DRILL & BLAST | TECHNICAL
The equipment required to expand the standpipes
comprises a high-pressure inflatable packer, O-ring sealed installation rods, and a high-pressure pump. The system is compact and easy to transport underground. All seals and the inflatable packer element are easily replaced on site, however a redundant expansion tool set up is recommended to minimize downtime should any of the components fail or become damaged.
DRILL-THROUGH TEMPORARY STANDPIPES An inflatable packer-based standpipe was used for the Rondout Bypass Tunnel Project in 2019. A packer with modular dual-wall standpipe
extensions is connected to the drill fitted with a BOP inside the TBM head. The inflatable packer is installed in a 104mm pilot hole in the tunnel face and energized with 20 bar (290 psi) water pressure via the annular space between the inner and outer extension rods using a simple hand pump. When the packer is in contact with the borehole wall and inflated with water, any pressure applied from within the borehole will boost the packer pressure to maintain a competent seal. The packer is designed to withstand up to 70 bar
(~1000psi) differential pressure. The inflated packer and BOP create a closed system that allows operators
to control groundwater inflow during drilling and provide pressure control during grouting. When drilling and grouting procedures are complete, the packer is deflated, the assembly is disconnected from the BOP and removed from the borehole, after which the system can be redeployed at a separate location. The inflatable packer element is designed to
withstand multiple cycles of inflation and deflation. However, if the element sustains damage during operations, the packer system is designed such that the packer element can be replaced on-site with minimal effort and tooling. Spare parts required for tool maintenance include packer elements and seal kits for redressing the packer and the dual-wall extension rods. Field experience has shown that the packer-based
standpipes perform well in TBM applications where the drilling machine is mounted rigidly in the machine. However, these systems have been less successful when used in conjunction with jumbo drills in drill and blast applications due to excessive boom movement while the drill hole is advanced. The expandable standpipe solution, discussed earlier, may be a better option for use in conjunction with jumbo drilling due to the lack of parts that can be damaged or fail when subjected to excessive boom movement.
CONCLUSION Use of grout-free standpipes minimize down time in PEG activities for tunneling projects. Expandable standpipes are effective when they can be installed outside the cutting face in TBM projects and in drill- and-blast operations utilizing jumbo drilling. Temporary standpipes using inflatable packers are advantageous in TBM projects because no steel is left in the cutting face of the tunnel, and they can be reused multiple times.
Spring 2023 | 43
Above: Photo of Standpipe and Installation Equipment
Below: Plot of Pressure-vs-Time for Standpipe Expansion, and Photo of Post-installation Pressure Test
8000 7000 6000 5000 4000 3000 2000 1000 0
1400
Installation completed
Touchwall and rubber compression
Packer inflation
1450 1500 1550 Time (seconds) 1600 1650 1700
Pressure (psi)
Yield and expansion
Pressurising
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