At Bradshaw, TBM tunneling means the use of a shield or wheel type tunnel boring machine (TBM).  It is propelled forward by jacked pipe or by thrusting itself forward off fixed conventional tunnel supports installed within the tail can of the TBM.  We call it “Analog Age Tunneling” because in all cases the operator rides underground within the TBM and uses their hands to pull levers or push buttons and their eyes to follow a laser beam to control the TBM.   While TBMs range in size up to 57’ OD, the typical utility tunnel TBM is 52” to 144” OD.  TBMs are manned and have complete face access, so removing obstructions or adjusting to variable soil conditions is sometimes easier with this method.  Additionally, manned tunnel operations often perform better on metrics like line and grade control than unmanned.  Remote control systems can be efficient but not necessarily flexible or adaptable whereas manned TBMs, like manned space flight, can deal in real time with unexpected conditions or equipment failures. The fixed conventional tunnel supports installed in the TBM tail can are traditionally rib and wood lagging, occasionally all steel, and increasingly concrete segments.  Jacked pipe is typically concrete or fiberglass.

• TBM pipe jacking or conventional fixed supports?
• What are the benefits?
• What are the risks?

TBM tunneling has been evolving for over 100 years and has truly become efficient and dependable over the past 35 years.  North America has the best TBM manufacturers in the world with Akkerman, Lovat, and Robbins.  Bradshaw primarily installs smaller diameter utility lines that are less than 2,000’ long; therefore, we have chosen an extensive fleet of Akkerman wheel and shield TBMs that range from 52” to 144” OD.  To prevent raveling or flowing soils from coming into the TBM, our wheel TBMs use closeable face doors while our shield TBMs have shelves and hydraulic breasting plates.  For larger and longer tunnels, we own Lovat TBMs equipped with a soft ground/EPB/soft rock cutterheads.  For hard rock, we use Robbins TBMs.  Each of these TBMs meets a specific tunnel size or soil need.  Groundwater control can be achieved with the more sophisticated wheel TBMs by upgrading them to EPB (Earth Pressure Balance) mode.  For shields and conventional wheel TBMs, ground water must be controlled through conventional dewatering systems, compressed air tunneling or ground modification (grouting, etc.).  At Bradshaw, we have compressed air locks for tunnels from 48” to 180” in diameter.

• What is the right TBM for your job?
• Is soil stabilization necessary?
• Is EPB necessary?

Bradshaw owns and operates the largest fleet of utility TBMs in the Eastern US.  Our TBM tunneling experience includes jacking pipe from 42” to 96” RCP up to 900’ in length.  These projects have included one pass RCP storm sewer and coal conveyor tunnels.  Bradshaw has experience in stretching the capacities of these machines to their limits.  We installed a single access shaft, 75” OD, rib & wood lagging TBM tunnel for a sanitary sewer in Arlington, VA, that included a 40 degree bend and was over 1,850’ long.  In addition, we installed a 1,200’ liner plate tunnel with 3 reverse curves in Atlanta, GA.  Our largest shield tunnel was 3,400’ of 144” OD for a 108” CSO in Richmond, VA.  Our Lovat TBM has been used in EBP mode under the water table to jack 84” RCP in Miami, FL.  It has also been used with a rock cutterhead to install rib & wood lagging supports in Elizabethtown, NJ, under the Raritan River.  In Charleston, SC, we installed 14,300’ of 99” OD unsupported TBM tunnel in Marl for a water intake tunnel, and several thousand feet of 83” OD hard rock TBM sewer tunnel in Lynchburg, VA.  Whether it is jacking pipe or installing fixed conventional tunnel supports, Bradshaw has the equipment and experience to successfully conquer the toughest of utility tunnel projects.

• Constructability – unexpected challenges?
• New TBM or refurbished?
• How much contractor experience is required for

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