Tunnel lubrication plays a pivotal role in the success of all trenchless methods while improving the performance of pipe jacking, microtunneling, guided boring, and horizontal directional drilling. Proper lubrication systems not only reduce frictional force along the pipe string, today’s advanced systems also incorporate variable flows, pressures, and additional pumping strategies that enhance material flow and maximize the mechanical properties of the trenchless equipment design.
Water is the primary ingredient to all drilling fluids in the trenchless industry. The water source should be fairly clean, clear, and fresh. Utilizing brackish or salty water will not work well. To properly mix the drilling fluids, it is critical to adjust the pH level of the supply water between 8.5 to 9.5 by adding soda ash to ensure the bentonite can be fully hydrated. It is common to add ¼ to ½ lbs. of soda ash per 100-gallons of water to see a change in pH levels, however it is important to continually monitor using test strips and adjust accordingly.
Additives such as bentonite should be gradually poured into the mixing tank per the recommended instructions on the packaging, however it is never recommended to exceed a rate of 50-lbs of bentonite in a 3-to-5-minute period. Adding the lubricant too quickly cause granules to settlement at the bottom of the tank, and your mixture will not fully hydrate. Once the lubricant is added you your mixing tank, the “engineering lubricant” requires proper mixing time to ensure full hydration. The time it takes to reach full hydration is dependent on the type of mixing unit you are using. Typical bentonite mixing units require upwards of 30 to 45 minutes. Akkerman’s series of lubrication pumps utilize a high shear mixing action which can cut mixing times down by as much as 50%.
A common misconception in the trenchless industry is that the bentonite coats the jacking pipe to make it “slippery”. Bentonite is a very special type of clay that is generally mined and processed from just a few regions of the world that contains weathered volcanic ash. Once bentonite is fully hydrated, it can quickly swell to as much as 10 times its original volume. A hydrated bentonite mixture reduces jacking forces by creating a filter cake around the annulus of the borehole while allowing the hydrostatic pressure between the jacking pipe and the borehole wall to keep soil from settling around the pipe.
A mud engineer will need to know the anticipated ground conditions along with the type of trenchless equipment that is going to be used on the project to help design the best engineered mixture for the application. A bentonite lube mixture is never considered as “one-size-fits-all” since various types of ground conditions react differently. Contractors often see increased productivity when lubrication mixes are adjusted based on the actual ground conditions encountered while advancing. Alternatively, using the incorrect mixture in a trenchless application can cause higher than anticipated loads resulting in delays, or even failure.
Below is a general guideline as a starting point on your next project. It is always recommended to consult with a mud engineer for on-site evaluation of your geology.
|Ground Type||Ground Conditions||Reactivity||Lubrication Mix|
|Coarse Soils||Sands, Gravel, Rock||Non-Reactive. Does not swell. Does not get sticky.||Water (pH controlled), Bentonite. Addition of PAC or Xanthan Gum may be required.|
|Fine Soils||Clay and Shale||Reactive. Tendency to swell with water. Can get sticky||Water (pH controlled), Bentonite with clay inhibitor. Surfactant to reduce stickiness.|
|Mixed Soils||Variable||Ground may react differently depending on the ratio of coarse/fine material.||Water (pH controlled) Mixture of Bentonite, Flocculant, or Clay Inhibitor|
Akkerman produces a variety of lubrication systems suited for the rigorous demands of the trenchless industry. These high-pressure lubrication pumps are a perfect complement to extending distances during pilot tube installations and can also be used for other pipe jacking applications including microtunneling, auger boring, tunnel boring, and directional drilling.
One of the challenges of being a GBM owner is understanding what the different tools and adapters are designed to accomplish. While most of them are used during every pilot tube installation, there is one item that operators seem to forget about. The Air & Fluid Adapter has been a standard part of the tooling package of all Akkerman GBM power packs for several years and is located in the tool storage compartment when a unit is delivered from the factory.
The Air and Fluid Adapter plays an important role on long-distance pilot tube installations by allowing the operator to purge “dry air”, or nitrogen, through the site path of the pilot tube. Shown in Figure 1, the adapter looks just like a standard molded pilot tube plug, however it is machined from steel to allow the inner and outer diameter of the pilot tube to be purged and flushed.
An NPT connection at the center of the adapter allows nitrogen to purge through the inner diameter of the pilot tube removing humidity, fog, or sometimes steam. This process improves the clarity of the guidance system for longer drives. A port on the outside of the adapter is generally used to flush clean water through the outside diameter once the pilot tube installation is complete. This process helps clean and flush potentially corrosive drilling fluids while it is still fully hydrated. Clean and maintained pilot tubes require less pump pressure allowing more lubricant to flow to the steering head which reduces the overall forces required.
The steering head and target housing is designed to allow both the air and fluid to purge through the port located on the steering head. The nitrogen, which is represented in red on Figure 2 below, passes around the LED target and is exhausted through two check valves. The flushing fluid, shown in blue, flows the same as drilling fluid when installing pilot tubes. The check valves are positioned so that drilling fluid or flushing water cannot enter into the inner tube sight path, while the other check valve prevents ground water or soil from infiltrating the pilot tube string.
If you haven’t used your Air and Fluid adapter recently, now is a great time to check the inventory in the tool storage compartment on the Akkerman power pack. Additional information can be downloaded by logging into the Akkerman customer portal and viewing the Operator’s and Part’s Manual. If you need replacement tooling, our Aftermarket Support team can assist by contacting our office at (800) 533-0386 ext. 0017.
Bullseye Boring requested a field technician for GBM crew refresher training on a project in Skokie, IL. The ground was perfect for pilot tubes, and Joe Murphy shows the operators how it’s done by pushing 520-ft. of them in one shift.
Did you know that Jack Lane III, mechanic, field technician, and incredibly likable co-worker, is also a dirt bike riding superstar?
Most recently, while on an extended field technician project in South Carolina, Jack entered the Mid-East Hare Scramble motocross event on September 19, 2021, at Harris Bridge II in Woodruff. He took first place in the Golden Master category, ranking him 11th overall out of 160 riders.
Jack attended the first-ever Amateur National Motocross Championship in 1982, racing in the 125 Expert Class. Now in its 40th year and considered the most prestigious motocross event in the world, Jack set his sights on returning with the support of his son Jack IV. The event is held in August at Loretta Lynn’s Ranch in Hurricane Mills, TN.
The stakes are high to become eligible to participate. To qualify for the championship, one must place in the top six at local events, then place in the top eight at a regional qualifier event against the best finishers from each area. Jack Senior and Jack Junior spent many weekends racing and advancing from area qualifiers all over MN and IA to get to the regional qualifier. Senior raced in the 50+ class (there wasn’t a 60+ option) alongside Junior, who races in the 30+ class.
They did not finish in the top eight against the best in the country to enter the championship in Tennessee. Still, they met their personal goals – Junior finishing as the top 30+ racer from Minnesota and Senior hitting double jumps at 60-years-old. And really, the most valuable winnings were realized through memories made while enjoying each other’s company and traveling the country to race dirt bikes.
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