Innovative Riverbank Erosion Control Retaining Wall System for the Brazos River-Paper

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The Highway 99 bridge over the Brazos River near Sugar Land, Texas, faced increasing risk as repeated floods drove the riverbank northward, eroding about 120 feet in three years and threatening the bridge abutment, approach embankment, and nearby levee.<br /><br />The project team selected a retaining wall of adjacent (tangent) drilled shafts supplemented by smaller seal piles to close gaps between the structural shafts. Compared with a secant-pile wall, the system was estimated to cost about 20% less and install 50% faster. The design combined anchored and cantilevered sections, using 5.5-foot- and 10-foot-diameter shafts up to 130 feet deep. Seal piles were installed between the shafts using augered cast-in-place grout or drilled-shaft methods.<br /><br />Hurricane Harvey brought record flooding in August 2017 and caused further erosion, making part of the original design unconstructible. The team revised the wall alignment and replaced concrete anchors with steel tie rods and sheet-pile deadmen. In the roadway corridor, 10-foot shafts were designed to act as a cantilever wall without anchors. The revised approach avoided constructing a complex wall and soil-nail system beneath the bridge.<br /><br />Shaft verticality and diameter were checked with sonic caliper testing. Measurements from the first 13 shafts were well within the specified tolerance, so further testing was not required.<br /><br />Despite the flood and significant redesign, the project was completed ahead of schedule and within budget. The authors emphasize that selecting the designer, general contractor, and specialty foundation contractor before final design enabled collaborative development of a cost-effective, adaptable solution and rapid response to changing site conditions.

Keywords

Highway 99 bridge

Brazos River

Sugar Land Texas

riverbank erosion

flood damage

drilled shafts

retaining wall

Hurricane Harvey

steel tie rods

sonic caliper testing