Railroad Embankment Slope Stabilization with Tiebacks and Micropiles-PPT Presentation

PPT Presentation

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A railroad embankment with a long history of ground movement and repeated repairs experienced renewed track movement, raising safety concerns. Stabilization had to be completed with limited site access and minimal disruption to active railway operations. Subsurface investigations, including borings and slope inclinometers, identified active shear zones and informed global slope-stability analyses.<br /><br />The repair used upper and lower stabilization systems, each comprising micropiles connected by concrete cap beams. The lower system combined compression micropiles socketed into rock with tieback anchors; the upper system used alternating tension and compression micropiles. Pile analyses incorporated measured soil movement, and design checks addressed pullout, shear capacity, and soil flow between piles.<br /><br />Testing revealed important uncertainties in load transfer. A tieback verification test supported the assumed bond strength, though behavior near the design load prompted additional testing. The initial verification test for micropiles intended to develop bond in soil did not adequately load the bond zone. The team therefore revised its approach: production compression piles were proof-tested, with a lower bond-strength factor of safety, a conservative assumed bond length, and extended creep testing. All proof tests passed. Strain gauges helped identify load shedding above the intended bond zone, including despite the use of a PVC sleeve.<br /><br />Construction took 28 weeks and was completed while keeping the railroad operational. The stabilization system was finished in June 2022; no subsequent slope or rail movement had been reported at the time of the presentation. The project highlights the value of inclinometers for identifying slip surfaces, strain gauges for understanding pile behavior, and close coordination among the owner, engineer, and contractor. Pressurized grout may help form micropile bond zones in soil, but the extent and direction of grout migration can be difficult to verify.

Keywords

railroad embankment

slope stabilization

micropiles

tieback anchors

ground movement

inclinometers

shear zones

proof testing

strain gauges

pressurized grout