Special foundation secures structures where conventional shallow foundations reach their limits: under high loads, difficult soils, groundwater, restricted space, or in existing buildings. It merges geotechnics, structural analysis, and construction methods into tailored foundation solutions and requires equally well-considered strategies for construction, adaptation, and deconstruction. Especially during deconstruction, low-vibration and precise methods are required, with tools such as concrete pulverizers or hydraulic rock and concrete splitters – in combination with suitable hydraulic power units – playing a central role. Practice ranges from removing pile heads to breaking up foundation blocks to rock cuts at the tunnel face.
Definition: What is meant by special foundation
A special foundation is a non-conventional foundation designed for particular boundary conditions. These include deep foundations such as bored piles and micropiles, combined pile–raft systems, diaphragm walls with load transfer, underpinning, as well as ground improvement measures. The goal is the safe transfer of vertical and horizontal loads into competent strata with controlled settlements. Construction stages, groundwater, vibrations, and neighboring buildings are also taken into account. Over the life cycle, special foundation is frequently adapted or partially deconstructed – for example for repurposing, adding storeys, tunnel connections, or the deconstruction of industrial facilities.
Construction types, methods, and application limits of special foundation
Special foundation spans a broad spectrum. The choice depends on loads, subsoil, space, noise and vibration limits, and schedule and environmental targets.
Bored piles (large- and small-diameter piles)
Bored piles transfer loads via end bearing and shaft friction. They are drilled into the ground, supported as required by steel casing or cement slurry, reinforced, and filled with concrete. Variants: cast-in-place piles, displacement piles, SOB piles. Typical applications include high-rise buildings in soft soils, bridge abutments, and excavation support systems. In deconstruction, pile head exposure and removal is often required.
Micropiles
Slender, mostly grouted piles for tight access or underpinning existing structures. They are suitable for additional foundation support, machine foundations, and structure lifting. In existing buildings, low vibrations are decisive; later adaptations often concern short lengths in the connection area.
Diaphragm walls and cut-off walls
As load-bearing and sealing elements in deeper excavation pits, diaphragm walls also serve as foundation. Load transfer occurs via flexural stiffness and shaft friction. During deconstruction, openings are created, capping beams are removed, or wall segments are selectively taken out.
Underpinning and combined systems
Underpinning secures existing foundations during deepenings or repurposing. Combined pile–raft foundations homogenize settlements. Interventions are usually local, often with limited headroom and strict emission requirements.
Jet grouting and ground improvement
Columns produced by high-pressure injections stabilize the ground or provide sealing. During deconstruction, solidified zones are partially removed or built over; fragmentation depends on cement content and strength gain.
- Advantages of special foundation: high load reserves, low settlements, adaptability in existing structures.
- Limits: complex planning, dependence on subsoil and water, increased documentation requirements, demanding deconstruction.
Materials, composition, and actions
Special foundation consists predominantly of reinforced concrete, in part with high reinforcement ratios, built-in components, and connection reinforcement. Actions include permanent, variable, and exceptional loads (e.g., earthquakes), earth and water pressure, and fatigue. For deconstruction, concrete grades, aggregates, reinforcement density, and bond conditions are decisive—they influence the choice between splitting, shearing with jaws, or sawing.
Planning and design: geotechnics, structural analysis, and construction stages
Planning is based on subsoil investigation, a foundation concept, and numerical design. Settlement predictions, soil–structure interaction, and verification for construction stages, for example with staged underpinning, are essential. For future modifications, a deconstruction-ready design with defined separation joints, accessible pile heads, and documented built-in components is recommended. Legal requirements and technical rules must be observed; project-specific requirements are to be clarified on a case-by-case basis.
Deconstruction of special foundation: methods and equipment deployment
Deconstruction aims for selective, low-vibration work with controlled load redistribution. In densely built or sensitive areas, hydraulic methods minimize noise, dust, and vibration.
Low-vibration splitting
Rock and concrete splitters and rock splitting cylinders generate wedge-shaped tensile stresses in concrete or rock by hydraulic pressure. In this way, massive foundation blocks and rock soles can be opened in a controlled manner and divided into manageable segments—advantageous in concrete demolition and special demolition, in rock demolition and tunnel construction, and in natural stone extraction.
Cutting and breaking
Concrete pulverizers grip reinforced concrete, crush sections, and separate reinforcing bars. Combination shears unite breaking and cutting, while multi cutters sever high-strength materials in confined areas. With high steel content, steel shears are used.
Hydraulic supply and integration
Hydraulic power packs supply split cylinders, concrete pulverizers, and shears with the required pressure and flow. Depending on access conditions, mobile or stationary solutions are appropriate, for example for work in existing structures or underground. For foundations near plant equipment, tank cutters can be relevant in peripheral areas when residual vessel or pipe sections near the foundation must be cut.
