Machine substructure

The machine substructure forms the static and dynamic base of mobile and stationary work machines in demolition, tunnel construction and rock excavation, as well as in natural stone extraction. It carries loads, transfers forces into the subsoil and decisively influences structural stability, precision and efficiency – e.g., when using concrete demolition shear or hydraulic rock and concrete splitters. A properly engineered substructure reduces wear, minimizes vibrations and increases process reliability during deconstruction, interior demolition and special demolition. In practice, a balanced interaction of stiffness, damping and load distribution determines how reliably tools can perform at their design capacity.

Definition: What is meant by the machine substructure?

Machine substructure refers to the entire load-bearing substructure of a machine – from the undercarriage (crawler or wheeled undercarriage) via frame, slew ring bearing and supports to set-up and foundation measures. This also includes aids for load distribution such as bearing plates, sleepers or ground protection mats. The machine substructure mechanically connects the machine to the subsoil, absorbs operating and impact loads, limits overturning moments and ensures structural stability and tracking accuracy under changing ground and loading conditions. Its stiffness, mass distribution and connection details directly affect positioning accuracy and tool guidance.

Structure and components of the machine substructure

The configuration depends on machine type and operating environment. In concrete demolition and special demolition, carrier machines with crawler undercarriage dominate; for urban interior demolition, compact wheeled undercarriages are often used. In natural stone extraction and tunnel construction, robust crawler undercarriages with high ground clearance and large-area load distribution play to their strengths. Material quality of frames and cross members, weld integrity and bolt preloads are critical to maintain torsional stiffness under alternating loads.

Typical elements

• Undercarriage/running gear: crawler undercarriage (track rollers, carrier rollers, tracks, idlers, drive sprockets) or wheeled undercarriage (axles, tires, hubs, steering)
• Frame and cross members: transfer forces into the ground, increase torsional stiffness
• Slew ring and slew ring bearing: transmit slewing moments, influence precision under lateral loads from concrete demolition shear
• Supports/dozer blade: increase structural stability, reduce overturning moments, serve as additional load distribution
• Set-up aids: bearing plates, timber sleepers, steel spreader beams, ground protection mats
• Fastening and connection points: bolted joints, weld seams and bearing seats for reproducible force introduction

Load paths and moments

With high-force tools – such as concrete demolition shear, attachment shear or steel shear – the load paths run from the tool through boom and upper carriage into the slew ring and ultimately into the undercarriage. Lateral cutting and splitting forces generate overturning moments; the substructure must absorb these moments with sufficient structural stability without permitting excessive deformation or slippage. Dynamic amplification, torsional inputs and impact peaks require adequate safety factors, fatigue-resistant connections and controlled compliance for vibration attenuation.

Load-bearing capacity of the subsoil and load distribution

The best substructure loses effectiveness if the subsoil is insufficiently load-bearing. Load-bearing capacity, settlement behavior, moisture and frost condition determine the necessary measures for load distribution. In sensitive environments – such as on slab surfaces during special demolition – calculated surface load (kN/m²) and stability verification are essential. Where heterogeneous layers or voids are suspected, on-site probing and trial loading improve reliability of assumptions.

Assessment of the subsoil

• Geometry: slope, flatness, steps and edges
• Material: soil class, compaction, load-bearing capacity of slabs and intermediate floors
• Actions: moisture, frost, heat, vibrations
• Interfaces: coverings, insulation layers, weak bedding or fill thickness transitions

Measures

• Use ground protection mats and bearing plates to reduce surface pressure (bearing pressure)
• Support with wide pads, lower the dozer blade, adjust boom position
• Route planning, load limitation and step-by-step working to minimize settlements
• Bridge weak zones with continuous load-spreading layers and verify allowable deformation

Influence of the machine substructure on concrete demolition and special demolition

When using concrete demolition shear, the quality of separation improves significantly with a steady, tip-stable stance. A stiff substructure reduces pendulum movements, enables controlled cut lines and protects the slew ring bearing and boom bearings. Hydraulic wedge splitters benefit from stable positioning because splitting wedges introduce forces more rectilinearly and crack propagation can be controlled more precisely. Correct support geometry also shortens cycle times, as slewing corrections and re-cuts are reduced.

