See who put this Engineers' Report together below.
The following opinions expressed represent the consensus of the undersigned members of the panel of geologists and engineers assembled at the request of the San Mateo County Board of Supervisors. The opinions expressed are based upon:
1. A site visit to Devil's Slide accompanied by Caltrans engineers and geologist on February 23, 1995.
2. Review of previously published reports and geologic data, by Caltrans and others, concerning three alternative solutions to the problem: the Martini Creek bypass, the Marine Disposal alternative, and the Tunnel bypass.
3. Independent review by panel members of site conditions relative to the current active landslide road failure, the Devil's Slide complex and surrounding San Pedro/Montara Mountain terrain.
4. Two meetings on March 2, 1995, one of which was held at the Board of Supervisors' conference room, for the purpose of technical interchange and discussion of alternatives.
We believe that among the options that have been considered for the solution of the Devil's Slide road failure problem, a tunnel bypass appears to provide the most reliable Highway Route 1 roadway connecting the north peninsula to the coastal areas to the south. Additionally, a tunnel bypass would avoid the environmental impacts of the other two options considered previously, and it could well prove less costly to construct.
It is anticipated that this tunnel (see Attachment 1 for approximate location) would be about 46 feet wide by 4600 feet long. The tunnel width would allow for two 12-foot wide traffic lanes and two 11-foot wide shoulders for emergency vehicle access. The tunnel could be completed in about two to three years, including design time, at an estimated cost between 50 million and 70 million dollars. The exact cost will depend on refinements in tunnel design, alignment, and the nature of the rock encountered.
The following advantages of tunnel construction warrant the serious consideration of a tunnel bypass:
1. Virtual elimination of new large cuts and fills in mountainous terrain, already recognized in published geologic reports to be potentially unstable.
2. Elimination of steep road grades. Presently, the maximum 6.5% grade allowed for highways is necessary to construct the inland bypass.
3. Reduction of hazards associated with rockfalls and dangerous cliff roadside drop-offs.
4. Virtual elimination of long term maintenance of large cuts and fills plus associated efforts at re-vegetation.
5. Tunnels are recognized to perform well and survive earthquake induced ground motion. A tunnel bypass would likely be the most reliable access to the coast after a strong local seismic event.
6. Virtual elimination of erosion and siltation concerns for inland creeks and the ocean associated with large cuts and fills of the other two surface alternatives.
7. Elimination of potential flooding problems to the San Pedro and Sanchez Creek drainages associated with the inland bypass cuts, fills, and road surface that would increase storm runoff within these drainages.
8. Excavation necessary for construction of a tunnel is almost entirely underground, and the resulting rock material would be usable and needed for construction of the approach road fills. No ocean disposal of rock would be required.
9. Visibility restrictions due to fog would be eliminated. Dense coastal fog will pose significant safety hazards for the Martini Creek bypass where it travels through higher elevations.
1. A tunnel would have essentially no impact on McNee Ranch State Park and Shamrock Ranch.
2. Noise levels associated with cars and trucks traveling on an elevated highway in mountainous terrain are eliminated. Also, the two or three year construction phase noise levels will be substantially less for a tunnel than for the Martini Creek bypass.
3. Visual impacts are virtually eliminated.
4. While there will be energy requirements associated with operating a tunnel ventilation system, there will be reduced fuel consumption by cars and trucks due to elimination of steep grades and shortening of the route.
5. The air pollution resulting from engine loading during the climb up the Martini Creek bypass and the engine braking during descent would be eliminated.
From a technical engineering, environmental, and quite possibly an economic viewpoint, our consensus is that a tunnel bypass is the logical choice. We therefore encourage its serious consideration as the long term solution to bypass Devil's Slide.
At the time of our February 23, 1995, site visit to the failed roadway area, Caltrans representatives indicated their planned response to the road closure would include installation and monitoring of two or three slope indicator casings. After an uncertain period of landslide inactivity, there will be placement of rock fall netting above portions of the failed roadway area, and filling-in of the dropped roadbed. Repaving of the roadway will also be completed.
It is the consensus of the panel that a more aggressive slide stabilization and road repair could be undertaken by Caltrans. Elevated ground water associated with saturation of the failed areas appears to be a key contributing factor to destabilization and continued movement of the failed area.
We believe efforts should be made by Caltrans to monitor and lower ground water levels within the failed landslide mass. This could be accomplished by installation of piezometers, vertical pumped wells and gravity feed horizontal wells.
Other safety measures such as additional down slope road stabilization and placement of ground movement monitoring/warning systems are recommended.
We believe that the substantially increased commuting time to thousands of San Mateo County residents and loss of revenue to hundreds of local businesses justifies the expense of such remedial measures, at least for the next several years, until a permanent roadway is completed.
