Yerba Buena Tunnel

Yerba Buena Tunnel

Eastern portal of the Yerba Buena Tunnel, upper deck. Pictured in December 1994.
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Overview
Other name(s)	Yerba Buena Island Tunnel
Location	San Francisco, California
Coordinates	37°48′34″N 122°21′56″W
Route	I-80
Crosses	Yerba Buena Island
Operation
Work begun	July 9, 1933
Constructed	1933–36
Opened	November 12, 1936 (1936-11-12)
Rebuilt	1961–62
Owner	Caltrans (District 4)
Traffic	automotive
Vehicles per day	250,000 (2014)[1]
Technical
Design engineer	Charles H. Purcell
Length	540 ft (160 m)
No. of lanes	10
Tunnel clearance	58 ft (18 m)
Width	76 ft (23 m)

The Yerba Buena Tunnel, also known as the Yerba Buena Island Tunnel, is a highway tunnel in San Francisco, California. It is the part of San Francisco–Oakland Bay Bridge complex that crosses Yerba Buena Island. The Yerba Buena Tunnel carries ten lanes of Interstate 80 (I-80) on two decks, connecting the two component spans of the Bay Bridge, the western suspension span and the eastern self-anchored suspension span. At the opening of the Bay Bridge in 1936, it was the world's largest-bore tunnel.

History

Preliminary surveys to lay out the route of the planned Bay Bridge were held in April 1931.^[2] Dedication ceremonies were held on February 24, 1932,^[3] and by April 1932, the final design for the Bay Bridge, including the single-bore tunnel through Yerba Buena Island, had been completed and submitted for approval.^[4] The contract to build the Yerba Buena Cable Anchorage, Tunnel & Viaduct segment was opened for bids on March 28, 1933, and awarded to the low bidder, Clinton Construction Company of California, for $1,821,129.50 (equivalent to $34 million in 2023^[5]).^[6][7] Yerba Buena Island was the main site of the official groundbreaking for the Bay Bridge on July 9, 1933, when President Franklin D. Roosevelt remotely set off a dynamite blast on the eastern side of the island at 12:58 p.m. local time.^[8][9] Former President Herbert Hoover and Governor James Rolph were onsite; the two men were the first to turn over the earth with ceremonial golden spades.^[10] Other ceremonies took place simultaneously in San Francisco (on Rincon Hill) and Oakland Harbor.^[8][11]

The Yerba Buena Tunnel opened, along with the rest of the Bay Bridge, on November 12, 1936. As of 2019,^[update] the tunnel lacks an official name.^[12]

Corrosion

On January 30, 2016, a chunk of concrete the size of an automobile tire fell from the tunnel wall into the slow lane of eastbound traffic on the lower deck of the Yerba Buena Tunnel, causing a minor accident. The concrete fell from where the upper deck is connected to the tunnel wall. Based on an examination of photographs, a professor from Georgia Tech postulated that water infiltration into the concrete wall had caused the reinforcing steel to corrode and expand, forcing a chunk of the tunnel wall out.^[13] A subsequent California Department of Transportation (Caltrans) investigation identified 12 spots on both sides of the tunnel wall in the lower deck space showed signs of corrosion-induced damage, but no immediate risk of further spalling. The apparent cause was rainwater leaking from upper deck drains. Caltrans engineers speculated the Masonite pads had swelled due to rainwater infiltration, cracking the tunnel walls and allowing moisture in to the reinforcing steel.^[14]

Repairs to the degraded concrete started in February 2017. Drains and catch basins were replaced to reduce the likelihood of clogging, and fiberglass-reinforced mortar was used to patch removed concrete. The repairs, which required some daytime lane closures, were expected to last until June 2017.^[15]

Design and construction

California Department of Transportation engineer C.H. Purcell served as chief engineer for the Bay Bridge, including the construction of the Yerba Buena Tunnel. Before starting excavation, the ground through which the western half of the tunnel would be bored was stabilized by injecting cement grout under pressure through 25 1.5-inch (38 mm) holes bored into the loose rock over the crown of the tunnel.^[6]

