An edge foundation is a load-bearing structural element at the outer termination of a structure. It transfers loads from walls, columns, or edge beams into the subsoil, stabilizes the floor slab against edge deformations, and protects the building envelope against frost and moisture. In existing buildings, the edge foundation is often a central starting point for selective deconstruction, adjustments, or refurbishments—such as conversions, extensions, or partial demolition. In such situations, the professional environment frequently employs concrete demolition shear or systems such as hydraulic rock and concrete splitters to proceed in a controlled manner, with low vibration levels and high dimensional accuracy.
Definition: What is meant by edge foundation
An edge foundation is the foundation arranged along the exterior edges of a structure, usually formed as a continuous strip foundation or as a reinforced edge beam of a floor slab. It takes over the load transfer from rising structural elements, limits settlements at building edges, and serves as constructive reinforcement against torsion, overturning moments, and shear. Depending on subsoil, building class, and climatic conditions, it can be executed as a frost-free foundation with appropriate depth, as an insulated frost protection solution, or as a combined edge beam of the floor slab. In existing buildings, edge foundations are often heavily reinforced and locally compacted, which requires a differentiated choice of tools and methods during deconstruction.
Structure, sizing, and reinforcement of an edge foundation
Edge foundations are generally made of reinforced concrete. Sizing is based on vertical actions (permanent and variable loads), horizontal loads from wind or earth pressure, subsoil parameters, and the geometry of the structure. Constructively decisive are sufficient foundation width to accommodate bearing pressures, a frost-proof founding depth, and appropriate crack-width control by reinforcement. For floor slabs, the edge zone often functions as a reinforced edge beam with increased shear and flexural capacity.
Material, reinforcement, and connection details
Normal concretes with a compressive strength appropriate to load requirements and exposure class are typical. The reinforcement is designed for bending, shear, and restraint effects; corner regions and lap joints require special attention. Connection reinforcement to the floor slab, sealing measures such as waterstops and injection joints, as well as a foundation earth electrode along the edge are frequently used. Clean load transfer and sealing guidance at the edge are essential for durability and serviceability.
Waterproofing, frost protection, and subsoil
The transition between edge foundation and rising components requires a functional waterproofing layer. In frost-prone locations, a frost-free founding or effective frost protection (for example by insulation and drainage) must be planned. The subsoil is assessed with regard to load-bearing capacity, deformation, and water conditions, since edge foundations are sensitive to differential settlements.
Lifecycle: construction, use, repair, and deconstruction
During construction, formwork alignment, concrete placement, and compaction at component edges are quality-critical. In service, edge foundations are subjected not only to loads but also to environmental influences such as moisture variation and temperature gradients. Repairs often concern waterproofing, cracks, and zones at risk of corrosion. During deconstruction, the edge zone is predestined for selective interventions—such as partial strip-out, openings, or trimming foundation edges without damaging adjacent components. Low-vibration techniques that create controlled crack planes or splitting processes are often preferred here.
Typical damage patterns in the edge zone
- Cracks due to restraint, temperature fluctuations, or differential settlements
- Spalling at edges caused by mechanical impacts or rebar oxidation
- Moisture ingress at connection and construction joints
- Frost damage in case of insufficient depth or inadequate protection
Deconstruction of edge foundations: methods and work steps
The deconstruction of edge foundations requires a coordinated approach to avoid uncontrolled reduction of reserve capacity in the existing structure, to protect attachments, and to limit emissions. Depending on boundary conditions, concrete cutter, concrete demolition shear, hydraulic splitter, and supplemental tools for rebar cutting are used. Hydraulically powered systems with external hydraulic power units allow controlled process steps with high repeatability.
Preparation and exposure
Before starting, utility lines are located, component build-ups are investigated, and the work area is exposed. In the “strip-out and cutting” phase, non-load-bearing layers are removed and, if required, separation cuts are made to secure load transfer and define clear deconstruction sections.
