An A-MAZE-ing Feat
At 3:41 a.m. on Sunday, April 29, 2007, an explosion and a huge ball of fire lit up the night skies along the east side of the San Francisco Bay in Oakland, Calif. A tanker truck carrying 8,600 gallons of gasoline crashed into a guardrail, overturned and caught fire on the eastbound 580 connector ramp from Berkeley to southbound I-880 to San Jose, located within the I-80/580/880 interchange. The intense heat melted the steel beams on the upper deck of the eastbound I-580 connector to Oakland directly overhead. A 165-foot-long section gave way, collapsing onto the I-880 connector, and closed both ramps. Fortunately, there were no deaths, and the injured truck driver managed to walk away.
The collapse created a gaping hole in the heart of the Bay Area’s busiest freeway interchange, also known as the MacArthur Maze, a distribution structure that serves as the eastern approach to and from the San Francisco-Oakland Bay Bridge. Closure of the two roadways eliminated routes used by some 80,000 vehicles each day. The local media projected that the connectors would be down for five months to a year and that traffic in the East Bay would be gridlocked indefinitely.
Contrary to the projections, the damaged section of the closed interchange was opened and full restoration to normal traffic flow was resumed on the evening of Thursday, May 24, a mere 26 days after the incident. What made the miraculous completion of this project possible was a clear sense of urgency and leadership by the state of California and local agencies; the close coordination and collaboration between transportation officials, law enforcement and transit agencies; and the innovative design and contracting methods by engineers and related professionals. Surveyors were actively involved in the process from Day One, providing critical information for accident reconstruction, and design and ramp restoration using advanced measurement technology.
Rapid ResponseThe California Department of Trans-portation (Caltrans) and the California Highway Patrol (CHP) Multidisciplinary Accident Investigation Team (MAIT) arrived on the scene shortly after the incident. Later that day, Governor Arnold Schwarzenegger toured the site, signed an emergency proclamation and requested emergency relief funds from the Federal Highway Administration. Caltrans Director Will Kempton immediately approved Director’s Orders, enabling contractors to perform demolition and traffic control within 12 hours of the incident.
While media outlets held live broadcasts on the smoldering site, arrangements were made with the city of Oakland and local transit agencies to detour traffic and provide multiple transit options in the affected areas. The governor’s declaration authorized funding for free transit services in the Bay Area for Monday, April 30. All local transit agencies began planning for extra commuters. Detours were set up to reroute traffic and the Monday commute was relatively light, despite predictions of snarled traffic.
Accident Investigation and Damage AssessmentTo begin repairs, Caltrans engineers needed a survey of the extent of the damage to the I-880 connector to determine if the bridge was salvageable. Larry Dews, Aerial Photography Branch chief of the Caltrans Office of Photogrammetry, contracted HJW Geospatial Inc. (Oakland) to capture on film the accident site on the afternoon of April 29. The requested one-day turnaround required other local aerial contractors to assist with the development of the film and prints. Enter Radman Aerial Surveys and Cartwright Aerial Surveys, both of Sacramento. Radman completed the film processing and Cartwright completed photo indexing. Radman subsequently captured both vertical stereo photography and color oblique photos of the site after the concrete and steel debris was cleared.
At 7:30 a.m. Sunday, Lieutenant Dave Fox, CHP MAIT team manager, advised Tony Grissim, forensic account manager for Leica Geosystems HDS (San Ramon, Calif.), that a MAIT team from CHP’s Valley Division was soon to arrive to investigate the scene using three-dimensional (3D) laser scanning technology. The CHP owns six Leica ScanStation scanners and MAIT teams are trained in their use. Grissim provided the CHP with onsite technical support. The CHP also made calls to Caltrans and to Leica employees living near the crash scene. An opportunity quickly unfolded in which laser scan data captured during the police investigation would aid the engineers assessing damage to the structure and planning the engineering effort to reopen the roadway.
