Microtunneling is a construction project which involves trenchless technology by utilizing specialized digging techniques that require heavy drilling equipment to construct small tunnels for sewers, pipelines, or other conduits. Typically, microtunneling or trenchless technology is deployed in high traffic areas which are not feasible for large trench digging such as busy roads or under large buildings. In most microtunneling operations, the machine is first pushed through an initial opening and then pipes are pushed behind the machine with immense force in a process called pipe jacking. This is process is repeated until the microtunneling machine reaches the opposite end at the reception shaft. The tunnels, while having a fairly small diameter, are still large enough to potentially allow an operator inside to operate the machine itself, though sometimes the operator controls everything from the surface using an array of advanced sensors, lasers, CCTV, and computers to guide the process.
Since microtunneling also involves moving a large amount of rock, dirt, sand, and other solids found beneath the surface, it needs an efficient way to dispose of this material. Typically, these materials are ground up by the tunneling machine and then pumped out through the machine using a combination of water jets and slurry pumps. The slurry system generally performs two functions. One is to remove the excavated ground spoils and cuttings by bringing them back up to the surface through slurry pipelines and hoses, and the other is to counterbalance any groundwater the machine may encounter using pressure sensors, eliminating the need for dewatering.
Microtunneling Slurry System
The slurry system consists of a closed pipeline loop which circulates the slurry mix through the head of the microtunneling machine where excavated materials are ground up and picked up into suspension, carried out of the tunnel and deposited into settling tanks on the surface of the operation. The settling tanks help to dewater the slurry, thereby removing the solids, allowing the water to be recirculated back into the microtunneling machine.
Assisted by Slurry Pumps
Slurry pumps help with slurry system circulation to and from the slurry separation location. Slurry feed pumps assist with slurry feed flow above the jacking shaft assisted by booster pumps with slurry return flow from the Microtunneling Boring Machine (MTBM), while the mid pumps aid the booster pumps on extended length drives and slurry return pumps assist with slurry return flow from the jacking frame to the slurry separation location. All pumps are VFD driven for variable flow volumes depending on the project specifications.
Typical Microtunneling Steps
- Excavate shafts for the launching of tunneling equipment and reception of tunneling equipment at the opposite ends of the tunneling drive.
- Hydraulic jacks in the launch shaft push a microtunnel boring machine (MTBM) into the earth using various cutterheads designed for the expected geology.
- Pipelines and hoses within the tunneling equipment containing slurry and mud transport the excavated materials to the surface for separation and disposal.
- Retract the pipe jacks and disconnect slurry lines and control cables.
- Lower a pipe or casing into the shaft and insert it between the jacking frame and the MTBM.
- Reconnect slurry lines and control cables and advance the MTBM another drive.
- Repeat the above process until the MTBM reaches the reception shaft.
- Retrieve the MTBM and trailing equipment using a crane after the pipeline has been installed.
How the EDDY Pump Can Enhance Microtunneling Operations
Less Clogging – The EDDY Pump does not use a traditional impeller but instead uses a geometrically designed rotor that allows a high tolerance for solids to pass through the pump without getting stuck or clogging the pump. This allows for more uptime and less downtime due to clogs or maintenance issues as often large shards of rock or other material will clog or disable traditional centrifugal pumps. With the 12-inch EDDY Pump capable of pumping solids of up to 11 inches in diameter, clogs will become a thing of the past!
Ability to move high viscosity and high specific gravity materials – The EDDY Pump rotor acts as a mixer on thixotropic materials and provides a shear thinning effect. The EDDY Pump’s ability to pump concentrated solids in a turbulent flow is perfect for moving viscous materials with less than 5% free liquid; an impossible task for centrifugal pumps. This makes the EDDY Pump ideal to move the heavy mud and thick slurry effectively through a long pipeline without the need for booster pumps.
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