Groundwater level

The groundwater level is a key boundary parameter for work in concrete demolition, special demolition, rock excavation, tunnel construction, and natural stone extraction. It influences structural stability, pore water pressure, work logistics, dust and noise emissions, as well as the choice of demolition and separation methods. In particular, when using concrete pulverizers or stone and concrete splitters, the groundwater level determines the sequence of work steps, necessary groundwater lowering measures, and the technical design of hydraulic systems. Darda GmbH provides technical fundamentals so that planners and contractors can incorporate hydrological boundary conditions early in work preparation.

Definition: What is meant by groundwater level

The groundwater level (also groundwater table) denotes the elevation of the free groundwater surface in an aquifer relative to a reference point, typically the ground surface or a vertical datum. It varies in space and time and is influenced by precipitation, inflow, abstraction, and geological properties. Above the groundwater table lies the unsaturated zone; immediately above it there is often a capillary fringe. In confined (artesian) groundwater, the piezometric groundwater level can lie above the actual aquifer position. The groundwater level is measured via monitoring points (gauges, piezometers) as water level height or as hydraulic head.

Hydrological significance and seasonal fluctuations

The groundwater level fluctuates seasonally due to precipitation patterns, snowmelt, evapotranspiration, and flow regimes; in urban areas, drainage, surface sealing, and groundwater abstraction add to this. In dry periods the level drops, in wet seasons it often rises significantly. This dynamics affects cones of depression during groundwater lowering, the stability of the excavation pit, and the behavior of cracks and joints in concrete and rock. For deconstruction and demolition, time scheduling should therefore consider natural highs and lows to appropriately size the effort for groundwater lowering and the loading on equipment and tools.

Hydrological basics and influencing factors

The manifestation of the groundwater level results from inflow, storage, and discharge within a geological system. Structural and climatic factors are decisive:

• Geology and stratification: Permeable gravel/sand allows fast groundwater responses; cohesive soils buffer and often lead to perched water tables.
• Permeability (kf-value) and porosity: They control flow velocities, cones of depression, and discharge rates.
• Relief and receiving waters: Proximity to rivers/lakes couples the groundwater level to their stage.
• Anthropogenic influences: Groundwater abstraction, excavation pits, cut-off walls, injections, and drainage installations alter local pressure conditions.
• Fracture and fault zones in rock: They preferentially conduct water and favor directed inflows into tunnel faces and rock cuts.

Relevance for concrete demolition, rock excavation, and special demolition

The groundwater level directly affects structural stability and the mechanics of separation and splitting. Pore water pressure reduces effective stress in soil/rock, can generate uplift on foundation slabs, and promotes flushing and erosion processes. At the same time, water suppresses dust and can dampen vibrations. This has consequences for the deployment planning of concrete pulverizers, stone and concrete splitters, hydraulic splitters, and the interaction with the hydraulic power pack and cutting tools.

Effects on cutting and splitting technology

Wet concrete and saturated joints behave differently from dry components: cracks close less due to friction, tensile forces may distribute unevenly, and loose particles are washed out. When working with concrete pulverizers and concrete crushers for deconstruction, component support within the groundwater lowering area must be monitored closely to avoid uncontrolled fractures. With stone and concrete splitters, water-filled separation joints and joint water influence the required splitting pressure and the number of starting points.

Rock mechanics and hydraulic fractures

In fractured rock, groundwater can act like a hydrostatic cushion: it reduces effective contact pressure but also favors sudden block slip. Splitting wedges and hydraulic splitters (wedge) should then be used with stepped pressure to activate joints in a controlled manner. At tunnel headings, groundwater inflow must be investigated; targeted preliminary measures (drainage, injection) limit water pressure and facilitate low-splinter operations.

Planning of groundwater lowering and groundwater drawdown

Groundwater lowering comprises all measures that keep groundwater out of the work area or lower the level. Depending on subsoil and component geometry, options include open dewatering (collecting and pumping seepage water), filter wells, wellpoint systems (vacuum dewatering), cut-off walls, or injection sealing. The aim is sufficient reduction of pore water pressure and safe accessibility for demolition and cutting work.

Design principles

Pumping and drawdown capacities can be estimated using permeability (kf), thicknesses, well spacing, and the desired drawdown. Darcy’s law provides the technical framework for this. Important aspects are: hydraulic radius of influence, monitoring of the cone of depression, effects on adjacent structures, and avoiding settlements caused by excessively strong or rapid drawdown.

Environmental and legal aspects

Permits may be required for groundwater drawdown. In general, the protection of water bodies, proper discharge or infiltration of pumped water, potential impacts on neighboring wells, and the preservation of sensitive wet habitats must be considered. Specific requirements depend on the location and must be clarified with the competent authorities as part of the respective procedures.

Practical guidance for the use of concrete pulverizers and stone and concrete splitters at high groundwater level

In saturated environments, stability, visibility, gripping torque, and force transmission require special attention. Hydraulic power units for wet sites should be positioned protected against splash water and moisture. Moving components are prone to slipping; access routes and standing areas must be made slip-resistant.

