What is thrust boring?​

Thrust boring, or auger boring, is typically performed by placing an auger equipped with a cutting head inside a 450mm to 1500mm diameter steel pipe.

The auger is then attached to the rotation shaft of a thrust boring machine. Steel pipe casing is typically installed in six metre lengths, so an entry pit at least 10.6 metres long is required to accommodate the combined length of the pipe and thrust boring machinery.

An exit pit is usually dug on the opposite end of the work area, although it is not always required. Thrust boring can be effectively used to install pipe sections with a maximum combined length of no more than 70 metres.

After the thrust boring machinery has been detached from the steel pipe, the carrier pipe is installed through the casing. Where grade pipe is installed, spacers are used to help maintain grade. Any remaining space is usually filled with a hi flow grout.

Tunnelling 2 - UEA

The Thrust Boring Machine

Step 1

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A large rectangular pit is usually dug on each side of the work area to accommodate the steel pipe and machinery used in this procedure. The pipe casing is jacked into place as the drilling is performed with any excess soil transferred out of the pipe by the auger’s blades.

Step 2

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Thrust boring is typically performed by placing an auger equipped with a cutting head inside a 220mm to 1500mm diameter steel pipe. The auger is then attached to the rotation shaft of a thrust boring machine. Steel pipe casing is typically installed in 6 metre lengths so an entry put at least 10.6 metres long is required to accommodate the combine length of the pipe and thrust boring machinery. An exit pit is usually dug on the opposite end of the work are although it is not always required. Auger boring can be effectively used to install pipe sections with a maximum combined length of no more than 70 metres.

Step 3

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Thrust boring generally works best in soils that are located about the groundwater table. When groundwater is present during a boring operation, special dewatering measures must be taken to prevent the steel pipe casing from being flooded with water. Once the final section of casing has reached the exit pit, the auger and cutting bit assembly is removed. After the thrust boring machinery has been detached from the steel pipe the carrier pipe or conduits are installed through the casing. Where grade pipe is installed, in the case of grade carrier pipes, timber blocks are strapped to the pipe to help maintain grade. Any remaining space is usually filled with a Hi flow grout. Once the installed pipe work is connected to existing or new infrastructure both the entry and exit its can be backfilled.

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