Posey and Webster Street tubes

The Posey and Webster Street tubes are two parallel underwater tunnels connecting the cities of Oakland and Alameda, California, running beneath the Oakland Estuary. Both are immersed tubes, constructed by sinking precast concrete segments to a trench in the Estuary floor, then sealing them together to create a tunnel. The Posey tube, completed in 1928, currently carries one-way (Oakland-bound) traffic under the Estuary, while the Webster tube, completed in 1963, currently carries traffic from Oakland to Alameda.

Posey and Webster Street tubes
Overview
LocationAlameda, California and Oakland, California
Coordinates37°47′16″N 122°16′38″W / 37.78778°N 122.27722°W / 37.78778; -122.27722Coordinates: 37°47′16″N 122°16′38″W / 37.78778°N 122.27722°W / 37.78778; -122.27722
Route SR 260
(Signed as SR 61)
CrossesOakland Estuary
Operation
Work begunJune 15, 1925 (1925-06-15) (Posey)
October 12, 1959 (1959-10-12) (Webster)
OpenedOctober 27, 1928 (1928-10-27) (Posey)
February 13, 1963 (1963-02-13) (Webster)
OperatorCalifornia Department of Transportation
Technical
Length3,545.1 feet (1,080.5 m)[1]
No. of lanes2 per each tube
Tunnel clearance14.67 feet (4.47 m) (Posey tube)
14.83 feet (4.52 m) (Webster St. tube)
Route map

The Posey tube is the second-oldest underwater vehicular tunnel in the US, preceded only by the Holland Tunnel. It is the oldest immersed tube vehicular tunnel in the world.

HistoryEdit

The Oakland Estuary (then known as San Antonio Creek) was first crossed by the Webster Street swing bridge for narrow gauge rail and road traffic, completed in 1871.[2][3][4] a second crossing was added in 1873 as the Alice Street swing bridge,[5] built for Central Pacific (later Southern Pacific) rail traffic.

Both the Webster and Alice bridges were replaced by new swing bridges completed in 1900 and 1898, respectively. The Alice bridge was replaced by the Harrison Street bridge, one block west.[6] The replacements were prompted by the Secretary of War, who stated the swing spans each needed to be at least 150 feet (46 m) to accommodate marine traffic in 1896. At first, it was planned to replace both bridges with a single bridge,[7] but Southern Pacific officials were unable to come to an agreement with Alameda County supervisors, and in 1897 the railroad declared the Harrison Street bridge, replacing the Alice bridge, would be devoted solely to rail traffic, accommodating both narrow and standard-gauge trains.[8] During the construction of the replacement Webster bridge, county supervisors initially rejected an offer to use the old Alice bridge as a detour for road traffic,[9] but later accepted, avoiding a more distant route through the eastern part of Alameda,[10] and teamster traffic moved to Alice in December.[11] The old Webster bridge was demolished by January 1899.[12]

By 1916, the War Department had declared the replacement Webster and Harrison bridges[13] were a menace to deep-water navigation and an obstacle to continued development of Oakland Harbor in 1916.[14] As an example, SS Lancaster rammed the Webster Street bridge in January 1926, causing the swing section to fall into the Estuary and forcing road traffic to be rerouted.[15][16] After the completion of the Posey tube, the Webster Street bridge was sold to Sacramento County for US$3,100 (equivalent to $50,000 in 2019) in November 1928.[17]

Posey TubeEdit

 
Posey tube entrance in Alameda

Preliminary plans for a tube had been explored as early as 1903, but detailed studies were not prepared until 1922.[18] However, the entry of the United States into World War I delayed the plans for a new connection between Oakland and Alameda.[14] A permit for the tube under the Oakland Estuary was granted in April 1923[19] and Alameda County voters approved a $5 million bond measure in May to build the tube.[20]

After the passage of the bond issue, test borings were taken in the Estuary, and bids were received for the work on March 23, 1925; the construction contract was awarded to the California Bridge and Tunnel Company (CB&TC) with a low bid of US$3,882,958 (equivalent to $56,610,000 in 2019), and excavation started from the Oakland end on June 15, 1925. The contract was let by Alameda County without state involvement.[14]

