Steve Dubnewych (alumni) and Sarah Wilson, Jacobs Associates, will present:
Design and Construction of a Deep Excavation for the Lake Mathews Outlet Facilities Project
ABSTRACT: The Lake Mathews outlet facility, operated by the Metropolitan Water District of Southern California, serves as one of the prime distribution sources of Colorado River Aqueduct water for Los Angeles, Orange and Riverside Counties servicing a population of 8.4 million. The seismic vulnerability of the existing outlet tower at Lake Mathews reservoir necessitated the design of a new outlet facility to assure serviceability of the facility following a major earthquake. One of the key components of the new facility is a 35 m deep excavation required for the construction of a new outlet tower. The excavation is entirely within highly weathered to fresh, blocky granitic rock. Construction of a 7 m high sheetpile cofferdam permitted excavation to proceed in-the-dry, and a comprehensive grouting program was performed around the excavation to control water inflows. The performance of the excavation was monitored with slope inclinometers and piezometers and by optical survey techniques and visual observations.
Claremont Tunnel Seismic Upgrade Project
ABSTRACT: The East Bay Municipal Utility District’s Claremont Tunnel is an 18,000-foot long water tunnel that crosses the Hayward Fault zone near Oakland, California. It was originally completed in 1929. This project involved the construction of a bypass tunnel through the fault zone, including an enlarged vault section designed to accommodate up to 8.5 feet of horizontal offset. Ground conditions encountered included sheared and crushed serpentinite and clayey fault gouge, and presented specific challenges for construction. A special excavation and support sequence used concrete-backfilled side drifts as foundations for the vault steel sets. It also allowed for a 20-foot-wide top heading and bench excavation in soft and squeezing ground conditions.
Joint Water Pollution Control Plant Tunnel and Ocean Outfall Project
ABSTRACT: The Joint Water Pollution Control Plant (JWPCP), operated by the Sanitation Districts of Los Angeles County (the Districts), treats wastewater generated by over 3 million people and processes wastewater solids generated by over 5 million people. The JWPCP Tunnel and Ocean Outfall Project, if constructed, would be one of the major marine outfall projects in the world. The new tunnel and ocean outfall system would provide relief to the existing outfall and allow inspection, maintenance, and repair of the existing tunnel and outfall system, portions of which were constructed as early as the 1930s.
Geologic conditions are challenging along the alignments within the study area being considered. Conditions include saturated alluvial soils, weak sedimentary rock, mixed face conditions, and squeezing ground conditions. Other significant challenges include the potentials for encountering up to 11 bars of water pressure, crossing seismically active faults, and encountering gassy and contaminated ground conditions. The discussion focuses on the details of the proposed project and the associated challenges.