The lower ground level is a height-related technical term from surveying, construction execution, and deconstruction. It defines the lower, relevant boundary of the terrain profile in a given area. It is central for planning, safe excavation pits, concrete demolition and deconstruction, and gentle rock removal. In many projects it influences the choice of methods and tools – for example in selective demolition with concrete demolition shear or in low-vibration separation with rock and concrete splitters – and provides a binding reference for measures in concrete demolition and special demolition, in building gutting and cutting, in rock excavation and tunnel construction, in natural stone extraction, as well as in special applications.
Definition: What is meant by lower ground level
The lower ground level (often abbreviated “LGL”) is the lower, decisive boundary line of the terrain profile in a section or plan. It serves as a vertical reference elevation to clearly define the position of excavation pit bottoms, undersides of foundations, toes of slopes, alignments, pipe inverts, or removal limits. In contrast, the ground level (finished grade) is the upper boundary of the terrain surface. lower ground level can refer to the existing condition (as-is) or to a planned target condition, for example after removal or after a temporary relocation of soil.
Technical classification and delineation
The lower ground level is not a component edge but a topographic reference line. It differs from “underside of foundation,” “underside of slab,” or “underside of base,” which are defined as component edges. In drawings, the lower ground level is specified as an elevation value, usually referenced to an official vertical datum or to a project-specific zero level. Precise definition avoids misunderstandings regarding excavation quantities, slope angles, and safety verifications. In construction practice, the lower ground level is often used for planning working spaces, for installing drainage, and for selecting low-vibration removal techniques.
Determination and surveying of the lower ground level
Determination is carried out by surveying the terrain geometry and deriving the lower relevant profile edge. Deviating from the purely minimal value over an area, the lower ground level is professionally interpreted in construction as describing the planned or existing lower contour of usable or stable terrain. Accuracy and reproducibility are crucial, as multiple trades are coordinated.
Existing survey and measurement methodology
For existing conditions, leveling, total station surveying, and GNSS are used. In complex situations – such as at break edges, in rocky terrain, or in shored excavation pits – laser scans and profiling at short station intervals provide a reliable terrain profile. Traceable documentation of benchmarks, instrument accuracy, and chosen reference elevations is important.
Planning: target definition and tolerances
The target lower ground level is derived from design profiles, earthwork plans, and safety verifications. Tolerances consider workability, settlements, and protective clearances, e.g., to the groundwater table. For demolition and separation work, a conservative tolerance strategy is recommended to stabilize slopes and avoid conflicts with utilities.
Influence on method and equipment selection in deconstruction
The position of the lower ground level controls accessibility, stability, and the permissible energy input. Steep slopes or deep lower ground levels require low-vibration, precise methods. Here, concrete demolition shears and low vibration rock and concrete splitters play to their strengths, because they separate selectively, generate low vibrations, and allow controlled removal steps.
Selective demolition with concrete demolition shears
Concrete demolition shears enable controlled removal of components in layers without destabilizing the slope at the lower ground level. They reduce demolition forces to what is necessary and improve separation precision at structural edges, for example at base slabs, bearing edges, or foundation heads near sensitive slope toes.
Non-explosive separation methods with rock and concrete splitters
Rock and concrete splitters generate defined splitting forces in the borehole and minimize vibrations in the ground. This protects the toe of the slope, reduces crack risks in the remaining structure, and lowers the danger of soil loosening in the area of the lower ground level. These properties are particularly relevant in concrete demolition and special demolition, in rock excavation and tunnel construction, as well as in natural stone extraction.
Additional tools in the context of the lower ground level
- Hydraulic power units provide constant pressure for concrete shears and splitting systems, enabling reproducible removal steps along sensitive terrain edges.
- Combination shears and multi-cutters support separation of reinforcement and attachments without introducing additional vibration into the slope toe.
- Steel shears and tank cutters are used for steel structures, tanks, or pipelines near the lower ground level when precise cuts are required and ground movements must be avoided.