The Posey tube, completed and opened to traffic on October 27, 1928, was named after George Posey (Cal '06),[21] who was the Alameda County Surveyor during the tunnel's planning and construction, and also chief engineer on the construction project.[22][23] It is the first tunnel for road traffic built using the immersed tube technique.[24]:268 However, the two-lane tube was considered inadequate shortly after completion; in a 1952 letter from Frank Osborne, mayor of Alameda, to Lloyd Harmon, mayor of Coronado, which was considering a similar tunnel to San Diego, Osborne stated "from the time it was completed the tube was never adequate for the purpose for which it was built ... I am firmly of the belief that the building of any underwater tube of less than four lanes—two in each direction—would be a serious mistake on the part of any engineers who contemplate it." In 1952, the Posey Tube was handling 30 to 36,000 cars per day.[25]

DesignEdit

The ventilation buildings that house the exhaust and fresh air fans are built in an art deco style;[26] local architect Henry H. Meyers is credited with the design of both portals.[27] The ventilation of toxic vehicular exhaust fume design was modeled on that of the Holland Tunnel's ventilation system, and Ole Singstad (who had designed the pioneering ventilation system of the Holland Tunnel) consulted.[28] A pair of canaries were used during construction as living air monitors; although one canary died during construction, it was an accident caused by being penned up with a pet cat and not a toxic atmosphere.[29] Up to that time, tunnels had been vented longitudinally, with fresh air blown in one end and out the other; the Holland (and Posey) Tube instead used fans to supply air into the tunnel through a space beneath the roadway, and exhausted air through a similar space above the traffic portion. Ducts were set in the curb and ceiling approximately every 15 feet (4.6 m) along the length of the Posey Tube, providing a system of "transverse" ventilation from bottom-to-top, rather than end-to-end, ensuring that any fires would not spread through the length of the tunnel.[30]

 
Typical section of Webster Street tube; Posey Tube sections are similar.

It was the first precast concrete tube to be constructed, assembled from 12 large segments. The concrete tube was protected from leaks through insulation and coverings applied to the outer surface.[30] Each segment was cast at Hunters Point by CB&TC. After they were completed, the segments were sealed and the space beneath the roadway was filled with water as ballast while floating each segment into position; when ready, wet sand was added to the roadway to sink the segment into a dredged underwater trench. Once the joint to the prior segment had been sealed, the water ballast was pumped out and the process was repeated for the next segment.[31]

Including the approaches at each end, the Posey Tube is 4,436 feet (1,352 m) long;[23][32] the tunnel portion itself is 3,545 feet (1,081 m) long.[31] Each segment is 203 feet (62 m) long and 37 feet (11 m) in diameter, and weighs approximately 5,000 short tons (4,500 t).[31] The walls of the tube are 2 12 feet (0.76 m) thick.[14] From Oakland, the approach extends from Sixth to Third along Harrison.[31] The maximum grade within the Posey Tube is 4.59%.[14]

Webster Street TubeEdit

 
Webster Street tube entrance in Oakland

The Webster Street Tube was constructed west of and parallel to the Posey Tube to accommodate increased traffic between Oakland and Alameda and to address the deficiencies of the original design, a single tube with only two lanes. In 1941, "final negotiations" were being made for a second tube,[33] and plans for a second tube at Webster Street had been advanced in 1948 as part of a Parallel Bridge scheme. The Parallel Bridge was one of the "Southern Crossing" designs which would have added another trans-Bay bridge south of the 1936 San Francisco–Oakland Bay Bridge.[34]

Construction began on October 12, 1959.[35] To prepare the Alameda site, a large Navy hangar was moved; at the time, it set a record for the largest building ever moved.[36] The Webster Street tube was completed and opened to one-way (into Alameda) traffic in 1963.[37] Upon completion of the Webster tube, the Posey Tube was closed temporarily and renovations were performed to convert it to one-way (into Oakland) traffic; during renovations, the Webster Street tube handled bidirectional traffic.[38]

Like the preceding Posey Tube, the Webster Street tube was constructed using immersed precast concrete segments; this time the twelve Webster segments were constructed in a graving dock built on Alameda. Divers were used to ensure each segment landed in the surveyed location. Piles were driven to support each segment, but the piles were designed to collapse after an additional 600 short tons (540 t) of ballast were added, to ensure the segments rested firmly on an bed of packed sand. Construction of the Webster tube started from the Alameda end and progressed towards Oakland, with the precast segments set before additional cast-in-place segments were added at each end.[35]