After excavating the western and eastern open portals, three drifts were bored from west to east along the path of the tunnel: one at the crown and the other two at the lower corners.^[6][9] The first drift broke through in July 1934, approximately one year after the start of construction.^[16] A ceremonial party led by Governor Merriam celebrated the completion of the first 12-foot-square (3.7 m) drift on July 24 by walking through it, followed by a short speech.^[17][18] The space between the three drifts was then excavated, resulting in a single arch-shaped bore (in cross-section), and the tunnel roof was constructed using 16-inch (410 mm) steel I-beam ribs spaced 3 feet (0.91 m) apart to support the rock, which were then embedded in concrete up to 3 feet (0.91 m) thick at the crown.^[6][19] No cave-ins occurred during the excavation of the tunnel.^[19]

After the roof was completed, the remaining core of rock between the tunnel roof and lower deck was excavated using a power shovel.^[6] By May 1935, work on removing the core was progressing and 40 steel ribs had been placed; concrete embedment was just starting.^[20] Removal of the core was completed on November 18, 1935.^[21] Once the excavation was complete, the upper deck was placed and the interior ceiling above the upper deck was lined with tiles.^[19] The last concrete poured during the construction of the Bay Bridge was part of the upper deck lining in late summer 1936.^[21] This included the emplacement of regularly spaced refuge bays ("deadman holes") along the south wall of the lower deck tunnel, escape alcoves common in all railway tunnels into which track maintenance workers could duck if a train came along.^[22] These remain and are visible to eastbound motorists today.

The completed tunnel bore is 76 feet (23 m) wide and 58 feet (18 m) high overall, and the dimensions of the tunnel interior are 66 feet (20 m) wide and 53 feet (16 m) high.^[23] In 1936, it was hailed as the world's largest-bore tunnel.^[24][25] The cross-sectional area of the upper half is 1,500 square feet (140 m²), and the lower half is 1,000 square feet (93 m²).^[26]

Decks and The Hump

Yerba Buena Tunnel cross-sections (facing east)

1938

1962

Redrawn from HAER drawings by Zachary Goodman

The tunnel has two decks. As originally completed, the upper deck was reserved for automobile traffic, and carried six lanes, each 9 feet 8 inches (2.95 m) wide.^[26] The lower deck was further divided into three lanes of traffic for heavy trucks (each 10 feet 4 inches [3.15 m] wide), and two railroad tracks on the south side (27 feet [8.2 m] wide for both tracks).^[23][26] The initial design in 1932 called for the two rail tracks to flank a central truck deck on the lower level.^[27] After Key System trains stopped running over the bridge in 1958, bids were opened on October 11, 1960, to rebuild the tunnel. The rebuild consisted of multiple stages of work:^[26][28]

1. Remove Key System rails, lower rail deck and repave
2. Lower the truck traffic half of the lower deck by 3 feet (0.91 m) and repave
3. Remove center columns supporting upper deck
4. Lower the upper deck by 16 inches (410 mm) by placing precast concrete units

After the reconstruction, the tunnel would handle only road traffic. The upper deck was lowered to accommodate heavy truck traffic, as each deck would now carry five lanes of unidirectional traffic. The upper deck was dedicated to westbound traffic, and the lower deck was dedicated to eastbound traffic.^[28] The impact to traffic during reconstruction of the tunnel was minimized mainly by working outside normal commuting hours and through the use of a portable steel bridge 26 feet (7.9 m) long and 58 feet (18 m) wide, designed to fit between the curbs of the existing upper deck.^[26] The bridge spanned the gap between the new upper deck and old upper deck, and the overall elevation change of 26 inches (660 mm) caused drivers to slow to 15 miles per hour (24 km/h), resulting in traffic jams.^[29][30] The first accident caused by "The Hump", the nickname the bridge acquired after prominent warning signs advertising its presence, occurred just twelve minutes after it was first deployed on November 25, 1961.^[31]

The new precast upper deck units were each 7 feet 8 inches (2.34 m) long, and were installed in two halves. One side of each half rested on a temporary falsework erected in the middle of the lower deck, and the other side rested on the shoulder of the tunnel wall previously used to support the old upper deck. After the two halves were fastened together, a steel form was used to close the 1-foot-6-inch-wide (0.46 m) gap between halves, and concrete was poured in the gap.^[26] The upper deck rests on 12-inch-wide (30 cm) shoulders built into the tunnel wall, padded by 1⁄2-inch-thick (1.3 cm) Masonite.^[14]

