Window and Windowless Samplers
Percussive window or windowless sampling involves driving cylindrical steel tubes into the ground using a high frequency percussive hammer. Usually the hammer is driven by a hydraulic power pack, but electric and pneumatic hammers are also available to suit particular site conditions.
The drilling rig is normally track or crawler mounted and some of the rigs are small enough to be driven through a conventional sized door way. However, in areas where there is low-headroom or access limitations then hand held equipment is also available.
The sample tubes are either 1 or 2m long and have a broad slot, or window, cut down one side. The soil material passes into the sample tube as it is driven into the ground. Drill rods are used to drive the sample tubes to greater depths. On reaching the required depth, the sample tube and drill rods are withdrawn using a mechanical jack. After removal from the borehole, the soil is inspected and the strata logged and sampled from the window.
Soil samples can also be obtained using a tube combined with a liner to enable easy removal of the core from the sampler. The system can be used to rapidly penetrate to the depth at which the sample is to be taken, or to provide a continuous core. Where the ground is unstable, steel casing can be employed around the outside of the driven tubes.
Window and windowless sample tubes of various diameters are available (35 to 80mm) and selected according to the ground conditions. Tubes are normally selected in a sequence of reducing diameters to penetrate to depth.
The depth which can be achieved depends upon the soil type and the presence of obstructions. Depths of up to 10m can be achieved in certain soil types where the borehole remains open without support, but more typically investigation depths of between 3 and 5m are obtained.