Feature by Allison Halvorson, CPSM
The McMillen Jacobs Associates Underground Division was founded in 1954 and has been providing underground engineering innovations that have advanced the state of the industry for nearly seven decades. Highlights include:
The Jacobs Sliding Floor (1959)
In 1959, Don Jacobs conceived and patented this self-propelled trackway system that significantly increased efficiency in drill-and-blast hard rock tunneling during the time when the drill jumbo, mucking machine, and muck cars were rail-mounted. Its first use was on the 5-mile-long (8 km) Camino Tunnel in Northern California’s Sierra Nevada.
North Outfall Consolidation N-2 Tunnel: First Use of an Earth Pressure Balance Machine in the United States (1980)
The firm helped the City of San Francisco implement the first earth pressure balance (EPB) tunnel boring machine (TBM) in the United States, changing the way soft ground tunnels are built in North America. Important lessons learned about EPB operation included how to induce small amounts of heave to counter surface settlements in very soft soils and how pore pressure variations influence consolidation settlements.
Tren Urbano Stacked Drift Mined Station (1999)
Tren Urbano in San Juan, Puerto Rico, stretches 17.2 kilometers (10.7 mi) with 16 stations. The most complex portion of our work was the cavernous Río Piedras Station—19 meters (62 ft) wide, 16 meters (52 ft) high, and 150 meters (490 ft) long, with only 4 meters (13 ft) of cover. At the time it was one of the largest diameter soil tunnels ever constructed—built using a stacked drift design in which the tunnel lining, consisting of 15 individual tunnels, forms a horseshoe-shaped arch.
North East Interceptor Sewer Dual Cell Shafts (2004)
The project upgraded the City of Los Angeles’ aging sewer infrastructure system. McMillen Jacobs provided multiple services during planning, design, and construction. The project included two figure eight shaped shafts excavated by hydrofraise (aka “hydromill”) through soft ground and sedimentary rock. These were some of the first multicell diaphragm slurry walls in North America.
Claremont Tunnel Seismic Upgrade (2007)
Our bypass tunnel design was the first of its kind. An expanded vault section across the Hayward Fault can accommodate up to 8.5 feet (2.6 m) of displacement without interruption of water flow. Inside the tunnel, a carrier pipe provides additional protection for water conveyance and will maintain lifeline service to customers following a magnitude 7.0 earthquake. The pipe rests on sliding cradles, enabling it to shift within the vault during fault rupture.
Arrowhead East and West Tunnels: High External Head Segmental Lining (2008)
The project consists of two 19-foot-diameter (5.7 m) tunnels: the 6-mile (9.6 km) East and 5-mile (8 km) West contracts. The lining design will allow the tunnels to withstand a magnitude 8.0 earthquake. A special lining, where the alignments cross San Andreas Fault’s three active splays, will accommodate fault rupture. The initial lining was designed to seal against over 900 feet of hydrostatic head, the highest pressure for precast segmental tunnel lining design at the time.
Willamette West Side CSO: First Use in the United States of a Large Diameter Slurry TBM (2011)
This project has over 10,000 feet (3 km) of near-surface storm sewer lines, a deep, over 18,000-foot-long (5.5 km) tunnel, and six deep shafts, including the Swan Island Pump Station. The 135-foot-diameter (41 m), 160-foot-deep (49 m) pump station is one of the largest shaft excavations in soft ground in the United States. The 120-foot-deep (37 m) tunnel, with water head exceeding 100 feet (30 m), crosses under the Willamette River. Its excavation involved the first large-diameter slurry TBMs used in the United States.
M4 East Tunnel: Triple Cell Ventilation Shaft (2017)
M4 East is Stage 1 of WestConnex and consists of two 5-kilometer-long (3.1 mi), three-lane tunnels. McMillen Jacobs provided geotechnical and structural detailed design of temporary and permanent supports for the mainline tunnels including water-resistant linings, cross passages, breakdown bays, substations, portals, ventilation shafts and tunnels, and temporary access tunnels. The ventilation shaft was designed as a triple cell excavation, another first in shaft design and construction.
Tieback Anchor Alignment and Access Device Patent (2021)
US and Australian patent offices granted McMillen Jacobs a patent and/or intellectual property protection for the Tieback Anchor Alignment and Access Device (TAAD), which makes building tieback walls easier. This double-wide flange steel insert for tieback retaining walls forms a hollow conduit to allow a drill rig to drill down through the device and quickly de-tension all tiebacks from the surface. When incorporated early in the design process, TAAD can provide significant savings in construction schedule for deep, waterproofed excavations associated with tall buildings and cut-and-cover transportation.