Soil failure describes the failure of the ground under load. The topic is equally relevant to construction and deconstruction practice: when removing foundations, opening excavation pits, in tunnels, and during rock works. Those who deconstruct components with concrete demolition shears or release massive blocks with rock and concrete splitters influence load paths, groundwater flows, and the stability of temporary construction stages. Careful planning and a low-vibration approach help prevent ground failure and protect adjacent structures.
Definition: What is meant by soil failure
Soil failure refers to the bearing capacity failure of the subsoil due to excessive loading. The soil experiences shear failures and can no longer carry the load; the result is sudden settlements, sliding, or punching through the foundation base. This is distinct from hydraulic heave (base heave, uplift, piping): uplift forces and groundwater flows lift the base of the excavation or wash out fine-grained constituents. Both phenomena affect shallow foundations, excavation pits, shafts, and edge areas of deconstruction and demolition zones.
Forms of soil failure and typical triggers
In practice, different failure patterns often occur in combination: bearing capacity failure in shallow foundations, near-edge soil failure due to concentrated point loads (e.g., in front of excavation slopes), hydraulic heave with a lowered ground surface elevation or deep excavation base, as well as localized liquefaction under dynamic loading. Triggers include excessive base pressures, unfavorable groundwater conditions, inadequate ground improvement, and unplanned load redistributions during deconstruction.
Bearing capacity failure under slabs and foundations
When loads exceed the soil’s shear strength, slip surfaces form; cone- or wedge-shaped bulging follows, accompanied by abrupt settlements. During deconstruction, this can occur when load-bearing components are removed and remaining foundations concentrate loads into the ground.
Hydraulic heave in excavation pits
With sandy or soft soils and high groundwater levels there is a risk of base heave. Uplift and seepage flows overcome the self-weight of the base; consequences include heaving, water inflows, or piping. This also concerns shafts, channels, and deep utility trenches in the vicinity of deconstruction sites.
Near-edge loading from construction logistics
Heavy equipment, material storage, or demolition debris near slopes and sheet pile walls increase base pressure at the edge. Local soil failure can initiate along the excavation wall if stand-off distances are not observed.
Vibrations and low-vibration alternatives
Additional dynamic loading promotes soil loosening and pore water overpressure. Rock and concrete splitters as well as concrete demolition shears work with low vibration and reduce risk compared to percussive methods. This can be decisive in sensitive temporary conditions.
Relation to concrete demolition and special deconstruction
During selective deconstruction, load paths change step by step. When walls, beams, or columns are removed with concrete demolition shears, the point loads on remaining supports increase. In combination with soft or water-saturated subsoil, this can lead to soil failure. Planned sequencing of removal, temporary shoring, and controlled downsizing of large components reduce load peaks. Rock and concrete splitters enable targeted breaking of foundations or rock edges without introducing additional vibrations into the ground.
Example: Removing foundations with concrete demolition shears
When removing foundations, the width of the remaining bearing should be dimensioned so that no impermissibly high edge pressures arise. Section-by-section downsizing with concrete demolition shears limits block sizes and avoids concentrated point loads from large demolition pieces. Leaving load cores (kern zones) in place until the end of removal and early unloading of heavy superstructures reduces the risk of soil failure.
Rock demolition and tunneling: splitting instead of blasting
In rock, controlled crack initiation with rock and concrete splitters makes load redistribution manageable. In tunnel headings or when opening caverns, a stepwise, low-frequency approach reduces the risk of local loosened zones and decreases the influence on adjacent unconsolidated rock areas. Hydraulic power units provide the required energy without introducing impact-type loads into the ground.
Planning and design: factors influencing stability
Safety against soil failure depends on soil, geometry, groundwater, and construction stage. Key factors are:
- Soil parameters: shear strength, density, stiffness modulus, grain size distribution, plasticity
- Water conditions: groundwater level, pore water pressure, permeability, seepage lines
- Loads: self-weight, traffic loads, temporary site loads, dynamic components
- Geometry: foundation width, embedment depth, slope inclination, distance to excavation walls
- Construction phases: intermediate states during deconstruction, load rerouting, temporary stabilizations
Design should consider the most unfavorable temporary condition. Partial safety factors and verifications follow recognized engineering practice and applicable standards. The information given here is general and does not replace project-specific design.
