Academy / Undisturbed samples
Obtaining high-quality undisturbed samples is one of the biggest challenges faced in the field of geotechnology. Poor quality samples may result in non-representative results being obtained in lab tests, the use of which may give rise to faulty designs.
Igeotest has developed a methodology for the extraction of undisturbed samples, as well as a specific device which offers a new perspective of an activity hitherto ill-considered in our country notwithstanding its vital importance when undertaking a geotechnical characterisation campaign.
The choice of sampling equipment, in terms of both the project needs and the type of soil, is key to obtaining high quality, representative samples.
The following table shows the sampling techniques available and the recommended applications for each, together with their advantages and disadvantages:
|Open drive||Thick wall||Cohesive soft to firm soils; Granular soils without gravel||Low cost
Easy to use
|High level of ground disturbance||L=600
|Thin wall Shelby (ASTM D 1587-74)||Cohesive soft to firm soils||Low cost
Easy to use
Boca corte Fácilmente deteriorable
|Fixed piston||FIXED (Osterberg)||Very soft to soft soils||Sample quality||Hard to use
link with Beguemann further down
|Very soft to soft soils||Very high sample quality
length of samples up to 19 m
Perforation by pressure
Hard to use
The bore diameter should be adjusted according to the needs of each specific project. The following values may be used as guides for deciding bore diameter.
|Percussion||Hard to perforate gravels and bolos|
Registration of perforation parameters
|Wire line||Surveys of great depth (>100 m)|
After extraction, a correct and careful procedure must be followed to preserve sample integrity. The following is a list of minimum precautions which should be observed: