Under-reaming bits and ring bits are used for drilling through overburden and unconsolidated ground. Some systems are recoverable while others are permanent; there are various trade names and products on the market. They are all similar in that they use a steel ring welded on to the bottom of the casing. The down hole hammer and steel ring are locked together, and the hammer drives on the steel ring. Together, they drill a hole large enough to allow the casing to be pulled into the drilled hole. A rock socket can be drilled below an under-reamed pile. We have experience with every type, and choose them based on overburden type, rock type and cost.
Under-reamers are particularly useful in offshore applications. We have many hanging lead drill systems that can utilize various under reaming systems from 12” to 36”.