The planned completion date for tunnel reconstruction was July 1962,^[32] but "The Hump" was not dismantled until October 27, 1962. The San Francisco Chronicle marked the occasion by quipping "[The Hump] produced more jams than Grandma ever made."^[31] After reconstruction, both the upper and lower decks featured 16 feet (4.9 m) of vertical clearance. Upper deck clearance is restricted by the tunnel portal, and lower deck clearance is restricted by the upper deck.^[26]

Gallery

• 
  Study of West Portal (1933)
• 
  Exiting western portal (2011)
• 
  Lower deck, showing "deadman" holes on south side (2013)
• 
  Westbound traffic approaches tunnel (1998)
• 
  Westbound traffic departs West Portal (1998)
• 
  Westbound traffic in tunnel (2006)
• 
  Westbound night traffic (2008)

References

1. "San Francisco-Oakland Bay Bridge". Metropolitan Transportation Commission. Retrieved December 20, 2017. FY 2014-15 Total toll-paid vehicles: 45,534,437
2. "Trans-Bay Bridge Nearing Reality". Healdsburg Tribune. April 28, 1931. Retrieved December 20, 2017.
3. "Impressive Ceremonies Mark Official Start of Work on Transbay Bridge" (PDF). California Highways and Public Works. Vol. 10, no. 2. California Department of Public Works. February 1932. pp. 22–23, 39. Retrieved December 20, 2017.
4. "General Final Plan Accepted for the San Francisco-Oakland Bay Bridge" (PDF). California Highways and Public Works. Vol. 10, no. 4. California Department of Public Works. April 1932. pp. 22–23, 42. Retrieved December 20, 2017.
5. Johnston, Louis; Williamson, Samuel H. (2023). "What Was the U.S. GDP Then?". MeasuringWorth. Retrieved November 30, 2023. United States Gross Domestic Product deflator figures follow the MeasuringWorth series.
6. "Safety Method of Boring Yerba Buena Tunnel Leaves Core to be Removed" (PDF). California Highways and Public Works. Vol. 13, no. 9. California Department of Public Works. September 1935. pp. 20–21. Retrieved December 20, 2017.
7. "Savings of Over $9,000,000 Shown in San Francisco—Oakland Bridge Bids" (PDF). California Highways and Public Works. Vol. 11, no. 4. California Department of Public Works. April 1933. pp. 4, 15. Retrieved December 20, 2017.
8. "Three fetes mark start of Bay Bridge". Healdsburg Tribune, Enterprise and Scimitar. July 13, 1933. Retrieved December 20, 2017.
9. "Huge Monolith Rises from Bay Waters to Bear Bridge Tower" (PDF). California Highways and Public Works. Vol. 11, no. 12. California Department of Public Works. December 1933. pp. 14–15. Retrieved December 20, 2017.
10. Purcell, C.H. (July–August 1933). "Governor Rolph, Breaking Ground for Bay Bridge, Puts Hundreds to Work" (PDF). California Highways and Public Works. Vol. 11, no. 7–8. California Department of Public Works. pp. 2–3, 12–13, 26. Retrieved December 20, 2017.
11. "President Expected to Assist in Bay Bridge Ceremony" (PDF). California Highways and Public Works. Vol. 11, no. 5. California Department of Public Works. May 1933. p. 6. Retrieved December 20, 2017.
12. 2019 Named Freeways, Highways, Structures and Other Appurtenances in California (PDF) (Report). California Department of Transportation. 2020. Retrieved May 31, 2021.
13. Van Derbeken, Jaxon (February 6, 2016). "New Bay Bridge corrosion probe: Concrete chunk falls in tunnel". San Francisco Chronicle. Retrieved December 21, 2017.
14. Van Derbeken, Jaxon (February 21, 2016). "More damage found to concrete wall in Bay Bridge tunnel". San Francisco Chronicle. Retrieved December 21, 2017.
15. Cabanatuan, Michael (March 19, 2017). "Daytime lane closures for Bay Bridge tunnel repairs". San Francisco Chronicle. Retrieved December 21, 2017.
16. "Yerba Buena Tunnel Diggers Near Light". Madera Tribune. June 23, 1934. Retrieved December 20, 2017.
17. "Governor Merriam Leads First Party Through Yerba Buena Pioneer Bore" (PDF). California Highways and Public Works. Vol. 12, no. 8. California Department of Public Works. August 1934. pp. 16–17. Retrieved December 20, 2017.
