Water Resources Engineer City of Santa Fe Utilities Santa Fe, NM
Abstract Description: The Nichols Dam conduit was constructed within the incised rock channel of the Santa Fe River. The conduit was constructed with 44 individual cast-in-place concrete segments that make four bends within the dam footprint. There were open construction joints between all of the segments. Water was seeping through two of the joints and pressurized water was emanating through three of the joints.
As part of the Nichols Dam Rehabilitation project, the City of Santa Fe Utilities wanted to change the operation of the dam from upstream hydraulic control to downstream control in order to install a hydroelectric turbine. The design of the relined conduit needed to address both the internal water pressure and external embankment loads, capacity to meet future water demand, and be constructed within the existing 5-foot diameter conduit with bends.
HDPE pipe was considered the superior relining method, due to the pipe being able to carry both the internal and external loads, durable and flexible nature of the material, and proven pipe reliability. The challenge was how to insert the heavy pipe into the existing conduit with bends.
The conduit was relined using stainless steel casing spacers attached to 420 linear feet of 28-inch DR 15.5 HDPE pipe. The spacers were placed every 10-linear feet along the HDPE pipe. Six 2-inch HDPE grout lines of various lengths were attached to the casing spacers as the HDPE pipe was slid into place. The calculated push pull force needed to insert the pipe and casing spacers and bend the HDPE pipe through the conduit was 24,000 lbs. The casing spacers were installed and the HDPE pipe was inserted into the conduit in a single 10-hour day.
Grouting was completed using a continuous placement to minimize the chance of high spots. Approximately 240 cubic yards of grout was placed over 40 hours. A video inspection was completed following grouting operations to confirm no high spots in the HDPE pipe.
This paper will present photos of the HDPE pipe welding, casing spacer installation and relining and grout placement.
Learning Objectives:
Demonstrate the multiple benefits of using casing spacers to reline conduits with multiple bends.
Demonstrate the benefit of using HDPE pipe to convert upstream control dam to downstream control for hydropower purposes.
Demonstrate the cost savings and minimizing construction schedule by the use of single stage grouting.
