STUDY ON BEHAVIOR OF CLOSELY SPACED TWIN TUNNELS WITHOUT CENTER PILLAR DURING EXCAVATION

In order to clarify the behavior of closely spaced twin tunnels without center pillar during excavation, analysis on the field measurement data obtained at closely spaced twin tunnels construction sites and numerical analysis using 3D and 2D finite different code were carried out. The results show that the influence of the second tunnel excavation on the first tunnel appears mainly as the increase of the sectional forces in support structure at the sidewall on the second tunnel side with the rapid change of the stress in the soil pillar. The load acting on the support structure of both tunnels at the soil pillar side varies depending on the distance between two tunnels, overburden height and deformation modulus of ground, and the support structure may support a load up to full overburden weight in some cases. 併設トンネルの離隔距離をほとんど確保しない超近接トンネルを無導坑で掘削した時の挙動を明らかにするため，これまでに得られている施工時の計測結果の分析を行った．さらに，数値解析により後進坑の切羽通過時における中間地山の応力変化と先進坑の挙動との関係，土被り，離隔距離，地山の変形係数が支保工に作用する荷重に及ぼす影響について検討を行った．その結果，後進坑の掘削による影響は，先進坑の中間地山側の側壁部に大きく現れること，後進坑の切羽通過時には中間地山の応力が急激に変化し，先進坑の断面力が大きく増加すること．中間地山側の支保工に作用する荷重は，土被り，離隔距離，地山の変形係数の影響を大きく受け，支保工に全土被り荷重が作用する場合があることが明らかとなった．