Gasketed box culvert, innovative planning mitigates flooding issues in Lubbock, Texas
Texas Parks and Wildlife describes the hundreds of playa lakes in the Texas Panhandle as, “arguably the most significant ecological feature in the Texas High Plains.” The playa lakes around Lubbock are shallow basins that collect stormwater. But in heavier downpours, these shallow lakes overflow, sending flood waters coursing through the northwest portion of the city.
The City of Lubbock addressed this longtime flooding issue in 2013, with an ambitious three-phase $70 million, multi-year plan to create a stormwater transfer system between 19 playa lakes. The complex project would require deep excavations through the city’s medical district and surrounding neighborhoods, tunneling under a railroad line and dealing with petroleum-contaminated soils in some areas.
Precast concrete box culvert sections, outfitted with Hamilton Kent’s prelubricated Tylox® SuperSeal™ gaskets, played a critical role in Phases 1 and 1A, which included 177 linear feet of 15’ x 7’ boxes and 11,031 linear feet of 10’ x 10’ boxes for construction of the storm sewer outlet.
Proof of Design
Parkhill, Smith & Cooper, a Lubbock-based engineering and architectural firm, served as the engineer of record, overseeing all construction during Phases 1 and 1A. Working with Utility Contractors of America, Parkhill supervised the “proof of design process” before construction that put HK’s SuperSeal gaskets to the test. The design called for a maximum operating pressure of 11 psi with proof that the gaskets were watertight at each joint, according the Parkhill website.
To simulate field conditions, the boxes were buried and pressurized. In addition, “box sections were placed on top of the buried pipe to account for backfill loads, and the apparatus was required to maintain an operating pressure of 11 psi but not more than 13 psi for 48 hours,” according to Parkhill.
The project demonstrates the versatility of gasketed precast concrete gasketed boxes, which stood up to rigorous testing throughout multiple installation scenarios. It was an innovative application of a box culvert run.
“Box culverts are designed for external loads. They’re not designed to be pressure tested,” said Bob Folser, P.E., who designed the box culvert system for J & G Concrete Products, which manufactured the boxes.
The challenge was to design a box culvert system that could meet the pressure test requirements. That’s where Hamilton Kent SuperSeal gaskets come into play.
“We weren’t allowed any leakage, and the gasket provided that,” Folser said. “It could not have been done with a mastic joint.”
Deep Excavations and Tunneling
It was a unique project for a unique ecosystem. The playa lakes do not have any natural drainage system, so the challenge was to create a drainage structure for the entire Northwest quadrant of Lubbock that would carry stormwater to a dam and creek in Hodge Park, which is part of the Buddy Holly Recreation Area.
During construction, open-cut excavations descended up to 47’ in an established neighborhood that abuts Texas Tech University, a medical center and popular recreation areas. The project manager worked with the city and the local community to ensure minimal disruptions, with no more than 200 linear feet of open excavation at any time. At these sites, the box sections were gasketed and lowered into the pit, then pulled together hydraulically.
Under the rail line, the contractor excavated a tunnel, of which 150 linear feet were boxed in-tunnel with a tunnel liner in place. The remainder were jacked into place without a tunnel liner. Tunneling took place at four other sites, adding approximately 700 linear feet. The design specified nitrile gaskets to neutralize the contaminated soil near the rail line. Hydrostatic testing took place at every 800 feet of box production.
The boxes, produced by J & G Concrete Products (now a Forterra company), and the HK Tylox® SuperSeal™ gaskets met every challenge, according to the American Concrete Pipe Association, which called the testing protocol, “the most stringent hydrostatic test in Texas.”
By finding a new way to use gasketed box sections to address the City’s concerns, the project saved time and labor and reduced open cutting, saving the city’s residents and businesses from disruptive road closures and the accompanying inconveniences. In addition, the consulting engineer and the manufacturer reduced the overall cost while still delivering a precast solution that will serve the city for many decades.
With the completion of this massive project, the playa lakes in Northwest Lubbock will continue to be an ecological and recreational focal point but will now drain excess stormwater into the existing waterways rather than flooding into the surrounding neighborhoods.