Interstate Highway 635 (LBJ) Managed Lanes Project
Interstate Highway 635 (LBJ) is one of the most congested roadways in the Dallas–Fort Worth metroplex. Its intersection with the Dallas North Tollway, at a major grade separation structure, creates a significant traffic bottleneck. To increase mobility and improve public safety through the IH 635 corridor, tunnels were investigated as a means of adding lanes while minimizing impacts to commuters during construction.
Early in the life of the project (1998–2001), Schnabel provided geotechnical and tunnel engineering services including conceptual tunnel design, constructability analysis, and cost estimating for a feasibility-level evaluation of proposed tunnel alternatives. These included twin 3-lane tunnels in each direction, with and without shoulders, at widths of 62 feet and 50 feet, respectively. The feasibility study resulted in a preferred alternative, with each tunnel having an excavated cross-section of approximately 62 feet by 31 feet, and the east- and west-bound tunnels roughly 1.5 and 1.9 miles long, respectively. Construction costs were estimated based on a sequential excavation (SEM/NATM) approach with rock bolts and fiber-reinforced shotcrete as initial ground support, membrane waterproofing, and a cast-in-place concrete final lining.
Beginning again in late 2004, we worked as the tunnel and underground specialist to advance the conceptual tunnel design to the 30% level for procurement using the concessionaire (finance, design, build, operate and maintain) contract delivery model. Specific tasks performed include specifying and analyzing the results of geotechnical investigations; preparation of project geotechnical reports; preliminary design of portals, tunnels, cross-passages, ventilation shafts, and other underground facilities; risk management program development and facilitation; oversight of all tunnel mechanical, electrical, fire protection, and life safety requirement development; and preparation of drawings, technical procurement specifications, and detailed tunnel cost estimates.