PROJECT PROFILES
SANDY RIVER CROSSING
Horizontal Drilling
Greater Portland, OR
BACKGROUND
Residents of the greater Portland area receive an average of 100 million gallons of water each day from the reservoirs in the Bull Run watershed. Three large diameter steel conduits are the backbone of this transportation system and yet range in age from 55 to 95 years old. Along the journey from the reservoir to Portland, this gravity-fed pipeline system crosses the Sandy River and numerous other rivers and streams.
Since the late 1990’s the Portland Water Bureau has been studying the water system and has identified locations that would be vulnerable if an earthquake, landslide, or human-caused problem were to occur. The Sandy River Crossing Conduit Relocation Tunnel Project was devised to safeguard two of the main conduits that currently cross the Sandy River on a 113 year old bridge just north of the City of Sandy. The Water Bureau plans to relocate these conduits in a tunnel under the Sandy River near the existing road and bridge.
PROJECT
Gregg Drilling was contracted by Shannon & Wilson to provide expert and complicated drilling services on short notice in March of 2009. The drilling was required to support the design of the Sandy River Crossing tunnel.
The prime contractor on-site was not allowed to proceed with the tunnel boring until drilling was completed and instrumentation installed. Time was of the essence as a substantial amount of people and equipment would be placed on hold while horizontal drilling, testing, and instrument installation was completed.
In addition to the time constraint, the complexity of the project was further increased by the requirements of the project. The project required a 14,000lb drill rig be lowered into a 70ft deep shaft. The borehole to be drilled through the wall of the shaft was an HQ3 diamond cored horizontal hole to 380ft. Further complexities of the project included horizontal packer testing and tolerance deviations that could not exceed 1%. Gregg Drilling employed their knowledge, experience, and specialized equipment to complete the task to the specified requirements. Gregg’s Mito track rig was used to drill horizontally through the shaft wall and an EZ shot tool was used to identify dip and azimuth.
Gregg also successfully installed and grouted in two casings, a cable, and a pulley assembly for a settlement profiling system. The profiler worked as designed throughout the duration of the tunneling operation. A member of Shannon & Wilson’s geology staff commented that “threading 900 feet of cable through two different sized PVC casings while keeping everything clean and in tact at the bottom of a muddy 30 foot diameter shaft was an impressive endeavor.”
The project was completed on budget and within only 90% of the allotted time, saving the prime contractor precious time and money. The packer testing was successful and the borehole deviation did not exceed the tolerances considered acceptable to the Client.
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Additional Information | |
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| See Also: | View/Print | |
| Exploration/Mining Services | Rotary/Coring Datasheet | |
| Mito Rig Specifications | Exploration/Mining Datasheet | |
Sandy River Crossing Conduit Reloation Tunnel Project Area
Sandy River Crossing Conduit Reloation Tunnel Diagram
Gregg's Mito track rig lowered in 70ft deep shaft
Gregg’s Mito track rig was used to drill horizontally through the shaft wall