Mexico City’s drainage system is corroding at an alarming rate. Mexico City, one of the most populous cities in the world, has more than 100 miles of combined sewers, and because of the large population (more than 20 million in the metropolitan area) and high amounts of rainfall, the combined sewers are very large, 5 m (16 ft, 4 in.) in diameter. Further complicating matters was the fact that the tunnels are 200 ft deep.
These combined sewers had severe corrosion, in many areas as deep as the steel reinforcing bars and beyond. To address the problem, officials decided to rehabilitate 1,500 m of 5-m diameter tunnel using Ameron’s T-Hab system. To complete the repair, the tunnel diameter was reduced to 4.6 m to provide a steel-reinforced, structural repair. Crews used a 4.6-m diameter form with a length of 36 m, consisting of six sets of 6-m long forms. Time required to rehabilitate 1,500 m using the T-Hab process was 90 days.
“There were a lot of logistics that needed to be planned for in a repair of this size,” Ameron International’s Bob Fisher said. “The grout alone had to be pumped 2,000 ft, which meant that the contractor needed to purchase one of the largest grout pumps in the world.”
Mexico City’s Sistema de Aguas, the agency in charge of Mexico City’s sewer and water systems, had repeatedly tried various methods of repair with little success before contacting Ameron’s Protective Linings Division of Brea, Calif., to help come up with a solution. Ameron recommended its T-Hab system, which utilizes its T-Lock technology and is specifically designed to rehabilitate existing concrete pipe and tunnels damaged by the long-term corrosive effects of sewer gases.
Sistema de Aguas ultimately approved the use of the T-Hab System. And in the end, it would provide a continuous leak-free lining to not only protect the old combined sewer tunnel but also provide structural reinforcement. T-Hab is a system that utilizes Ameron’s T-Lock PVC liner technology.
When installed, the “T” shaped ribs of the T-Lock sheet are mechanically locked into the interior wall of the existing concrete sewer tunnel. Formwork is brought in and assembled inside the tunnel. In the case of Mexico City, after the tunnels were cleaned and inspected, the contractor, Construcciones y Trituraciones S.A. de C.V. (Cotrisa), lowered the collapsible T-Hab form down into the tunnel. Precisely pre-measured T-Lock sheets (with the “T” ribs facing out) were then placed over the form and then moved into position. To achieve the mechanical bond between the sheets and the old sewer tunnel wall, a specially engineered quick-curing grout, designed specifically for this project, was pumped into the annular space between the lining and the damaged tunnel surface. When the form expanded to meet the tunnel wall’s surface, the projecting T-shaped ribs in the liner system “lock” into the grout. Once this was done, the contractor moved the form to the next section of repair and repeated the process.
While this task was being performed, a separate crew worked behind the form to clean, then heat-weld, the overlapping seams. This provided a continuous gas-tight lining over the entire structure. In total, 1,500 m of 5-m diameter tunnel were completed, rehabilitated and restored to full service in 90 days.
Fisher says that teamwork was the key to success in a project of this magnitude. “First and foremost, this was a project where it was vitally important for all parties to work together, and they did, with a very high degree of success. More than anything, the City of Mexico placed a lot of faith in the hands of the engineering firm that recommended the rehabilitation method, the contractor to install it properly and the manufacturer of the rehabilitation technology to provide the material design and procedural expertise to ensure the installation was a success.”
Project Owner: Mexico City’s Sistema de Aguas
Engineer: Consultoria Integral en Ingenieria, S.A. de C.V. (CONiiSA)
Contractor: Construcciones y Trituraciones S.A. de C.V. (Cotrisa)
Materials: Ameron International, Protective Linings Division (rehabilitation system), Moldequipo (formwork)