Measures against hydraulic heave in excavation pits
Where deep pits or shafts lie within the groundwater, precautions are needed to control uplift and piping:
- Lowering the groundwater level where filter stability is sufficient
- Impermeable enclosures (e.g., tight wall-to-base connections) with sufficient embedment depth
- Counterweight through sufficiently thick, unexcavated soil layers or temporary base slabs
- Filter and drainage measures to prevent scour; controlled water discharge
- Staged excavation management and limiting the open base area
- Observational methods with defined trigger values (monitoring points, visual inspection)
When deconstructing massive basements and lower floors, check whether partial demolition increases uplift. Moderate sequencing and avoiding large, open base areas help prevent hydraulic heave.
Site indications and warning signs
Typical signs of incipient soil failure should be taken seriously and assessed immediately:
- Sudden settlements, edge breaks, heaving of the base
- Sheet-like cracks in the ground, shear fissures, turbidity plumes in the water
- Unexpected water inflows or sandy, boiling water (piping)
- Deformations of sheet pile walls, bulging, yielding of tie-back anchors
- Unusual noises indicating sliding movements
Visual inspections, simple settlement markers, and documented walkdowns before, during, and after critical work steps increase safety.
Instrumentation and monitoring
A tiered monitoring approach supports early detection of change:
- Settlement markers and leveling at foundations and excavation edges
- Piezometers to control pore water pressure
- Crack gauges on adjacent components
- Inclinometers or visual markers on shoring elements
In practice, a simple traffic-light scheme with clear trigger values is recommended. If anomalies occur, stabilize the temporary condition, reduce loads, and involve specialist designers.
Natural stone extraction and special applications
In quarries, local soil failures can also occur on benches where cover layers are softened or discontinuities carry water. Targeted pre-splitting with rock wedge splitters and orderly detachment of blocks prevent uncontrolled load redistribution. For equipment and temporary storage, provide load-bearing, drained work platforms with sufficient setback from edges.
Interfaces with other equipment in deconstruction
Depending on the material mix, combination shears, multi cutters, steel shears, or tank cutters are also used. The choice of tool influences load and vibration input. An orchestrated interplay with concrete demolition shears and rock and concrete splitters enables a stepwise, controlled approach that protects the ground and neighboring development.
Practical checklist for construction and deconstruction phases
- Preparation: investigate the ground, record water levels, identify critical temporary conditions, define load plans and removal sequences.
- Select work equipment: prioritize low-vibration methods; plan concrete demolition shears and splitting technology for controlled separation and reduced block sizes.
- Site logistics: maintain stand-off distances to slopes/shoring, drain work platforms, distribute material storage.
- Execution: proceed in sections, use temporary shoring, limit open base areas, control water management.
- Monitoring: observe settlements and water pressures, define thresholds, have measures ready for anomalies.
- Aftercare: secure the temporary condition, normalize water levels, compact or backfill areas, complete documentation.
Common mistakes and how to avoid them
Several recurring patterns can be prevented with simple rules:
- Underestimated construction phases: plan intermediate states, not only design the final condition.
- Edge loads: do not bring concentrated loads up to slope edges or shoring.
- Vibrations: avoid percussive methods where soil failure or piping risk exists.
- Water: detect unexpected inflows early and discharge them in a controlled manner.
- Communication: share observations promptly, define intervention criteria in advance.
Terminology: soil failure, slope failure, settlements
Soil failure means bearing capacity failure beneath a foundation or base. Slope failure describes the failure of an inclined ground surface (hillside, excavation slope). Settlements are initially deformations without failure; they can be precursors of soil failure, but do not have to be. In deconstruction, these phenomena often arise from the interaction of load changes, water conditions, and ground structure.