为解决公轨合建水下隧道分离后，地铁隧道长距离并行近接下穿明挖隧道过程中面临的变间距下穿扰动、地层脱空的问题，以济南黄河隧道北岸段地铁下穿明挖公路隧道为依托，建立考虑可张开地层-结构界面和结构变形缝的精细化三维仿真模型，探究不同加固方案下盾构施工对地层脱空及既有结构的影响。结果表明： 1）相比于无加固措施，采用立柱桩加固后，最大地表沉降减少52%，沉降曲线峰值叠加效应得到有效控制； 2）采用立柱桩配合三轴搅拌桩加固，盾构下穿过程中既有结构底板横向最大差异沉降减少43.4%，最大沉降降低47.0%； 3）无加固措施下，盾构掘进导致既有隧道结构底板与地层之间脱空效应明显，最大脱空位移达1.44 mm，相比于三轴搅拌桩加固，采用立柱桩加固更能有效减少结构底板脱空； 4）无加固措施下既有结构最大拉应力增量超限（1 MPa），采用单一三轴搅拌桩加固有增大既有结构注浆范围内拉应力增量趋势，而采用立柱桩配合三轴搅拌桩加固，可有效减少50%的既有结构拉应力增量。盾构并行下穿既有结构时，相比显著强化单一加固措施，综合考虑地层位移控制（防脱空）和结构应力控制的加固措施更加安全有效。
After the separation of the highway and railway in an
underwater tunnel, varying spacing underpass disturbance and detachment between
soilstructure occurred during a metro tunnel parallelly crossing an
existing opencut tunnel. In this study, a case study
is conducted on the metro tunnel on the north bank section of the Yellow rivercrossing tunnel in Jinan, China, and a refined threedimensional simulation model considering the detachable stratastructure interface and structural deformation joint is established
to investigate the influence of shield tunneling on 〖HJ2.7mm〗stratumstructure detachment and the
existing structure under various reinforcement schemes. The results reveal the
following: (1) The maximum ground settlement is reduced by 52% and the peak
superposition effect of the settlement curve is effectively controlled after
the column pile reinforcement is adopted. (2) The maximum lateral differential
settlement and the maximum settlement of the existing structure floor are
reduced by 43.4% and 47.0%, respectively, during shield tunneling after using
reinforcement of column pile and threeaxis mixing
pile. (3) The maximum detachment between the tunnel floor and the soil due to
shield tunneling is 1.44 mm without reinforcement. Compared with the
reinforcement of threeaxis mixing pile, the
reinforcement of column pile is more effective in reducing the detachment
between the tunnel floor and the soil. (4) The maximum tensile stress increment
of the existing structure without reinforcement measures exceeds the control
limit, and the reinforcement of threeaxis mixing pile
tends to increase the tensile stress increment within the grouting range of the
existing structure, while the use of column pile combined with threeaxis mixing pile reinforcement can effectively reduce the tensile
stress increment of the existing structure by 50%. When shield tunneling
parallelly under existing structure, it is safer and more effective to take the
ground displacement control (antidetachment) and
structural stress control into consideration than to strengthen the single
reinforcement measure.
