EARTH PRESSURE BALANCE MACHINE (EPBM)
Earth Pressure Balance Machine
Earth Pressure Balance Machine (EPBMs) Systems are used for direct pipe jacking, concrete segments, liner plate and ring beam and lagging tunnel installations of 102-in. OD pipe diameters and larger on runs generally exceeding 1,000-ft. lengths in poor soil conditions. They install pipe by pipe jacking or segment erecting methods for straight and curved extended length alignments with extreme accuracy. EPBM systems are complex in design and performance and are custom built to suit project parameters.
EPBM systems are most suitable for saturated and flowing ground conditions, and foam bentonite slurry injection is used to stabilize and balance machine and soil pressures to minimize ground settlement and prevent subsidence. Ideal EPBM project ground conditions present good plastic deformation, soft consistency and low water permeability. Introducing foam bentonite slurry into the ground lowers the density of the soils, increases water impermeability to seal the tunnel face, and reduces friction and wear on the equipment. Because of the soil conditioning, EPBM operators are able to achieve consistent excavation and production rates.
An EPBM is specified over a microtunneling system for its ability to balance soil conditions on projects presenting little groundwater. If the groundwater pressure is high, the tendency for ground collapse increases, therefore balancing the soil pressure with foam is not feasible and microtunneling is a more suitable option.
The pipe jacking EPBM and pipe sections are advanced by a hydraulic jacking frame in the launch shaft. The segment erecting EPBM positions concrete segments to form a ring to build the tunnel. This EPBM advances itself off of the previously built ring with hydraulic cylinders which applies pressure to the segments and the thrust block.
Excavated soil from the EPBM cutting chamber is removed through a screw conveyor system to the haul unit’s dirt bucket for removal from the pipeline.
Trailing back up cars follow behind the EPBM in the tunnel and contain the main hydraulic drive pumps, electric motors, conveyor lift, operator’s station, variable frequency drives, foam and slurry, transformers and tunnel ventilation equipment. Above ground system components are the control and power containers and foam and slurry plant.
Accuracy is maintained on an EPBM alignment with the AZ100 Total Guidance System.