TRENCHLESS | RED RIVER VALLEY
Right, figure 4:
Minger lowering the EPBM into the launch shaft for Contract 5a
structure at the Sheyenne River in Griggs County.
Contract 7 is evaluating the design of 20 trenchless crossings of wetlands, creeks, roads, and railroads.
RRVWSP TRENCHLESS INSTALLATIONS Across Contracts 5 through 7, 39 trenchless crossings spanning 2233m (7325 LF) have either been constructed, are actively being installed, or are in various stages of design as shown in Table 1. Trenchless installation facilitates the delivery of this pipeline while reducing disturbance of sensitive wetlands and creeks as well as preventing the interruption of service on highways, railroads, and utility lines.
TRENCHLESS BORING MACHINES Trenchless solutions are employed to meet to the frequent challenge of constructing and installing linear conveyance infrastructure in ground conditions where traditional cut and cover methods are either not feasible or may be detrimental to sensitive environments. For the RRVWSP programme, construction in varying ground conditions was possible due to advancing technology in tunnel machine manufacturing – specifically, slurry Microtunnel Boring Machines (MTBM) and Earth Pressure Balance Machines (EPBM) were leveraged to execute this work.
MTBMs For Contract 2, a slurry MTBM was employed to directly install the conveyance tunnel from the wet well shaft to the intake structure in the river using a one-pass system. A jacking frame in the launch shaft (Figure 3)
28 | October 2023
applies pressure to the casing pipe which advances the MTBM, which in turn advances the pipe alignment. Additional pipe segments are connected and jacked into place from the launch shaft as the MTBM progresses forward. Slurry lines are also extended to facilitate continuous
muck removal. A guidance system within the MTBM is employed to assist with installing pipe to required line and grade tolerances. This process continues until the MTBM reaches the reception shaft. Once the MTBM reaches the reception shaft, the MTBM is removed, and the process of making connections to existing structures can begin. Slurry MTBMs are applicable to coarse-grained
ground with high groundwater conditions, such as those anticipated in Contract 2.
EPBMs For Contract 5a, an EPBM was employed to construct the trenchless crossing beneath the railroad and highway to minimise environmental impacts and disturbance to existing infrastructure (Figure 4). Like the MTBM, the EPBM also utilises a jacking frame to apply pressure to the pipe segments to advance the alignment as the machine excavates forward. EPBMs are more suitable for fine-grained, or clayey
ground, which can be conditioned to turn the excavated material into a fluid that balances the pressure at the face of excavation. Without the need of a dedicated slurry separation
plant, the construction footprint around the launch shaft is smaller.
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