Depending on the geotechnical surveying investigation, different situations call for different approaches. There are drilling rigs available that are huge in scale and their capability is unparalleled, but they have a sizeable footprint. On the other hand, there are drilling rigs with a smaller footprint, but have diminished capability as a result.
Not surprisingly, there are also a range of rigs and methods that sit somewhere in between this spectrum. Window sampling is one such drilling technique. A window sample ground investigation provides an effective drilling solution with minimal disturbance to the environment when compared to its larger counterparts.
Our team at Borehole Solutions have made this blog to explore further into window sampling; what it is, how it works and when to use it.
What is Window Sampling?
This methodology involves using a hydraulic drop-hammer (a pneumatic hammer may be used if the sampling is being carried out in a handheld manner) to insert cylindrical rods and sample tubes (between 50 to 80 mm in diameter and around one metre in length) down into the ground, creating a borehole. The sample tube has a square cut on its side which resembles the shape of a window, hence the name of this method.
As the sample tube and rods are driven into the ground, the soil enters the opening in the sample tube. The inserted rods and sample tube are extracted using a manual or hydraulic jack once the sampling depth has been reached. It is important to take care with less consolidated formations to prevent borehole collapse by installing casings. Some instances require the cored sample to be isolated – a uPVC liner system is used to extract the soil profile at the full one metre length, as opposed to the smaller soil samples collected through the window of the sample tube using the window sampling method.
When to Use Window Sampling?
This technique is ideal for smaller scale site investigations and soil sampling. It tends to be used for cohesive formations and sands for geotechnical and chemical investigations. Window sampling can also be used for contaminant logging and the installation of monitoring wells (both water and gas). Generally, the method utilises rigs such as the Dando Terrier and the Archway Dart, which can provide a range of testing; from SPTs to U38s and many more.
The sampler is usually mounted onto rubber tracks; hence it is highly manoeuvrable. When combined with the relatively small frames of the rigs (tending to weigh in at 150 – 200 kg), it makes for a rig that is ideal for environmentally sensitive situations where minimal disruption is necessary.
There is a reason, after all, why this technique has become so popular amongst geotechnical drilling contractors. Some of the reasons include:
- The collection of high-quality and almost undisturbed samples.
- The cost-effectiveness of the method.
- It is very reliable.
- The rig requires very little maintenance.
Despite certainly being a popular sampling method, like anything, there are situations where window sampling may not be the best choice. For example, the method is not designed for coring into harder formations and strata. Another limitation is that it requires two people to operate, although in reality this does not tend to be an issue for larger drilling companies. The other downside is that the method can only be used for shallow formations, with a maximum depth of up to 4.5 metres.
Window sampling provides a cost-effective solution for smaller scale geotechnical investigations and those projects where an environmentally conscious approach is required. The rigs are highly manoeuvrable and cause minimal disruption to the land, whilst providing top-quality samples. Contact our friendly team today to find out more about our window sampling services at Borehole Solutions!
Contact our team today on 01733 200 501.