新建隧道斜交下穿既有盾构隧道的变形分析

随着轨道交通的迅猛发展,地铁隧道之间相互穿越不可避免,既有地铁结构随着新线施工的附加变形发展规律成为目前地下工程建设的热点问题。本文结合北京某浅埋暗挖法隧道斜交下穿既有盾构隧道工程的施工和监测,分析了斜交下穿施工各阶段既有盾构隧道的变形规律,提出既有盾构隧道沉降理论公式,并且基于提出的理论公式及沉降实测数据进行拟合分析,得到既有盾构隧道沉降曲线的地层损失率为0.013%～0.948%,基本处于天然地层数值范围内的较低水平。增大拱脚受力面积的施工辅助措施对控制地层损失率有一定作用,既有盾构隧道沉降槽宽度参数为1.13～16.96,远大于天然地层数值,根据拟合值及以往地层经验参数给出穿越各阶段既有盾构隧道的沉降公式的相关参数的建议值。通过监测数据分析发现,穿越施工既有盾构隧道变形以沉降为主,呈现“双凹槽状”纵向柔性变形特征,且主要发生在上台阶穿越施工期间,水平位移相对较小,盾构隧道椭圆度变化与竖向净距有一定关系。

Deformation Analysis on the Existing Shield Tunnel Obliquely Crossed by New Tunnel

With the continuous development of city construction and underground transport project construction rapidly, subway crossing construction projects continue to increase. In order to realize the safety, we need to know more about the development of the existing structure with the new line construction. Combining with the adjacent tunnel construction obliquely undercrossing the existing shield tunnel, deformation rule of the existing shield tunnel is carried out. The settlement formula of existing shield tunnel is put forward. Based on the proposed theoretical formula and the measured settlement data, the fitting analysis shows that ground loss ratios are from 0.013% to 0.948%, at a lower level in the range of natural formation values. The construction auxiliary measures to increase the stressed area of arch foot have certain effect on controlling the ground loss ratio. The width parameters of the settlement trough are from 1.13 to 16.96, far more than the natural formation value. According to the fitting values, the suggested values of the related parameters of the settlement formula of the existing shield tunneling through each stage are given. Through the analysis of field monitoring data, the settlement of existing shield tunnel mainly occurred during the construction of the upper step crossing, presenting "double groove shape", and the horizontal displacement is relatively small. The change of shield tunnel ellipticity in the construction can be related to the vertical clearance.