Pipe ramming is a trenchless technology used to install underground piping without digging a continuous trench. Pipes are struck by a ramming tool energized by a pneumatic system with consecutive blows, which force the open end of the pipe deeper into the soil. The spoil that fills the pipe as it moves through the terrain is removed through the action of an auger, compressed air or water jetting.
A cutting shoe is attached to the front edge of the pipe in order to penetrate the soil and direct the cuttings into the pipe. Pipes may also be lubricated in order to reduce friction as it progresses through the soil.
This trenchless technique ensures that the installed pipe is stable in the ground as there is very little disturbance to the structure of the surrounding soil. It is thus suitable for use where there are difficult soil conditions, underneath rivers or infrastructure like rail roads etc.
Pipe ramming has been combined with horizontal directional drilling (HDD) techniques to assist the normal HDD operation in specific circumstances.
Conductor Barrel or Washover Casing Method
Conductor barrel is a trenchless technique where pipe ramming is used to install a pipe casing through difficult soil conditions. When desirable soil conditions are reached, HDD techniques can then be used to complete the project.
The conductor barrel is rammed into the ground at a predetermined angle in order to reach the desirable soil conditions. Typical applications for this process are where a pipe is being installed underneath a riverbed. Pipe ramming is used to get through the loose soil of the riverbank until the dense soil underneath the riverbed is reached. An added advantage is that the conductor barrel can be used as a frictionless section during pullback.
Conductor barrels can be installed at the entry and exit points of the installation, thus dealing with problematic soil conditions on both sides of a riverbed, for example.
During an HDD pipe installation, 3 steps are required:
- Pilot bore – drilling a small bore along the pipe route
- Pre-ream – enlarging the bore to facilitate installation of the piping
- Pullback – the process of pulling the piping back through the bore created by HDD
Hydrolock or pipe jamming can happen during pullback due to the soil conditions, the pressure of groundwater or drilling fluid pressure. These pressures cause the pipe to get stuck in the soil, or to be exposed to tensile stresses beyond its design conditions.
Pullback assist is accomplished by attaching a pneumatic pipe rammer to the product pipe during pullback. The constant percussive strikes on the rammer keep the pipe moving through the soil and help to break the hydrolock and free the pipe when jammed.
An added advantage of pullback assist through pipe ramming is that the stress exerted on the drill rig to install the product pipe in the bore is reduced, resulting in less maintenance and longer life of the drill rig itself.
There are 3 main connection methods from the pipe rammer to the product pipe. The first method involves the installation of a steel sleeve, which is attached to the rammer by collets. The second involves the connection of the rammer to a casing via collets. The casing is then connected to an high-density polyethylene (HDPE) pipe through a flange compression kit. The third method involves the attachment of the rammer to the casing with collets and then the bolting of the casing to the HDPE pipe via side holes in the pipe.
Bore salvage is the operation to remove the partially installed product pipe, which has become stuck in the bore so that the process can be started again. The pipe rammer is attached to the end of the pipe so that the percussive blows will have the effect of loosening the pipe in the soil. A winch, or any other kind of pulling device, is attached to the rammer to pull the pipe from the ground as the rammer strikes its blows. The pulling of the pipe can also be done through a fabricated sleeve to reduce the effects of friction.
HDD Drill Rod Recovery
If a drill rod has become jammed in the ground during horizontal directional drilling, a pipe rammer can be used to loosen the rod and recover it to the surface. A predesigned and fabricated adapter is attached to the pipe rammer and then welded to the drill rod. The percussive force loosens the drill rod in the soil. If the drill rod is still attached to the drill rig, the rig is used to pull the rod out of the soil.
Removal of Abandoned Pipe
The bore salvage technique has also been adapted to remove abandoned or damaged piping from an existing installation. The combination of pipe ramming to loosen the pipe in the soil together with a winch or pulling device enables the removal of piping without extensive environmental impacts or the need for more sophisticated technology.
Trenchless technology and the use of HDD techniques for product pipe installations is developing on a continuous basis. Contractors are combining different trenchless methods to improve efficiencies and reduce costs. The use of pipe ramming techniques to assist HDD operations is one example of this trend.