After Caltrans engineers determined that the structure was stable, and once the site had cooled off later that morning, the CHP used one of its ScanStation units to document the site. The scene at MacArthur Maze would be CHP’s largest and most complex laser scanning project to date. Approximately 20 million points were collected to create a comprehensive 3D database of the entire site. Scanning was completed after midnight. From his experience with both the CHP and Caltrans, Leica’s Grissim acted as liaison between the two organizations. “The CHP was extremely cooperative in sharing scan data from the scene,” says Robert Dolan, transportation surveyor, Caltrans District 4 Surveys-Oakland, who later registered the seven scans to the California State Plane Coordinate System using Leica’s Cyclone post-processing software.
Demolition and DesignWithin 12 hours of the accident, Cleveland Wrecking Company began demolition of the collapsed deck. Damage assessment of the I-880 connector, which took the brunt of the collapse, was the No. 1 priority. Near the eastern shoulder of the connector, at ground zero where the heat reached upwards of 3000 degrees Fahrenheit, the sag was as much as 1 foot. From materials testing, it was determined that the bottom structure was salvageable. It was evident that the steel I-beams under the I-880 structure needed repairs; stabilizing beams were put in place to shore up the freeway deck, and the viaduct was jacked to correct the deflection of the freeway’s girders. Repairs of the concrete deck were necessary before the I-880 connector could be opened to traffic. On May 2, the governor announced that the southbound connector would be opened within seven to 10 days.
The familiarity of Caltrans surveyors with the site as well as a well-established network of control points nearby contributed to the rapid collection of additional survey points on the structure. On Monday morning, April 30, Caltrans Field Area Supervisor C. J. Vandegrift contacted Survey Party Chief Ric Erskine, who had been working on a nearby bioponds drainage mitigation project. Vandegrift and Erskine visited the site and looked for possible impacts of the bridge collapse on the drainage project, finding only a few access obstacles.
In order to geo-reference the scanned point clouds, Caltrans surveyors Chuck Tuomainen and Dolan met with Erskine to establish NAD 83 horizontal and NGVD 1929 vertical values on control points and some suitable “Post Identification” points. These values were imported into Cyclone’s constraints list and registration process, and then referenced to the survey control, thereby geo-referencing the database.
Several digital images captured with an external camera were draped or “burned” onto the point cloud to aid with visualization and for presentation purposes. Cyclone’s “Virtual Surveyor” feature--which assigns descriptor and feature codes to specific points--was utilized to identify pertinent points and polylines, and to export them to the Caltrans roadway design applications with the appropriate coding. This, along with the registered and geo-referenced point cloud, was made available to all relevant parties.
In addition to providing survey control, Erskine’s survey crew collected additional topographic data using a Leica Geosystems (Norcross, Ga.) 1103+ total station and Trimble (Sunnyvale, Calif.) TSCe data collector. The crew profiled the I-880 deck and as-built the I-580 connector, including the bearing plates and the bridge deck. Tuomainen and Dolan processed the data in CAiCE Visual Survey (Autodesk, San Rafael, Calif.) and Microstation (Bentley, Exton, Pa.) CAD software. By mid-day on Tuesday, May 1, the Caltrans Survey Division delivered a digital terrain model (DTM) of the deck to bridge engineers onsite and to the structure design units in Sacramento. By the time the bridge shoring was completed for the jacking operation, the soundness of the concrete had been confirmed and elevation reference marks were in place to control the repair work.
Over the next few days, the site continued to be a beehive of activity. The diligence paid off: the I-880 connector was reopened to traffic on May 7, just eight days after the collapse.
Laser Scanning ResearchBecause certain site conditions had changed due to the demolition work, Caltrans decided to undertake additional 3D laser scans. On May 7, through an existing research contract with the University of California at Davis (UC Davis) Advanced Highway Maintenance and Construction Technology (AHMCT) Research Center, additional data was collected using a Leica ScanStation owned by the university. Four “ScanWorlds,” or point clouds, were completed that focused on the immediate area of the collapse, generating a database of approximately 12 million points. Caltrans’ Dolan processed the data with assistance from the team. The ScanStation was used as a total station: set up on a known point and backsighted to a known point in each ScanWorld. This facilitated efficient registration and geo-referencing. The updated database, the points and polylines mined from it, and the point cloud were made available to all interested parties.
