UNCOVERING AN UNKNOWN UNDERGROUND ASSET THROUGH CONFINED SPACE MANNED ENTRY
Dibble designed improvements for the City of Phoenix along 35th Avenue to move water from the Salt River Project (SRP) system northward to the Central Arizona Project (CAP) service area. These improvements will help to reliably deliver water to the northern parts of the City during periods of drought and during times when the availability of CAP water is reduced. This included replacing approximately 2.5 miles of an existing 36-inch water transmission main (WTM) with a new 42-inch WTM along 35th Avenue from Thunderbird Road to Grovers Avenue.
During the utility evaluation for the new pipeline’s alignment, Dibble discovered that the preferred alignment would be in close proximity to a large-diameter storm drain for approximately one mile, between Acoma Drive and Paradise Lane. When Dibble and the City were unable to locate as-builts for the one-mile segment in question, Dibble proposed a manned entry field survey as the best solution to document the storm drain. Prior to the manned entry, Dibble determined the risk of flash flooding was minimal. A subconsultant was available on site to assist with any safety concerns and confirm safety prior to the team entering the storm drain.
Dibble’s survey team determined the horizontal and vertical alignment of the storm drain during the manned entry using a robotic total station. They entered the storm drain via manholes approximately every 500 to 600 feet. Dibble also conducted a visual structural inspection to document existing conditions of the storm drain so the City could identify any needed maintenance or repairs. The team performed the investigation using both visual and non-destructive physical proving and documented conditions via photographs and video.
The survey and structural teams discovered that while most the pipeline was straight, the pipeline varied greatly in direction at the Greenway Road intersection. The data obtained at this location added valuable details to the construction documentation.
Although manned entry is relatively uncommon, Dibble successfully used it to accurately locate the 35th Avenue storm drain on construction documents and assess the condition of the storm drain for future maintenance efforts.