TECHNICAL | DRILL & BLAST
Insert standpipe
Insert inflatable packer setting tool
Expand standpipe anchor section Right:
Grout-free expandable standpipe installation
Retrieve setting tool and conduct standpipe pressure test
Drill through standpipe to target depth
Pump grout
OPTIONAL: Remove standpipe extension after grouting
● Drill-through Expandable Standpipes – an elastomer-covered standpipe that is installed using an in-situ hydroforming technique and utilizes a high-pressure inflatable packer to expand and press the standpipe directly to the borehole wall.
● Drill-through Temporary Standpipes – utilizes an inflatable packer to create a seal during drilling and grouting activities, and can be removed to be re-used in another location. These systems are also particularly effective in tunnel boring machine (TBM) operations because no steel is left in the probe/grout holes once activities are completed.
DRILL-THROUGH EXPANDABLE STANDPIPES The grout-free expandable standpipe was developed for a drill and blast mining operation that required extensive PEG to control groundwater ingress. Initially, the operator was using conventional standpipes with centralizers and cementitious grout to withstand
grouting pressures exceeding 70 bar (~1000psi). The operator experienced a high rate of failure with the conventional approach that required a 24hr grout cure time and thus experienced significant costly down time.
High pressure inflatable packers have been used
for setting expandable casing patches in water wells for many years. This same technology is now being applied for installing elastomer-covered standpipes in rock holes. The expanded standpipe conforms to the borehole wall and acts as an anchor and sealing component, eliminating the need to grout. The expansion process is completed in a matter of minutes, after which the sealing and anchoring integrity of the standpipe can be tested immediately.
42 | Spring 2023
Once the standpipe is fully expanded, the inflatable packer is removed, and the standpipe can be pressure tested. The minimum length of the expanded portion of the standpipe is approximately 1m (3.3ft). The seal length can be extended simply by moving the expansion tool to a new location and re-energizing the expansion tool. The length of expanded standpipe required to achieve adequate sealing will be dependent on-site geologic conditions.
Typical standpipe dimensions are 73mm o.d.
(2.875-in) and 3m-long (10-ft). Length and diameter can be adjusted to suit project needs. Installation is achieved by first drilling a pilot hole slightly longer than the standpipe length. After the pilot hole is flushed to remove cuttings and debris, the standpipe is inserted leaving the desired length of stick-out at the face. The expansion tool is then inserted into the standpipe
and energized to approximately 480 bar (~7,000 psi) to expand the standpipe and compress the elastomer
cover against the borehole wall. It is energized using either an air-driven liquid pump (water inflation), or a battery-powered hydraulic pump (oil inflation). Under no circumstances should gas be used as an inflation medium for this process. The expansion process takes approximately 200
seconds from initiating packer inflation to completing the expansion. The pressure-vs-time plot demonstrates the distinct phases of the expansion process: a) packer inflation within the standpipe b) increasing packer pressure in the elastic range of the standpipe
c) standpipe yield and expansion, and d) standpipe coming in contact with the borehole wall and compression of the elastomer cover.
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