Those unfamiliar with stitch-boring may find the term slightly misleading. The use of a HammerHead Mole, fundamental to Miller Pipeline’s stitch-boring, does not remove material as a true boring technique does, such as auguring or horizontal drilling. It displaces material, compressing it to the sides as the mole progresses. Sometimes referred to by installation crews with nicknames such as ‘gopher’ and ‘missile,’ the mole model used by Mr Oxenrider’s crews is a 4 ft long self-advancing pneumatic piercing tool that operates on 35 cfm of compressed air at 110 psi.
Utilities installation contractors usually select a mole to accommodate the lines they are installing in diameters ranging from 2 to 5.75 inches. HammerHead trenchless equipment offers 24 mole models in this range to maximise production in the customer’s ground conditions. All of Mr Oxenrider’s three-man stitch-boring crews on this contract carry a 3 inch diameter mole to create bores for 2 inch high-density polyethylene (HDPE) gas line. After making a shot, the line is pushed through the bore by hand or attached to the mole’s air hose and pulled through. In the toughest conditions it will be attached directly to the mole and shot back through the bore.
One of the typical jobs in Hershey involved shooting six bores for two side-by-side residences from the main distribution line in the street. The crew sent its 3 inch Active Head Mole in a series of 30 ft shots from a launch access in the street to a target pit at the houses.
They began by cutting a 3-by-5-ft opening where the utilities company had marked water and electrical locations in the street. Physically verifying utilities not only eliminates the risk of disturbing other services but also gives the crews an entry pit to use that does not impact the property. Once utilities were located, the crew determined the placement and depth for launching the mole.
The six shots were completed and the lines set in place for both houses in a single eight-hour shift.