What is “Jack and Bore” trenchless technology and when should it be used on road construction projects?
Jack and Bore or “Horizontal Auger Boring” (“HAB”) is one of the oldest and most widely used trenchless technologies used for installing steel pipes and casings underground.Read more
HAB can be generally described as follows:
First, a starting point and end point for the pipe or casing are located. Next, a pit large enough to fit the HAB equipment is dug at the starting point (the “entrance pit,” “drive pit,” or “main shaft”), and a pit large enough to effectively work is dug at the end point (the “exit pit” or “reception pit”). Then, the HAB equipment is placed into the entrance pit. Next, a cutting head is attached to the lead auger and then inserted inside the front casing. The front casing is then loaded onto the equipment in the entrance pit.
Once the equipment is in place, the cutting head cuts through the soil causing the soil to fall into the casing onto the auger. The auger then draws the soil along its coils as it rotates. Once the soil reaches the entrance pit (now “spoil”), it can be removed manually, by a conveyor, or with other mechanical equipment. The jacking equipment is used to supply the force necessary to drive the casings through the ground while the cutting head is penetrating further along its course. Driving the casings while the auger is removing the soil helps prevent the soils from collapsing.
Because spoil is removed (rather than simply displaced) as it is bored, Jack and Bore may be a contractor’s best option when surface heave is a primary concern. HAB is well suited for medium stiff clays and silts all the way up to hard clays and some highly weathered shales. HAB is also well suited for medium to dense sands above the water table, and gravels with cobbles less than 4 in. in diameter.
Early engagement of a licensed attorney is recommended if changed conditions are encountered during the performance of HAB work.