Building a 17 mi, 108-in. Steel Waterline through Urban Houston: What Could Possibly Go Wrong?

The Northeast Transmission Line (NETL) is part of an initiative to meet the Harris-Galveston Subsidence District’s (HGSD) mandate to restrict the use of groundwater. This mandate was put into place to substantially alleviate surface subsidence throughout southeastern Texas from years of withdrawal of oil and water from the ground. The landmark NETL construction of the City of Houston Public Works is a $450 million undertaking, consisting of nearly 17 mi of large diameter pipeline that ranges in diameters of 54-in. through 120-in., with the majority being 108-in. This is the third paper in a series that discusses various aspects of the NETL project’s design and construction. Although the majority of pipe was installed using open cut, this paper will focus specifically on tunneling applications with its greater risk that produced most of the program’s significant problematic issues. There were 55 tunnels on this project in total. After discussing specifications and manufacture of the steel casing pipes and related QA/QC issues, attention is given to challenges faced in tunneled sections due to soil conditions, unconventional tunneling methods, challenges with broken TBMs underneath bayous, encountering unforeseen buried obstacles underground, and a number of other topics. It is hoped that these discussions will help the design processes and how designers can better incorporate construction considerations, as well as how contractors can better prepare for projects of this magnitude.