Sewer drilling is a key method in underground utility construction, in the rehabilitation of wastewater and supply networks, and at the interfaces with concrete demolition, special demolition, and tunnel construction. It comprises guided and unguided bores to create route alignments, connections, and penetrations in soil, rock, and reinforced concrete. Wherever drill heads reach their limits or openings need to be enlarged in a controlled manner, hydraulic tools such as rock and concrete splitters or concrete demolition shears are frequently used in practice, for example when enlarging pilot bores, opening shafts, or dismantling the launch and reception structures of the bore line. The interlinking of these methods enables low-vibration and precise construction workflows—especially in sensitive inner-city areas.
Definition: What is meant by sewer drilling
Sewer drilling refers to the targeted creation of underground voids to accommodate sewer lines, ducts, pressure pipes, or connections without extensively opening the surface. This includes pipe jacking (microtunneling), horizontal directional drilling, press boring with earth augers, and core drilling through existing reinforced concrete structures. In existing environments, sewer drilling is often combined with deconstruction and cutting works to build launch and reception shafts, create penetrations through foundations, or open concrete pipes in a controlled manner. In these interface works, hydraulic concrete demolition shears and rock and concrete splitters have proven their value due to their precision and low vibrations.
Background and distinction from related methods
Sewer drilling must be distinguished from conventional open trench utilities: it shifts construction activities underground and minimizes interventions at the surface. Compared to pure core drilling in structural elements, it targets longer alignments in soil or rock. Methods such as pipe jacking or horizontal directional drilling are steerable, keep alignment and gradient within tight tolerances, and enable long distances. Core drilling is used more for structural penetrations and is often supplemented by controlled breaking or widening—here, hydraulic splitting and shear tools from Darda GmbH allow material-appropriate opening of reinforced concrete components as well as the low-vibration release of rock or concrete along defined lines.
Geotechnical and structural fundamentals
The choice of sewer drilling method depends on subsoil conditions, groundwater, required diameter, alignment length, and constraints of the existing environment. Unconsolidated soils often require support or slurry media; in hard rock, drill heads with suitable tooling or a combination of predrilling and splitting techniques are advisable. In existing structures, load-bearing capacity, sensitivity to vibration, and existing utilities determine the process chain. Permits, offsets from buildings, settlement requirements, and protected assets must be reviewed on a project-specific basis and are usually defined in coordination with the authorities.
Subsoil and groundwater
In cohesive and non-cohesive soils, support fluids or casing systems stabilize the face, while in rock the cutting performance and thermal load of the tools are paramount. If water inflow increases, pressure control and tightness of launch and reception shafts are crucial. When bores encounter boulder layers, concrete remnants, or old foundation heads, rock and concrete splitters enable targeted removal of obstacles from within the shaft—without extensive excavation.
Diameter, gradient, and tolerances
Sewers require a defined gradient and precise alignment. Permissible deviations are small, particularly for house connections and tie-ins to existing shafts. For structural penetrations, concrete demolition shears complement core drilling by bringing openings to the required dimension, exposing reinforcement in a controlled manner, and minimizing edge spalling.
Methods of sewer drilling
The methods can be broadly divided into guided drives for longer distances and localized drilling for penetrating structural elements or short crossings. Selection depends on geology, alignment length, installation depth, and required accuracy.
Pipe jacking (microtunneling)
In pipe jacking, the face is excavated with a steerable cutterhead; pipe strings are hydraulically jacked forward from the launch shaft. Slurry or earth-pressure systems stabilize the face. A breakthrough in the reception shaft often requires opening or enlarging the shaft wall: concrete demolition shears create precise openings in reinforced concrete, while rock splitting cylinders or rock and concrete splitters assist in releasing rock benches at the shaft invert.
Horizontal directional drilling (HDD)
Horizontal directional drilling proceeds in three steps: pilot bore, reaming, and pipe pullback. In heterogeneous strata, boulder layers or concrete remnants can disrupt reaming. From launch and reception pits, such obstacles can be loosened and retrieved using targeted splitting techniques. The controlled, low-vibration approach protects adjacent structures and utilities.
Press boring and earth augers
Unguided press bores with earth augers are suitable for short crossings. If they meet reinforced elements or steel sections, combination shears, multi-cutters, or steel shears can cut embedded elements; hydraulic power packs reliably supply these tools—even in confined spaces.
Core drilling and manual heading
Core drilling through walls, slabs, and bases creates clean penetrations. If openings must be enlarged to the sewer diameter, a sequence change can be beneficial: pre-drill, break to size with concrete demolition shears, separate reinforcement in a controlled manner, and finish the edges. In rock inverts or natural stone masonry, splitting techniques allow defined enlargement along predrilled hole rows.
