May 1, 2008To do an auger boring job is to attempt an under appreciated art form. Art created by contractors who have spent countless hours perfecting their craft, but who have done so all over the world in conditions that are most times less than ideal. The work is done through experience, using tried-and-true processes that engage in successfully carrying out a method textbook by thought, but complex in the real world scenario.
The textbook method would be tested on unforgiving grounds in Kendallville, Ind., where American Augers helped supervise an auger boring job, which product support technician Jim Lee described as one the most “challenging bores performed in [his] 37 years of service.”
Lee was contacted by the project’s contractor Selge Construction, Niles, Mich., to see if the manufacturer could lend its experience in determining if this job was even feasible. Selge Construction explained that its goal was to auger bore 500 ft for the purpose of installing a 54-in. diameter gravity-fed sewer line. Lee’s initial response was: “No job is too tough, as long as the operating crew has the experience and the right tools to tackle unforeseen obstacles.”
Experience was not an issue, as Selge Construction owner Marv Selge was described by Lee “as having a world-class auger boring operation,” and the right tool to handle those unforeseen obstacles would be an American Augers 60-1200 NG auger boring machine.
Now that the discussions were complete, the real work began, as both Selge Construction and American Augers moved from the office to the jobsite.
Jobsite preparation is what Lee calls the “element that makes or breaks the bore,” and Selge Construction took every step possible to ensure that the performance of this bore would be nothing short of reaching their goal. The overall pit size would measure 57 ft long by 14 ft wide and was approximately 6 ft deep. The issue in the pit was that the ground conditions compounded by the force that the machine would integrate into the hole would require a substantial amount of reinforcement of the working area. Ground conditions were a substantially sandy clay formation with a light mixture of gravel. Clay, which is sticky by nature, can be a detriment to the ability to remove spoils from the hole, as it does not stick well to the auger sections. To create a friendlier working environment, mud lines were run on the inside and outside of the product casing. The purpose of this action was to improve spoil removal by turning the clay into a more mud-like slurry, which enhances spoil removal by allowing the clay to slide through the rotating auger, but also reduces overall friction inside the casing.
Additional pre-boring preparation also called for a 4-in. concrete pad to be poured inside the working area. The concrete was necessary to ensure that the pit’s working floor maintained a level surface and was able to support the auger boring machine’s nearly 30,000 lbs of total weight. The weight of the machine is only a portion of the actual weight inside the hole, as the weight of the product casing, auger sections, extension track, other essential jobsite tooling needs and the working crew must also be factored into the total thickness of the base material. According to Lee, “With the length of this job, the size of the product, the machine being used and the need for accuracy, if you cannot accommodate the machine staying level from start-to-finish, you probably shouldn’t even attempt the bore.”
Once the base was created, Lee and the Selge Construction crew were able to place the machine, as well as the 50 ft of extension track into the pit. Using an excavator, the machine was placed in workable sections and assembled while in the hole. The idea of a “split” machine is actually a benefit to the contractor, as it allows the machine to be separated into sections to accommodate lighter and faster lifts into and out of the bore pit, and aids the operator in being able to facilitate better and safer machine positioning. Lee also describes the machine and track placement, as a “tense time” of the preparation period, as it is important to account for and achieve proper line and grade for the job’s needs. “You’ve got to get it right the first time because line and grade is not likely to improve once the bore has begun,” he said.
With an attention to detail, Lee and Selge’s crew were able to complete all of their pre-bore preparations, but concern still existed because of the ground conditions and the need to maintain a line and grade factor of .001 percent. The real challenge had just begun, as an extremely low percentage grade on a flat surface is a grossly cumbersome obstacle when factoring in the length of the total bore with the size diameter of product being installed.
Even before a single inch of product was placed into the Indiana countryside, the auger boring crew took additional steps to secure the pit and provide an optimum chance to maintain line and grade throughout the bore. Shore boxes were placed on the exterior sides of the hole. To adhere to the pressure caused by the machine during operation, a back stop steel plate was fixed behind the machine. That steel plate was reared up by an additional slab of concrete, dirt and another shoring box was buried to be the final supporting element of this precisely planned, yet tensely optimistic bore.
The final step was to create a steering head that would be fixed to the end of the product casing. This action was important to give the operator a “fighting chance” to make the right tooling adjustments in line and grade corrections to the casing. “We did everything we could think of to make sure we put ourselves in a position to be successful and achieve what the customer needed for this bore … if it was possible, we did it,” said Lee.
With every possible scenario accounted for in pit preparation, the crew was finally able to begin auger boring operation. The first 40 ft of the bore were achieved in about 35 minutes, and the crew was able to maintain within five hundredths of grade during the initial push. The next four to five hours were used to properly weld the next few sections of product casing, but within the next week the crew had pushed 490 ft of the total distance.
At this point, and with a noticed change in ground conditions, as the sandy clay spoils were now producing a wet sandy content, the crew elected to dig out the exit side of the pit to expose the casing. The wet sandy formation could impact the bore because the heavy ground was now a factor that could force the project off line and grade, as both the machine and operator were subject to making inaccurate corrections to presumed soil conditions. “Attention to detail is always important. And because we noticed the ground change, we reacted to the change and we were able to continue the bore without issue,” said Lee.
At certain points, the crew utilized every bit of the machine’s 1.2 million lbs of thrust and 180 hp before reducing the thrust output to 500,000 lbs to complete the bore distance after the casing was exposed.
In total, the job took almost a week and a half to complete, but according to Lee: “The machine did its job, the Selge crew did their job and I was glad to be part of this bore.” More importantly to the crew, when all was said and done, the job was completed with line and grade maintained.
Finally, jobs like this show that auger boring, like all underground construction, is performed by the few who learn a skill where they work in conditions that they don’t control, but handle these situations through decisive planning techniques and being aware that only .001 percent was the difference between the jobs success or failure.
Rob Foster is marketing manager for American Augers, which is headquartered in West Salem, Ohio.