Areas of application at a glance and interfaces
- Concrete demolition and special demolition: pile head removal, lowering of foundation soles, removal of capping beams with concrete pulverizers and splitting technology.
- Strip-out and cutting: creating recesses, openings, and cable penetrations in foundation areas; combination with sawing and drilling methods.
- Rock breakout and tunnel construction: rock cuts below foundations, enlargement of caverns and adits; split cylinders for low-vibration advance.
- Natural stone extraction: analogous splitting of block stone; transfer of experience to foundation blocks and rock foundations.
- Special deployment: work in hospitals, laboratories, transportation structures, or explosion-hazard areas with stringent requirements for emissions and safety.
Step-by-step: pile head and foundation deconstruction
- As-built assessment: drawings, reinforcement ratios, concrete grade, subsoil, neighboring buildings, utilities.
- Structural evaluation: load redistribution, temporary supports, define construction stages.
- Deconstruction concept: separation joints, sequence, equipment selection (splitting, shears, cutters), protective measures.
- Access and logistics: access routes, load capacities, work platforms, set-down areas, disposal routes.
- Preparations: expose, clean, mark, drill splitting holes, dust and noise protection.
- Primary opening: split massive sections with rock and concrete splitters, if necessary in stages.
- Fragmentation: reduction with concrete pulverizers; separate reinforcement, cut steel with steel shears.
- Handling: safe load pickup, removal, intermediate storage, sorting into fractions.
- Control: measurements (vibrations, settlements), visual inspection of separation joints and remaining sections.
- Documentation: progress logs, evidence, photo documentation, handover to design.
Equipment selection: criteria for concrete pulverizers and splitting technology
- Component geometry: section thickness, accessibility, edge distances, built-in parts.
- Material: concrete grade, reinforcement ratio, bond, rock content.
- Emissions: low-vibration, low-noise, low-dust—requirements of the surroundings.
- Hydraulics: pressure/flow rate, hose lengths, heat dissipation, power pack position.
- Safety: kickback effects, pinch and shear points, emergency stop, safety clearances.
- Productivity: cycle times, segment sizes, jaw reach, cutting force, maintenance effort.
Safety, health, and environment
Deconstruction work on special foundation requires a rigorous safety concept. Protection against low- and high-pressure hydraulics, falling loads, dust, noise, and vibrations must be ensured. The applicable regulations apply; project-specific requirements are to be coordinated with the responsible parties. Environmental aspects include the separation of concrete, steel, and mixed fractions, handling of potentially contaminated areas, and measures to reduce dust, water, and noise emissions.
Quality assurance and documentation
Key elements are approvals for construction stages, measurement concepts (settlements, vibrations), equipment and test protocols, maintenance records of the hydraulic power packs, and approvals upon section completion. Seamless documentation facilitates acceptance and forms the basis for future adaptations over the life cycle.
Sustainability and circular economy
Selective size reduction with concrete pulverizers and controlled splitting produces single-grade fractions. Reinforcing steel can be sent directly for recycling; concrete rubble can be processed into recycled construction material if the framework conditions are met. Low-vibration methods protect existing structures, reduce damage to neighboring buildings, and lower follow-up repairs.
Typical challenges and solution approaches
- High reinforcement density: prior detection, segmented approach, combination of splitting and cutting.
- Restricted access: compact concrete pulverizers, modular split cylinders, external hydraulic power packs.
- Groundwater influence: sealing measures, water control, controlled cutting guidance.
- Unclear as-built documentation: exploratory pits, scanning, trial milling and pilot openings.
- Vibration-sensitive environments: priority for low-vibration splitting technology and finely metered hydraulics.
Practical execution tips
- Place pre-drilled holes for splitting wedges orthogonal to the main reinforcement to achieve effective crack guidance.
- Select the gripping and cutting zones of the concrete pulverizer to protect cover and anchor zones if residual structure must remain.
- Position hydraulic power packs away from sensitive zones, secure hose routing, and protect against crushing.
- Cycle planning with clear hold points to control settlements and vibrations.
- Clarify waste disposal logistics and recycling routes for concrete and steel fractions early.
Collaboration and competence profile
Successful projects link geotechnics, structural design, execution, and occupational safety. For special foundation the rule holds: the more complex the boundary conditions, the more important pilot trials, test fields, and coordinated equipment combinations of rock and concrete splitters, concrete pulverizers, steel shears, and matching hydraulic power packs. Darda GmbH is often associated with robust, precise, and compact tools in such projects—without letting the technical approach take a back seat to equipment specifications.