基于既有模型和改进模型，对粉质黏土、粉土、 砂土及与砂卵石共4 种地层进行端头加固统计计算，讨论 纵向加固范围与盾构直径之间的关系，验证端头加固的尺 寸效应，给出大小盾构分界的建议: 在盾构始发与到达端 头加固研究中，直径小于 10 m 和大于10 m的盾构隧道端 头土体纵向加固范围与直径的关系曲线表现出明显不同 的变化特征，10 m 直径可以作为大小盾构的有效分界线。 对于直径大于10 m 的盾构隧道，使用改进模型进行端头 加固计算，更科学、更符合实际，结论更可靠。以北京地铁 14 号线大盾构始发与到达工程为背景，从强度、稳定性及 渗透性 3 个方面分析大盾构端头加固方案的可行性。

Current and improved models were used in calculation and statistical analysis for four typical strata including silt-clay, silt, sand and gravel strata. Relationships of longitudinal reinforcement ranges with changes of diameters of EPB shields were discussed. Based on the statistical computation results, the size effect of soil reinforcement and the boundary between large - and small - diameter EPB shields was studied. It has been concluded that the relationships of longitudinal reinforcement ranges with diameters of EPB shields show obviously different characteristics for diameters of shields smaller and bigger than 10 meters, and 10m diameter can be fixed as the effective boundary between big and small shields. Therefore, for largediameter shield tunnel engineering, especially for those with shield diameter la ger than 10 meters, the load equivalent model will be more scientific and suitable for actual engineering design, and the conclusion will be more reliable. Feasibility analysis of soil reinforcement has been made based on strength, stability and permeability theories, with the launching and arrival of large-diameter EPB shields on Line 14 of Beijing metro taken as the research background.

U455． 43

北京市科委重大项目( D08050600390000)