Pipe reaming can often be used instead of pipe-bursting. A new HDPE or PVC pipe is pulled in behind the reamer. The pipe pieces are flushed out the bore hole with the drilling fluid. A reamer is pulled through the existing pipe, which cuts the pipe into small pieces. To compensate for potential magnetic interference that might distort magnetic readings in downhole systems, an artificial electro-magnetic grid is created at the surface using what is called a Tru-TrakerTM system.Ī variation of directional boring called pipe reaming can be used to replace existing clay, asbestos cement, non-reinforced concrete and PVC pipe. Gaining in popularity are newer downhole wireless systems such as the Polaris EM System, which transmits the data through the ground by an electro-magnetic signal to a stationary receiver. At the surface, the data from the wire is decoded by a computer to provide depth, angle, rotation, direction, and other information. The most commonly used type of downhole system is called a "wire-line" and uses a wire to transmit the data up the inside of the drill pipe. When conditions do not allow a receiver to be positioned over the sonde or interference causes degradation of the signal, a "downhole system" is used. At the surface, a receiver is manually positioned over the sonde and the signal decoded and steering directions relayed to the operator of the bore machine. The information is then encoded into an electro-magnetic signal, which is transmitted through the ground to the surface. A sonde, or transmitter, behind the bore head registers angle, rotation, direction, and temperature data. The most commonly used equipment for determining the location of the bore head is called a "walk-over" locating system. Most machines are track or trailer mounted, with a few smaller machines designed to be used in pits. Sizes range from small machines with a few thousands pounds of thrust and pullback to the largest with over a million pounds of pullback force. Once the pipe is installed, the exit and entry points are excavated, if necessary, and connections made as needed.ĭirectional bore machines are rated by thrust and pullback force and rotary pressure. This type of installation is known as "drill and leave." The swivel prevents rotation of the product pipe.įor some telecommunications or power cable projects, the drill pipe itself becomes the conduit and is left in the ground upon reaching the exit point. Drilling fluid is pumped downhole to provide lubrication, and the product pipe is pulled in while rotating the drill pipe and reamer. When the bore hole is at least 25% larger than the pipe to be installed, the end of the drill pipe is connected to a reamer attached to a swivel connected to the product pipe. Drill pipe is added behind the reamer or hole opener so that there is always drill pipe in the bore hole. The reamer is pulled back while rotating the drill pipe to enlarge the bore hole, with as many consecutive passes as required. Upon reaching the exit point, the bit is detached and the end of the drill pipe is attached to a reamer or hole opener (for rock), if the bore hole must be enlarged. Some systems use a dual pipe exclusively. In cases where the ground is unstable, a washover pipe, or casing, can be pushed down the bore hole to prevent the collapse of the hole walls. Steerage is accomplished by aligning the angle of the mud motor to the desired direction. In rock, a mud motor, which converts the hydraulic pressure of the drilling fluid into mechanical rotation, is used to rotate the bit and the drill pipe is not continuously rotated. The directed jet of the drilling fluid and forward thrust cuts a new path. To steer, rotation is stopped, the angle of the bit is aligned to the desired direction, and forward thrust is applied. In softer soils, an angled bit is used and the pipe string is rotated, if necessary, to bore straight. Drilling fluid is classified as non-toxic and can be disposed of accordingly. As fluid is pumped down the hole, the cuttings are carried back out to the surface, where they are either allowed to settle out in a pit or removed mechanically in a cleaning system. In softer soils, the high-pressure jet of fluid cuts through the soil, with the cuttings suspended in the fluid. Drilling fluid is generally a mixture of bentonite clay and water, with additives used to improve performance. Most directional boring machines use drilling fluid (mud), with a few machines designed to use air or air and foam. As each joint of drill pipe is pushed into the ground, a new one is added behind. The process begins when a directional bore machine pushes a bore head connected to hollow pipe into the ground at an angle.
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