Structural deformation of overlying subway tunnels induced by tunnelling

The Chongwenmen subway station of Beijing Metro Line No.5 is the first one beneath the existing subway tunnel in China,which is constructed by use of the mining method.The newly-built subway station tunnel undercrossing the existing subway is 24.2 m in width and 11.46 m in height,and the distance between the newly-built tunnel and the existing subway structures is just 1.98 m.The monitoring data show that the structural settlement is the prominent response style of the existing subways,and the settlement mainly happens during the pilot-drift construction.The existing subway tunnel structures have obvious characteristics of rigid body,whose settlement curves are linear.The structural deformation slot of the existing subway tunnel has the largest settlement,31.26 mm;and the biggest difference settlement of the two sides of the structural deformation slot is 14.0 mm.The trackbed deformation curves are nonlinear,and the inconsistent settlement makes the trackbed disjoin the tunnel structure.The largest disjoining gap is 12.7 mm and the largest disjoining length is 7.0 m between the trackbed and tunnel structure.By filling grouting,the disjoining areas are filled.By uplit grouting,the existing subway tunnel structures are heaved up,and the largest upheaval reaches 16.0 mm.With the measures,the settlement of the existing subway structures is finally controlled to be less than 16.75 mm,and the existing subway line is normal during the construction.