Underground Installation Projects: Determining the Best Approach

August 2008 Vol. 63 No. 8

Ramming: Pipe ramming is a trenchless method for installing steel pipes and casing under roads, highways, rail beds and other structures. Pipe ramming tools have the ability to install steel casings up to 84 inches (and sometimes much more) in diameter, and are most useful for shallow installations where other trenchless methods could cause surface settlement or heaving. The majority of installations are horizontal, although the method can be used in vertical applications. One of the most common uses is to install casings for sensitive utilities and replace damaged culverts under roads and railroad tracks.

Pipe ramming tools can also be used to assist in HDD projects. To help overcome hydro lock situations, the hammer can be attached to the product during the pullback. The percussive action keeps the pipe moving and helps prevent high levels of pullback stress. This process can also be used to help free immobilized product.

Auger boring: Auger boring uses a rotating cutting head to bore a horizontal hole inside a casing. As the cutting head cuts through the ground, the resulting spoil is moved by the flighted auger out of the casing and the steel casing is jacked into place. Auger boring is ideal for boring in rock, cobble and unstable soil.

Horizontal directional drilling (HDD): Directional drilling is used for installing infrastructure, such as telecommunications, electric, water, sewer, gas, oil and product pipelines up to 60 inches in diameter. It is used for crossing waterways, roadways, shore approaches, congested areas, environmentally sensitive areas and areas where other methods are not practical or more expensive. HDD provides for reduced traffic disruption, lower cost, deeper and/or longer installation, no access pit, shorter completion times, directional capabilities and environmental safety. This method has extensive use in urban areas for developing subsurface utilities as it helps in avoiding extensive open cut trenches.

Combining methods

According to Dave Gasmovic, president and CEO of McLaughlin in Greenville, SC, a project may take more than one trenchless method for the job to be cost effective.

For example, portions of a sewer installation project may be suitable for directional drilling while an auger boring machine might be more suitable for a segment that requires a 400 foot grade shot.

“We encourage engineers not to tie contractors into one specific method,” says Gasmovic. “Tap into the contractor’s expertise to select the most cost effective method to complete the project.”