浅埋黄土隧道洞身穿越岩土分界受力变形特征

Stress and Deformation Characteristics of Shallow Loess Tunnel Crossing the Rock-Soil Boundary

靖神铁路横山隧道为黄土地区浅埋单线铁路隧道,围岩自稳性很差,地质条件极为复杂,隧道暗挖段洞身穿越岩土分界地层。本文以横山隧道为工程背景,运用FLAC3D的interface单元,通过数值模拟和现场试验研究隧道洞身穿越岩土分界的变形和受力规律,确定施工变形控制措施。研究结果表明:超前小导管、两台阶法+临时横撑+扩大拱脚+掌子面加固施工方法可有效控制围岩变形,保证隧道安全施工。进一步分析了超前支护和初支控制变形的作用,超前小导管起到了限制围岩变形的作用。掌子面全为黄土时围岩变形量、支护受力明显较大,应确保加强拱脚与墙脚支护,并及时施作仰拱,超前支护采取双层超前小导管,而当隧道穿越岩土分界线时,应当尤其注意加强拱脚支护。FLAC3D的interface单元可较好地模拟隧道穿越岩土分界线时围岩及支护的受力变形状况,计算分析和现场实测都表明:地表沉降、拱顶下沉和洞周位移均小于15 mm,控制隧道地表沉降及围岩变形效果较好,保证了隧道安全稳定。

Hengshan Tunnel of Jingshen Railway is a shallow single-track railway tunnel in the Loess area.Surrounding rock self-stability is very poor,and geological conditions are extremely complex.In addition,tunnel excavation section through strata dividing rock and soil.Based on the engineering background of Hengshan Tunnel,apply the FLAC3D interface unit,the deformation and stress law of the tunnel body crossing the rock-soil boundary are studied by numerical simulation and site tests,and the deformation control measures in construction are determined.The results show that:advance small conduits,two-step method+temporary transverse supports+expanded arch foot+tunnel face reinforcement construction method can effectively control surrounding rock deformation and ensure the safe construction of the tunnel.The effect of advance support and primary support on deformation control is further analyzed.The leading small pipes play a role in restricting the deformation of surrounding rock.When the excavation face is all loess,the deformation of the surrounding rock and the supporting force are obviously larger.The support of arch foot and wall foot should be strengthened,and the inverted arch should be done timely.In addition,a double-layer advance small conduit is adopted for advance support.When the tunnel passes through the boundary of rock and soil,special attention should be paid to strengthening the arch foot support.The interface element of FLAC3 D can better simulate the stress and deformation of surrounding rock and support when the tunnel passes through the rock-soil boundary.The calculation analysis and field measurement show that the ground settlement,vault settlement and displacement around the tunnel are all less than 15 mm.The construction measures have a good effect on controlling the surface settlement and surrounding rock deformation of the tunnel,which ensures the safety and stability of the tunnel.