Rehabilitating a Texas-sized drain

March 24, 2016

In the border town of McAllen, Texas, dealing with storm water run-off is a challenge. For local municipalities, it is paramount to modify storm-water infrastructure to keep up with rapid growth, and handle large amounts of water when the weather rapidly fluctuates.

After a severe drought prior to summer 2013, heavy rains in McAllen created a problem with the failing Rado Storm Drain near the Rio Grande River. The drain consists of two side-by-side, 120-in. corrugated metal pipes (CMP) that each extend more than 2,200 linear ft. Despite repairs in various sections over the past decade with non-structural shotcrete and bitumen coating, Rado’s issues persisted.

Following the rains, the soil became saturated, resulting in heavy infiltration and ground water flows that caused heavy corrosion, partial collapse, sinkholes and additional damage to previous pipe repairs. Large-scale separation of the joints and infiltration continued to be major concerns.

Since non-structural repairs on this particular application had been unsuccessful, the local municipalities investigated several repair options including Cured-in-Place-Pipe (CIPP), slip-lining and Milliken Infrastructure Solutions’ GeoSpray solution, a fiber-reinforced geopolymer mortar that facilitates the creation of a new structural pipe within the old pipe.

The community determined CIPP and slip-lining to be expensive options that would have complicated the repair process due to the large diameter of the pipe. GeoSpray lining was chosen for the structural application as a durable and cost-effective alternative. As a member of the Houston-Galveston Area Council (HGAC) Buy, a competitively bid contract organization, the county avoided the costly process of bidding the project itself and specified the GeoSpray geopolymer mortar system.

Flow was diverted in order to repair Rado’s side-by-side pipe sections one at a time. Each pipe section was cleaned by hand and inspected for joint failure and cracking to ensure stoppage of water infiltration and creation of a continuous surface for the application of GeoSpray mortar. Sections were then sprayed, at rates of 150-300 ft, with the final engineering designed thickness of 1.5 in. The ability to apply a 1.5-in.-thick layer in a single spray pass saved both time and cost for the asset owner.

During most days of operation, the contractor was able to apply between 20,000 and 40,000 lb of GeoSpray material in a single run within the pipe, creating a truly monolithic structure. Using GeoSpray geopolymer to create a new pipe within the existing CMP structure, the repair was completed in less than five months. Quality-control samples were taken on 32 different days during the repair to be tested by an ACI accredited third-party lab and reported to the engineer and asset owner.

Only a single utility truck and material loader were needed onsite, helping complete the project on schedule and under budget. GeoSpray geopolymer, which is compatible with ambient environmental conditions of 100°F or greater, also enabled significant cost savings when compared to trenchless repair techniques such as CIPP and slip-lining. The new pipe is now ready to handle the unpredictable storms of southern Texas for years to come.

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