Diaphragm walls are key structural elements in structural engineering when deep excavation pits must be secured, groundwater cut off, or structures underpinned. They combine high stiffness with excellent sealing performance and are constructed panel by panel in the ground. In practice, diaphragm walls are encountered in both new-build projects and existing structures, for example for tie-in openings, breakthroughs, or the removal of wall heads. In such situations, low-vibration, low-impact methods are required – this is where, among others, concrete pulverizers as well as hydraulic rock and concrete splitters from Darda GmbH are used, particularly in application areas such as concrete demolition and deconstruction, strip-out and cutting, or special operations.
Definition: What is meant by diaphragm wall
A diaphragm wall is a continuous reinforced concrete or cutoff wall constructed in the ground, consisting of a series of adjoining panels. The wall is excavated in a trench stabilized with support fluid (bentonite or polymer slurry), then reinforced and concreted via a tremie pipe. Diaphragm walls serve as excavation enclosures, to support adjacent structures, as groundwater cutoff, or as permanent exterior walls of basements. Because of their low deformations and high watertightness, they are an alternative to sheet pile walls, bored pile walls, or injection cutoff walls.
Configuration and construction method of the diaphragm wall
Execution is carried out panel by panel: First, the trench is excavated to depth under support fluid using a grab or a cutter. A toe block or a sealing slab can be provided. Then reinforcement cages are lowered, and the trench is concreted while displacing the support fluid. The panels abut via joint profiles, waterstops, or tongue-and-groove geometries. After hardening, the wall head is exposed, aligned, and prepared for subsequent bracing (anchors, struts, floor diaphragms).
Structural characteristics: panels, joints, and wall head
Diaphragm walls consist of individual panels with typical thicknesses of 60–150 cm and lengths of 2–7 m. Joints serve watertightness and load transfer. Reinforcement cages are designed project-specifically, often with double mats and starter reinforcement for slabs or anchor heads. After removal of excess concrete (capping), the wall head receives its final elevation and geometry.
Support fluid and slurry management
The support fluid stabilizes the diaphragm wall excavations in the ground. Its density, viscosity, and sand content are monitored. Treatment and reuse are common for environmental and quality reasons.
Panel excavation with grab or cutter
Grabs are flexible in heterogeneous soils; cutters provide high dimensional accuracy at great depths and in cohesive strata. Obstructions in the subsoil are documented and selectively removed.
Concreting using the tremie method
Concreting proceeds continuously from bottom to top. Mix design and placement rate are matched to the support fluid and panel geometry. Sampling and fresh concrete properties secure quality.
Applications and construction phases
Diaphragm walls take on temporary and permanent functions:
- Excavation enclosure with anchors, struts, or slab bracing (top-down method).
- Groundwater cutoff as a sealing wall against hydraulic loads and uplift.
- Underpinning and stabilization of existing buildings.
- Tunnel construction in urban areas, e.g., as excavation walls for launch and reception shafts.
Especially in confined inner-city environments, low deformation is one of the strengths of the diaphragm wall. Later in the life cycle, openings are often created or wall sections removed—typically low-vibration and low-dust.
Design, deformations, and construction stages
Design accounts for earth and water pressures, traffic loads, construction stages, anchor forces, and settlements. Deformations are monitored by inclinometers, anchor tests, and settlement measurements. In deeper excavations, intermediate bracing or floor diaphragms are decisive for the serviceability of adjacent infrastructure.
Diaphragm wall in existing structures: openings, adaptations, and deconstruction
In special demolition and strip-out around diaphragm walls, controlled, low-vibration methods are required to protect structures and neighboring buildings. The following methods have proven effective:
- Concrete pulverizers: For controlled removal of wall heads, projections, and bearing edges. Nibbles layer by layer and limits cracking; particularly suitable for reinforced concrete with dense reinforcement.
- Rock and concrete splitters with rock splitting cylinders: After core drilling, they create defined separation joints within the wall cross-section. Advantage: very low vibration, well suited for concrete demolition and special demolition as well as special operations in sensitive areas.
- Steel shears or combination shears: For freeing reinforcement bundles in opening areas; often in combination with concrete pulverizers.
- Multi cutters: For cutting embedded parts, sections, and cross beams in the wall head area.
- mobile hydraulic power units: To supply concrete pulverizers, splitting cylinders, and shears—important for mobile, space-saving, and quiet operation on tight construction sites.
Typical use cases include breakthroughs for service routings, temporary relief openings, creating connecting passages, or partial deconstruction for change of use. In rock excavation and tunnel construction, rock and concrete splitters can also cleanly separate transitions between rock and diaphragm wall. Strip-out and cutting in the area of the diaphragm wall benefit from sequential steps with core drilling, splitting, and subsequent exposure of reinforcement.
Work sequence for deconstruction
- As-built assessment: wall build-up, reinforcement layout, joint locations, anchors, utilities.
- Preparation: define drilling grid; check load transfer and safeguards.
- Pre-cutting/core drilling: define separation joints; avoid stress redistributions.
- Splitting/nibbling: use rock and concrete splitters and concrete pulverizers; sectional removal.
- Cutting free the reinforcement: steel shears/combination shears; safe handling of bars.
- Removal and sorting: separate fractions; observe dust and noise protection.
Quality assurance and monitoring
Quality assurance includes records of panel excavation, measurements of the support fluid, concrete testing, rebar inspections, and documentation of joints. In operation and in existing conditions, watertightness checks, visual inspections, and measurements of deformations and anchor forces are common. During deconstruction, vibration monitoring and dust and noise measurement complement the monitoring.
Occupational safety, environment, and neighbor protection
When constructing and processing diaphragm walls, attention must be paid to low-dust and low-noise methods, safe load handling, and fall protection. Support fluids must be properly stored, treated, and disposed of. During deconstruction in existing structures, load-bearing capacities and safeguards must be checked in advance; the notes are general and do not replace project-specific planning or permits.
Distinction from alternatives
Compared with sheet pile walls, diaphragm walls offer higher stiffness and better watertightness with reduced vibration. Bored pile walls are flexible and modular but do not always achieve the same tightness. Injection and jetting methods (e.g., HDI) are suitable for sealing bases or cutoff bodies, but often complement the diaphragm wall rather than replace it. The choice of construction method is project-dependent and considers geology, groundwater, available space, and neighbor protection.
Typical challenges and practical solutions
- Inhomogeneous subsoil: Flexible choice of grab/cutter, trial panels, close monitoring.
- Tight inner-city locations: Top-down method, low vibration, low-dust deconstruction concept with concrete pulverizers and splitters.
- Tightness requirements: Careful joint detailing, controlled concreting, suitable waterstops.
- Conversions in existing structures: Sequential cut–split–nibble, structural safety measures, documented load redistribution plan.
Checklist for planning, execution, and deconstruction around diaphragm walls
- Capture boundary conditions: geology, groundwater, neighboring buildings, traffic.
- Choose the wall concept: thickness, depth, panel length, joint system, construction stages.
- Secure quality: support fluid, tremie concrete, reinforcement logistics, testing concept.
- Plan bracing: anchors, struts, floor diaphragms, monitoring.
- Work in existing structures: core drilling plan, split and nibble strategy, use of hydraulic power units, concrete pulverizers, and rock and concrete splitters by Darda GmbH.
- Environment and safety: dust/noise protection, vibrations, disposal, access concepts.