Istanbul’s variable geology, hydrology and propensity for seismic activity, combined with high water pressure and large-diameter/double-deck tunnel configuration, make the Eurasia Tunnel one of today’s most challenging and complex projects worldwide.
In order to minimize the project risk exposure and meet employer requirements, the contractor, a joint venture between Yapi Merkezi of Turkey and SK Engineering and Construction Co. Ltd. of Korea (YMSK JV), established a system to control the risks during all phases of the project execution, including conceptual planning, final design, construction and facility operation. An important component of such system is to assign an Independent Design Verifier (IDV), who is to ensure that the project’s major design risks are addressed by the Designer through design deliverables in accordance with planned construction program (schedule). HNTB Corp. was selected as the IDV.
In light of the project’s accelerated schedule, the IDV role was critical in reviewing the design for correctness, identifying potential risk issues, verifying corrective actions, and minimizing potential that any critical issue may “fall through the cracks.”
The following is a brief summary of the project’s most critical technical issues that had consumed significant attention of the design, construction and IDV teams. Selected action items had been undertaken to mitigate major risks, primarily:
Tunnel Boring Machine (TBM) Issues: Addressing mixed-face tunneling conditions due to the region’s complex geology and hydrology. This included required improvements to the TBM to enable the machine to deal with high hydrostatic pressures and full control groundwater control,
Seismic design due to the region’s propensity to high seismic activity, and in addition, numerous miscellaneous technical issues have been addressed.
The IDV reviews provided multiple recommendations that were adopted by Designer. The recommendations have assured the design compliance with Employer’s Requirements and design criteria, codes and standards, have reduced construction risks, improved constructability, increased safety and efficiency of the facilities, and decreased operational costs. It was proven that the project was set up from its very onset to incorporate multiple tools to successfully recognize, manage and mitigate construction and commercial risks, the IDV process being one of them.
The information was excerpted from the paper “Istanbul Strait Road Tube Crossing Project Uses Good Practices to Manage Risks,” which was written by Sanja Zlatanic and Nasri Munfah of HNTB Corp., and Mehmet Ozturk, YMSK JV and presented at the World Tunnel Congress 2015. It is being used with permission.