Microtunneling is state of the art remote-controlled pipe jacking by computer, which is why we call it “Digital Age Tunneling”. One person above ground operates the microtunneling system using a computer to advance and steer the microtunnel boring machine, jack the pipe, and excavate the soils.  When computerization is combined with slurry microtunneling’s ability to balance both groundwater and earth pressures, you have a truly revolutionary tunneling method for installing 18” to 96” OD tunnels.  The microtunneling method can be either “one pass” with the permanent carrier pipe jacked directly in place or “two pass” with a permanent carrier pipe installed inside a temporary tunnel casing jacked in place.  One pass is the most efficient and least costly method of tunneling.  Pilot tube microtunneling (PTMT), also known as guide bore microtunneling (GBM), combines the accuracy of visual theodolite guidance with the cost advantages of ultra-small access shafts (<12’ OD) and one pass pipe jacking of 6” to 30” OD carrier pipes.  Guided auger boring uses the same pilot tube system as PTMT/GBM to install auger bored steel casing up to 48” in diameter within 1”+/- of the designed elevation and alignment.

• Is slurry type microtunneling the best method?
• What are the jacking length limits?
• Should it be one pass or two pass pipe jacking?

Slurry microtunneling equipment was invented in Japan, perfected in Germany, and recently copied in the US.  Bradshaw’s modern fleet of microtunneling machines (MTBMs) was manufactured by Herrenknecht (German) and Rasa (Japanese).  The Herrenknecht MTBMs allow face access down to 59” OD which is critical to effectively mine hard rock.  The Rasa MTBM also has face access and has proven very successful mining through boulder-laden glacial deposits and till.  MTBM cutterhead and cutting tool design and selection is critical to the success of any microtunneling project. Bradshaw excels at these designs and now has a wide range of soft ground, mixed face, and rock cutterheads for all sizes of its MTBMs.  Bradshaw uses the Akkerman pilot tube microtunnel (PTMT)/guided boring system (GBM).  This is an extremely accurate pipe jacking/auger bore type system.  It is used for pipes too small to be effectively microtunneled (<18” OD) and to guide conventional auger boring machines (12”-48” OD).  In both uses, the soils should be relatively uniform, not too hard or dense, and essentially above the water table because slurry isn’t used.  It is a highly accurate method of pipe jacking/auger boring lengths up to 300’.

• Is MTBM face access necessary and why?
• What type of rock can be mined with MTBMs?
• Can MTBMs mine boulders?

Bradshaw completed the first microtunnel in the Mid-Atlantic in 1991.  We own and operate the largest fleet of Herrenknecht and Rasa slurry microtunneling equipment in the US.  We have six microtunneling systems and our fleet of eight MTBMs range in size from 30” to 96” in diameter and have mined lengths up to 1,500’.  We are the only microtunneling contractor in the US to successfully mine over 8,000’ of hard crystalline rock with UCS strengths from 10,000 to 43,500 psi (70-300 MPA).  We have installed numerous raw water and cooling water intake lines requiring wet retrieval of our microtunnel boring machines in water up to 50’ in depth.  Bradshaw was an early adopter of the pilot tube microtunnel (PTMT)/guided bore method (GBM) and has completed 3,000’+ of 12” VCP pilot tube microtunneling and 5,000’+ of 36”-48” pilot tube guided auger bores up to 300’ in length.  Whether microtunneling in zero blow count silts, boulder-laden till, or hard rock, Bradshaw has the equipment, personnel, and over 20 years’ experience completing microtunnels throughout the East and Midwest US. 

• What is enough cover over a slurry microtunnel?
•  How do you define microtunnel obstructions?
• How accurate is microtunneling?

To answer these questions and any others about your next project, please contact us.