Contract Plans and BiddingIn step with the governor’s directive to fast-track the repairs to the I-580 connector, Caltrans advertised bids for the repairs of the collapsed freeway connector on May 2. The advertising period for this work was shortened to four days, with bid opening set for Monday, May 7. The target date for completion was set for June 27 with a $200,000 per day bonus for work completed early, and a $200,000 disincentive for every day late. To enable a design and bid package that would allow for speedy reconstruction, Caltrans decided to:
- use as-built plans and other available historical data,
- ascertain the availability of material,
- allow alternative material for long-lead fracture critical steel members,
- commit to partner with the material suppliers and construction contractor,
- use incentive-based informal bid contracting and
- empower onsite staff at the fabrication facilities and workshop.
Based on seven bids received, Caltrans awarded an informal bid contract to C.C. Myers Inc. of Rancho Cordova. C.C. Myers Inc. is a heavy highway engineering and bridge building company known for finishing emergency projects ahead of schedule.
Construction SurveyingOn Tuesday, May 8, at 10:00 a.m., C.C. Myers contacted Andregg Geomatics of Auburn, Calif., to provide as-built surveys of the existing concrete decks, ramps and columns. The 61-year-old surveying and mapping firm used the construction control provided by the Caltrans survey crews. In addition to an accelerated schedule, Andregg’s crew was challenged to acquire measurements with fabrication tolerance requirements within a quarter inch while overcoming a crowded, tight and active worksite. The crews located the columns and the girder bearing seats with a Trimble S6 total station and a Leica ScanStation. These two sets of independent measurements gave Andregg Geomatics a high degree of confidence in the results.
Office staff worked overtime to produce CAD deliverables for the steel fabricators. Using Andregg’s measurements, Con-Fab, a fabrication company in Lathrop, Calif., was able to construct a 55-foot-long, 243,750-pound bent cap--a concrete beam that spans the existing columns. The measurements were also used to fabricate 16, 78-foot-long, 4-foot-high, 20,000-pound steel girders that would hold up the concrete deck. When Stinger Welding, the steel fabricator in Coolidge, Ariz., needed confirmation of the bearing plates on the I-580 structure, survey crews were able to provide this data almost immediately. A discrepancy had been found, and it was during this process of checking that C.C. Myers, with the help of Caltrans engineers, finally confirmed the exact nature of the bridge joints and the relationship to the bearing plates. This was a critical review that prevented errors in the girder lengths.
On May 15, the concrete bent cap was lifted into place and locked onto the columns with fastening bolts. Working very closely with steel suppliers from Pennsylvania and Texas and the fabricators in Arizona and California, Caltrans and C.C. Myers worked around the clock, seven days a week, to install all the girders and construct the deck falsework by Sunday, May 20.
The last time-critical function performed was the final staking prior to pouring the deck. Caltrans surveyors worked alongside the carpenters and steel workers as they finished the preparations for pouring the deck. Surveyors laid out the alignment on the plywood forms almost as they were being placed. Everyone breathed a sigh of relief and the deck construction began. The construction continued around the clock. At 8:45 p.m. on Friday, May 24, the ramp was reopened in time for the Memorial Day weekend.
Celebration and Lessons LearnedThe intense and timely work completed at MacArthur Maze demonstrates a successful collaboration between public and private entities. Leica Geosystems HDS provided onsite support within hours of the explosion and facilitated data transfer between two of its customers. C.C. Myers proved its reputation for delivering a project well ahead of schedule and earned a $5,000,000 bonus. Caltrans had an important infrastructure component repaired, and the public had less time waiting in traffic. The impressive results displayed how a mix of public and private entities could respond to a critical situation together and exceed all expectations.
The project also demonstrated how different technologies and the surveyors trained in their use can be successful on an accelerated, high profile project. Photogrammetry and laser scanners documented the site prior to debris removal. Total stations and laser scanners provided the dimensions for prefabrication at remote locations. Three-dimensional data facilitated cross-functional teamwork between the forensic investigator, surveyor, engineer, fabricator and contractor.
A scenario such as that at MacArthur Maze is not without miscommunications, false starts and frustrations. But the impressive team members persevered. The lessons learned on this project will help all local agencies to plan and prepare for future inevitable emergencies and disasters, whether natural or man-made. In the end, the pride of accomplishment and being part of a successful team trumps all.