Rotary drilling is another one of the drilling methods that DCE are experienced in supervising, both open hole and core drilling. This type of drilling is able to reach further depths than the standard window sampler rig, recovering metre long cores of superficials and bedrock. Drilling will normally be carried out by a minimum of a two-man crew using a rotary rig, core barrel and attendant downhole equipment, casings (where necessary) and a flushing medium, a diesel-powered rig will most likely be used. The core barrel would either be conventional or wireline type. The flushing medium will conventionally be water, compressed air, air/mist, foam, polymer mud or bentonite. Coring can be carried out from ground level or from the base of pre-bored hole. Where a pre-bored hole is to be used it should be of sufficient diameter to accommodate subsequent coring.
Double tube barrels of various configurations are available, the most commonly used conventional barrels being the H to S sizes, or similar from the metric T series, and wireline barrels being S size. The barrels are usually fitted with a semi rigid plastic liner (coreline) in which the core is withdrawn from the barrel and preserved prior to logging. Core bits would normally be of the tungsten carbide, diamond or poly-crystalline diamond type. The metre long cores recovered should be withdrawn from the barrel in the coreline and placed in core boxes, being logged on site by the lead DCE engineer.
The diameter and depth of core runs and the diameter and depth of all casings will be noted on the Rotary Drilling Journal along with depths at which water is encountered, strata descriptions (given the limitations imposed by using coreline), tests carried out and any other relevant information. On completion of drilling, the borehole will either be grouted up or a monitoring device installed. The boreholes will be properly reinstated so that no depression is left; a certain amount of mounding may be required to achieve this in the long term.