PIPE RAMMING PROVES GOLDEN FOR HDD PROJECT IN COLORADO
Pipe ramming and horizontal directional drilling may seem like an odd combination, but many times you can find the two trenchless methods on the same project, often being used in a most complimentary manner. Over the years, the two methods have teamed up on countless pipeline installation projects for many different industries. Recently pipe ramming played a key role in the HDD installation of a gas transmission main in in the US state of Colorado.
In the heart of what many would consider beer country, Golden, a pipe ramming HDD assist technique helped facilitate the installation of a Ø 500 mm diameter gas main under a highly traveled roadway and adjacent to several important water sources. BTrenchless was contracted by Global Underground Corp, Colorado Springs, Co., to install a Conductor Barrel™ casing through pneumatic pipe ramming in an effort to manage drilling fluid. In order to install the Ø 1.200 mm conductor barrel casing, a Ø 600 GrundoramTaurus from TT Technologies was used.
According to BTrenchless Project Manager Chris Gray the installation was not without challenges. He said, “We needed to take into consideration a variety of issues from the soil conditions to the layout of the job site itself to make this project successful. But in the end, we were very pleased with the results.”
Pipe Ramming & HDD
The saying goes, “Necessity is the mother of invention,” and that saying holds true when it comes to using pipe ramming to assist with difficult horizontal directional drilling projects. One such method is the Conductor Barrel casing. During that process a casing is rammed into the ground, at a predetermined angle, until desirable soil conditions are met. The spoil is removed from the casing with an auger or core barrel. Drilling proceeds within the casing in the desirable soil conditions. In addition to assisting drilling operations at the start, the conductor can also serve as a friction-free section during pullback.
For the project in Golden, the conductor barrel was key in helping the drilling contractor prevent fluids from forcing their way into the area waterways. In this sense, the conductor barrel acted like a containment system.
HDD Assist techniques
In addition to the Conductor Barrel technique, several other pipe ramming HDD assist techniques have been developed that today, in many cases, become standard practice in the HDD industry.
TT Technologies pipe ramming specialist Rick Melvin explained, “It’s very common now for HDD contractors to have pipe ramming equipment on site, ready to go on their HDD jobs. Probably the most common HDD Assist technique we see is during pullback, Pullback Assist. We can often overcome hydrolock during pullback by putting a rammer on the back of the product pipe and add some percussive action. This tends to loosen things up and assist in completion of the bore.”
Pipe rammers can also be used to remove a stuck product pipe (bore salvage) or remove stuck drill stems (drill stem recovery). In these situations, the pipe rammer is attached to the end of the partially installed product pipe or the end of the stuck drill stem in a way that it can be used to assist in pulling the pipe or drill stem out. In many cases, the percussive power of the pipe rammer is enough to free the stuck pipe and allow it to be removed from the ground.
Ram, Remove & Repeat
The bore path for the gas main installation was designed to travel from a bore pit on the south end of the project, under railroad spur for the local brewery, a creek and Highway 58 to an exit area on the north end, approximately 730 m away. Before the pilot bore could begin, crews needed to install the Ø 1.200 mm conductor barrel casing. Gray said, “The intention was to install the casing and seal it into the bedrock approximately 15 m below grade. So we set up to ram the steel casing at a 12-degree angle, 23 % slope, which was the predetermined bore angle, and began ramming the casing. If it worked, we would essentially seal off the ground water in the area from entering the casing.”
The ramming pit was excavated to meet the slope requirements of the drilling angle. Crews utilized the tracks from an auger boring machine to create a ramming platform at the proper angle of attack for the installation. This would also allow crews to use a Ø 1500 boring machine with Ø 1.200 augers to clean the spoil from the conductor barrel.
Once the platform was complete, the first section casing was moved into position and the Ø 600 pipe rammer was connected to casing. For the pipe ramming operation, BT used three air compressors of various sizes. Gray said, “The elevation of Golden Colorado is approximately 1670 m above sea level. For every 300 m in elevation, you lose a percentage of your air compressor capacity. In order to compensate, additional compressors are sometimes needed. We wanted to make sure we had plenty of power for the rammer on this project.”
Ramming operations progressed to a point where crews thought they had reached bedrock. Crews cleaned the spoil out with the auger system and encountered several large boulders, which required individual retrieval from the casing. A soil analysis, however, determined that the casing had not yet reached bedrock and additional ramming would be required. Crews continued ramming to a point of 58 m until the desired bedrock formation was reached. Little did Gray and his crew know the whole process would need to be repeated again on the same project.
Initially, the project only included one casing installation, however BTrenchless was later called back to the site to install another one at the exit pit. Gray said, “Global Underground contacted us again after the HDD process began. Once the pilot bore cleared the bedrock on the north end of the project, the bore pit was inundated with ground water that had traveled back along the HDD route. The objective here was to ram a casing down to bedrock on the north and encapsulate the drill head. This took some careful planning, calculations and execution.”
Not everyone was convinced that this method would solve the ground water issues or that BTrenchless would be able to hit the location of where the HDD drill head exited the bedrock. Using the same type of set up used on the first Conductor Barrel, crews rammed 56 m of Ø 1.200 mm steel casing on the north end of the project for the exit pit.
Ultimately, it was determined that the casing on the north end of the project entered the bedrock within a couple of tenths of where the center of the HDD drill head exited the bedrock and sealed off the ground water. Melvin said, “This was a very impressive project from a pipe ramming point of view. Hitting the target on that second Conductor Barrel alone takes the right contractor and obviously BTrenchless was more than up to the task.”