Waste Water Force Main Pipe Construction Alternatives to Protect Existing Foundations in the City of Chandler: Case Study

To provide additional wastewater capacity and redundancy in South Chandler, Arizona, a new 28" High Density Polyethylene (HDPE) force main was installed from the upsized Kyrene Lift Station three miles east to tie into an existing 66" transmission sewer line. The force main was installed under the State Route Loop 202 (SR 202L) freeway through existing 48" steel casings constructed ten years prior. Additionally, the force main was constructed through a narrow Arizona Department of Transportation (ADOT) corridor, which required clearance from existing utilities, including overhead 69 kV power poles. Two locations required innovative solutions to both access the existing sleeves and cross the transmission power pole foundations: 1) crossing of the 69 kV power pole required detailed slope stability analysis and location specific trench backfilling; and 2) access to the existing 48" was within 15 feet of an existing ADOT sound wall. Various alternatives for access were analyzed in this paper including temporary shoring, sheet pile installation, and full wall replacement and reconstructing on drilled shafts. Based on the objectives above, the existing power pole does not have sufficient embedment for maximum design loads but is stable with reduced load factors and lower operation wind forces. Also, for construction issue with the existing ADOT sound wall, the temporary shoring and sheet piles used due to the geotechnical conditions and construction costs.