Pipe ramming is a versatile trenchless method of pipeline installation that is used as such and also in conjunction with other trenchless methods such as horizontal directional drilling (HDD).
Pipe ramming is basically a casing installation method in which a pneumatic hammer slams the casing into the ground using repetitive percussive blows. To reduce friction between the soil and the casing, bentonite or polymer lubricant may be used, and a cutting shoe is often welded to the front of the lead casing.
Pipe ramming can be used to install pipes and casing with diameters ranging from 4-147 inches, and lengths up to 150 feet (though longer lengths have been installed.)
Pipe ramming is most suitable for projects in the following situations.
Projects in Soft Soil
Pipe ramming can be carried out in many different soil conditions except solid rock. But there are some soils in which pipe ramming works better than other trenchless methods. Pipe ramming works best in soft to very soft clays, silts and organic deposits, sands above water table, and soils with cobbles, boulders and obstacles lesser than pipe diameter. Medium to dense sands below the water table, medium to hard clays, weathered shale, and soft or fractured rocks can also support pipe ramming but it may be difficult. In rocky ground conditions pipe ramming can be carried out by first punching a pilot hole using a pneumatic tool, after which the pipe can be rammed in.
Projects with Shallow Installation Depths
Open excavation to install pipelines under railway embankments and highways can cause a lot of disruption. Most of the trenchless installation methods such as pipe jacking and microtunneling can cause considerable settlement of ground since these installations are at shallow depth, and there is a chance of larger settlement due to soil loss.
Pipe ramming is an excellent method for installation of pipes where ground loss is expected due to the shallow depth of installation, because it utilizes displacement method unlike other trenchless techniques.
The advantage of installing different size casings without affecting surface structures such as roads and railway lines is a very attractive benefit.
Projects with Space and Muck Disposal Issues
Pipe ramming does not utilize a slurry system resulting in wet spoil. The spoil generated is removed from the casing and only contains the soil's natural moisture content, making it easier to handle.
For other trenchless methods such as microtunneling, sufficient space is required for handling wet soil generated from the process. The spoil generated from pipe ramming is much lesser compared with pipe jacking or microtunneling.
Projects That are to be Installed in Straight Runs
Unlike pipe jacking or microtunneling, the pipe ramming process is not guided or steerable, and thus, pipes installed using this method are installed in a straight line. Pipe ramming can be used for horizontal, vertical and angled applications.
This type of drilling can be done at required slope, but it can’t be done when a curved trajectory is required. For longer runs, sections of pipe one at a time can be installed or an entire length of pipe can be installed at once for projects with short installation lengths.
For Vertical Projects
Pipe ramming is typically used for horizontal installations under railroads and bridges. However, it can also be applied for vertical projects such as piling or micro-piling.
An example of vertical application is an installation of vertical supporting piles from a bridge through a body of water, when the bridge cannot support the weight of a crane necessary in a traditional method of installation of such piles.
When compared to other trenchless methods, pipe ramming is cost and time effective when ground conditions are suitable. It has been found that installation time can be reduced to 40% shorter because of the smaller width and depth of pits.
The installation time is also faster because 40 to 60 feet sections can be rammed in half an hour, compared to half a day when horizontal auger boring (HAB) is used. It can also be used to install larger pipes over shorter distances, and also those installations with shallow depth.
Another benefit of pipe ramming is that it can be combined with directional drilling to free a stuck product pipe during pullback. This is done by attaching the ramming tool to the end of the product pipe and giving percussive blows to keep the pipe moving.
Pipe ramming is a non-steerable method and there is little control over the line and grade of installation due to soil conditions and obstructions such as rocks and cobbles.
The accuracy of the pipe ramming method is usually better than ± 1% (both vertically and horizontally) of the length of the bore.