San Diego County Water Authority’s Rapid Response to Thrust Restraint Issues in the Second Aqueduct at Moosa Canyon
The San Diego County Water Authority’s Second Aqueduct, which comprises Pipeline 3 (72 in. diameter welded steel pipe), Pipeline 4 (90 in. diameter PCCP), and Pipeline 5 (96 in. diameter PCCP), makes a 20° horizontal bend at Moosa Creek at the bottom of the Moosa Canyon, where the creek has changed course over the years, and soil has been eroded, resulting in reduced soil cover and variable soil stiffness along the thrust restraint zone of the three pipelines. Despite the relatively mild bend angle, high internal pressures at this location increases the importance of adequate thrust restraint. In fall 2019, a leakage in the first PCCP segment adjacent to the bend in Pipeline 4 prompted an emergency declaration by the Water Authority and subsequent condition assessment and emergency carbon fiber reinforced polymer (CFRP) strengthening of the bend and several adjacent PCCP segments. Shortly thereafter, similar inspections and analyses were performed on the adjacent Pipelines 3 and 5, which indicated inadequacy of thrust restraint in Pipeline 5 as well and resulted in similar CFRP strengthening. This paper presents the Water Authority’s response with support from its consultant for these projects and some key takeaways from the Water Authority’s perspective.