Loading Effects on Battered Micropiles Supporting Lateral and Compression Forces-Paper

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The paper examines the renewed use of battered micropiles to resist lateral loads and explains why their design requires more than simple static force calculations. Battered piles fell out of favor after earthquakes exposed failures at pile heads and connections, but improved detailing has made them viable again when properly designed.<br /><br />Micropiles can carry substantial axial loads, but their small diameter gives vertical micropiles relatively low lateral and bending capacity compared with larger steel piles or drilled shafts. Installing micropiles at an angle can efficiently help resist lateral forces. However, battered piles experience bending and shear from soil–structure interaction—even when a simplified equilibrium model predicts axial forces alone. Compression can also cause elastic shortening, which pushes battered piles laterally against the surrounding soil and induces additional moments. Installation tolerances can further increase bending.<br /><br />The authors recommend analyzing battered micropiles with methods that model nonlinear soil–pile interaction, such as p-y analysis, and checking all relevant load combinations, connection fixity, and combined axial and bending stresses. This is particularly important for heavily loaded structures, seismic demands, and small-diameter uncased bar or hollow-bar micropiles, which have limited bending stiffness.<br /><br />As a practical safeguard, the authors strongly recommend reinforcing micropile heads with steel pipe, extending approximately 20–25 drill-hole diameters below the pile cap to cover the zone where bending moments may occur. Uncased bar or hollow-bar micropiles without this reinforcement should be avoided under significant compression or lateral loads.

Keywords

battered micropiles

lateral loads

soil-structure interaction

p-y analysis

axial loads

bending moments

elastic shortening

micropile head reinforcement

seismic design

uncased micropiles