改良地盤における杭の耐震性能の検討

抄録

A design method, in which ground improvement is made around the heads of pile foundations constructed in soft ground and ground subject to liquefaction and the increased shear strength is reflected in the horizontal resistance of piles, was put to practical use. In this design method, the range of influence of the horizontal resistance of piles, or the necessary range of ground improvement, is supposed to be a three-dimensional domain formed with the gradient of passive earth pressure θ = (45° + φ/2) from the depth of the characteristic length of piles, 1/β. Horizontal subgrade reaction of piles is determined by converting the shear strength S of improved ground to the modulus of deformation E. In this study, earthquake resistance, such as reductions in the displacement and bending moment of piles caused by earthquake motions, achieved from ground improvements around the pile heads was confirmed through a series of centrifuge shaking tests. The influence of the difference in strength between the original and improved grounds on piles during an earthquake was studied through numerical analysis using the dynamic elastic finite element method, and the potential practical applicability of the design method was essentially verified.