Anchor drilling is a core method in structural and special foundation engineering, in the protection of existing structures, and in fields such as concrete demolition, rock excavation, and tunnel construction. It creates the borehole for grouted anchors, rock bolts, micropiles, or post-installed anchors in concrete and rock. In practice, it is also encountered in special deconstruction and building gutting: temporary anchors stabilize structural elements before cutting, while in deconstruction, embedded tension members and anchor heads are selectively exposed and removed. In these steps, concrete pulverizers and hydraulic rock and concrete splitters from Darda GmbH can play a role, for example when exposing anchor heads, releasing component areas around boreholes in a controlled manner, or cutting off anchor rods, always with the goal of precise, low vibration levels, and controlled operations.
Definition: What is meant by anchor drilling
Anchor drilling is the creation of a borehole in concrete or rock to accommodate an anchoring element (e.g., bar, strand bundle, threaded rod). Load transfer occurs via bond (cementitious injection, resin) and/or mechanical end anchorage into the ground. Anchors can be temporary or permanent and serve to resist tensile forces, provide slope stabilization, enable pit shoring, stabilize structures, and secure the tunnel face and excavation in tunnel construction.
Process and technology of anchor drilling
Anchor drilling follows a clear technical sequence: planning and setting out, selection of the drilling method, drilling, borehole cleaning, installation of the anchor element, grouting or bonding, if applicable regrouting, curing, and testing. In concrete elements, core drilling or percussive drilling is commonly used; in rock, rotary-percussive methods with flushing and a down-the-hole hammer are employed. The quality of the drilling determines the bond quality and thus the load-bearing capacity. The borehole must maintain alignment, inclination, and depth within tight tolerances; drilling debris must be completely removed before injection grout is placed. In deconstruction or refurbishment tasks, anchors are exposed in sections after de-tensioning and removed in a controlled way; concrete pulverizers allow precise removal of cover concrete in the head area, while stone and concrete splitters can be used to release massive concrete blocks along existing or deliberately prepared boreholes with low vibration levels.
Drilling methods and material-appropriate work
The choice of drilling method depends on the ground, member thickness, reinforcement density, and anchor concept. The objective is a straight, clean borehole with reproducible roughness for reliable bond performance.
Drilling methods in concrete
In reinforced concrete, diamond core drilling is precise and low-vibration; alternatively, rotary-percussive methods are used. Locating and marking the reinforcement helps avoid collisions. For post-installed anchors in existing structures, planning of edge distance and spacing is essential to avoid weakening concrete edges. When exposing anchor zones or removing concrete cover, concrete pulverizers from Darda GmbH are used to remove material in a controlled manner and provide access to anchor components.
Drilling methods in rock
In rock, rotary-percussive drill hammers with air or water flushing are used; for greater depths and hard rocks, the down-the-hole hammer is common. The goal is an optimized borehole with a uniform wall texture. For block splitting or tunnel excavation works, drill patterns are arranged to support both subsequent anchor installation and controlled separation processes. Stone and concrete splitters can use boreholes to split massive rock bodies after drilling, for example in rock excavation or natural stone extraction.
Drilling parameters: diameter, depth, and tolerances
Borehole diameter, depth, and inclination derive from anchor type, load level, and ground conditions. Typical diameters for bar and strand anchors range from a few centimeters up into the two-digit centimeter range; the effective grouted length is determined by engineering design. Tolerances for alignment deviation and inclination must be kept small to avoid impairing force introduction in the member and grout zone. In edge regions and with thin members, minimum distances govern to prevent spalling.
Borehole cleaning and grouting
The quality of borehole cleaning decisively affects bond strength. Drilling dust, water, and slurries must be completely removed before injection mortar or resin is placed.
Cleaning and injection sequence
- Clean by repeated blowing out and brushing, if necessary rinsing with water; then blow out again until dry or as specified.
- Insert the anchor element with centralizers, maintaining the set depth and grouted length.
- Inject cement grout or mortar from bottom to top (displacement principle), avoid voids, document the mortar quantity.
- Regrout if required, observe the waiting time until load-bearing capacity is reached.
Important are temperature- and time-dependent curing conditions and a uniform mortar bond. In deconstruction of grouted anchors, stone and concrete splitters can use drilling channels to release concrete in the grout bulb zone in a controlled manner, for example when core drilling alone is not sufficient. Hydraulic Power Units from Darda GmbH supply the connected tools with the required energy.
