What Does Pipe Ramming Mean?
Pipe ramming is a trenchless method of pipeline installation that drives a casing or pipe through the ground using a percussive hammer. The hammer is attached to an open-ended casing, using an adapter and the percussive action of the hammer drives the casing into the ground. The spoil within the casing is removed when the casing is fully driven into place.
The pipe ramming method works on the principle of displacement and causes little to no ground slump making it ideal for places where ground loss is expected. It is preferred for installations under railroads, embankments, roads, and landscapes as it is cost-efficient, time-saving, and non-disruptive.
Pipe ramming can be used in a wide variety of soil conditions and can be used for horizontal, angled, or vertical installations. Sometimes, contractors use pipe ramming in conjunction with other trenchless methods such as when a pipe becomes stuck in a horizontal directional drilling (HDD) operation. In such cases, pipe ramming can be used to dislodge the pipe for the HDD process to continue.
However, pipe ramming lacks the precision of sonde-guided drilling or even microtunneling. It is faster than the pipe jacking method but matches the speed of auger boring or horizontal directional drilling operations. It is recommended to use steel casing pipe when using the trenchless method of pipe ramming.
Pipe ramming can also be used in harder soil conditions, but it is difficult and time-consuming. When used in the rocky ground it will require the use of a pneumatic tool to punch a pilot hole before the pipe can be rammed. However, since pipe ramming utilizes limited equipment it can be performed in places that are space-constrained and cannot support heavy equipment.
Trenchlesspedia Explains Pipe Ramming
Pipe ramming can be carried out at depths varying from 18 inches to 20 feet below the surface. For very shallow excavation ground surface monitoring above the line of installation is very crucial. The ramming process is not steerable and hence pipes installed using this method are laid in a straight line. This method works most efficiently above the water table in soft clay, organic deposits, silt, loose or dense sand, and cobbled soil with cobbles less than the pipe diameter.
The Design Phase
The design phase is very crucial in pipe ramming to avoid damage to other utilities by direct hit or vibration caused during the ramming process. Mapped data is used to determine the location of utilities passing through that area which may not be exhaustive and precise. It is advisable to use tolerance boxes, the size of which will depend on the accuracy with which the utility lines are identified. The route layout can then be planned from the tolerance boxes instead of the utility lines.
The Ramming Process
The leading edge of the first pipe has a welded band that protects the pipe and provides a slight overcut. The nominal designed overcut is between ¼ inch and 1½ inch to reduce friction between soil and pipe. The ramming tool rams the pipe into the soil using repetitive percussive blows till the pipe exits at the receiving pit.
For shorter pipe segments, the first segment is rammed in and the ramming tool is returned to its original position. The next segment is then welded or fitted onto the first segment already in the ground and the process is repeated. Compressed air powers the pneumatic hammer which rams the open-ended casing into the soil till it reaches the exit.
To lengthen the drive, additional pipe lengths can be welded onto the casing. For longer lengths, periodic cleaning is required to lessen the drag due to the weight of the soil accumulated in the pipe. Spoil is removed by using compressed air or water jets for smaller diameter pipes and by augers for larger diameter pipes.