开挖卸荷对邻近地铁隧道的变形影响是城市基础设施建设正面临的一个难题。考虑地铁双线隧道之间的“双洞效应”,基于Mindlin基本解和能够反映土体变形连续性的Pasternak弹性地基梁理论,建立明挖卸荷对下卧双洞隧道纵向变形影响的解析分析方法,推导并求解隧道在附加荷载作用下的平衡微分方程,并对简化弹性空间法得到的地基参数进行修正以提高计算精度。依托实际工程将所提方法运用于某近接地铁双线隧道的基坑工程,预测和分析明挖卸荷引起的下卧双洞隧道附加变形和内力的分布规律。研究表明:开挖卸荷所引起的邻近双线隧道附加应力和变形在一定程度上受到“双洞效应”的影响,与土体自由位移场条件下单洞隧道的计算结果相比偏小;利用简单工况模型下通过解析试算获得的修正地基参数,能较准确地对实际复杂工况条件的隧道变形进行预测和分析;隧道变形的解析解与实测数据相比具有良好的一致性,验证了方法的有效性。
The deformation effect on subway tunnels due to adjacent excavation is a challenge to the urban infra- structure construction. Considering the "double-hole effects" of double-tube metro tunnels, an analytical model based on the Mindlin basic solution and Pasternak elastic foundation beam theory was proposed to study the longitudinal deflection of underlying tunnels caused by open cut unloading. An equilibrium differential equation of tunnels with the additional load was derived and solved accordingly. To obtain more accurate results, the foundation parameters derived from simplified elastic method were corrected in analysis. The proposed method was applied to the foundation pit project adjacent to a metro tunnel of Shenzhen Metro Line 11 to study the dis- tribution law of deformation and stress of the underlying double-hole tunnels. Research found that the addition- al stress and deformation of double-hole tunnels caused by adjacent excavation were affected to a certain extent by the "double-hole effects". The calculation results from the double-hole tunneis were smaller than those from the single-hole tunnel under the condition of soil free displacement field. The modified foundation parameters obtained by analytic trials under the simple working condition model can predict and analyze more accurately the tunnel deformation under practical complex working conditions. The analytic solution to tunnel deflection, consistent with in-situ measured data, verified the rationality of the proposed method.