邻近隧道盾构施工的现场实测分析

为研究新建隧道对既有隧道的附加作用,本文通过现场监测,从附加应力、附加变形两方面研究了新建盾构隧道施工对既有隧道的附加作用。分析了既有隧道管片附加作用的动态变化规律,给出了附加作用与掌子面距离的关系,同时对管片附加作用的空间分布规律进行了分析。监测结果表明:①既有隧道管片的附加环向、径向应力远大于附加走向应力。②既有隧道拱顶、拱底处环向附加应力为拉应力,且拱顶处拉应力远远大于拱底处拉应力,两侧拱腰处为压应力,靠近新建侧附加压应力大于远离侧附加应力,前者约为后者的2倍。③既有隧道管片的走向附加应力是压应力,其中拱底处最大,近侧拱腰处次之,拱顶处较小,远侧拱腰处最小。④既有隧道管片的径向附加应力为压应力,大小为0.1~0.5 MPa,近侧拱腰处最大,远侧拱腰处次之,拱顶较小,拱底最小。其表现为“侧向大,竖向小”“近大远小,上大下小,不对称”的分布规律,即逆时针旋转90°的“非对称葫芦形”分布。⑤附加地表沉降呈对称U型沉降槽分布,影响半径为1倍埋深,影响角约45°,沉降最大点在隧道正上方,当掌子面到达监测断面时沉降速率最大。⑥既有隧道管片的附加净空收敛值依次经历了侧向收缩、缓慢扩张、快速扩张、缓慢回落,趋于稳定5个阶段。净空收敛值回落至峰值的三分之一,其变化范围在-1~3 mm。⑦既有隧道管片的附加拱底沉降依次为上浮、回落、快速上浮、快速回落、回落至初始状态,其变化范围为-1.0~2.5 mm。

Analysis on Field Measurement of Shield Construction of Adjacent Tunnels

To study the additional action of new tunnels on existing tunnels, through field detection, this paper studies this action from the aspects of additional stress and additional deformation. It presents the distance relation between additional action and tunnel face after the analysis of dynamic change law of the additional action of existing tunnels, and it also analyzes spatial distribution law of the additional action of the segment. The monitoring results show that the additional hoop stress and radial stress of the existing tunnel segments are much larger than the additional longitudinal stress. The additional stress in the circumferential direction of the existing tunnel vault and arch bottom is tensile stress, and the tensile stress at the vault is much larger than the tensile stress at the bottom of the arch. The additional stress at the arch waist on both sides is known as compressive stress, and the additional compressive stress near the newly built side is greater than the stress away from the newly built side, and the former is about twice the latter. The additional longitudinal stress of the existing tunnel segments is compressive stress, at the arch bottom being the largest, near the arch waist being the second, at the arch top being smaller, and the stress away from the arch waist being the smallest. The additional radial stress of the existing tunnel segments is compressive stress, ranging from 0.1~0.5MPa, with the stress near the arch waist being the largest, away from it being the second, at the arch top being smaller, and at the arch bottom being the smallest. The distribution law of the compressive stress manifests as “the compressive stress at both sides is larger than that in the vertical direction, with the stress near the arch waist larger than that away from the arch waist, and the stress at the top larger than that at the bottom”, that is, the “asymmetrical gourd shape” distribution when rotated counterclockwise by 90 °. Additional ground settlement is distributed at a symmetrical U-shaped settling tank with the radius of influence 1 time that of buried depth and an influence angle of about 45°. The maximum settlement point is directly above the tunnel, and the sedimentation rate is the largest when the tunnel face of reaches the monitoring section. The additional headroom convergence values of the existing tunnel segments have undergone five stages: lateral contraction, slow expansion, rapid expansion, slow fall, and gradual stability. The headroom convergence value falls back to one-third of the peak value, which varies from -1 to 3 mm. The additional arch bottom settlement of the existing tunnel segments first floats upward, then falls back, then floats upward rapidly, later it falls back, and at last falls back to the initial state, with a range of -1.0~2.5mm.