By Kevin Wilcox
Engineers on a road project in rapidly growing Sugar Land, Texas, are contending with poor soils, a tall bridge, and a new rail crossing at grade, all within just half a mile.
Designers hope to make the bridge appealing by adding a thin brick veneer to the columns, which extend above the deck to form pilasters, and by using a combination of smooth and rough finishes on the concrete beams. Courtesy of Lockwood, Andrews & Newnam
April 18, 2017—The new extension to University Boulevard now under construction in Sugar Land, Texas, is only 0.5 mi long, but there are an extraordinary number of engineering challenges in that half a mile, including a new rail crossing at grade, an elevated water line, and a bridge that spans a Union Pacific Railroad line and a stream named Oyster Creek.
When complete, the four-lane divided highway will provide a crucial link in a rapidly developing part of this city of more than 100,000 residents near the Gulf Coast. The surrounding area is home to Constellation Field, the city's minor-league baseball stadium, a large Nalco Champion chemical facility, and a new mixed-use development on 700 acres of land surrounding a former Imperial Sugar refinery site.
The project will provide an important connection to Route 90A, diverting traffic from neighborhood surface streets and facilitating an expansion of the Nalco facility for an additional 1,200 employees, according to Christopher Steubing, P.E., M.ASCE, the city engineer.
The project draws funding from several sources, including the city, Fort Bend County, and Johnson Development Corp., a Houston-based land developer. The team hired the engineering firm Lockwood, Andrews & Newnam, Inc., headquartered in Houston, to address a number of formidable engineering challenges, among them poor geotechnical conditions along the alignment.
"The soils are sandy and silty. There are some soft clays. They have very low bearing capacity," notes Lauren Van Andel, P.E., the bridge section leader at Lockwood, Andrews & Newnam and the project manager for the extension. What is more, a very soft stratum beginning about 20 ft below the surface has virtually no bearing capacity. Van Andel likens the soils near Oyster Creek to quicksand, a condition that becomes more pronounced with proximity to the water.
Founding the bridge was one of the most challenging aspects of the project, but so was ensuring that the design would meet the 23 ft 4 in. vertical clearance required by Union Pacific without sacrificing any of the aesthetic appeal that the designers wanted for this growing neighborhood. This led to a tall bridge bounded on either side by retaining walls.
The bridge will be founded on a series of drilled shafts 42 in. diameter, some extending to approximately 100 ft. Because of the poor soils, some of these shafts will be installed in permanent casings using slurry displacement.
For the foundations under the retaining walls, the team considered several options, including replacing soil with cement-stabilized sand, before deciding on rigid inclusions, that is, soil improvements effected either by using aggregate mixed with cement or grout or by using elements made of plain concrete. The bridge contractor, Harper Brothers Construction, of Houston, will displace the soil with grout throughout the entire area of the retaining wall. "That is able to penetrate through the soft layer and provide more confidence in the ability to withstand any future settlement," Van Andel says. "It's a very stout and good soil foundation improvement method."
The bridge is a robust structure of reinforced concrete, its prestressed-concrete beams being 121.6 ft long. The span uses a concrete substructure, and columns that are square in cross section incorporate aesthetic elements common to the surrounding development. These square columns rise above the superstructure, essentially serving as pilasters.
The bridge has the added complexity of raised sidewalks, a raised median, and four railings, two of them at the edges of the road surface and the other two at the outer edges of the bridge. The bridge also carries a large water main that will serve the rapidly developing area.
Because guidelines set by the American Railway Engineering and Maintenance-of-Way Association discourage placing a water line over active railroad tracks, Van Andel says the team took a proactive approach with Union Pacific in solving this problem and did not have to resort to the costly option of burying the line in poor soils beneath the creek. The solution was encasing the 12 in. water main in a 20 in. steel pipe.
The bridge problems solved, the team next turned to the grade crossing, which is now complete and operational. The road had to cross three rail lines, and two belong to Union Pacific's Glidden subdivision and form part of a busy east-west corridor that carries between 32 and 37 trains per day. The third, a spur line serving the Nalco Champion facility, was originally too far from the first two to be part of a single crossing and was also 2.5 ft lower in elevation.
The solution was to relocate the spur so that it would be adjacent to the other two lines and then elevate it to the same grade level. This meant working with Nalco Champion to change how its facility was served by the spur. Union Pacific also required the elimination of two grade crossings to develop a new one. The city was able to eliminate a separate Nalco Champion private crossing, as well as a crossing at Wood Street that saw little use. The rail relocation project was constructed by Webber, LLC, of The Woodlands, Texas.
The crossing required a great deal of coordination and testing. As many as 10,000 cars are expected to use this portion of the University Boulevard extension, and more than 60,000 cars travel nearby and connect to Route 90A. The trains will have traffic preemption, meaning the traffic signals will stop cars as a train approaches.
"From the city's perspective, we have 9 to 10 signals on that [90A] corridor, and there are about 60,000 plus cars a day. So, with 34 to 37 trains a day, you can imagine the nightmare we have from the traffic side with preemption at each crossing, clearing each crossing, getting the signals back in cycle for the entire stretch through the city. There was a lot of coordination on that," Steubing says. "It was quite the adventure, but so far, we've heard nothing but accolades from the adjacent business owners."
Keisha Seals, a project manager for the city, notes that one of the reasons that the crossing construction went smoothly was that it involved a new, unopened road. "That was probably the easiest part of the whole project—the fact that we didn't have existing traffic crossing over the rail line."
The final link in the extension, the bridge, is now under construction and is slated for completion early in 2018.
"It was a large collaboration and coordination project," Steubing says. "It's the most expensive stretch of road that I think I've ever been a part of, but it's going to be a great asset to the city when it's done."