A contractor recently punched through a utility corridor near the old Texas Stadium site and hit a lens of saturated sand that wasn't on any bore log. The crew lost three days pumping and regrading. This is what tunneling in Irving looks like when the geotechnical model underestimates the variability of the Eagle Ford and Woodbine layers. The city sits on a transition zone where stiff Cretaceous shales grade into alluvial terrace deposits and pockets of high-plasticity clay, and a tunnel alignment that drifts fifty feet east can go from competent rock to ravelling ground without warning. We run the grain-size distribution, Atterberg limits, and consolidated-undrained triaxial tests that give the TBM operator a real-time sense of what the face will do, because in a city with 240,000 people and a summer heat index that pushes 43°C, you don't excavate blind.
In Irving's Woodbine Formation, a 2-foot lens of unclassified silty sand has stopped more TBMs than bad rock ever will.
