粉细砂地层大断面隧道暗挖注浆试验及地表沉降规律研究

粉细砂稳定性差,暗挖施工时容易引起较大的地表沉降。通过粉细砂特性分析及室内试验得到注浆加固前后土体的物理力学参数,试验结果表明:注浆加固对土体的含水量、黏聚力、内摩擦角和压缩模量均有明显的改善。运用加固后的土体物理力学参数,通过数值计算和现场监测分析,对粉细砂地层浅埋暗挖大断面施工地表沉降规律进行研究。结果表明:上导洞施工时对地表沉降的影响最大,施工时应重点加强此部位的注浆;上、下导洞施工时应错开距离不宜小于10 m;上导洞上台阶施工时应预留核心土;临时支撑分段破除长度不宜大于10 m;粉细砂地层深孔注浆加固设计时,除拱顶范围外,侧墙和拱脚一定范围也应进行注浆加固。实践表明理论分析与现场监测结果吻合,沉降满足设计及规范要求。

Study on Large Cross-section Tunnels Underground Excavation Grouting Test and Surface Subsidence Rule in Silty Sand Layer

Silty sand has poor stability and is likely to cause large surface subsidence during the tunneling construction. The physical and mechanical parameters of the soil before and after reinforcement are obtained based on the analysis of the characteristics of silty sand and laboratory tests. The results show that the grouting reinforcement has obvious improvement on soil water content, cohesion, friction and modulus of compression. Based on the physical and mechanical parameters of the soil after reinforcement, numerical analysis and site monitoring are carried out to study the surface subsidence rule during the shallow-buried and large cross-section construction in silty sand layer. The results show that the construction of the pilot heading tunnel has the greatest influence on the surface subsidence. The construction should focus on strengthening the grouting at this location; the upper and lower pilot heading should be staggered at a distance of not less than 10 m; core soil should be reserved for construction in the upper pilot heading; temporary support section breaking length should not be more than 10 m; during the silty sand deep-hole grouting, the side wall and arch foot should also be reinforced with deep-hole grouting except the vault. Practice demonstrates that the theoretical analysis is consistent with the site monitoring results, and the surface subsidence meets the design and code requirements.