Rotary Drilling

What Is Rotary Drilling?

Rotary drilling is used to collect soil and rock strata samples, or to form deep observation boreholes as part of Geotechnical and Environmental ground investigations. This is a fast drilling technique used where penetration is required through very dense soils and rock to investigate the sub-surface conditions of a development site. Rotary drilling advances a borehole using impact energy plus rotation.

The drilling rigs can be track or lorry mounted depending on access and the area of the site investigation. The drilling rigs use high levels of torque and rotation to enable the penetration of very dense soil and rock strata. The drill has a rotary cutting head at the end of the drill shaft, which rotates rapidly (50 and 120 rpm) and advances through the ground.

The dual speed and high frequency of rotations mean that this form of drilling can carve through hard rock easily, and softer ground. The rapid rotating cutting heads require cooling down so are lubricated with air, water, or drilling mud, as appropriate. The results of rotary drilling can be used to provide interpretive reports for Geotechnical and Geo-Environmental Ground Investigations for a wide range of services including:

• Foundation Designs
• Piled Foundation Solutions
• Basement and Retaining Wall Design
• Piling Mat Design
• Mine workings

Earth Environmental & Geotechnical Ltd. provides a full range of drilling services throughout the UK for Geotechnical and Geo-Environmental Site Investigations.

What Are the Different Types of Rotary Drilling?

There are two main types of rotary drilling, Rotary core drilling, and Rotary open-hole drilling.

Rotary Core Drilling

Rotary core drilling is used when core samples of rock are required to investigate the structural details and composition of the underlying rock. Rotary Core Drilling is frequently used when a development site may need deep foundations or heavy loadings. The core is brought to the surface for further analysis within the inner barrel using a wire rope or attached line to a recovery tool. The rock cores are carefully extracted, photographed, and stored in wooden core boxes.

The cores are then logged by our experienced geo-environmental engineers in accordance with the relevant British and European standards (BS EN ISO 14688-1 and BS EN ISO 14689-1 )
The samples taken from rotary drilling may be tested on-site or sent for laboratory testing e.g.

• Unconfined Compression Test -UCS Tests

• Point Load Tests

• Standard Penetration tests (SPT)

Rotary Open-Hole Drilling

Rotary open-hole drilling is used when rapid progress is required on projects such as mining investigations. Rotary open-hole drilling is appropriate when the structural details of the rock are not necessarily required, but the presence of voids and depth of rock is required. Rotary open-hole drilling is often used for investigating shallow mine workings etc.

Often gas and groundwater monitoring pipes are installed in the borehole to allow later measurements and monitoring especially if drilling through old mine areas

Rotary Open Hole drilling is an ideal Site Investigation drilling method for :

• Site Investigations for Mineworkings (coal seams, mine shafts, etc.)
• Site Investigations for Underground Cavities and Chalk Dissolution Features
• Site Investigations to locate specific sampling depth in rock
• Site Investigations for Installation for Gas Monitoring and Groundwater Monitoring in rock