The Disputes Review Board (DRB) determines that the 8in steel well casing hit by TBM Bertha in December 2013 represented a Differing Site Condition (DSC) under the terms of the contract between WSDOT and its design-build contractor Seattle Tunnel Partners (STP).
The report says that WSDOT was in an “excellent position” to have known about the exact nature of the well, and to have included its specifics in the GBR contract documentation after lifting the well cover to carry out a pump test in 2010 just prior to the project going out to bid.
In the immediate aftermath of the ruling STP, the joint venture of Dragados and Tutor Perini, said it agreed with the recommendation. Project owner WSDOT says it is “concerned with the reasoning used by the DRB” in reaching its decision and that it “does not consider the matter resolved.”
An 18-page summary of the March hearing reveals that “none of the WSDOT personnel present […] were aware that the steel casing boring existed in TW-2 prior to the TBM encountering it.” It further reveals that STP made its own pre-excavation enquiries directly to Shannon & Wilson, which was responsible for carrying out borings and well installations on the project on behalf of WSDOT. For TW-2, the well in question, a computer listing identified its depth at 107.9 (ft) under a heading “Depth_Bottom_PVC”. This and other conflicting data “may well have satisfied STP that the casing left in TW-2 was, in fact, PVC casing,” said the Board.
The DRB was also told by a representative of Shannon & Wilson that it “did not maintain a written record of the casing (depth or material type) placed or left in place in the borings.”
No determination is made as to whether the steel casing was in any way responsible for the 17.6m diameter TBM’s subsequent breakdown, nor any cost implications arising from that – which STP put at US$125 million in project documentation obtained by Tunneltalk.
In its summary report the DRB says that under the terms of the contract, and as agreed by both WSDOT and STP, the Geotechnical Baseline Report (GBR) was to be considered the “primary document” of reference – though it was actually in the GEDR that any relevant information as to the location and construction of TW-2 was to be found.
“While the Parties have agreed to look to the GEDR […] as the basis for making a determination in this dispute, the Board believes the information, or lack of information, contained in the GBR must be considered in preparing the Board’s Recommendation.”
“The contract specifies that the order of precedence in the relative importance of these documents [the GBR, EBR and GEDR] shall be in the same order as listed above. The Contract further specifies that only contractual documents can be used to identify a Differing Site Condition (DSC) and that other non-contractual ‘reference documents’, although available for review, should not be relied upon.”
An indication of the likely steel construction of the casing was given in email correspondence sent to STP by Shannon & Wilson, which included information that both TW-1 and TW-2 were drilled by a cable tool drill rig, the only two out of 589 borings to be constructed by such a method. The report says that steel casing is “commonly used” cases where a cable tool is used, and that it is “frequently” the case that jacking equipment that comes with the cable tool is used to retract such casings following the completion of boring work. This, however, was not done.
The report says that although a tunneling contractor might not be expected to be familiar with the implications of using the cable tool drilling method, the Owner’s geotechnical consultant who did the work would be. “As such, the Owner's team would be in the best position to be aware of the potential that steel casing still remained in the ground at TW-2. Further, the Owner selected the large diameter tunnel construction approach and the final alignment for replacement of the Alaskan Way Viaduct that put TW-2 within the tunnel excavation limits.”
It continues: “WSDOT, however, has taken the position that had STP removed the existing cover plate at the TW-2 location during its site investigation responsibilities under the contract, they would have observed the steel casing in the ground. Hence, the presence of the steel casing in TW-2 is not, in WSDOT’s opinion, a ‘latent’ condition as is required for the determination of a Type 1 DSC.
“Interestingly, WSDOT conducted a pump test in TW-2 in March of 2010 that would have required not only removal of this cover plate, but actual downhole operations shortly before the RFP went out in June of 2010.
“Hence, WSDOT and its consultants were in an excellent position to identify the existence and depth of the steel casing in TW-2. Furthermore, the timing was such that this potential obstacle could have been noted in the GBR before the project went out to bid in June 2010. Yet, WSDOT has declined any knowledge that steel casing existed within TW-2 prior to being encountered by the TBM.
“In the DRB’s opinion, removal of the cover plate by STP would have disclosed the steel casing at the surface but provided no indication of how deep the casing extended. Hence, the steel casing would meet the requirements of a ‘latent’ condition as required under the terms of a Type 1 DSC.
“The DRB thus concludes that the steel casing in TW-2 meets the requirements of a Type 1 Differing Site Condition. Further that the contract requirements to investigate site conditions during STP’s design and construction efforts were satisfied by the efforts expended in pursuing information through WSDOT and S&W, Inc. which seemed to support numerous referrals in the contract to plastic PVC casing within the ‘wells.’ ”
Alaskan Way Viaduct Replacement Program Administrator Todd Trepanier said: “It is important to emphasize the specific question before the DRB was narrow in scope and only addressed one issue: whether an existing 8in steel well-casing is a ‘differing site condition’ under the terms of the SR99 tunnel contract.
“The hearing and subsequent recommendation did not deal with how the tunneling machine was damaged or the costs associated with repairs. The process of resolving disputes can be complicated and must follow the contract. WSDOT disagrees with the recommendation and does not consider this issue to be resolved. We are concerned with the reasoning used by the DRB in reaching the recommendation. We are reviewing it and will continue to pursue the best interests of taxpayers as we determine the appropriate next steps.”