Analysis of tunnel face stability with advanced pipes support

To keep the tunnel face stable is very important for tunnel construction.In this paper,the tunnel face stability under the advanced pipe was analyzed using the Winkler foundation model and rigid limit equilibrium.The tunnel face deformation characteristics were also analyzed using the numerical simulation.The influence of parameters on the deflection of the pipe roof and the stability of the tunnel face were discussed.The results show that the tunnel face stability can be improved through increasing the pipe diameter,decreasing the initial displacement at the beginning of the pipe seat,and adopting the short round length and small excavation height.With the increase of tunnel burial depth,the safety factor of tunnel face stability first decreases,then increases,and then remains unchanged.The deformation at the center of the tunnel face is larger than the deformation at the surround sides and at the corner.The horizontal displacement varies little with the increasing of the pipe length.The horizontal displacement at the center of the tunnel face increases with the increase of the pipe ring spacing and the pipe longitudinal spacing.There is an optimum external angle.

隧道初期支护型钢开孔对其安全性能的影响

在软弱围岩地段隧道施工中,常在工字钢腹部穿孔打设超前小导管。为了研究开孔对工字钢安全性能的影响,采用分级加载法,结合材料力学、数值模拟和相关试验,对比验证所建立模型的正确性,然后分析不同外荷载下开孔对工字钢的位移、应力、塑性应变等的影响,进一步分析开孔大小对其变形受力的影响。结果表明,工字钢跨中翼缘首先屈服;发生屈服的临界塑性荷载,数值模型解与理论模型解较一致,而试验值偏小。跨中上翼缘的两侧位移要大于中间的位移。当外荷载较小,工字钢处于弹性阶段,开孔直径对工字钢受力性能影响小;而当外荷载较大,工字钢处于塑性阶段,开孔两侧拱腰的塑性应变较孔周其他部位要大,大的开孔对工字钢影响较大,呈现的是非线性增长,且增长梯度越来越大。建议为了避免翼缘两侧产生过大的变形,工字钢翼缘与围岩接触侧以及上下翼缘之间,喷射混凝土应喷射密实,必要时,可以在工字钢上下翼缘侧焊接加强联系筋。对直径超过50mm的大直径超前支护,不应在工字钢腹部开孔;如要开孔,必须采取加强加固措施,如大直径导管管内必须注满浆液,导管尾部与工字钢焊接牢固,并在孔周边焊接加强钢筋或钢板,或者从工字钢外侧打入超前小导管。