18. "Island shaft for Bay span is completed". Healdsburg Tribune. United Press. July 25, 1934. Retrieved December 21, 2017.
19. Andrew, Charles E. (February 1937). "Construction History of San Francisco Bay Bridge" (PDF). California Highways and Public Works. Vol. 15, no. 2. California Department of Public Works. pp. 10–11, 20. Retrieved December 20, 2017.
20. "Bay Bridge to Have 16 Toll Stations All Located on the Oakland Approach" (PDF). California Highways and Public Works. Vol. 13, no. 5. California Department of Public Works. May 1935. pp. 12–13. Retrieved December 20, 2017. Far inside Yerba Buena, miners have bored ribs down from a crown tunnel to two side tunnels and placed 40 I-beams in these lateral drifts. For 20 feet [6.1 m], steel lining has been placed on top of the I-beam ribs, and the space between these plates and the rock roof has been packed with broken rock. The work of concreteing this loose rock above the steel, all of which later will be encased in concrete, has just been started.
21. Purcell, C.H. (November 1936). "Chief Engineer Purcell Tells Construction Story of the Bridge" (PDF). California Highways and Public Works. Vol. 14, no. 11. California Department of Public Works. pp. 6–8. Retrieved December 20, 2017.
22. "Tunnel Section and Details, Yerba Buena Crossing, San Francisco-Oakland Bay Bridge, Sup. Drawing No. 19A" (PDF). State of California, Dept. of Public Works. June 1934. Archived from the original (PDF) on April 18, 2003.
23. "Yerba Buena Tunnel Bore Completed with Removal of all Core" (PDF). California Highways and Public Works. Vol. 13, no. 12. California Department of Public Works. December 1935. pp. 26–27. Retrieved December 20, 2017.
24. "Ready great fetes start bridge trips". Madera Tribune. November 10, 1936. Retrieved December 20, 2017.
25. "Facts about the San Francisco-Oakland Bay Bridge". Madera Tribune. November 12, 1936. Retrieved December 20, 2017. The Yerba Buena Island Tunnel, 65 feel wide by 52 feet high, through which a four-story building could be towed upright, is the largest diameter bore in the world.
26. Raab, N.C. (January–February 1962). "Bay Bridge: Second Phase of Reconstruction Nearing Completion" (PDF). California Highways and Public Works. Vol. 41, no. 1–2. California Department of Public Works. pp. 36–43. Archived (PDF) from the original on December 3, 2017. Retrieved December 20, 2017.
27. Purcell, C.H. (January 1932). "Transbay Bridge Tunnel Unit to be World's Largest Cross-Section Bore" (PDF). California Highways and Public Works. Vol. 10, no. 1. California Department of Public Works. pp. 6–7, 17. Retrieved December 20, 2017.
28. "Bid Opening Set for Yerba Buena Tunnel" (PDF). California Highways and Public Works. Vol. 39, no. 9–10. California Department of Public Works. September–October 1960. p. 40. Archived (PDF) from the original on August 26, 2016. Retrieved December 20, 2017.
29. "Commuters Learning to Live with Bay Bridge Tunnel Hump". Madera Tribune. United Press International. November 28, 1961. Retrieved December 20, 2017.
30. "Bay Bridge Hump Work On". Madera Tribune. United Press International. December 28, 1961. Retrieved December 20, 2017.
31. Nolte, Carl (February 5, 1996). "Bridge Has Been on This Road Before / Bay span's revamp was a mess in '60s". San Francisco Chronicle. Retrieved December 21, 2017.
32. "Bay Bridge Hump Is Inspected By Works Director". Santa Cruz Sentinel. Associated Press. December 27, 1961. Retrieved December 20, 2017.

External links

• Yerba Buena Tunnel at Structurae
• "Yerba Buena Tunnel". Bridgehunter. October 2, 2014. Retrieved December 20, 2017.
• "Folder: Bridges, Bay, Yerba Buena Tunnel". San Francisco History Center, San Francisco Public Library. 1936–1961. Retrieved December 20, 2017.
• "Folder: Bridges, Bay, Construction, Yerba Buena Tunnel". San Francisco History Center, San Francisco Public Library. 1934–1936. Retrieved December 20, 2017.