隧道初期支护型钢开孔对其安全性能的影响

Influence of Section Steel Opening for Primary Support to the Safety of Tunnel

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。

During tunnel construction in section of soft and poor rock, advanced small pipe is often used through the hole on I-beam web. In order to study the influence of the opening on the safety of the Ibeam, the simulation model under grading loading method is built and verified by the material mechanics and the relevant experiments. Then the influence of the hole on the displacement, stress and plastic strain of I-beam under different load is analyzed; and further analysis of the impact of the size of the hole on its deformation is studied. The results show that the critical yield load of the I-beam of the flange is first yielded, and the solution of the numerical model is consistent with the theoretical model, but the experimental value is too small. The displacement on both sides of the upper flange is greater than the middle of the I-beam. When the external load is small, the I-beam is in the elastic stage, and the diameter of the hole has little effect on the I-beam＇s mechanical performance. When the external load is larger, the I-beam is at the plastic stage; and the larger hole has a greater influence. Some suggestions on construction and design are proposed. In order to avoid excessive deformation on both sides of the flange, the shotcrete should be dense between the flange side of the I-beam and the contact side of the surrounding rock and between the upper and lower flange. If necessary, the upper and lower flange sides of the I-beam can be connected by contact bars. It should not be in the abdominal I-beam openings when the diameter of the advance support is larger than 50mm. It is better to set larger advanced pipe through the outside of the I-beam and some reinforcement measures must be taken.