Zachry Construction Corporation Rebuilds One of Texas Interstate System’s Steepest Grades
Making the Grade: Migratory Birds, 60-Foot Cuts, and 2.1 Million Cubic Yards of Embankments Complicate Eastland County’s I-20 Realignment
A six percent grade — one of the steepest in the Texas interstate system — combined with a sharp curve and an increasing volume of trucks and other traffic created significant issues along three miles of I-20 at Ranger Hill in Eastland County, Texas. Although the Texas Department of Transportation (TxDOT) made several safety enhancements in recent years, the roadway still didn’t meet current design and safety standards.
“It’s been a problem for years, so with the support of state and local elected officials, we had begun preliminary realignment design, looking at alternatives and getting estimates,” said Jason Scantling, Director of Transportation and Development for TxDOT’s Brownwood District. “When we unfortunately had a couple of severe accidents at the location, it escalated the need. In late 2014, TxDOT administration gave us two years to get the project let. That included right-of-way acquisition, utilities adjustments, plans, schematics, and environmental clearance. A normal timeline for a project like this would be closer to five years. The passage of Proposition 1 in 2014 and Proposition 7 in 2015 really helped get this project funded, as well.”
Financed with a combination of federal Highway Safety Improvement Program and Texas Statewide Connectivity funds, the project will realign and rebuild I-20 to improve safety and mobility. General Contractor Zachry Construction Corporation, headquartered in San Antonio, Texas, will reduce the grade to 3.5 percent, straighten the curve, add an additional climbing lane for slower vehicles, increase shoulder widths to allow refuge for stranded or stalled vehicles, and add frontage roads on both sides to assist first responders and minimize traffic backups when incidents occur.
Despite environmental delays, huge excavation cuts, and significant earthwork for embankments of almost 60 feet, close coordination and planning have kept the $76 million, three-year project on schedule for completion in summer 2020.
Delayed by Birds
To achieve the accelerated schedule, “We were extremely creative with overlapping tasks as much as we legally could in the project development phase,” Scantling said. “We had very close coordination between each aspect.”
Despite those efforts, nature intervened. “In the environmental investigation, we discovered there were nearby Golden-Cheeked Warblers (an endangered species of bird),” Scantling related. “We were required to do field visits under specific criteria for temperature, wind, and other factors because of potential habitat in the area. Through two of those surveys they didn’t hear or see anything. During the third survey, they saw a Black-Capped Verio (another endangered species of bird) on the project and heard Golden-Cheeked Warblers beyond the outside of the project. That required another round of surveys with the U.S. Fish and Wildlife Service, which delayed our schedule.”
Instead of the original December 2016 target, the project let in March 2017. Unfortunately, most of the work lay on a hill full of brush. Under the project’s environmental requirements, all the vegetative clearing needed to be completed outside the spring and summer nesting season of the migratory birds. Letting in March could have postponed work until the following October.
To avoid that lengthy delay, “As soon as we received environmental clearance in late October 2016, we let a separate contract to clear all the brush,” Scantling said. “That allowed Zachry to begin work on the hill immediately upon execution of their contract in summer 2017. As a result, we’ll deliver the project seven months earlier than if we let it all as one contract.”
Jump-Start to Bidding
Protecting the migratory birds created a chain of challenges. “Until we got environmental clearance, we weren’t able to clear brush for our geotechnical investigation,” Scantling said. “The brush was so thick, we had to doze swaths to get access and a level path for the drill trucks, then we could finally core through all the rock to determine exactly what rock formations we had.”
As part of the geotechnical investigation, TxDOT drilled 44 core logs throughout the project area. To help bidders develop an accurate estimate of the work required, “We kept the core logs in wooden boxes and provided access to all the potential contractors before bidding,” Scantling said. “Several contractors came and put their hands on it to get an idea of how hard the material was.”
In addition, “We provided access to the site and had several contractors bring out different pieces of equipment to see how hard it would be to excavate and get an idea of their production costs,” Scantling said.
TxDOT also released the project’s 95 percent plans in September, six months before the project let. “We feel like we saved millions of dollars by providing all that data,” Scantling said. “It removed a lot of the unknowns from the excavation.”
Blasting, Crushing, and Surface Mining
Zachry won the low-bid contract and began construction in July 2017. Much of their work focuses on earthmoving as they shift the centerline of the roadway 500 feet south of the current alignment.
With the new mainline lanes and frontage roads in each direction, “Our physical section is approximately 200 feet wide of concrete pavement at the top,” Scantling explained. “Then we have 3:1 embankment slopes for 60 feet, so the bottom of the embankment section is approximately 720 feet wide – or three-and-a-half football fields – at the bottom.”
Excavation for the project totals more than 1.6 million cubic yards. Because the embankments need 2.1 million cubic yards, Zachry will borrow 500,000 cubic yards of offsite material.
The excavation employs both blasting and surface mining. “There are three materials at different levels in different locations,” explained Matt Anderson, Zachry’s Project Manager. “The bulk of the top excavated material is sandstone, then it moves into a shale material, then down into limestone – but there are places on the project, such as the far west end, where the limestone is near the surface. We surface mine what we can, but if the material’s too hard – like the limestone – then we have to blast and crush harder materials.”
For the surface mining, subcontractor Mario Sinacola Companies of Frisco, Texas, uses two Wirtgen 2200 SM machines and one Wirtgen 2500 SM. After blasting, Zachry uses a couple of onsite mobile crushers to get the rock to the size TxDOT requires for reuse in the project’s embankments.
“Our typical application allows boulders up to 2 feet in diameter,” Scantling said. “However, that provides some opportunity for voids in the embankment, especially with this project’s field height of 50 to 60 feet. As a result of our geotechnical investigation, we required all the aggregate in the embankment to be smaller than 4 inches. We didn’t want long-term differential settlement creating a poor ride on the pavement and ruining our investment.”
Zachry self-performs most of the contract. “We have subcontractors for crushing and surface mining, but we self-perform the dirt work,” Anderson said. “We also self-perform concrete paving, wall construction, two bridges, slips, and all the rail.”
Across the 3 miles, the project requires almost 100,000 cubic yards of concrete, including 248,000 square yards of concrete paving.
To deliver the project as soon as possible, “It’s almost a daylight to dark operation, and sometimes a 24-hour operation,” Scantling said.
Zachry expects to complete phase one of the project in early June 2019, with final completion a year later.
Key Project Personnel
- Owner –Texas Department of Transportation Brownwood District; Jason Scantling, P.E., Director of Transportation and Development; Chris Graf, P.E., District Design Engineer; Andrew Chisholm, District Environmental Specialist
- Program Consultant – AECOM, Dallas; Mary Belle Chavez, P.E., Principal Engineer; Krishna Peapully, P.E., Project Manager; Irene Alanis, P.E., Project Engineer
- Project Manager (Construction Engineering Inspection) – Raba Kistner, Inc., San Antonio, Texas; Lynne Passmore, P.E., Project Manager; Justin Nipp, P.E., Project Engineer
- Geotechnical Consultant – Terracon, Dallas; Tim Abrams, Project Manager
- General Contractor – Zachry Corporation, San Antonio, Texas; Gary Doty, Vice President of North Texas Operations; Matt Anderson, Project Manager; Rick Finch, Project Engineer; Jerry Johnson, Project Superintendent; and Russell Dixon, Business Manager
- Surface Mining – Mario Sinacola Companies, Frisco, Texas