How Phoenix Overcame Challenges to Complete a Major System Resiliency Project: CMAR Alternative Delivery Method Impacts

Phoenix embarked on a major potable water transmission project in 2018 that included over 15 mi of 42″−66″ pipelines, three new booster pump stations along with numerous system interconnections and pressure reducing stations. At the beginning of the project, the City selected a program manager, engineers, and construction manager at risk (CMAR) contractors for each project component. This proved beneficial especially for the Segment 1–66″ pipeline portion of the project. Segment 1 is located along a major north south corridor in the center of the City’s water service area, including through a mountain preserve, next to a dam, sensitive neighborhoods, along and under a state highway. In addition to COVID, supply chain issues, and cost escalation, the City and its team overcame numerous other challenges, including neighborhood opposition at the initial stages of the project, numerous jurisdictional washes within the alignment, designing, and building a pipeline in a 40′ wide corridor with a steep slope up to homes with backyard pools on one side of the corridor and a 20′ tall highway sound and retaining wall on the downslope side. To avoid going under a 30′ long 20′ deep storm drain drop section and other critical transmission pipelines next to the highway wall, the team came up with a plan to use an existing planter space between the drop section and the wall to route the pipe above grade, protected with concrete encasement. The encasement is screened by a wall matching what was once a planter. Low water use cactus and shrubs were placed in the planter to return area to its planter aesthetics. Within the mountain preserve, the depth to rock is between 3 and 4 ft and testing showed it to have an unconfined compressive strength from 3,000 to 20,000 psi. Due to the fact that there is a major Corps of Engineers flood control dam in the preserve, blasting for trenching was not allowed. The engineers and CMAR worked together to understand the trenching conditions including completing rock coring and testing as well as test excavations with various excavation methods and equipment. In addition to the presence of hard rock, testing and geologic observations showed the rock to be tilted with variable depth particularly along the location where the pipeline needed to cross under the freeway. This required the team to conduct additional investigations, included drilling a boring in the middle of the freeway at night and implementing additional monitoring of the tunnel boring machine excavation under the freeway during construction. This presentation will describe the challenges and how the City and its engineer and CMAR team worked through them resulting in a successful project meeting the Water Services Department’s goals.