深埋隧道与浅埋隧道划分方法研究

Division method for deep and shallow tunnels

隧道开挖后,围岩土体中的土压力拱效应显著地影响作用在隧道衬砌结构上的土压力。隧道结构设计时,界限埋深是确定围岩压力的基本参数之一。基于隧道开挖时围岩土体中附加荷载的特点,编制可以合理考虑土的应力路径相关性的弹塑性本构模型子程序,利用二次开发后的有限元分析软件ABAQUS对隧道开挖过程进行了三维有限元模拟。从围岩土体的变形规律和应力重分布两个方面分析了隧道开挖过程中的土压力拱效应,提出了深埋隧道与浅埋隧道的划分方法,即洞顶土体竖向位移达到稳定值时对应的埋深为界限埋深,当有支护结构与围岩土体相互作用时,洞顶上方地表处土体最大沉降对应的埋深作为界限埋深。通过与规范法确定的界限埋深比较,表明提出方法可较好地反映隧道开挖时围岩土体变形的宏观规律,并可考虑多种因素的定量影响。

The earth pressure applied on the lining is affected significantly by the soil arching effect during tunnel excavation. The critical depth becomes one of basic parameters to determine the pressure of the surrounding rock when designing the tunnel structure. Based on the additional load characteristics of the surrounding rock, a user-defined elastic-plastic material subroutine(UMAT) of the constitutive model considering complex stress path of soils is complied. Three-dimensional finite element analysis of tunnel excavation is carried out by means of the secondarily-developed ABAQUS with the UMAT. The soil arching effect is studied from two aspects: the deformation law of the surrounding rock and the stress path. According to the results, a new division method for deep and shallow tunnels is proposed, which can be illustrated by the critical depth. The critical depth is determined as the depth in accordance with the vertical displacement of ceiling becoming steady when there is no supporting structure, and the depth in accordance with the maximum settlement of the surface soil above the tunnel when supporting structures exist. Compared with the critical depth determined by the code, the proposed method can reflect the macroscopic deformation law of soils. Moreover, the quantitative impact of various factors is taken into account at the same time.