At first, the Folsom South Canal Pipeline Project seemed to be a straightforward undertaking. It involved the installation of approximately 24,000 linear feet of 72-inch steel pipe at depths of up to 25 feet (some of which was in solid rock) to create part of a new 17-mile pipeline to deliver water from the Sacramento River to Sacramento County and the East Bay region of California.
Plans called for the pipeline to pass beneath the nearby Mokelumne River, about 45 feet below grade. The standard way to do this is micro-tunneling (horizontal drilling), which requires the construction of vertical shafts on each side of the river. Due to the size of the shafts to be constructed (24 feet in diameter and 34 to 48 feet deep), the challenging geological conditions and the high water table, the team decided to construct the shafts using an innovative new technique that had never before been used in the U.S.
The Bauer Cutter Soil Mixing method uses a crawler-mounted rig equipped with two large cutting wheels that can be operated in both directions. A nozzle located between the wheels injects cementitious material into the freshly dug earth, which is then mixed with the soil by the rotation of the large cutters. Reversing the direction of the cutters forces the soil-cement mixture up the sides of the mixing unit to form the walls of the vertical shafts.
This technique proved to be a better way of dealing with the river’s challenging geotechnical conditions, which ultimately saved time and money.
East Bay Municipal Utility District
Folsom South Canal Pipeline