A backfilling shaft is a shaft structure that is permanently taken out of service and properly filled with suitable material, or used as a controlled intake point for backfill. The term appears in mining, tunnel and sewer construction, in the deconstruction of industrial facilities, and in municipal infrastructure. In all cases, safe decommissioning or controlled backfilling is paramount—with attention to structural stability, low settlement, tightness, and occupational safety. Preparatory deconstruction work on the shaft head and shaft wall is often part of the scope; for non-explosive methods, concrete demolition shears as well as hydraulic rock and concrete splitters are particularly suitable.
Definition: What is meant by a backfilling shaft
A backfilling shaft is either a shaft to be filled and decommissioned (e.g., inspection, mining, or service shaft) or a shaft through which backfill material is introduced and distributed in a controlled manner. The goal is the permanent abandonment of the shaft’s function, the creation of a load-bearing, void-free fill body, and—depending on requirements—a sealed shaft closure. The term covers both the construction-technical preparation (e.g., demolition of shaft covers, opening of shaft walls, removal of built-in components) and the actual backfilling method (granular backfilling, flowable backfill material, cement or injection backfilling).
Objectives and application scenarios
Backfilling a shaft serves traffic safety, prevents settlement, separates groundwater from surface water, decommissions underground structures that are no longer needed, and prepares for deconstruction. Typical scenarios include shaft backfilling in historic mining, decommissioning of pump and inspection shafts in concrete demolition and special demolition, abandonment of excavation shoring shafts, or creating a shaft closure in tunnel construction. Preparatory work on the shaft structure is often carried out with hydraulic demolition tools and splitting technology; particularly low vibration levels methods such as rock and concrete splitters are established in sensitive environments.
Planning and preparation
Planning starts with a technical survey of geometry, material composition, and surroundings. Utility isolation, boundary structural conditions, groundwater conditions, and adjacent buildings must be clarified, as must access, logistics, and emissions control. In confined conditions, the sequence is often organized in small work packages to ensure material flow and safety.
Survey and concept
- Survey and subsoil: shaft depth, cross-section, wall build-up, connection to utility lines, rock or soil interface.
- Water and gas management: inflows and outflows, potential gas formation, drainage concept.
- Component inspection: cover, bearing/support, built-in parts, reinforcement, inlet openings, shaft heads.
- Backfilling strategy: granular layers, flowable backfill material, cement or grouting mortar, or mixed variants.
Occupational safety in focus
- Entry only after clearance measurement and safeguarding; shaft work is classified as work in confined spaces.
- Rescue plan, anchorage points, suitable lifting devices, and communication equipment.
- Dust, noise, and vibration management, especially in inner-city locations.
Construction pre-works on the shaft structure
Before backfilling, covers, superstructures, and obstructive built-in components must be removed and inlet openings created or sealed. Hydraulic tools that do not require explosives are suitable for controlled opening and careful deconstruction.
Use of concrete demolition shears
Concrete demolition shears target shaft heads, slabs, and concrete walls. They allow edge severing, nibbling off obstructions, and exposing reinforcement with low vibration levels. In combination with steel shears, exposed reinforcement and built-in parts are separated.
Rock and concrete splitters for massive cross-sections
Rock and concrete splitters as well as rock splitting cylinders generate high splitting forces in the borehole, enabling controlled, crack-free release of thick concrete and natural-stone cross-sections. This is advantageous in areas with sensitive adjacent buildings, on listed surfaces, or in shafts with limited accessibility.
Supplementary cutting and separation works
- Combination shears and Multi Cutters separate composite components made of concrete with inserts, pipes, and sections.
- Steel shears cut reinforcement, frames, risers, and anchors without sparking in confined areas.
- Cutting torches are used in special operations to separate tanks or double-walled steel components in shafts.
Methods of shaft backfilling
The choice of method depends on depth, diameter, material, water conditions, and the required end use (e.g., to be built over). The following methods are common and can be combined:
Granular backfilling with compaction
- Material: gravel, sand, crushed stone, or graded mineral mixtures.
- Placement: layered placement, compaction with vibrators, rammers, or drop weight.
- Advantages: robust, well draining, immediately loadable; suitable under dry conditions.
Flowable backfill and self-compacting materials
- Material: pumpable, soil- or cement-stabilized mixes with low bulk density and a defined modulus of elasticity.
- Placement: pump or gravity placement via the backfilling shaft; self-compacting, low compaction effort.
