Geotechnical surveying investigations are not a one-size-fits-all approach. There will always be varying situations and environments which call for different approaches to the investigative process. Wide open spaces, for example, make available huge drilling rigs with an unparalleled capacity. More enclosed ones, however, tend to employ rigs with a smaller environmental footprint, but with a far more diminished capacity. The best of both? Window sampling.
Unsurprisingly, there are a number of rigs and methods which sit between both ends of the spectrum. None, however, quite match the effectiveness of a window sample investigation. To delve deeper into these geotechnical techniques, the team at Borehole Solutions have shared our guide to show what a window sample is, how it works, and when you should be using it.
What is Window Sampling?
This site investigation technique drives cylindrical rods and 50 – 80 mm sample tubes into the ground to form a borehole. A square window can be cut into the side of these one-meter-long tubes, giving the method it’s pertinent name. As they are driven deeper into the earth, soil enters the opening in the side of the tubes. Once the desired sampling depth has been reached, this is extracted using a manual or hydraulic jack.
In some instances, however, the cored sample may be required to be isolated. Should this be the case, a uPVC liner system can be used. This extracts the soil profile at the full one-meter length, compared to the smaller samples collected through window sampling’s opening.
When should you perform a Window Sample Investigation?
Window sampling is particularly suited for small scale site investigations, soil sampling, and areas with restricted site access. It is also ideal for cohesive formations and sands for geotechnical and chemical investigations, contaminant logging, and installing monitoring wells. Typically, this method utilises rigs such as the Dando Terrier and Archway Dart. These rigs can be mounted on rubber tracks to ensure high manoeuvrability. Furthermore, these rigs are able to provide a range of testing methods, including SPTs, U38s, and many more. This, in combination with the small and lightweight frames of these sampling rigs, makes window sample investigations ideal for environmentally sensitive situations where minimal disruption is of the utmost importance.
Benefits and Limitations
Surely, there has to be a reason why this geotechnical sampling process has quickly risen in popularity amongst drilling companies? Well, for a start, it is incredibly cost-effective. In addition, it’s also able to provide high-quality and almost entirely undisturbed samples with ease. What’s more, the rig is highly reliable and requires little maintenance – further adding to its minimised environmental impact.
Like all sampling methods, however, this highly popular technique does come with its drawbacks. In particular, it can only be used in shallow formations with a depth of up to 4.5 metres. Additionally, it’s also generally unsuitable for sampling or coring in harder formation and strata, for example. Nevertheless these limitations are still far outweighed by this practice’s overall capabilities. To find out more about window sampling, or any of the other site investigation techniques that we offer, contact the Borehole Solutions team on 01733 200 501 or click here to contact us directly.