Each of the Webster segments were of comparable size and configuration to the earlier Posey tube segments, measuring 200 feet (61 m) long and 37 feet (11 m) in diameter, with walls 2 12 feet (0.76 m) thick.[35] However, the Webster segments were equipped with rectangular collars 45 ft × 43 ft (14 m × 13 m) (W×H) at each end, and weighed more, approximately 5,700 short tons (5,200 t) each.[39] The roadway within the Webster tube is 24 feet (7.3 m) wide, and the minimum vertical clearance is 15 ft 1 38 in (4.607 m).[35] Including approaches, the Webster Street tube is 5,923 feet (1,805 m) long,[38] of which 3,350 feet (1,020 m) are underwater.[40]

A novel fluorescent continuous-line lighting system was designed for the Webster Tube.[41] Fresh air is supplied through the lower lunette space beneath the roadway, and exhaust is drawn through the upper lunette space above the tube's false ceiling. Each portal building contains four blowers and four exhaust fans, and are capable of nearly 1,000,000 cu ft/min (470 m3/s) of airflow in total.[35] Nearly the entire interior surface of the Webster tube is tiled.[42]

The Webster Street tube project cost more than $20 million in total,[40][43] including renovations to the older Posey tube; the construction contract for Webster was US$17,363,000 (equivalent to $145,000,000 in 2019) alone.[40]

