We recently had a new experience in using a sonic drilling rig for our site investigation for the first time. We had previously drilled with a conventional cable percussion rig, but were unable to progress past 10m below ground level, due to bands of strong mudstone within the ground. A basement swimming pool and gym are being planned at the site, and so, deeper information was required to aid pile design.
Unlike the conventional cable percussion rig, which works by dropping heavy weights into the ground and effectively chiselling its way through; or the rotary rig, which works like a big drill, advancing with a rotary motion; the sonic rig advances using high frequency (150 Hz) oscillation of the drill string to advance through the ground.
This oscillation liquefies a very thin zone of soil around the drill string and so allows its progress with very little friction. This leads to a rapid rate of drilling (we completed 2 boreholes and 25m of drilling through banded Gault Clay mudstone and very stiff clay in the Oxfordshire/Cotwolds area, plus mobilisation on and off site in one easy day). Also as you can see from the photo above, a near 100% rate of very good quality sample is recovered that allows for better evaluation and testing of the soil, leading to a more robust structural/ geotechnical design.
Other added bonuses are, firstly, the cleanliness of the drilling method, when compared to rotary, which usually requires either water, foam or mist flush to lubricate, clean and cool the drill as it advances; and secondly, its safe operation, with all travelling and drilling operations being remote, it's robot arm and it's full caged working area.
If you have experienced difficult ground conditions or require a cost effective SI consultant to help with planning conditions or geotechnical design, why not drop us a line at firstname.lastname@example.org