Gas utilities have long sought less expensive, disruptive and time-consuming methods of installing mains and service lines. Typically, the installation of mains involves trenching. There is increased pressure to avoid trenching given the high value of the public way and even higher cost for its restoration. For gas utilities, there was a clear need for a simple, economical, trenchless tool that is easy to mobilize and operate and can be counted on to hit the target with regularity.

To address this problem, Foster-Miller has developed a steerable underground drill, or "Guided Mole." Foster-Miller's mole is a pneumatically operated impact tool incorporating existing percussion technologies with a novel steering mechanism that makes the system easy to operate and control. The innovative guidance system allows the tool to be launched from a pit or to enter the ground at a slant, then level off at the desired depth. It can be made to resurface or exit below grade in an excavation pit. Two significant breakthroughs have made the guidance system possible. First was the development of pitch and roll sensors and a transmitting beacon rugged enough to withstand the physical punishment of the piercing tool. This beacon location and sensor combination allows the operator to know the exact location and attitude of the tool at all times and the ability to monitor any corrections that are made to re-direct it back to the required course.

The other breakthrough involves the design and control of the patented steerable head that can be re-oriented relative to the centerline of the tool. To change direction, the operator can alter the shape of the head by manually rotating the pneumatic hose attached to the tool. The operator is able to achieve the desired course correction by aligning the asymmetric head to the correct tool face angle using the signals from the roll sensors for active feedback.

The Guided Mole offers several benefits over other small boring tools:

• Surface launch and retrieval is practical.
• It dramatically extends the usable range of piercing tools.
• It is simple to operate, requiring a two-man crew.
• It is a low-cost alternative to other types of trenchless technologies.

Units are commercially available from T.T. Technologies of Illinois.

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