SOIL STABILIZATION/GROUND IMPROVEMENT
SANTA ANA RIVER LEVEE IMPROVEMENT
SANTA ANA, CALIFORNIA
In 2010, Sacramento Regional County Sanitation District (SRCSD) completed the installation of 12 foot diameter sewer lines that would improve the sewer system in the Natomas area of Northern Sacramento County. The construction method used to install this sewer line was by micro-tunneling, also known as horizontal drilling. In locations where manholes were installed, the horizontal drill remained idle, loosening the surrounding soils due to vibration.
Particular locations that saw the greatest impact were at the Zone 3 and 18 manholes which began to form substantial subsidence sinkholes that could pose a significant public safety hazard. In 2012, SRCSD contracted Great Lakes E&I for remediation services covering 100% of the area of concern using Deep Soil Mixing (DSM), or In Situ Stabilization (ISS), to accomplish the necessary ground improvement.
The Upper Northwest Interceptor Ground Improvement Project included In Situ Stabilization of approximately 650 cy of soil. Great Lakes E&I developed a mix design that was to achieve a minimum of 20 psi in 28 days with a minimum 90% core recovery. All deep soil mixing was performed within one foot of live underground utilities including a pressurized 36 inch water line and a 12 foot diameter sewer line. Great Lakes E&I performed the In Situ DSM using an ABI 14/17 drill rig with a 4 foot diameter auger, a fully automated MPS 100 grout plant, a low profile silo, and an intricate computerized monitoring system to complete the scope of work. Great Lakes E&I management used modern drafting and GPS technology to precisely layout the columns achieving 100% effective treatment. The computerized monitoring system combined with GPS technology allowed treatment of areas to within one foot of live utilities as well as real time quality control monitoring of pressure, verticality, flow, and auger speed (revolutions per minute).
Due to environmental concerns related to the Giant Garter Snake, Great Lakes E&I completed the base contract, along with a total of seven different field directives, within a very narrow work window. The difficulty of completing the work within a compressed time frame was made more difficult by the fact that Zones 3 and 18 are approximately five miles apart, requiring duplicate field efforts implementing best management practices to mobilize, protect areas adjacent to the work, conduct DSM operations, and perform final levee restoration. Despite the narrow work window and a five mile distance between the two work locations, the project was completed ahead of schedule and under budget. As a result of this success, SRCSD contacted additional phases utilizing this same method of treatment.
The second phase of the project was awarded in 2014 and involved remediation of an additional 19 zones, and included excavation and replacement of approximately 1,000 cy of soil and In Situ Stabilization of approximately 6,700 cy of soil.