter drilling patterns are advisable.
• Edge distances: Stable edge distances prevent breakout cones; member geometry determines the splitting direction.
• Hydraulic parameters: Required splitting pressure and the sizing of the hydraulic power pack are derived from strength and drilling pattern.
• Sequence and timing: Staggered activation limits uncontrolled crack propagation and supports targeted block release.

Hydraulic power packs and system tuning

Hydraulic power packs (compact hydraulic power units) provide the flow rate and pressure for concrete demolition shears, rock splitting cylinders, combination shears, multi cutters, steel shears, or tank cutters. Derived from the test data are:

• Required pressure range: depending on concrete compressive strength, contact geometry, and the necessary splitting force.
• Flow rate: determines working speed, especially for long splitting sequences or serial shear operation.
• Thermal reserve: continuous loads in tunnel construction or during large-area strip-out require adequate cooling.
• Energy supply and emissions: select electric, hybrid, or low-emission operation to comply with site constraints and indoor use.

Specifics in the application areas

Concrete demolition and special demolition

In concrete demolition, key aspects are the detection of reinforcement and possible prestressing, the member thickness, and support conditions. Prestressed concrete requires increased care: tendon ducts must be located, and areas with prestressed tendons – where necessary – must be exposed separately and safely neutralized by qualified procedures. For massive cross-sections, a combination of splitting boreholes and concrete demolition shears can structure removal and control load redistribution. Temporary supports and sequential release are planned to prevent progressive failure.

Strip-out and cutting

In existing structures, embedded items, utility lines, fire-protection layers, and composite layers are often heterogeneous. Subsoil investigation clarifies cut lines, member thicknesses, and line routings. Concrete demolition shears can selectively detach components, while multi cutters and steel shears separate embedded parts and profiles. Low vibrations protect remaining members. Fire load and dust management are defined in the method statement, with containment where required.

Rock excavation and tunnel construction

In rock, joint systems, layering, water inflow, and degree of weathering govern fracture behavior. Splitting devices exploit natural weaknesses and create defined separation planes with very low vibrations – advantageous in sensitive environments. The subsoil investigation records joint orientations, block sizes, and the stability of the crown and tunnel face to define splitting direction, drilling pattern, and stabilization measures. Where groundwater is present, inflow control and drainage are integrated to maintain face stability.

Natural stone extraction

For predictable block dimensions, bedding planes and joints are central. The investigation identifies anisotropic properties and preferred splitting directions. Splitting cylinders are placed along natural separation planes; concrete demolition shears are used for breaking down reject blocks or for prying at edges. Surface quality targets and block handling logistics are aligned with the splitting strategy.

Special applications

Special tasks – such as opening vessels or tanks – require testing for residual contents, media, coatings, and spark hazards. Tank cutters are used only after clearance measurements and the implementation of suitable protective measures. In general, measures must be planned and executed in accordance with recognized rules of practice and applicable safety requirements. Additional precautions include inerting where required, earthing, and exclusion zones with continuous gas monitoring.

Interpreting key parameters correctly

• Compressive strength: High-strength concretes require higher splitting forces and a tighter drilling pattern; concrete demolition shears engage with appropriately shaped jaw surfaces.
• Crack and joint pattern: Existing discontinuities serve as intended fracture lines; splitting direction is chosen parallel to zones of weakness.
• Reinforcement/prestressing: Reinforcement density governs the choice of shears or pre-splitting; prestressing systems define exclusion zones and procedures.
• Moisture/water: Influences dust, friction, and electrical measurement methods; in rock, water affects stability and the required splitting pressure.
• Member geometry: Thickness, cantilevers, supports, and neighboring members determine the sequence of splitting, cutting, and removal.
• Heterogeneity: Variations in aggregates, overlays, or repairs lead to local parameter adaptations and segmented work steps.
• Residual stresses/constraints: Restraints and load paths influence crack propagation and must be reflected in the cut and split sequence.

Typical mistakes and how to avoid them

• Underestimating prestressing: Systematically search for tendons before interventions; comply with release processes.
• Insufficient rebar locating: Plan pre-drilling and shear grips to avoid collisions; adapt the drilling pattern for dense reinforcement networks.
• Overly coarse drilling pattern: Leads to uncontrolled crack paths; couple hole spacing to strength and anisotropy.
• Missing edge checks: Offset splitting and shear grips sufficiently from edges to avoid breakout cones.
• Ignored environmental requirements: Consider vibrations, noise, dust, and utility lines early; define suitable protective measures.
• No monitoring baseline: Establish initial crack width and vibration levels to enable meaningful comparison during execution.
• Static assumptions not updated: Revise drilling and cutting plans promptly when findings deviate from the desk study.

Documentation, quality assurance, and monitoring

Traceable documentation increases safety and efficiency:

• Logs of measurements and probes with positional reference.
• Mapping of reinforcement, tendon ducts, lines, and layer boundaries.
• Definition of drilling patterns, shear grips, cut sequences, and hydraulic parameters.
• Continuous control of vibrations, crack widths, and removal progress to enable adjustments in case of deviations.
• Photo documentation and, where feasible, georeferenced datasets to support traceability and later audits.

Practice-oriented selection matrix: from findings to measures

• Thin, lightly reinforced members: Splitting with wider hole spacing or lower jaw pressure; low vibrations.
• Thick, heavily reinforced sections: Pre-splitting for stress relief, followed by targeted crushing with concrete demolition shears; reinforcement separated with steel shears if required.
• Rock with pronounced jointing: Splitting direction along joints; reduced splitting forces; larger block sizes achievable.
• Heterogeneous existing slabs with utilities: Precise locating, tightly guided cuts, limited shear grips; splitting boreholes outside utility zones.
• Tank/vessel work: After clearance measurements and safeguarding, use suitable tank cutters; observe spark and media management.
• Confined spaces or sensitive neighbors: Favor low-vibration splitting, small-step sequences, and continuous monitoring with predefined trigger values.

Safety and organizational aspects

Subsoil investigation is part of the hazard analysis. It serves to minimize risks from collapse, uncontrolled fractures, media releases, or impermissible vibrations. Measures must be planned based on general safety requirements, recognized rules of practice, and applicable specifications. Binding case-by-case assessments remain reserved for specialized professionals and the respective competent authorities. Required permits, qualifications, and emergency plans are defined before execution, with responsibilities and communication paths clearly assigned.