A drop shaft is a vertical structure that is “dropped” into the ground in a controlled manner to access underground infrastructure, create launch and reception points for pipe jacking, or rehabilitate existing shafts. In densely built areas, groundwater-bearing layers, or rocky ground, this method enables safe, low-vibration construction and, later, targeted deconstruction. In such confined, emission-sensitive situations, hydraulic demolition and separation tools are often used, including rock and concrete splitters, concrete pulverizers, as well as steel shears and combination shears by Darda GmbH.
Definition: What is meant by a drop shaft
A drop shaft (also sinking shaft or sinking well) is a shaft whose structural body—usually made of precast reinforced concrete elements, cast-in-place concrete, or segmental lining elements—is constructed near the surface and then brought to the planned depth by successive undercutting and controlled lowering. The shaft wall stabilizes the ground during sinking; the base slab is sealed according to hydrogeological conditions. Drop shafts serve as access, assembly, and work space for underground utilities, as launch or reception shafts in pipe jacking and microtunneling, as operation or service shafts in tunnel construction, and for inspection and later maintenance.
Construction methods and design principles
The basic principle is that the shaft body is guided against the surrounding soil with a cutting shoe or sliding ring at its base, while material is excavated inside the shaft and conveyed to the surface. Through self-weight and, if necessary, additional ballasting, the shaft lowers in a controlled way. Depending on geology, water pressure, and space constraints, different construction types are applied.
Open construction versus sinking well
In stable, dry soils, a shaft is often excavated in open construction and secured laterally with shotcrete, sheet pile walls, secant pile walls, or diaphragm walls. The classic drop shaft (sinking well) is, by contrast, predestined for settlement-sensitive, soft, or water-bearing layers. Here, segmented reinforced concrete rings or monolithic shaft bodies with a sharpened cutting foot form the supporting structure, while internal undercutting progresses ring by ring.
Shaft construction with precast units, cast-in-place concrete, and segmental linings
Depending on load transfer and required tightness, precast rings, cast-in-place shafts, or segmental linings are used. Segmental linings are particularly common in tunnel and heading construction and enable a segmented, rigidly connected shaft wall. The base sealing is achieved by underwater concrete, a sealing base slab, injections, or ground freezing, aligned with groundwater level and pore water pressure.
Hydrogeology, groundwater control, and sealing
Dealing with groundwater is central: groundwater lowering/dewatering (filter wells, vacuum dewatering), temporary ground freezing, injection curtains, or a sealing base slab are combined project-specifically. The goal is a safe excavation environment without impermissible settlements or hydraulic base failure. Annulus grouting and joint sealing ensure the durability of the shaft structure.
Groundwater lowering and ground freezing
Under high inflows, inflow paths are reduced or temporarily “frozen” to allow work in the dry. Alternatively, water is captured and pumped in a controlled manner. Decisions require a geotechnical forecast; they are site-specific and determined during planning and permitting.
Annulus grouting and base slab sealing
The rigid and watertight integration into the ground is achieved by grout mortar, suspension fillings, and base concrete. Waterstops, swelling profiles, and injectable strip systems reduce the risk of leakage. Watertightness and deformation compatibility are coordinated with each other.
Significance in infrastructure and tunnel construction
Drop shafts are typical launch and reception structures for pipe jacking, microtunneling, and trenchless pipeline construction. They serve for assembling heading machines, threading-in and retrieval of pipes, and as operation or ventilation shafts. In sewer construction they function as access shafts or special structures (e.g., drop shafts). In rock, the drop shaft is often used as an access to galleries, where rock classification, rock bolts and shotcrete concepts, as well as safe access must be considered.
