- July 30, 2019
- Posted by: GRM Development Solutions
- Category: Service, Team
Dynamic sampling, more typically referred to window sampling (WS) is a ground investigation technique typically used to obtain soil samples from shallow to up to 5m depth, although depths of up to 15m can be achieved. The technique involves percussively driving a series of reducing diameter steel tubes into the ground, which are then hydraulically removed from the ground with the soil column retained in plastic liners, which are then split and logged by our in-house engineers who have followed our Geol Soc accredited training course.
The drilling rigs are transported to site either on a trailer or in the back of a long wheel-based van. The window samplers are mounted onto rubber tracks for ease of transport and in order to keep disturbance to a minimum, so are very useful on active sites where everything must be kept neat and tidy. The rigs can be driven through a standard domestic doorway and are ideally designed for use on sites where access is restricted, requiring a working area of only 3x5m. They can be driven up slopes and in some cases are designed so that they can be used in basements and other areas with low head room. They also come with a coring attachment so that holes on hardstanding can be undertaken easily. The table below provides some information about the dimensions of window sampling rigs.
Standard WS Rig Specification:
|Engine||Diesel 435cc single cylinder 9 HP.|
|Length (in transport mode)||2600 mm|
|Length (in sampling mode)||2800 mm|
|Closed track width||770 mm|
|Maximum track width||1080mm|
|Height (in transport mode)||1450 mm|
|Height (in sampling mode)||3100 mm|
|Average noise whilst idling||71.4dBA|
|Average noise during sampling||74.3dBA|
|Peak noise during sampling||94dBA|
In addition to allowing a description of the underlying geology and disturbed samples to be taken for geotechnical and environmental testing, modern WS rigs can also take in-situ SPTs (in accordance with BS EN ISO 22476-3) using either split spoons for cohesive soils or a cone for granular soils along with the ability to take 100mm undisturbed samples (U100) for geotechnical laboratory testing, such as undrained shear strength.
Once the holes are complete they can be with backfilled appropriately or installed with a gas or water monitoring standpipe to take additional environmental information which will feed into the risk assessment for the site.
A window sample crew will usually be able to complete around 30m of drilling per day. This typically equates to between 6 and 8 holes including geotechnical testing and the installation of gas/water wells, depending on how many holes need to cored, depth of the holes and strength of the soil.
To see a window sample rig in action, play the video below: