Drilled Shafts in Karst Geology - I35 NEX Case History-Video

Video Transcription

Video Summary

The presentation described geotechnical work for a major San Antonio highway project involving elevated roadways supported by large-diameter drilled shafts. Although the site was not mapped as karst terrain, limestone geology, faults, and historic drainage suggested possible clay-filled cavities. The team conducted extensive borings, rock coring, and geophysical surveys, developing detailed foundation profiles and generally excluding end bearing where karst was suspected.<br /><br />During construction, an eight-foot shaft encountered substantial clay-filled zones. Drone inspection confirmed the cavities, and additional coring identified sound limestone at greater depth. The team lowered the shaft tip rather than requiring permanent casing, then verified that revised shaft capacities and lateral stability met design needs. The project’s detailed, shaft-specific investigation and adaptable design process enabled successful construction. Subsequent progress photos showed the bridge advancing as expected. The speaker contrasted this work with a nearby project where extensive karst required air-track testing and skin-friction-only design.

Keywords

geotechnical engineering

karst limestone

drilled shafts

highway bridge foundation

subsurface investigation