Segmentation, splitting, and downsizing
- Establish separation cuts and predetermined crack planes along the desired edge alignment.
- Drill wedge holes at defined spacing.
- Use hydraulic splitter and rock wedge splitter to open the edge foundation in a controlled manner and divide it into segments—with low vibration levels and limited crack propagation.
- Secondary breaking and profiling with concrete demolition shear for precise edge shaping and to expose reinforcing steel.
- Cut exposed reinforcement with steel shear or suitable cutting tools; for complex cross-sections, combination shears or Multi Cutters can offer advantages.
- Orderly removal of segments and haulage logistics.
This sequence enables selective deconstruction in the edge zone, as required in “concrete demolition and special demolition” in inner-city settings. In sensitive environments with strict emission requirements, splitting methods are preferred, while shears allow precise finishing.
Special boundary conditions
Where adjacent components have a low tolerance to vibration—for example near sensitive installations or in “special demolition”—controlled splitting with hydraulic cylinders offers advantages. In areas with high reinforcement density, a combination of splitting and downsizing can be sensible to expose steel selectively and cut it with steel shear.
Selecting suitable tools for edge foundations
The choice between concrete demolition shear and hydraulic splitter depends on component thickness, reinforcement ratio, edge distances, and environmental requirements:
- Splitters are suitable where low vibration levels, low noise, and minimal impact on the existing structure are required. They generate predictable crack patterns along predefined drilling rows.
- Concrete demolition shear excel at precise contouring and downsizing of reinforced edge zones, especially after a preceding splitting step.
- Combination shears and Multi Cutters can, depending on configuration, both crush concrete and cut profiles, reinforcement, and embedded parts—helpful at changing material transitions in the edge area.
- Hydraulic power pack by Darda GmbH provide the required drive power for mobile, compact systems with high operator control.
Safety, emissions, and environmental protection
Dust and noise mitigation, low-vibration work, and safe handling of loads are key requirements in the edge zone. Coordinated water spray system, pinpoint force application, and the use of low-noise procedures support environmental protection. All work should be planned and executed in accordance with the applicable rules of the art and relevant occupational safety requirements, without generalizing the individual case.
Relation to application areas: from concrete demolition to tunnel construction
Edge foundations occur particularly often in “concrete demolition and special demolition”—for example during selective removal of building edges. In the area of “strip-out and cutting,” separating preliminaries serve clean segment formation. Parallels exist to “rock excavation and tunnel construction” as well as to “natural stone extraction”: Controlled splitting with hydraulic cylinders, as offered by Darda GmbH, follows the same physical principle, adapted to the material concrete with reinforcement. “Special demolition” includes situations with restricted access, sensitive neighbors, or strict emission specifications—typical framework conditions at building edges.
Planning, costing, and feasibility
For a structured sequence, component data (thickness, reinforcement, concrete compressive strength class), subsoil conditions, accessibility, and disposal routes are recorded. Costing considers the mix of drilling, splitting, downsizing, and cutting as well as required safeguarding measures. Pilot sections or a field trial/test can help optimize drilling grids and segment sizes and validate the performance of hydraulic splitter and concrete demolition shear in the specific existing structure.
Quality assurance and documentation
Documentation includes drilling and splitting plans, tool parameters used, and evidence of emission reduction and protection of adjacent components. Ongoing checks of edge quality, adherence to tolerances, and monitoring of ground vibration monitoring and noise emission safeguard execution quality. For rebar cuts, traceability from segmentation to steel cutting is helpful, particularly where residual load-bearing capacity must be maintained.
Practice-oriented tips for the edge zone
Narrow foundation strips benefit from closely spaced splitting points and short segment lengths to avoid unwanted crack propagation. For heavily reinforced edge beams, it is advisable to first open the concrete cover by splitting, then downsize the matrix with concrete demolition shear, and finally cut the exposed reinforcement with steel shear. In tight courtyards or occupied existing buildings, the use of compact hydraulic systems by Darda GmbH supports a safe, low-emission process.