• Concrete pulverizers: Dewater or support components beforehand to minimize uplift and undermining (erosion); adjust cutting and jaw sequence and avoid hot-starting the hydraulics when components are soaked.
• Stone and concrete splitters: Control joint water; with water-filled boreholes, press on carefully, increase pressure in steps, and place splitting points symmetrically.
• Hydraulic splitters and Multi Cutters: Divert inflowing water to ensure clear visibility and defined cutting joints.
• Steel shears and concrete pulverizers in reinforcement zones: Corrosion products and sediment can fill the cutting gap; regular flushing prevents blockages.
• Tank cutters in underground installations: Consider groundwater ingress, pump out cavities, and secure atmospheric conditions.
• Hydraulic power packs: Route hose runs so they do not lie in puddles; keep couplings dry and clean after contact with water.

Measurement, monitoring, and documentation of the groundwater level

A robust measurement concept increases execution safety. It combines preliminary investigation, regular measurements, and straightforward documentation. The goal is to detect trends, define thresholds, and adjust measures in time.

Measurement methods

• Open standpipes/observation wells: Direct reading of the water level, robust and simple.
• Piezometers/pressure probes: Continuous recording of pore water pressure, suitable for confined groundwater.
• Manual spot checks: Complementing sensor systems, e.g., prior to critical work steps.
• Monitoring networks: Multiple monitoring points to capture gradients and cones of depression.

Monitoring during operations

Ongoing control of water levels, discharge rates, turbidity, and settlement markers supports the adaptation of groundwater lowering. Changes in the groundwater level should be synchronized with the demolition sequence, for example before deploying concrete pulverizers on load-bearing components or before activating stone and concrete splitters in jointed rock.

Safety and structural stability in saturated zones

Water reduces the shear strength of soils and increases uplift on components. Accordingly, slope angles, shoring, and bearing pressure must be checked. Construction machinery requires load-bearing, non-softening subgrades; access routes must be secured against sinking.

• Uplift and base heave: Secure foundation slabs against floating, provide surcharge or preliminary drawdown.
• Slope stability: Flatter slopes or shoring; avoid erosion due to seepage water.
• Work routes: Plan slip resistance, pump sumps, and orderly water management.
• Hydraulic safety: Hose protection and leakage control; consider oil–water separation behavior.

Impact on typical application areas

The groundwater level affects all relevant fields of application, but with different focal points. The following sketches characteristic situations.

Concrete demolition and special demolition

Basements, foundation slabs, or underground parking decks are often in the groundwater. Before using concrete pulverizers, assess uplift forces on foundation slabs. Rebar exposure with steel shears is hampered by seepage water; flushing and orderly water routing improve visibility. Segmental deconstruction with stone and concrete splitters limits vibrations and reduces the risk of hydraulically induced crack propagation.

Building gutting and cutting

When separating foundation beams, diaphragm walls, or transfer beams, groundwater can rise through cracks. Cutting and gripping sequences must be planned so that component bearings are not undermined (erosion). In underground tanks, when using tank cutters, groundwater ingress must be controlled in advance to ensure controlled atmospheres.

Rock excavation and tunnel construction

Fractured rock with groundwater inflow requires a combination of pre-drainage, injection, and controlled splitting. Hydraulic splitters and stone and concrete splitters work particularly efficiently when pore water pressure is reduced. In tunnel construction, controlled inflows reduce erosion of fines and stabilize the tunnel face and sidewalls.

Natural stone extraction

In quarries, working floors often fill with ground and surface water. Organized sump management and temporary drawdown facilitate the parallel placement of multiple splitting points. Water in separation joints affects the quality of fracture surfaces; the sequence of initial cuts should be adjusted accordingly.

Special applications

In sensitive environments with constraints on noise, vibration, and emissions, the combination of groundwater lowering and low-splinter methods with concrete pulverizers or splitting technology can be advantageous. The increased coordination effort is offset by greater process reliability.

Material and tool care in moist or wet environments

Moisture promotes corrosion and affects the service life of seals and joints. Hydraulic power packs, hoses, and couplings must be kept clean and dried after water contact. The ingress of dirt and sediment into moving components of concrete pulverizers, steel shears, and Multi Cutters must be avoided; regular flushing and lubrication increase availability. Store tools dry and perform visual inspections for cracks, spalling, and proper seal seating.

Typical sources of error and how to avoid them

• Underestimated pore water pressure: Check the groundwater level before releasing loads and lower it if necessary.
• Insufficient water management: Seepage water must be captured and discharged in a targeted manner, otherwise scouring threatens.
• Lack of pump redundancy: Provide a backup pump and power supply, set up alarms.
• Overly steep slopes: Increase safety factors in saturated soils, install shoring early.
• Unfavorable splitting sequence: In wet joints, stage splitting energy, work symmetrically, and set intermediate safeguards.

Example workflows with varying groundwater level

1. Preliminary investigation: Check monitoring points, determine kf-values and geological stratification, document boundary conditions.
2. Measurement concept: Define thresholds for water level/pore water pressure, set intervals, clarify responsibilities.
3. Groundwater lowering: Select an appropriate method (open, filter wells, wellpoint, sealing), set up monitoring.
4. Demolition/splitting sequence: Coordinate the sequence with uplift, undermining, and visibility; schedule concrete pulverizers and stone and concrete splitters accordingly.
5. Control: Continuously observe water levels, discharge rates, settlements, and component movements and document them.
6. Decommissioning of groundwater lowering: Scale back step by step, observe after-effects, and restore the site.

Data quality and uncertainties

Groundwater is a dynamic system. Single measurements provide snapshots; only time series yield reliable trends. Measurement accuracy, location of monitoring points, filter lengths, and seasonal effects influence interpretation. Conservative sizing of groundwater lowering and robust execution practices increase process safety.