Phoenix, Arizona

Services Provided:  Civil Engineering, Land Planning, Storm Water Management, Landscape architecture

Project Description: Adobe Dam is an earthen dam structure located in north Phoenix from 30th Avenue to 43rd Avenue crossing Deer Valley alignment and providing flood control via Skunk Creek.  It is owned and maintained by the MCFCS.  A 200-acre plot of land above the 100-year flood pool, Adobe Highland, was eligible for residential development.  The City of Phoenix stipulated a gravity sewer system with outfall just east of 35th Avenue, which was south and across Adobe Dam making penetration of the dam necessary.  It was necessary to coordinate with the following regulatory agencies from the design process through the construction of the actual sewer:  ACOE, ADWR Dam Safety, MCFCD, and City of Phoenix.

The project requirements were not to disturb the dam’s core nor create a path for any impounded water.  The ability to monitor the real time impacts and provide for permanent inspection were challenges that had to be met in addition to the sewer design and as-built criteria.  After much research and discussion regarding penetration techniques, it was determined that pipe ramming would be the means used to penetrate the dam.  It met the criteria and had been used by ADOT in other projects with success; in addition, there was local experience with the process.

The recommended solution consisted of the pipe ramming of a 24-inch, 0.656-inch thick steel casing beneath the dam into which the 10-inch gravity sewer line would be installed.  Pipe ramming is a trenchless technology process that utilizes a hydraulic hammer to advance a steel casing pipe through otherwise undisturbed soil.  No voids or pockets are created by the advancing pipe.  The earth within the casing pipe is removed following its complete installation.

With thorough knowledge of soil conditions, dam construction, and vigilance during the entire project, there was no impact to the dam and the 10-inch sewer was successfully installed across Adobe Dam.