Numerical Assessment of the Permeability for the Pleistocene Sand Gravel Deposits Considering the Subsurface Stratigraphy of Kansai International Airport

Abstract

長期沈下が懸念されている関西国際空港の基礎地盤は，更新統粘土と砂礫の互層が厚く堆積する構造を有しており，隣接する二つの空港島の建設によって両空港島基礎地盤内に複雑な相互作用を引き起こしている。本稿では，こうした更新統層の地盤挙動を弾粘塑性有限要素法によって解析し，隣接埋立による関西国際空港基礎地盤の相互作用を含む長期挙動を包括的に議論する。解析の際，更新統砂礫層のマクロな透水性を評価するため，"mass permeability"と"standard hydraulic gradient"という概念を導入することによって，不均質性を持って広がっている関西国際空港の更新統砂礫層の透水性能を評価する解析スキームを提案する。適用した解析手法の妥当性については，水平地盤モデルと実地盤モデルの結果と実測値を比較することによって検証する。

A series of elasto-viscoplastic finite element analyses is performed to assess the long-term deformation including the interactive behavior of the reclaimed Pleistocene foundation due to the adjacent construction of the offshore twin airport. Attention is paid to the modeling of permeability for the Pleistocene sand gravel layers considering the sedimentation environment because the performance of excess pore water pressure is strongly dependent on the extent of distribution as well as the change of thickness of those permeable sand gravel layers. The mechanism for the propagation and dissipation of excess pore water pressure due to construction of the adjacent reclamation is discussed through the numerical procedure using the concepts of "mass permeability" and "standard hydraulic gradient" for the Pleistocene sand gravel layers. The mode of advance in settlement of the Pleistocene clay layers associated with the process of the generation/dissipation and propagation of excess pore water pressure is also carefully discussed. The proposed procedure is validated by comparing the calculated performance and the in-situ measured results. The calculated performance can well describe the actual behavior of the Pleistocene deposits due to construction of the adjacent 1st and 2nd phase islands of Kansai International Airport (KIX).