Monitoring Drilled Shafts Supporting a Bridge over a Landslide in Northern AL-PPT Presentation

PPT Presentation

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A large landslide affected US-231 near Lacey’s Spring, Alabama, in February 2020. A replacement bridge was built in seven months, with drilled shafts designed to resist ongoing landslide movement. The project team installed monitoring equipment to track ground and shaft behavior.<br /><br />The system included ShapeArrays, inclinometers, vibrating-wire piezometers, and wireless remote communications. ShapeArrays measure three-dimensional movement, which the team projected onto a plane across the slope for analysis. Monitoring showed periods of shallow ground movement, while displacement in the drilled shafts remained small. The observed shaft movement coincided with known free-field movement and precipitation, and occurred in shafts connected by a common grade beam. The team reported the greatest displacement at two shafts near Southbound Bent 6, though there were no obvious signs of distress around the grade beam.<br /><br />The monitoring system proved functional: ShapeArrays provided high-precision measurements, and remote monitoring was stable and convenient. The data supported the design approach and provided reassurance that the shafts were performing as intended despite shallow sliding.<br /><br />Interpreting shaft displacement was difficult because movements were very small, the site was not planar, the bridge structure behaved as a frame, and there were no baseline “zero” readings. The volume and complexity of the four-dimensional dataset also made visualization challenging. For future projects, the presenters recommended installing ShapeArrays immediately after construction or taking post-installation inclinometer baseline readings, and considering strain gauges in the grade beam. They also cautioned that collecting too much data can complicate analysis.

Keywords

landslide

US-231

Lacey's Spring

Alabama

replacement bridge

drilled shafts

ShapeArrays

inclinometers

vibrating-wire piezometers

monitoring system