Planning, sequence, and interfaces
- Survey of existing conditions and utility detection, surveying and alignment
- Subsoil investigation, groundwater analysis, definition of tolerances
- Selection of method, machinery, and auxiliary structures
- Construction of launch and reception shafts, securing and underpinning
- Pilot bore, guidance, reaming, and stabilization
- Pipe pull-in or jacking of casing pipes/sewer pipes
- Breakthrough, tie-in works, and structural penetrations
- Pressure and leak-tightness tests, surveying (as-built), and documentation
Launch and reception shafts
Shafts must be stable, dry, and accessible. In existing environments, selective deconstruction is often required, such as opening foundation beams or enlarging access points. Concrete demolition shears work in a controlled manner, while rock and concrete splitters assist in releasing massive components or rock heads in the invert.
Handling obstacles
Old utilities, sheet pile walls, bundled reinforcement, and rock benches are typical obstacles. A combination of cutting and splitting has proven effective for their removal: steel shears for steel sections, multi-cutters for reinforcement, concrete demolition shears for reinforced concrete, and rock splitting cylinders for rock. This aligns with the application areas of concrete demolition – deconstruction as well as rock demolition – tunnel construction.
Quality assurance and documentation
Key aspects include positional and elevation control, maintaining the gradient, tightness, and the load-bearing capacity of the bedding. After completion, surveying (as-built), CCTV inspection where applicable, tightness tests, and logging of material and installation data are carried out. Clean edges at penetrations and fully bearing seating surfaces reduce consequential damage; this is where material-appropriate processing with shears and splitting techniques pays off.
Occupational safety and environmental protection
Work in shafts and confined structures requires special care: access and rescue concepts, gas and oxygen measurements, safe load handling, and controlled management of drilling fluids and wastewater must be planned. Low-emission, hydraulic processing with rock and concrete splitters and concrete demolition shears supports exposure control, limits vibrations, and protects adjacent structures. Requirements regarding permits, disposal of drill spoil, and dewatering vary regionally and are defined on a project-specific basis.
Emission control and low-vibration methods
Particularly in sensitive locations—hospitals, laboratories, listed buildings—low-vibration methods are advantageous. Splitting instead of percussive breaking reduces vibrations and secondary damage and preserves dimensional accuracy at connection faces.
Typical applications
- Urban crossings beneath roads, tracks, and waterways
- Service connections to existing sewers with penetrations through foundations
- Industrial sites with complex existing conditions and confined shafts
- Rocky alignments in rock breakout and tunnel construction with upstream or downstream splitting techniques
- Rehabilitation projects in concrete demolition and special demolition with controlled opening of structural areas
Selection of equipment and tools
In addition to drilling rigs, guidance, and slurry systems, the equipment includes tool carriers for selective deconstruction and opening structural areas along the bore alignment. The combination of tools depends on the material, access conditions, and safety requirements.
- Rock and concrete splitters: Enlarging pilot bores, releasing boulder layers, and controlled separation along predrilled hole rows.
- Concrete demolition shears: Precise opening of reinforced concrete in shafts and structural penetrations, controlled exposure of reinforcement.
- Hydraulic power packs: Power supply for shears, splitting cylinders, and cutters where space is limited.
- Combination shears and multi-cutters: Separating reinforcement, rolled sections, and embedded components in existing structures.
- Steel shears: Cutting sheet piles, casing pipes, or steel sections at launch and reception shafts.
- Rock splitting cylinders: Defined release of rock at shaft inverts and connection points.
Sizing, alignment, and gradient
For sewers, self-cleansing velocity, minimum gradient, and adequately dimensioned cross-sections are decisive. In guided drives, minimum allowable radii, entry and exit angles, and pipe stiffness determine the alignment. Tight radii require higher precision in the pilot bore and reaming; penetrations in existing structures are ideally core drilled and brought to the target dimension with concrete demolition shears to avoid fit inaccuracies.
Specific boundary conditions in existing environments
Restricted access, shallow cover, aged masonry and concrete, and protective measures for utilities and structures characterize many projects. Hydraulic splitting and shear techniques enable controlled interventions, reduce disturbances to neighboring buildings, and allow clean tie-in of the new pipeline—for example when notching out foundation ribs or opening concrete pipes in the reception shaft.
Materials and media
Concrete, GRP, vitrified clay, PE, or cast-iron pipes are used. Transitions between materials, sleeves, and couplings require dimensionally accurate openings and smooth, burr-free interfaces. Prior core drilling with subsequent shaping using concrete demolition shears provides smooth bearing surfaces and protects sealing faces. When installing utility conduits (e.g., cable protection pipes), low vibrations have a positive effect on the integrity of the existing structures.
Cost-effectiveness and scheduling
Cost-effective solutions minimize reinstatement effort and risk. Trenchless sewer drilling reduces surface reinstatement, and consistently low-vibration processing at shafts and penetrations avoids consequential damage. Contingency buffers for obstacles, alternative tool concepts (cutting and splitting), and coordinated logistics in existing environments contribute to reliable schedules and costs.