Relation to typical areas of use
The lower ground level is a unifying parameter across several practical fields. It helps manage risks, plan material flows, and select the appropriate separation technique.
Concrete demolition and special demolition
In underpinning, foundation exposure, or partial removals, the lower ground level defines the permissible excavation depth and the location of working spaces. Concrete demolition shears allow layer-by-layer removal above the lower ground level, while rock and concrete splitters detach members without significant vibrations.
Building gutting and cutting
Even inside buildings, the lower ground level plays a role, for example when base slabs, basement slabs, or deeper floor build-ups are processed. The exact elevation prevents damage to adjacent utilities and minimizes settlement risks.
Rock excavation and tunnel construction
In rock removal, the lower ground level describes the controlled toe of removal. Non-explosive splitting limits vibrations and protects structures, utility lines, or slope toes. In tunnel heading and shaft structures, a clear lower ground level definition is decisive for cast-in-place foundation slabs and excavation pit safety.
Natural stone extraction
The lower ground level marks the toe of the extraction face. Rock and concrete splitters allow opening of separation joints along the planned lower ground level, which can positively influence block quality and yield without additional blasting vibrations.
Special applications
In spatially confined locations, such as inner cities or sensitive infrastructures, the lower ground level limits impacts on adjacent buildings. Equipment selection and sequence – for example first separating with concrete demolition shears, then targeted splitting – are aligned with it.
Stability, water balance, and environmental aspects
The lower ground level influences slope stability, water runoff, and the interaction with groundwater. These factors should be considered already during work preparation.
Slopes and slope toes
The lower ground level position determines the effective slope height. Low additional vibrations, for example through splitters instead of percussive methods, reduce the risk of slope failure. Temporary shoring is adapted to the lower ground level.
Groundwater and drainage
As the lower ground level approaches the groundwater level, dewatering and filter layers must be planned. Precise separation methods avoid unnecessary low points that collect water and facilitate backfill planning.
Vibrations, noise, dust
Loads and sensitivities accumulate in the area of the lower ground level. Methods with low vibration and dust emissions – such as controlled shearing or splitting – contribute to emission reduction.
Planning, documentation, and quality assurance
Careful planning and verifications regarding the lower ground level secure schedule, costs, and occupational safety. A continuous data path prevents deviations between design, execution, and billing.
- Set references: Choose a height reference system and define control points.
- Measure: Capture existing conditions, profiles, and break edges.
- Target definition: Clearly dimension the lower ground level in plans and specify tolerances.
- Reconcile: Check construction progress against the target and document deviations.
- Monitor: For sensitive slopes, observe deformations and groundwater levels.
Typical mistakes and how to avoid them
- Unclear reference elevations: Always include the zero level used and name it in the plans.
- Profiles too coarse: Plan sufficient measurement density at break edges and along slope lines.
- Underestimated vibrations: Evaluate methods with lower energy input, e.g., concrete demolition shears or splitters, at an early stage.
- Missing dewatering: Compare the lower ground level against the groundwater level and plan drainage.
- Uncoordinated equipment logistics: Plan access along the lower ground level so that slopes are not adversely loaded.
Practical examples: application of the lower ground level
When deconstructing a foundation slab on a slope, the lower ground level is defined as the slope toe. First, concrete demolition shears cut the slab into panels; subsequently, rock and concrete splitters release the remaining bodies with low vibration so as not to destabilize the slope toe. In a second project, the lower ground level marks the target depth of an excavation bottom above utilities. Removal takes place in layers, hydraulic power packs supply shears and cutters for precise cuts at edges and bearing points.
General notes on standards and organization
Planning and execution rules for surveying, earthworks, structural stability, and occupational safety must be taken into account. Requirements can vary by region and project. It is advisable to coordinate requirements for measurement accuracy, tolerances, dewatering, and documentation at an early stage and to align the equipment strategy – such as the use of concrete demolition shears or rock and concrete splitters – with the conditions of the lower ground level. Legal aspects must be checked on a project-specific basis.