E-19 Seguin to Nacogdoches Road, Segments 1 and 2

Project Details

Microtunneling, Open Shield Pipe Jacking, Hand Mining

  • 96″ steel casing for 78″ FRP sewer
  • 88 & 106″ steel liner plate for 60″ & 78″ FRP sewer
  • 23 drives totaling over 11,000 feet

Geotechnical Conditions

  • Very stiff to hard clay
  • Gravelly clay
  • Soft claystone/marlstone


  • Large diameter casing/tunnel
  • Fast raveling to flowing conditions
  • Constrained work areas with congested overhead utility corridor
  • Coordination with SAMMC property
  • UPRR and TxDOT encroachment permits
  • Creek crossings

Project Overview

As a subconsultant to Kimley-Horn, Bennett Trenchless Engineers provided trenchless design services for over 11,000 feet of trenchless casing installations for the San Antonio Water System through the San Antonio Military Medical Center base.  Microtunneling was specified for much of the trenchless installation due to gravelly conditions below the water table that can be prone to flowing behavior.  A significant challenge was working within the existing narrow right-of-way which was constrained by parallel overhead utility lines which complicated use of large equipment to excavate the launch and reception shafts.  Unstable soil conditions also posed a significant challenge and required the use of microtunneling to stabilize the face and control groundwater inflows into the large diameter tunnels.