Effect of eccentricity on ultimate lateral unit earth pressure of tetrapod piles in clay

This study investigates the ultimate lateral unit earth pressure of rigid tetrapod foundation imposed by eccentric loads, based on a couple of two-dimensional adaptive finite-element limit analyses with lower-bound, upper-bound and 15-node mixed Gauss element formulations. A parameter study is conducted to emphatically explore the influence of eccentricity as well as to assess the role of additional parameters such as soil-pile interface strength and pile spacing on the normalised lateral earth pressure factor Np. Results from the numerical analyses reflect that the presence of loading eccentricity may lead to significant reduction in lateral soil resistance, the maximum diminution is up to 45% for the case that eccentricity equals to 0.5 times spacing. Three representative failure mechanisms are identified associated with various eccentricities. Pile spacing and interface strength additionally affect the variation of failure mechanisms with eccentricity increases. Finally, the eccentricity reduction factor, defined as the ratio of the Np considering the effect of loading eccentricity to the Np omitting this effect, is proposed, and the variation of this factor with eccentricity is presented for different values of pile spacing and soil-pile adhesion factor.