Use of rammers for HDD continues to grow, diversify.
Improvements in equipment continue to expand capabilities, experience and project owner recognition of the benefits of horizontal directional drilling. This leads to boosting the use of HDD for increasingly difficult projects.
Many of these projects pose risks not found on "routine" HDD installations. Even so, many contractors take on such projects knowing there are options that can help them overcome issues that once could mean failure to complete a project.
One of the most widely used bore salvage tools is the pipe rammer, a powerful tool designed to ram steel pipe and casings into the ground, either horizontally, vertically or at an angle. Conductor barrels are used to provide a stable path to launch a HDD pilot bore and stabilize the exit point at the opposite end of the installation.
The conventional use of a pipe rammer is to attach the tool to a section of steel pipe or casing and hammer it through the ground with rapid percussive blows powered by compressed air. The ramming mechanism operates inside a steel casing. Depending on job requirements, spoil is removed by compressed air, water or augers.
These tools can be adapted to assist the completion of difficult HDD installations, to remove drill pipe that becomes stuck in the bore hole and to remove sections of old pipe from the ground.
"TT Technologies has developed several HDD assist techniques using our Grundoram pipe rammers to assist on HDD projects," said Rick Melvin, national product specialist. "We can use our hammers along with our expanders to assist in the extraction and salvage of drill pipe as well as product pipe.
"The expanders originally were designed to pull HDPE in a pipe bursting application. We have adapted them to work on steel product pipe as well as drill stem. Typically the contractor does the fabrication on site after we supply the hammer and expander to whatever size is needed."
The most common HDD assist procedures are:
Pullback Assist--Hydraulic forces can halt product pullback, freezing the product in the hole. Connecting product pipe to a rammer during pullback allows the rammer's percussive action to keep the pipe moving and reduces stress on the drill unit making the pullback.
Drill Stem or Product Recovery--The pipe rammer is fitted with a special sleeve and the stuck drill stem is welded to the rammer sleeve. Percussive force frees up the drill stem so that the driller can then rotate and either pull the stem from the hole or resume regular drilling operations.
Bore Salvage--A similar process is used to remove product that becomes struck in the bore hole during pullback and the drill rig is unable to complete the installation. The rammer is attached to the product pipe and percussive force initiated. A winch or other pulling devise can assist the rammer during the operation.
Removal of Abandoned Pipe--A similar process is used to remove sections of abandoned, failing, or failed pipelines with the rammer attached to old pipe for removal. "We are finding this procedure is being used much more often," said Melvin.
Conductor Barrels--Unfavorable soils at the entry and exit ends of drilling installations can be stabilized with conductor barrels. At the entry, the barrel pipe is driven down at the correct angle to launch the bore to a point where conditions are bettered suited to begin drilling. In addition, barrels can be used to prevent drilling fluids from entering surrounding soil. Patented conductor barrels also are being used on direct pipe installations to provide the cutting head with a solid starting point. TT Technologies conductor barrels are patented in the United States, Canada and Germany.
Mears Group Inc. frequently utilizes a pneumatic hammer for installing large diameter conductor barrels at the entry and/or exit approaches of an HDD crossing when problematic soil conditions or other operational challenges need to be addressed, said Neil Smith, senior vice president.
"The casing isolates the drilling and reaming work from the surrounding soil and improves efficiency," he explained.
Mears used this method to install 60-inch casings to mitigate the risk of inadvertent returns of drilling fluid and subsidence due to weak soils for the relocation of a raw water line for Norfolk's Elizabeth River Tunnel Project.
"Prior to commencement of the drilling activities for the installation of the 36-inch steel pipeline," Smith said, "the casings were installed using a TT Technologies' Grundoram Taurus hammer on the entry and exit sides of the river crossing. Approximately 320 feet of 60-inch steel casing was installed on this project."
Southeast Directional Drilling uses pneumatic hammers to remove buried pipe for various reasons.
On a recent project in Oklahoma, an 18-inch Grundoram hammer was used to remove approximately 1,500 feet of 24-inch steel gas pipe Tests found the recently-installed pipe could not hold pressure.
"We connected an extractor to the pipe and used the hammer to push the pipe from the hole," said Kyle Pellinen, general superintendent. "Set up took a day and then a day to extract the pipe."
A 500,000 pound pullback American Augers HDD unit pulled a 36-inch reamer through the vacated hole twice to prepare it for new pipe, then pulled 24-inch steel pipe in place.
Southeast also uses conductor pipe when needed to stabilize HDD installations at entry and exit points of HDD installations, said Pellinen.
At an installation in Hawaii, a 48-inch conductor pipe was driven through the ground by a 24-inch hammer for 150 feet to cross the North Channel at Pearl Harbor. The conductor pipe surrounded the pilot hole and the 20-inch fusible PVC water pipe that was installed.
"The conductor pipe," said Pellinen, "served as a barrier to contain potential contamination of soils during the installation.
(800) 533-2078, www.tttechnologies.com
Wears Group Inc. HDD Division
(281) 448-2488, www.mears.net