Analysis Approach for Slide-Stabilizing Micropile Walls-PPT Presentation

PPT Presentation

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The presentation outlines an analysis approach for slide-stabilizing micropile walls, emphasizing that their resistance comes largely from axial forces and shear rather than bending alone. Case histories from Littleville, Alabama, and Blue Trail, Wyoming, found that measured bending moments were lower than predicted, while axial capacity could govern performance.<br /><br />Design begins with a limit-equilibrium back-analysis of the failed slope. Engineers identify critical slip surfaces, set target factors of safety for relevant loading conditions, and calculate the additional resistance needed. They then select a micropile layout and model the micropiles and cap beam as a pile group. The modeled slope is moved downslope until the combined axial and shear resistance meets the required value. Mobilized axial, shear, and moment demands are checked against structural capacities, and embedment is checked for adequate geotechnical resistance.<br /><br />An illustrative example required 46 kips of additional resistance per foot of slope to raise the factor of safety from 1.0 to 1.25. A trial micropile arrangement mobilized 186.5 kips of resistance per pair, meeting the 184-kip requirement. The example’s moment, shear, and socket-length checks were also satisfactory.<br /><br />The method is intended for preliminary design or smaller projects; major projects may warrant more detailed soil–structure interaction analysis, such as finite-element modeling. The authors recommend considering near-vertical downslope micropiles to use axial resistance efficiently and reduce pile length. Where anchors are combined with micropiles, anchor loads should be limited to one-third of the micropile resistance to avoid reversing micropile action. Installing and stressing anchors before micropiles may help mobilize both systems more effectively.

Keywords

micropile walls

slide stabilization

axial resistance

shear resistance

bending moment

limit-equilibrium analysis

slope stability

pile group modeling

soil-structure interaction

finite element modeling