In December 2012, Urban Systems and the City of Kamloops, British Columbia, Canada, put out a select tender to pre-qualified bidders for the Kamloops Sewage Treatment Center (STC) Upgrade. This project would upgrade the existing 9.774 million gallons/day (37,000 m³/d) of treated sewage to 15.850 million gallons/day (60,000 m³/d).
The City of Kamloops STC Upgrade required that the sewage continue to be received and treated during the project. The operators of the facility had to be involved throughout the construction period to deal with any potential impact on the existing facility. This requirement resulted in a critical path method with the construction schedule. A new fixed horizontal outfall was required to be placed out into the Thompson River which will be structurally supported with pilings.
Kamloops Augering & Boring Ltd.’s vast experience in pipe ramming in all types of ground conditions and working environments allowed the company to be the trenchless contractor of choice for the successful bidder, Maple Reinders Inc. This casing installation would have been a traditional pipe ram of 36-in. (900-mm) size casing into the Thompson River. Now, the installation became more technical and precise due to the construction schedules and water levels and the installation of the pilings. This dramatically changed the crossing. A spring construction schedule being timed with low water was part of the game plan. The very gradual slope of the riverbed also required precise grade control and there was little room for error.
Kamloops Augering & Boring offered a turnkey package for the general contractor in which it excavated its own jacking pits and provided all its own support to get the job done as efficiently and timely as possible. However, the anticipated and historically low water levels were not a reality and excavation of the contractor’s jacking pit had to start. The entry pit had to be moved approximately 10 m back so crews could control the water table. Two 3-in. sumps were installed at the front of the pit for water control. The easy part of this project was now complete. How was the Kamloops crew going to install the 36-in. (900-mm) casing approximately 82 m on line/grade and between the pilings out in deep water and a fast moving current?
Kamloops Augering & Boring was very comfortable with the expected ground conditions and maintaining a dry pit for ramming the casing. The overall distance was manageable and the contractor had the technology for installing the pipe as per design. The crew had to make use of its Guided Bore Machine (GBM) for this installation. However, the river water levels were not dropping as had been expected. This was very concerning as how do you deal with the pilot tube rods? Typically, there is an exit pit for breaking the rods off when you reach your target and begin installing the casing.
The river posed a unique challenge. Crews had hoped that the river would be much lower and that the dynamic river bed movement due to sediment loading and re-deposition would be favorable. This was not the case and even using divers for breaking off the rods became a workplace hazard Kamloops Augering & Boring did not want to even consider so it began brainstorming and thinking outside the box.
Kamloops Augering & Boring made some adjustments to its elevations for installing the pilot tubes. The crew knew it could easily drill the pilot tubes to the edge of the river bank and be used as a guide for the installation. Once the pilot tubes were in place, the crew installed nominal 12-in. (300-mm) pipe. This pipe was used to engulf the pilot tubes. The crew split the auger bore machine so it could still use the GBM to rotate the pilot tubes during the 12-in. (300-mm) installation. With the ABM hydraulics and GBM rotation, the crew could spin the rods and move the rods like a piston, while the 12-in. (300-mm) pipe engulfed the rods.
The crew then employed its Gigant pneumatic hammer for driving the 12-in. (300-mm) pipe into place originally and then had to employ its Koloss hammer due to the increase in required energy. The crew stopped rotating the rods and was able to drive the pipe to the desired distance. This worked as well as anticipated, but difficult to complete. The 12-in. (300-mm) pipe was secured from moving within the 36-in. (900-mm) via a cable system that ran internally through the 12-in. (300-mm) then back through the annulus and between the split in the ram segments. The cable then went over the hammer and was anchored to a 330 Kobelco Excavator at the back of the pit. Now, the crew had 12-in. (300-mm) pipe complete with pilot tubes as its guide for the 36-in. (900-mm) pipe.
A Taurus Pipe Rammer was used to install the 36-in. (900-mm) pipe with one 825 cfm (23.1 m³/min) up to the 100-ft (30-m) mark. Another 825-cfm (23.1 m³/min) compressor was added to advance the casing to the 200-ft (60-m). A third company owned a compressor of the same magnitude and it was employed to drive the casing through but short of the pilings. Now the casing was on line and grade, but full of material and guide pipe/pilot rods.
The engulfment method for controlling line and grade proved to be very successful in the ground conditions encountered. However, removal was a difficult task. Kamloops Augering & Boring used its Hydraulic Thrust Boring Machine to pull the pilot tubes and the 12-in. (300-mm) from the outfall casing. After this pipe/pilot tube configuration was removed the water inflow from the high river level was not manageable. The jacking pit was now flooded. To solve this problem a 36-in. (900-mm) inflatable test plug was installed in the pipe in the pit. Once the crew was able to control the inflow, the pit was pumped dry.
The final stage for installing the 36-in. (900-mm) casing was for the general contractor to install the support beams between the piles out in the river. A pile driving barge with a crane and divers was required.
Everything now was in place for to advance the casing the final 30 ft (10 m). With the Taurus Hammer, Kamloops Augering & Boring installed the outfall casing into the design position. The divers then installed a uni flange and blind flange to the end of our pipe. This allowed test plug to be removed and the remainder of the material to be augered out.
Harry Dickinson, AScT, is project coordinator for Kamloops Augering & Boring Inc., which is based in Kamloops, British Columbia, Canada.