- Advantages: void-free filling, low vibration levels, suitable for complex geometries.
Cement and grouting backfilling
- Material: cement suspensions, flowable grout, injection materials with defined strength.
- Placement: grouting lances, staged fill and vent points for controlled air displacement.
- Advantages: dense, low-settlement fill bodies; suitable where water ingress occurs and for shaft closures with a sealing function.
Material selection and technical criteria
Material selection is based on load-bearing capacity and sealing requirements, subsoil, water flow, and planned overbuild. Important criteria include gradation, bulk density, water-cement ratio, modulus of elasticity, compressive strength, freeze–de-icing-salt resistance, and chemical compatibility. For granular backfilling, the ability to achieve compaction in narrow shafts must be considered; for pumpable materials, flow behavior, venting, and heat of hydration must be taken into account.
Equipment selection and hydraulics around the shaft
Hydraulic tools enable controlled interventions with a small footprint. hydraulic power units reliably supply concrete demolition shears, rock and concrete splitters, combination shears, Multi Cutters, steel shears, and cutting torches with energy. In sensitive environments, low vibration levels splitting technology is advantageous to avoid crack formation in adjacent structures. The choice of equipment depends on wall thicknesses, reinforcement density, accessibility, and emission requirements.
Quality assurance and documentation
Traceable documentation of the backfilling process is essential for verification and future use. This includes material certificates, placement data, compaction records, sampling, and—for flowable materials—records on consistency and density. Settlement measurements at the surface and inspections of shafts with endoscopy or probes help detect voids early and regrout them.
Typical challenges and solutions
- Water ingress: preliminary or accompanying dewatering, adjustable flow grouts, multi-stage grouting.
- Limited accessibility: segmental removal with concrete demolition shears, borehole splitting technology, compact hydraulic power packs.
- High reinforcement ratio: combination of concrete demolition shear and steel shear; preliminary separation cuts with Multi Cutters.
- Neighboring structures: low vibration levels methods (rock and concrete splitters), low drop heights, noise-reduced work sequences.
- Complex geometries: pumpable, self-compacting materials, vent points, controlled fill levels.
Procedure for professional shaft backfilling
- Cordon off, perform clearance measurement, and set up safety equipment.
- Remove covers, support rings, and built-in parts (e.g., with concrete demolition shears, steel shears, Multi Cutters).
- Create fill and vent openings; seal unused connections.
- Dewatering and preparation of the subgrade (a blinding layer if applicable).
- Place the backfill material: in layers or pumpable, with accompanying compaction or venting.
- Check for voids; regrout if required.
- Create the shaft closure (e.g., cover slab, load-bearing cover, or superstructure) according to the planned use.
- Documentation and final inspection of the surface and adjacent structural elements.
Backfilling shafts in application areas
Concrete demolition and special demolition
In the deconstruction of industrial facilities and foundations, shafts are decommissioned and backfilled. Non-load-bearing superstructures and upstands can be removed in a controlled manner using concrete demolition shears, and massive shaft walls opened with rock and concrete splitters. Backfilling and closure are coordinated with the subsequent surface use.
Strip-out and cutting
In existing buildings, decommissioning service shafts requires low vibration levels methods. Combination shears, Multi Cutters, and steel shears separate built-ins, while splitting technology and concrete demolition shears control the concrete structure. Pumpable materials are suitable for long, slender shafts with many built-in components.
Rock excavation and tunnel construction
In underground works, backfilling shafts serve to abandon blind shafts or to grout voids. Rock splitting cylinders act directly in the rock to release embedments. Cementitious grouting seals permanently against water and stabilizes the adjacent rock mass.
Natural stone extraction
In quarries, old hoisting or exploration shafts can be decommissioned. Splitting technology is obvious due to the geology; granular backfill or grouting mortar provides structural stability.
Special operations
For shafts with steel built-ins, tanks, or contaminated components, controlled separation and packaging workflows are crucial. Steel shears and cutting torches enable safe segmentation before backfilling and closure.
Practice-oriented guidance for selecting the approach
- Depth and diameter: slender, deep shafts favor pumpable, self-compacting materials.
- Water flow: with continuous inflow, dense grouted bodies offer advantages; the construction phase may require dewatering.
- Surroundings: in vibration-sensitive environments, rock and concrete splitters and concrete demolition shears are the first choice.
- Overbuild: for future traffic areas, consider load-bearing capacity, low settlement, and surface build-up.