experimental evaluation of micropile bearing capacity and soil interaction in liquefiable sands using 1g shaking table tests

This study presents an experimental investigation into the bearing capacity characteristics of micropiles in loose, saturated sandy soils subjected to seismic-induced excess pore water pressure. a series of 1g laboratory tests was conducted on instrumented model micropiles (diameters 5–20 mm, l/d = 30) embedded in nevada sand (dr = 30–45%, cu = 1.8, gs = 2.65) under varying levels of induced pore pressure (ru = δu/σ'₀ = 0.2–1.0). the experimental setup incorporated a laminar shear box equipped with pore pressure transducers, lvdts, and load cells to systematically evaluate the evolution of micropile bearing capacity during pore pressure generation and dissipation phases. key findings reveal that micropile bearing capacity exhibits a nonlinear reduction with increasing pore pressure ratio, with approximately 60% of initial capacity retained even at ru ≈ 1.0. three distinct failure modes were identified: (1) shaft resistance-dominated failure at low ru values (ru < 0.5), (2) mixed shaft-toe failure at intermediate ru levels (0.5 ≤ ru ≤ 0.8), and (3) toe-bearing dominated failure under full liquefaction conditions (ru > 0.8). a new bearing capacity reduction factor (ψ) is proposed to account for pore pressure effects, expressed as a function of relative density, pile slenderness ratio, and normalized excess pore pressure. the study provides quantitative relationships between pore pressure development and bearing capacity degradation, offering practical design equations for seismic micropile design in liquefiable soils. results demonstrate the importance of considering partial drainage conditions and post-liquefaction strength regain in capacity calculations, challenging conventional fully-drained or fully-undrained design approaches.