In mediaEdit

ReferencesEdit

  1. ^ Baughn, James. "Posey Tube". Bridgehunter. Retrieved 19 March 2019.
  2. ^ "Oakland Items: Chance for Contractors". Daily Alta California. August 6, 1870. Retrieved 10 September 2020.
  3. ^ "Where's Alameda?". The California Farmer. November 17, 1870. Retrieved 10 September 2020.
  4. ^ "Oakland Items: Tax to Pay for Webster-street Drawbridge". Daily Alta California. April 12, 1871. Retrieved 10 September 2020.
  5. ^ "Oakland Items: Railroad Improvements". Daily Alta California. April 6, 1873. Retrieved 10 September 2020.
  6. ^ "The Harrison Street Viaduct a Model". San Francisco Call. July 19, 1898. Retrieved 10 September 2020.
  7. ^ "Will Bridge the Creek Together". San Francisco Call. December 3, 1896. Retrieved 10 September 2020.
  8. ^ "There Will Be Two Bridges". San Francisco Call. April 7, 1897. Retrieved 10 September 2020.
  9. ^ "Supervisors Decline the Railroad's Offer". San Francisco Call. July 12, 1898. Retrieved 10 September 2020.
  10. ^ "The Alice Street Bridge to be Saved". San Francisco Call. July 24, 1898. Retrieved 10 September 2020.
  11. ^ "Oakland News Items". San Francisco Call. December 9, 1898. Retrieved 10 September 2020.
  12. ^ "Oakland News Items". San Francisco Call. January 26, 1899. Retrieved 10 September 2020.
  13. ^ "Oakland and Alameda Soon to Be Linked by Tube Underneath Bay". Calexico Chronicle. Associated Press. December 22, 1927. Retrieved 9 September 2020.
  14. ^ a b c d e Baker, N.D. (December 1926). "The Oakland-Alameda Estuary Tube: A New Departure in Traffic Tunnel Construction". The American City. Vol. 35 no. 6. p. 815. Retrieved 9 September 2020.
  15. ^ "Traffic to Alameda Diverted Following Bridge destruction". Berkeley Daily Gazette. January 8, 1926. Retrieved 9 September 2020.
  16. ^ "Isthmian Line Freighter Hit Bridge Near Oakland, Knocked Operator and Two Boys Off". San Pedro Daily News. January 8, 1926. Retrieved 10 September 2020.
  17. ^ "After fatal turn, Alameda revamps bridge". East Bay Times. April 5, 2007. Retrieved 10 September 2020.
  18. ^ "Community Forum: What About a Trans-Bay Tube?". Coronado Compass. March 10, 1949. Retrieved 9 September 2020.
  19. ^ "War Department Gives Alameda Estuary Permit". Stockton Independent. April 3, 1923. Retrieved 11 September 2020.
  20. ^ "Alameda County Voters Vote for Tube". San Luis Obispo Tribune. May 11, 1923. Retrieved 9 September 2020.
  21. ^ "Tube Engineers Cal. Graduates". California Aggie. October 7, 1925. Retrieved 9 September 2020.
  22. ^ "Oakland-Alameda Tube Opens". Sausalito News. October 26, 1928. Retrieved 9 September 2020.
  23. ^ a b "Alameda-Oakland Tube A Success". Coronado Eagle and Journal. December 12, 1928. Retrieved 9 September 2020.
  24. ^ Gursoy, Ahmet (1996). "14 | Immersed Tube Tunnels". In Kuesel, Thomas R.; King, Elwyn H.; Bickel, John O. (eds.). Tunnel Engineering Handbook (2nd ed.). Boston, Massachusetts: Kluwer Academic Publishers. pp. 268–297. ISBN 978-1-4613-8053-5.
  25. ^ "Alameda Tunnel Letter of 1952 And Conditions in Alameda Today". Coronado Eagle and Journal. January 27, 1955. Retrieved 9 September 2020.
  26. ^ "Building Spotlight: Historic Posey Tube and 2016 Renovation Plan". Jack London Improvement District. Retrieved 2017-06-12.
  27. ^ "Henry H. Meyers Collection, 1901-1942". Online Archive of California. Retrieved 10 September 2020.
  28. ^ Bjork, Kenneth O. (1947). Saga in Steel and Concrete: Norwegian Engineers in America. Norwegian-American Historical Association. pp. 191–202. Archived from the original on September 26, 2015.
  29. ^ "Big Tube Near Completion". Madera Tribune. United Press. March 15, 1928. Retrieved 9 September 2020.
  30. ^ a b "More Theories Engineers Upset". Madera Tribune. United Press. October 6, 1928. Retrieved 11 September 2020.
  31. ^ a b c d Byron, Wm. C. (14 November 1928). "Setting forth merits of the vehicular tube". Coronado Eagle and Journal. Retrieved 2 May 2017.
  32. ^ "Oakland Estuary Tube Nears Completion". Sausalito News. May 7, 1927. Retrieved 9 September 2020.
  33. ^ "New Oakland Estuary Tube to Be sought". Madera Tribune. September 12, 1941. Retrieved 10 September 2020.
  34. ^ "Bay Crossings Report". California Highways and Public Works. Vol. 27 no. 11–12. Division of Highways, Department of Public Works, State of California. November–December 1948. p. 5. Alternate URL
  35. ^ a b c d e Parker, P.E.; Whitlock, H.J. (March–April 1960). "Webster St. Tube". California Highways and Public Works. Vol. 39 no. 3–4. Division of Highways, Department of Public Works, State of California. pp. 11–12, 67. Alternate URL
  36. ^ "Record Move". California Highways and Public Works. Vol. 38 no. 11–12. Division of Highways, Department of Public Works, State of California. November–December 1959. pp. 42–43.
  37. ^ Names, W.C.; Wolfson, William F. (March–April 1963). "Webster St. Tube". California Highways and Public Works. Vol. 42 no. 3–4. Division of Highways, Department of Public Works, State of California. pp. 10–14. Alternate URL
  38. ^ a b Sinclair, J.P. (May–June 1963). "Bay Area Report—1963". California Highways and Public Works. Vol. 42 no. 5–7. Division of Highways, Department of Public Works, State of California. p. 28;32–33. Alternate URL
  39. ^ Greene, George A.; Pomeroy, E.G. (January–February 1961). "Tube Report". California Highways and Public Works. Vol. 40 no. 1–2. Division of Highways, Department of Public Works, State of California. pp. 25–31. Alternate URL
  40. ^ a b c Sinclair, J.P. (May–June 1962). "Bay Area Report". California Highways and Public Works. Vol. 41 no. 5–7. Division of Highways, Department of Public Works, State of California. p. 14. Alternate URL
  41. ^ Skootsky, Harold; Brass, John R. (September–October 1959). "Tunnel Lighting". California Highways and Public Works. Vol. 38 no. 9–10. Division of Highways, Department of Public Works, State of California. pp. 43–46, 53.
  42. ^ Sundahl, Carl (August 14, 1961). "Tile Layers 19 Notes". Organized Labor. Retrieved 11 September 2020.
  43. ^ "Bridges". California Highways and Public Works. Vol. 40 no. 11–12. Division of Highways, Department of Public Works, State of California. November–December 1961. p. 56. Alternate URL
  44. ^ "THX 1138". Berkeley Art Museum and Pacific Film Archive. Retrieved 10 September 2020.

Further readingEdit

External linksEdit