The percussive window or windowless sampling method involves driving cylindrical steel tubes into the ground using a high frequency percussive hammer driven by a hydraulic power pack. The drilling rig is track mounted and small enough to be driven through a conventional sized door way. In areas where there is low-headroom or access limitations then hand held equipment can be used.
With the windowless sampler we can undertake Standard Penetration Tests (SPTs) at any specified depths, we can work indoors venting the exhaust and we can install gas/groundwater monitoring equipment with a stopcock cover.
The sample tubes are usually 1m long and have a broad slot, or window, cut down one side. The soil is pushed 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 On reaching the required depth, the sample tube and drill rods are withdrawn using a mechanical jack.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, the soil core is logged and sampled from the window.
Soil samples can also be obtained using a tube combined with a plastic 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 installed around the outside of the driven tubes.
Window and windowless sample tubes of various diameters are available (0.048 to 0.116m) and selected according to the ground conditions. Tubes are selected in a sequence of reducing diameters.
The depth which can be achieved depends upon the soil type and the presence of obstructions. Depths of up to 12m 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.
The holes can be reinstated with concrete, blacktop or a stopcock cover if an installation is required.