浅埋暗挖矩形隧道施工方案比选研究

针对某新建地铁浅埋暗挖矩形隧道的工程特点,采用FLAC3D软件对各导洞不同开挖顺序的施工方案进行数值模拟。通过对比分析地表沉降、隧道拱顶沉降、底板隆起位移、初期支护内力等指标,寻求区间隧道周边地层变形及结构受力的特点和规律,从而选出最优的施工方案。研究表明:矩形隧道断面6导洞(先中间后两边)非对称开挖顺序可有效控制地层变形和结构受力;地铁区间隧道地表沉降曲线呈现"凹槽"形状,在隧道横断面方向影响范围约为4倍开挖跨度,掌子面开挖过后监测断面处地表沉降量所占比例约为60%;隧道拱顶沉降和底板隆起位移大部分发生在掌子面位于监测点前后10 m范围内,各导洞开挖顺序对支护结构内力影响较小;工程应用实践表明采用推荐的6导洞施工方案是安全可行的。

Comparison and Research of Construction and Excavating Scheme for Shallow Rectangular Tunnel

In view of the engineering characteristics of a new shallow excavated rectangular tunnel,simulations are made with FLAC3 Dsoftware for the construction schemes of pilot tunnels with differentexcavation sequences. Analysis is conducted of the surface subsidence, vault settlement, uplifts of thebottom of tunnel, the internal force of primary support to find out the characteristics and laws of thetunnel surrounding strata deformation and structural stress so that the optimum construction scheme can beselected. The research results indicate that the asymmetric excavation of the six pilot tunnels of therectangular tunnel(both side of the tunnel after the middle) can effectively control the strata deformationand structural stress. The surface subsidence curve of the tunnel shows groove shape and tends to affectabout 4 times of excavation width in the direction of cross section. The surface subsidence at themonitoring cross-section after tunnel face excavation makes up about 60% of the total settlement. Most ofthe vault subsidence and uplifts of the bottom of tunnel occur where the tunnel face is within 10 metersbefore and after the monitoring point and the pilot tunnel excavation sequence has little influence on theinternal forces of the supporting structure. The engineering practice proves that the recommendedconstruction scheme with six pilot tunnels is safe and feasible.