We have completed a preliminary review of the Devil's Slide issue and have presented the above opinions from a technical viewpoint with the goal to encourage a long term solution to the Devil's Slide problem that will maximize public safety, provide long term public transportation, and preserve natural resources. We hope our effort will prove useful to the people who rely on the road, to tax payers, to the counties of San Mateo and San Francisco, and to those State and Federal agencies involved with this project.
John A. Albritton, Registered Civil Engineer #6900 (Georgia)
John C. Bowman, Registered Geologist #692 (California)
Certified Engineering Geologist #317 (California)
William R. Bechtell, Registered Civil Engineer #20,002 (California)
Registered Geotechnical Engineer #129 (California)
Douglas H. Hamilton, PhD, Registered Geologist #56 (California)
Certified Engineering Geologist #31 (California)
Alan Kropp, Registered Civil Engineer #23,921 (California)
Registered Geotechnical Engineer #487 (California)
Tim J. Manzagol, Registered Geologist #3560 (California)
Certified Engineering Geologist #1040 (California)
Mr. John A. Albritton worked 32 years for the U.S. Army Corps of Engineers on projects that included stabilization of a major landslide at Oahe Dam on the Missouri River, and subsurface rock excavation for the NORAD defense facility in Colorado. After retiring from the Corps, Mr. Albritton was a Resident Engineer with Woodward-Clyde Geotechnical Consultants. He currently is employed by the Community Service Consulting Group, designing and managing municipal improvement projects, and resides in San Bruno.
Mr. John C. Bowman was employed by the U.S. Army Corps of Engineers for 30 years, and was in charge of siting, exploration, design and construction of many large military and civil works project in the U.S. and overseas. The projects included dams, canals, airfields and harbor facilities. Upon retiring from the Corps, he became San Bernardino County Geologist, responsible for investigating and mitigating geologic hazards in that county. Mr Bowman was the Tunnel Construction Geologist for the live lake tap hydropower tunnel in Snettisham, Alaska. He presently is employed by the Community Service Consulting Group, inspecting the construction of deep pile foundations and underground utilities. He is a resident of Montara.
Mr. William R. Bechtell has worked for the California Department of Water Resources, the U.S. Navy Facilities Engineering Command, and is presently employed by the U.S. Army Corps of Engineers, South Pacific Divsion office. He has participated in the design and construction of many large public works projects such as dams, highways, levees, flood control systems, airfields and harbor facilities. Mr. Bechtell worked on the construction of the California Aqueduct, and is currently involved in the design and construction of the Seven Oaks Dam on the Santa Ana River. This is a 550 foot high rockfill dam which includes a 3000 foot long diversion tunnel. Mr. Bechtell has resided in Montara since 1976, and has been actively involved in finding a solution to the Devil's Slide problem since 1980.
Mr. Douglas H. Hamilton earned his PhD from Stanford University in 1984. He has over 35 years of experience in engineering geology. Mr. Hamilton was a founding partner and President of Earth Sciences Associates (1969-1993) and is presently a partner and Principal Geologist with Leland R. Gardner and Associates. He has worked on several underground mining projects in New Mexico, and numerous tunnels for PG&E, Santa Clara Valley Water District, and other water agencies.
Mr. Hamilton has also investigated rock slide problems on many projects, including the north portal of the Mount Olympus tunnel. Mr. Hamilton is a resident of Atherton.
Mr. Alan Kropp has 23 years experience in geotechnical engineering, and started his own firm, Alan Kropp and Associates, in 1978. His firm has worked on nearly 5000 projects, many dealing with difficult hillside environments and landslides. Mr. Kropp's firm has investigated over 500 landslides in the Bay Area in the past 15 years, including landslide repairs to Grizzly Peak Boulevard (a project reviewed and approved by Caltrans) in the Berkeley hills. He is frequently an invited lecturer to local and national audiences on landslide investigation and repair techniques. Mr. Kropp is a resident of Berkeley.
Mr. Tim J. Manzagol has 22 years of professional geologic consulting experience. He has been an independent consultant and owner/principle of Applied Earth Sciences Consultants since 1982. His firm specializes in fault, landslide and groundwater investigations. Many projects focus on geologic hazards relative to site development. Mr. Manzagol has also worked on mass transit systems, global underground defense communication systems, hazardous waste, dams, tunnels and power plant siting studies. He was a field exploration manager for the North Fork Stanislaus hydroelectric project, and the proposed Los Angeles Rapid Transit District 18 mile subway. He also participated in engineering geologic studies for the addition of the underground cyclotron tunnel at the Stanford Linear Accelerator complex. Mr. Manzagol resides in Woodside.