Deconstruction, modification, and rehabilitation inside the drop shaft
Beyond construction, structurally controlled deconstruction plays a major role, for example when replacing linings, retrofitting seals, or decommissioning old shafts. In confined shafts, low-noise, low-vibration methods are required. Hydraulic techniques are suitable here, working precisely and protecting the surroundings. For concrete demolition in the shaft, concrete pulverizers are considered for selective fragmentation of linings, ring beams, and intermediate slabs. For rock removal or breaking massive base slabs, rock and concrete splitters as well as rock wedge cylinders show their strengths, because the splitting action is controlled and produces few cracks. Steel shears cut reinforcement and sections; combination shears and Multi Cutters assist when changing material bundles (concrete, steel, cast iron) are encountered. In special operations, such as deconstructing thick-walled steel components in shafts, specialized tank cutters can be used, provided the boundary conditions allow.
Rock and concrete splitters in the shaft
Hydraulic splitting technology uses drill holes to build up high splitting forces inside the material. This is practical for shaft construction, because the energy is supplied through hoses from hydraulic power packs at the surface, which can avoid exhaust gases in the shaft. Advantages include low vibration levels, good control of the fracture pattern, and reduced secondary damage to adjacent components.
Concrete pulverizers and combination shears in existing structures
During modifications, concrete pulverizers can remove shaft heads, circumferential bands, stiffening rings, and internal installations section by section. Combination shears allow switching between crushing and cutting, which is useful when removing reinforcement, service penetrations, and embedded parts. For pure steel packages, steel shears are used. Multi Cutters provide additional flexibility with mixed materials.
Safety, logistics, and workflows
Working in shafts requires particularly careful organization: secured access, a gas-free atmosphere, ventilation, rescue concepts, and reliable lifting and conveying logistics are essential. Hydraulic tools can be supplied remotely; ideally the hydraulic power packs are placed aboveground, resulting in fewer emissions and less heat introduced into the shaft. Dust suppression and noise reduction measures, ergonomic load handling, and a clear communication structure increase occupational safety. Legal and regulatory requirements must always be considered on a project-specific basis.
Low-emission methods in confined spaces
Compared to percussive methods, splitting technology and shear-based processing reduce vibrations and noise. This protects neighboring buildings and installations. A water spray system or localized dust extraction improves dust control. Where possible, steps are sequenced to maintain clear escape routes and stable intermediate states.
Planning, site supervision, and quality assurance
For the drop shaft, the ground model, design of the shaft wall, sealing concept, and water management are integral parts of planning. Measurement and monitoring concepts (settlements, inclination, water levels) accompany the sinking. The selection of demolition and separation tools is integrated into construction scheduling, especially when concrete demolition and special demolition or work in rock are planned. Requirements regarding noise, vibration, and working hours are coordinated and documented.
Typical challenges and proven solutions
Challenges include unforeseen water inflows, boulder layers, running sand, obstacles in the sinking path, or binding shaft rings. Proven approaches include pre-injections, temporary relief boreholes, friction reduction at the cutting shoe, local loosening using splitting technology, and targeted removal of wedges. In deconstruction, concrete pulverizers have proven effective for selective work, while rock and concrete splitters generate controlled fracture lines without excessively loading the shaft wall.
Products and application areas in the drop-shaft context
In the context of a drop shaft, the work touches several application areas: In concrete demolition and special demolition, concrete pulverizers, combination shears, and steel shears support structured deconstruction of linings and reinforcement. In rock excavation and tunnel construction, rock and concrete splitters as well as rock wedge cylinders enable low-vibration removal in the access shaft. For strip-out and cutting, Multi Cutters and steel-specialized tools are used to separate embedded parts, pipe penetrations, or steel rings. For special operations, a tank cutter may also be considered, depending on the boundary conditions. The hydraulic supply is provided by suitable hydraulic power packs from Darda GmbH, which, due to the separation of drive and working tool, integrate well into shaft-appropriate logistics.
Terminology and application examples
Drop shafts are to be distinguished from conventional excavation pits, which are predominantly constructed in open construction. Typical application examples include launch shafts for microtunneling in inner-city sewer construction, reception shafts under traffic areas, access to service tunnels, or rehabilitation shafts in existing networks. In all cases, planning and execution benefit from methods that work in a controlled, low-emission, and precise manner—characteristics that distinguish hydraulic splitting and shear technology in shaft environments.