Text For Citation: 02 Item/Group: 001 Hazard: FALLING

Title 40.1-51.1(a), Code of Virginia: The employer did not furnish employment and a place of employment which were free from recognized hazards that were causing or likely to cause death or serious physical harm to employees in that employees were exposed to a tunnel cave-in hazard while constructing a pedestrian walkback tunnel (south end) at Dulles Airport. On November 1, 2000, an employee of Kiewit Construction Company was killed when a section of the tunnel collapsed. During the week prior to the accident the Employer experienced deteriorating soil conditions and three falloffs of more than 1.0 cubic yard (cy) of soil during tunneling operations between October 24th and October 31st. The falloffs increased in severity from 1.0 cy on October 24th to 4.0 cy on October 25th to 5.0 cy on October 31st, the day before the accident. No tunneling occurred on October 29-30, 2000. Based on tunneling records, it appears that there were only a total of ten falloffs equal to or exceeding 1.0 cy, including the three already mentioned, that occurred at the site in the six months preceding the accident. The tunnel was being built using the soft ground tunneling method known as the New Austrian Tunneling Method (NATM). Contract specifications required that an NATM engineer report for work at the site at least six weeks prior to commencement of the access ramp excavation and to remain at the site for a minimum of four weeks after completion of all mined tunnel concrete lining work. The employers NATM engineer was apparently not on site during the entire month of October, 2000 and was on site for only a brief portion of September, 2000, to perform the following duties, among others, under the contract: To supervise the excavation to ensure safety and quality of construction. To devise and implement local support measures as required by the ground conditions, coordinating remedial measures when ground loss at mined tunnel heading or instability of mined tunnel occurs, or when they appear likely. [NOTE: Local Measures are defined under the contract specifications as grouted pipe spiling, rebar spiling and metal sheeting installed in a systematic or non-systematic manner installed individually or otherwise in addition to pre-support specified for the respective Excavation and Support Class, for local stabilization and safety during tunneling.] To prepare a written daily interpretation of instrumentation measurement readings during excavation. To hold daily discussions with the Metropolitan Washington Airport Authoritys Contracting Officers Technical Representative (COTR), Parsons Management Consultants (PMC), at the tunnel face regarding ground conditions and corresponding excavation and support requirements and other supports and keeping written records thereof. The NATM engineer was not present to address this escalating level of falloffs, nor had he even apparently been contacted on the falloffs. Kiewits NATM superintendents, approved under the contract, made no changes in the tunneling method or tunnelingsequence, nor applied local measures as defined in the contract to support areas where the falloff occurred, beyond filling the falloffs holes with shotcrete. Contract drawing specifications define the tunnel excavation sequence and support mechanisms: All support (flashcrete, shotcrete plus reinforcement) for each excavation round must be completed as shown prior to commencing next excavation round in sequence. Support was to be applied immediately upon the completion of tunneling each round: apply 2 inches of flashcrete to all surfaces, install the girders and spiling bolts (designed to reinforce the soil and stabilize the heading), apply an additional 6 inches of shotcrete, before beginning tunneling on the next round, contract drawings specified that the employer was supposed to stay 4 rounds ahead on the southeast side of the tunnel, and alternate tunneling operations between one round on the southeast side and one round on the southwest side of the tunnel, a total of five rounds on the southeast side must be fully supported with flashcrete, girders, spiling bolts and 8 inches of shotcrete before the employer could begin digging on the southwest side. As allowed under the contract specifications, the above sequence could be modified if approved by PMC. Apparently in response to stable ground conditions, the employer decided to only completely support one round on the southeast side with 2 inches of flashcrete, girders and spiling bolts, and 6 inches more of shotcrete, then dig 4 more rounds ahead and apply the initial 2 inches of flashcrete coating. The employer would then start tunneling the next round on the southwest side while workers on the southeast side were putting up the girders, spiling bolts, and additional 6 inches of shotcrete on the remaining 4 rounds on the southeast side. This revised tunneling sequence resulted in both headings lacking full support and stabilization at the same time during tunneling operations. When ground conditions deteriorated during the week before the collapse, the NATM engineer was not present to address the escalating level of falloffs. He was not available to revise the tunneling sequence to conform to contract specifications. Kiewits NATM superintendents made no changes in the tunneling method or tunneling sequence in response to the deteriorating soil conditions, nor applied local measures as defined in the contract to support areas where the falloff occurred, beyond filling the falloff holes with shotcrete. One feasible and acceptable abatement method among others to correct this hazard is to comply with the contract specifications, Sheet T3.4, Note 5. The employer, with the approval of PMC , reduced the number of spiling bolts to be installed on each girder from approximately 19 to 13 as part of the tunnel support system, by agreement dated August 22, 2000. PMC approved this reduction on two conditions: 1) that the tunneling was being conducted in stable ground conditions, and 2) is approved on a case-by-case basis based on the employers NATM engineers observations and recommendations. The NATM engineer was apparently not on site during the entire month of October, 2000 to observe the escalating level of falloffs and deteriorating soil conditions in the week leading up to the tunnel collapse. The NATM engineer was not available to approve or change from the continued use of 13 spiling bolts instead of the 19 or more provided for in the contract, nor had he even apparently been contacted on the falloffs. One feasible and acceptable abatement method among others to correct this hazard is to comply with the contract specifications, Sheet T3.4, Cross Section A. Contract specifications provide that no excavation shall be permitted in the absence of sufficient amount of shotcrete available at the face. For a significant period of time, the employer had been experiencing problems with shotcrete application to the walls of the tunnel. The shotcrete machine became clogged on a frequent basis and less frequently the shotcrete failed to adhere to the walls. On the day of the collapse, the employer was found running the tunneling machine while the shotcrete machine was clogged. Work was ordered stopped by PMC until the shotcrete machine became available. Immediately before the accident, the shotcrete machine apparently clogged again. At the time of the collapse, the employer began using the tunneling machine again, even though the shotcrete machine had not been put back in service. One feasible and acceptable abatement method among others to correct this hazard is to comply with the contract specifications, Section 02951-17, paragraph 3.08(11).