HCTRA Barrier-Free Tollway Program

Project Background

In 2022, Harris County commissioners unanimously approved approximately $38 million for the Harris County Toll Road Authority’s (HCTRA) transition to all-electronic tollways, or AETs. The tolling transition covers eleven (11) segments of the tollway system within Harris County. The HCTRA Barrier-Free Tollway Program, as defined by HCTRA, is part of an effort to transition from the traditional toll system to an all-electronic tolling (AET) system. According to HCTRA, an all-electronic tollway system is safer, more efficient, and less costly to manage than staffed toll plazas. Additionally, the new tolling system will help prevent crashes and injuries and reduce property damage.

HVJ was part of the design team led by AtkinsRéalis, Inc. for the Sam Houston Tollway segment from West Little York to about 0.5 miles south of Hammerly Road in Houston, Texas. As the acting Geotechnical Consultant, HVJ provided geotechnical engineering services, including field exploration, laboratory testing, and engineering analysis. Throughout the project's life, HVJ provided Geotechnical design and construction recommendations for new bridges, retaining walls, high mast lighting, and overhead sign boards.

The Challenge

As part of the tollway conversion, the existing roadway will be widened. This involves the construction of new bridge structures and retaining walls to support additional traffic lanes. During the design of the new retaining walls, HVJ had to provide a retaining system that would not compromise the integrity of the existing walls and bridges. We gave special attention to areas where the existing walls were shorter than the proposed ones. This will require excavation next to the existing wall to reach the necessary bottom elevation for the new wall.

Our Solution

Sloped ground was observed in front of most of the existing MSE retaining walls. The proposed roadway widening required the new MSE retaining walls to be built at a horizontal distance from the face of the existing walls. This design requirement means the new walls must be constructed near the top of a slope. To prevent the bottom of the new retaining walls from being placed on sloped ground, the existing ground will need to be excavated so that the final grade elevation is below the bottom of the existing wall. Excavating the on-site soils for the new retaining wall construction may disturb the existing wall's foundation soils, weakening its stability.

After internal discussions among HVJ’s Geotechnical team, we decided that a composite retaining wall system comprising a soil nail retaining wall and a Shored Mechanically Stabilized Earth (SMSE) retaining wall could be a potential solution to our design challenge. The design incorporates the composite wall with a cut wall (soil nail wall) from the bottom elevation of the existing wall down to the future grade. The composite wall will transition from a cut wall to a fill wall from the bottom of the existing wall to the top of the pavement.

In this system, the construction begins with the soil nail wall from the existing grade to the future grade. During this construction sequence, soil is excavated in small vertical intervals while nails are installed to reinforce the soil just below the bottom of the existing retaining wall. Once the soil nail wall is in place, construction of the SMSE wall can proceed from the top of the soil nail wall up to the top of the pavement.

* See image for a visual representation of the proposed composite retaining wall system.

The Results

HVJ's recommended retaining wall system will keep the existing retaining wall in place. This approach eliminates the need for demolition and avoids designing and constructing temporary earth retaining systems that could affect the project's budget. Additionally, it will prevent disturbance to the existing wall’s foundation soils, which are essential for the stability of the wall and existing bridges.

HCTRA Barrier-Free Tollway Program

Project Background

The Challenge

The Goals

Our Solution

HVJ Associates, Inc.

Practices

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Company