暗挖地铁车站平行下穿既有隧道的变形控制及规律研究

Study of Deformation Control and Deformation Law of Existing Tunnel with Parallel Running Underneath Subway Station

北京地铁15号线奥林匹克公园站全站平行密贴下穿既有城市大型隧道,如此大面积的长距离密贴穿越,为国内罕见。为控制既有隧道变形,提出单层导洞预撑支柱法。采用数值模拟方法对新工法和传统PBA工法引起的既有隧道变形进行对比,并根据实测值对下穿施工既有隧道变形规律进行分析。研究表明:(1)单层导洞预撑支柱法在控制车站施工引起的既有隧道变形、减小降水引起的地层及既有隧道沉降以及保护地下水资源方面具有优势。采用消除下层导洞和形成桩基支撑托换体系两个措施后,既有隧道最大沉降比PBA法的减小36.5%。(2)既有隧道变形以横截面变化为主,实测最大沉降42.2mm。施工过程中,沉降增量最大的是导洞施工阶段,其次是扣拱阶段,而站厅层及站台层施工阶段最小。(3)施工过程中,既有隧道变形模式逐渐变化。差异沉降增量最大的是扣拱阶段,其次是导洞施工阶段,而站厅层及站台层施工最小。其中,扣拱阶段是影响既有隧道安全性的关键阶段。

The Olympic Park Station of Beijing Metro Line 15 runs parallel to and closely under the existing large tunnel.Such a long distance with closely running under the existing tunnel is the first time in China.In order to control the deformation of existing tunnel,the monolayer pilot-tunneling pre-support pillar method was proposed.In this paper,the deformation of existing tunnel induced by the new method and the traditional PBA method was compared by the numerical simulation method.The deformation law of the existing tunnel with construction underneath was analyzed according to the measured value.The research shows that：（1）the monolayer pilot-tunneling pre-support pillar method has advantages in controlling the deformation of the existing tunnel caused by the station construction,decreasing the settlement of the ground and existing tunnel caused by dewatering and protecting groundwater resources.Compared with the PBA method,the maximum settlement of the existing tunnel is decreased by 36.5% after the adoption of two measures of removing lower pilot tunnels and forming apile foundation underpinning system.（2）The deformation of the existing tunnel is mainly reflected in the change of the cross section,with the measured maximum settlement of 42.2 mm.In the process of construction,the deformation increment of the existing tunnel is mostly found in the pilot-drift con-struction,followed by the buckle arch stage.Minimum settlement is found in the construction of the station hall layer and platform.（3）In the construction process,the deformation mode of the existing tunnel is gradually changed.The differential settlement increment of the existing tunnel is mostly found in the buckle arch stage,followed by the pilot-drift construction.Minimum differential settlement increment is found in the construction of the station hall layer and platform.The buckle arch stage is the key stage that influences the safety of the existing tunnel.