Spatial Variability of Kinematic Pile Response in Liquefiable Slopes: Effects of Static Shear Bias and Partial Drainage

Liquefaction-induced lateral spreading in sloping, layered ground can impose highly non-uniform kinematic demands on adjacent piles, yet most design checks assume uniform soil pressures. We present dynamic centrifuge tests on a three-layer deposit (dense crust over loose sand, underlain by a dense crust) at slopes of 5° and 10° with piles at upslope, midslope, and downslope positions, and introduce three indicators, the static-to-cyclic bias ratio (Ψ), the stress-reversal fraction (SRF), and an effective Deborah number (Deeff) to time drainage feasibility. During shaking, response is largely undrained (Deeff > 1), with a greater tendency for stress non-reversal at the steeper slope; partial drainage becomes effective mainly post-shaking, first near the surface, with vertical extent governed by drainage-path length and loose-layer permeability. Spatial heterogeneity in excess pore pressure and stiffness yields inter-pile differences: downslope piles mobilize the largest co-seismic moments; and after shaking pile-head segments re-stiffen quickly while deeper segments retain 0.6-0.9 Mpeak over the 0-250 s post-shaking window. JRA-based envelopes reproduce overall shape at 5° but, under stronger static bias (10°), systematically underpredict mid-column curvature near the loose-crust interface and overpredict base demand; free-field Rankine bounds confirm the plausibility of measured magnitudes. The results establish a mechanism-driven framework to identify where and when curvature concentrates, to interpret the role of post-shaking drainage, and inform the use of code-based envelopes.