黄土地区地铁盾构隧道近距离下穿既有线影响规律及控制标准研究

为研究黄土地区盾构隧道近距下穿既有线的影响规律及控制标准,以西安地铁5号线盾构隧道下穿既有2号线隧道工程为背景,分析在既有隧道与下穿隧道竖直净距为盾构隧道管片外径0.2倍、0.4倍、0.6倍、0.8倍及1.0倍5种工况下的地表沉降和既有隧道在其与新建隧道正交截面上的拱顶及拱底位移、附加应力情况。由结果可知:随着既有隧道与新建隧道竖直净距的减小,地表和既有隧道的拱底拱顶位移均呈线性增大的趋势;地表沉降曲线与既有隧道拱顶沉降曲线呈单峰形态,而拱底位移曲线呈双峰形态,且左峰值小于右峰值;既有隧道在盾构过程中产生正弯矩,应力在盾构穿越其正下方时出现分化;应尽量避免竖直净距小于0.2倍洞径的双线盾构下穿,当采用0.4倍洞径竖直净距下穿时,应将新建隧道拱顶沉降值控制在13 mm以内。

Study on the Influence Law and Control Standard of Metro Shield Tunnel in Loess Area

In order to study the influence law and control standard of shield tunnels passing under existing lines at short distance in Loess area, this paper, with reference to the shield tunnel of Xi'an Metro Line 5, analyzes the ground settlement, the displacement of arch roof and arch bottom, and the additional stress of the existing tunnel in orthogonal section with the new tunnel where the vertical net distances between the existing tunnel and the underpass tunnel are 0.2 times, 0.4 times, 0.6 times, 0.8 times and 1.0 times of the outer diameter of the shield tunnel segment. The results show that with the decrease of the vertical clearance between the existing tunnel and the new tunnel, the displacement of the arch crown of the ground surface and the existing tunnel tends to increase linearly; the settlement curve of the ground surface and that of the arch crown of the existing tunnel show a unimodal pattern, while the displacement curve of the arch bottom presents a bimodal pattern, and the left peak value is less than the right peak value; the positive bending moment of the existing tunnel occurs in the process of shield tunneling, stress differentiation occurs when the shield crosses directly below the tunnel; double-line shield tunneling with vertical clearance less than 0.2 times hole diameter should be avoided as far as possible; when passing under with 0.4 times hole diameter vertical clearance, the settlement value of the vault of the new tunnel should be controlled within 13 mm.