Practical recommendations

1. Perform lateral cutting operations close to the ground with the dozer blade lowered
2. Select boom geometry so that the center of gravity remains as far as possible within the track/tire gauge
3. On slab surfaces: verify allowable surface load (kN/m²), size load distribution mats
4. Organize material flow to avoid slewing on the steepest gradient
5. Engage swing brake during static cutting, and minimize unnecessary superstructure oscillation
6. Keep support points clean and free of debris to avoid local indentations

Machine substructure in rock excavation and tunnel construction

In tunnel construction, impact loads, vibrations and transverse forces arise from extraction tools, attachment shear and rock splitting cylinders. Crawler undercarriages with a large contact area and durable running gear increase traction on debris piles. A low build height of the undercarriage reduces overturning moments on cross slope. Additional bearing points and wedges are useful to compensate for uneven invert surfaces. Corrosion protection and sealed bearings extend service life in wet or abrasive conditions.

Vibrations and structure-borne noise

A massive, backlash-free substructure damps vibrations and protects attachments. The maintenance condition of track rollers and bushings influences the transmission of vibrations to the upper carriage, hydraulic components and operating personnel. Elastomer inserts, correctly preloaded bolts and matched pad hardness help decouple structure-borne noise and reduce fatigue.

Natural stone extraction: stability and precision

When splitting natural stone, reproducible crack paths are required. The more stable the substructure, the more controllably splitting forces can be introduced. The use of underlay material prevents the tracks from sinking into soft bedding – important for uniform split openings when using hydraulic wedge splitters. Where blocks are undercut, verify residual support width and use additional sleepers to maintain stable geometry.

Interior demolition and cutting in indoor areas

On intermediate slabs or in confined spaces, substructure and set-up must be planned with particular care. Compact wheeled undercarriages support short maneuvering paths but require adequate load distribution to comply with slab load-bearing capacities. For concrete demolition shear, cutting torch or steel shear, control of tipping edges at the perimeter of openings is critical. Edge protection, ramp gradients and turning radii should be coordinated so that no unintended load peaks occur at slab recesses or joints.

Power units and set-up of mobile units

mobile hydraulic power units for hydraulic wedge splitters or attachment shear require a tip-stable, level stance so that vibrations do not transmit into hoses and couplings. Rubberized standing surfaces reduce structure-borne noise and protect substrates. Organized hose routing along load-bearing paths reduces tripping and crushing hazard. Quick-release connections should be strain-relieved and positioned outside swing and travel paths.

Maintenance and inspection of the machine substructure

Regular inspections ensure function and service life. Play in slew ring bearings, worn track rollers or damaged tires impair precision and increase accident risks. A well-maintained substructure keeps the tools – whether concrete demolition shear, attachment shear or cutting torch – on the intended cut line and reduces energy losses. Documented torque checks, wear measurements and lubrication intervals form the basis for predictive maintenance.

Key inspection points

• Running gear components: track rollers, track/tire wear, tracking
• Slew ring: preload, lubrication, axial and radial play
• Supports: hydraulic tightness, support pads, cracks in the frame
• Bolted connections: tightening torques on load-bearing cross members
• Set-up accessories: condition of mats, sleepers and bearing plates
• Fasteners and bearing seats: check for fretting, ovalization and elongation of holes

Safety and organizational measures

Safety takes precedence. Stability verification, clear travel routes and coordinated lifting and cutting sequences are fundamental. Notes on legal requirements and standards may vary by region; it is advisable to consistently implement generally applicable protective measures such as barriers, load-bearing set-up areas, load distribution appropriate to bearing capacity and qualified personnel. Exclusion zones, signal protocols and emergency routes should be defined before work starts.

Work organization

• Ensure communication between operator and signaler
• Keep swing areas clear, mark tipping edges
• Monitor weather and subsoil changes, adapt measures
• Use standardized hand signals or radio, and assign clear responsibilities

Typical mistakes and how to avoid them

• Underestimated surface pressure (bearing pressure): leads to sinking and tipping tendency – countermeasure: mats and wider supports
• Lateral cutting loads without blade/support: increases slew ring bearing wear – countermeasure: support, adjust boom angle
• Wrong tire/track choice: insufficient traction – countermeasure: match tread and track width to the subsoil
• Insufficient maintenance: play in the substructure – countermeasure: regular inspection, lubrication, replace worn parts
• Uneven or contaminated support surfaces: local overstress – countermeasure: level and clean set-up points, use full-surface pads

Selection criteria for the right machine substructure

The choice between crawler and wheeled undercarriages, support concept and set-up accessories depends on application, tool use and subsoil. Under high transverse loads – e.g., when cutting with concrete demolition shear on massive structural elements – a wide crawler undercarriage with a low center of gravity shows its advantages. For rapid relocations in interior demolition, wheeled undercarriages with suitable load distribution are sensible. In special demolition tasks, the combination of traction, build height, support capability and transport logistics is decisive. Early involvement of structural verification and route planning improves availability and minimizes unplanned downtime.