Interstate Highway 635
Interstate Highway 635 (LBJ) is one of the most congested roadways in the Dallas/Fort Worth metroplex and it intersects with the Dallas North Tollway (DNT) at a major grade separation structure. Both highways carry very heavy volumes and their intersection is 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.
Very early in the life of the project (1998-2001) Lachel provided geotechnical and tunnel engineering services including conceptual tunnel design, constructability analysis and cost estimating for a feasibility level evaluation of proposed tunnel alternatives. The alternatives included twin 3-lane tunnels in each direction, with and without shoulders, at widths of 62 ft and 50ft, respectively. The feasibility study resulted in a preferred alternative with each tunnel having an excavated cross-section of approximately 62 ft by 31 ft, and the east- and west-bound tunnels roughly 1.5 and 1.9 mi 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, Lachel worked as the tunnel and underground specialist to advance the preliminary tunnel design to the 30% level for procurement using the concessionaire (finance, design, build, operate and maintain) contract delivery model. Specific tasks performed in the procurement of the project included specifying and analyzing results of geotechnical investigations; preparation of project geotechnical reports; assessment of tunnel alignment and grade alternatives; preliminary design of portals, tunnels, crosspassages, utility niches, 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. Lachel also assisted TxDOT in the bid phase of the work, and is now slated to assist in project oversight.