Chandra Shekhar Goit

Model tests and numerical analyses on horizontal impedance functions of inclined single piles embedded in cohesionless soil

Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics. Two practical pile inclinations of 5° and 10° in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are considered. Results obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of piles. Horizontal impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination increases. Distinct values of horizontal impedance functions are obtained for the ‘positive’ and ‘negative’ cycles of harmonic loadings, leading to asymmetric force-displacement relationships for the inclined piles. Validation of these experimental results is carried out through three-dimensional nonlinear finite element analyses, and the results from the numerical models are in good agreement with the experimental data. Sensitivity analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems.

Model Tests on Horizontal Impedance Functions of Fixed-Head Inclined Pile Groups under Soil Nonlinearity

The effects of soil nonlinearity on the dynamic behavior of fixed-head floating inclined pile groups are investigated experimentally in the form of horizontal impedance functions (IFs) and internal forces in piles. A 2×2 model of inclined pile groups embedded in dry cohesionless soil and subjected to a broad range of lateral harmonic loadings at the pile-cap level are examined. Piles with a spacing-to-the-diameter ratio (s/d) of 5 with practical pile inclinations of 0, 5, and 10° along the direction of loading are reported. Results show a profound impact of local nonlinearity and resonance of soil on the horizontal impedance functions. The inclined pile groups show higher values of horizontal IFs than the vertical pile group, in accordance with the general understanding. Influence of pile inclinations on the horizontal IFs is further examined through the variation of soil reactions along the depth of the piles. Semiempirical expressions for estimating the soil reactions, as a function of pile inclinations, are proposed. As for the internal forces in piles, bending strains for the inclined piles are smaller than the vertical pile; the axial strains show an opposite behavior.