MOS Grondmechanica has a wide range of equipment for geotechnical drilling operations at its disposal, the drilling is done manually or mechanically. The desired drilling depth and ground formation are determining factors for the drilling method and the equipment used.
Geotechnical drillings (manually and mechanically) are executed in accordance with NEN-EN-ISO 22475-1, the classification of the soil is executed and presented in accordance with specific regulations, most often accommodated for Dutch circumstances. If so desired by the client, drillings are also possible in accordance with other regulations.
During geotechnical drilling operations, disturbed or undisturbed soil samples can be taken for research in our geotechnical laboratory.
Pneumatic drilling machines
Up to the level of the groundwater, the phreatic surface, drillings can be performed as (non-hollow stem) auger drilling, beneath the phreatic surface the drilling is done with a hollow stem pneumatic drill. When encountering rigid, connected layers or rubble beneath the phreatic surface, the auger is used when the pneumatic drilling is not successful.
During the drilling operation below the phreatic surface, water is added to ensure that the water level in the stem is either above or equal to that of the phreatic surface. Hereby, the inflow of groundwater at the bottom of the drill stem and that of the soil material from the bottom is prevented. Normally, drilling mud is not used; if necessary clean water is added.
This drilling method is registered in the MOS Grondmechanica quality system. Details of the drilling procedures are adapted based on experience and the encountered soil types during the work activities.
Geotechnical drillings with a short length can be performed manually. This is carried out with auger or soil drills that are screwed in manually; every 10cm a record is made of the soil composition. Drilling manually is a particularly suitable method for obtaining a good impression of the surface layers and the phreatic groundwater level. Depending on the soil type the drillings can be done down to a depth of 5m below ground level. In the case of very weak soil, manual drillings are possible to larger depths.
Manual drillings are also performed as a pre-drilling at various research locations (probes, pressure monitoring wells or mechanical drillings) where cables or pipes are present in the soil. These drillings are usually done up to a depth of 1.5 to 3.0 m below ground level.
Core drillings can be performed in rock formations and/or overburden clay (clay deposit layers that overlay bauxite), in soil which is stabilized with grout or cement or in grout-cement (deep) walls.