• Fort Bend County, Texas


  • TxDOT Houston District


CobbFendley provided the design and PS&E development of the on-system bridge replacement at Fairchilds Creek. The existing bridge was a 3-span pan girder structure, being replaced with a proposed standard 3-span slab beam structure. Preliminary bridge geometry was established and bent location for the middle span was selected to avoid the existing foundations while also being centered on the channel so that columns were outside of the Ordinary High Water (OHW) elevation and existing channel erosion. Roadway geometry was established for this on-system FM roadway to meet criteria for design speed of 60 mph with desirable 12-foot lanes and 10-foot shoulders. H&H analysis, HEC-RAS modeling, and drainage/scour reports were completed showing no hydraulic impacts and approval was received from TxDOT and Fort Bend County Drainage District.

This project included existing erosion present in the ditch and at outfalls into the channel that washed out existing interlocking paver mats. With the widened proposed condition, ditches became very constrained with steep slopes. Along the roadside ditches, we detailed concrete riprap (slope paving) with 36-inch toe walls to mitigate undermining the slopes for slope stability. At the ditch tie-ins with channel (on all four corners), we detailed 18-inch stone riprap to dissipate velocities of ditch runoff entering the channel and to stabilize the channel slopes.

To maintain access for traffic during bridge closure, we evaluated all available on-system and local road routes. The best route in this rural area went through the town of Fairchilds using local county/city roads. We successfully coordinated with the local municipalities to use these local roads during the project.