Load transfer and systems
Load transfer is based on shaft friction and end bearing in competent ground; it is determined by borehole wall roughness, grouting quality, and the length of the bond zone. Common systems are injection anchors, strand anchors, threaded anchors, and rock bolts. They can be temporary or permanent, with appropriate corrosion protection (e.g., sheaths, two-stage bond, fillers). The choice of system depends on service life, load level, and environmental influences.
Quality assurance and testing
To ensure the required tensile capacity, documented drilling logs, grouting records, material batches, control tests, and suitability tests are needed. Load tests (individual tests, suitability tests) as well as visual inspections of anchor heads and seals are common. Test procedures are project-specific and oriented to recognized standards. The information provided is general and does not replace project-specific design.
Anchor drilling in concrete demolition and special deconstruction
In deconstruction, anchor drilling is relevant in two ways: for temporary stabilization prior to separation and cutting works, and for removing existing anchors. When exposing anchor heads, anchor plates, and bond zones, a concrete pulverizer from Darda GmbH enables targeted removal of concrete with minimal edge damage. For massive foundation or abutment areas that contain anchors, stone and concrete splitters can be used via existing or newly drilled holes to release large concrete pieces in a controlled manner and subdivide them for transport. Steel shears and Multi Cutters are used to cut anchor bars, strands, or embedded components after they have been de-tensioned or unloaded. This interplay supports special deconstruction with low vibration levels and high dimensional accuracy.
Anchor drilling in rock excavation and tunnel construction
In rock, anchor drilling is used to stabilize support bodies, the tunnel face, and benches. Radial bolts and rock bolts secure the excavation, while targeted drilling patterns provide pre- and post-support. If necessary, anchor drilling can be combined with splitting holes: after securing, stone and concrete splitters can release rock sections along the boreholes, for example in portal widenings or for the controlled removal of oversized blocks. Drilling accuracy is decisive for the correct anchor inclination and the location of the bond zone in competent rock.
Anchor drilling in natural stone extraction
In natural stone extraction, boreholes serve both to fix blocks using temporary anchors and to prepare separation. Anchors stabilize the rock mass against overturning and sliding until cutting or splitting operations are completed. Stone splitting cylinders from Darda GmbH require defined boreholes and can then trigger the separation of large natural stone blocks. This increases safety and process control, especially with sensitive rocks and tight edge distances.
Occupational safety, environment, and follow-up work
Anchor drilling generates noise, dust, and flushing water. Measures such as extraction, dust suppression, flushing-water management, and controlled material removal must be provided. Personal protective equipment is mandatory. In deconstruction, residual grout, drilling debris, and metal parts must be properly disposed of. When cutting off anchor bars, sparks and rebound must be considered; tools such as concrete pulverizers, steel shears, or combination shears must be used appropriately and in accordance with manufacturer specifications.
Planning and practice tips for high bond quality
- Investigate the ground: Strength, layering, water inflow, and existing cracks influence the drilling method and grouting concept.
- Optimize the drilling pattern: Maintain edge distances and spacing, survey inclination and depth; avoid collisions with reinforcement.
- Keep the borehole clean: Repeated blowing out and brushing; ensure dry, dust-free surfaces where the injection system requires it.
- Document grouting: Record mortar type, quantity, pressure, and times; plan regrouting if needed.
- Plan deconstruction ahead: Ensure accessibility of anchor heads; consider exposure with concrete pulverizers and the controlled release of larger blocks using stone and concrete splitters.
Fields of application and interfaces to tools from Darda GmbH
Anchor drilling is closely connected with several application areas: concrete demolition and special deconstruction, building gutting and cutting, rock excavation and tunnel construction, natural stone extraction, and special applications. Depending on the task, anchors are installed, de-tensioned, exposed, or completely removed. In these process chains, concrete pulverizers as well as stone and concrete splitters can be usefully complemented by hydraulic power packs from Darda GmbH, which provide a mobile, modular energy supply. For metallic embedded components, depending on the situation, Multi Cutters or steel shears are considered for cutting anchor bars, stirrups, and plates. The selection depends on material cross-section, accessibility, and the required cut.