考虑软化效应的隧道围岩自稳时间解析模型

现行隧道自稳时间解析法中未考虑地下水的软化作用，导致过高估计亲水软化性岩石的围岩质量。以具有典型软化特性的石膏岩为研究对象，探索水的软化作用对隧道围岩自稳时间的影响。采用试验和理论相结合的方法研究围岩自稳时间。首先，进行不同浸水时间下的石膏岩软化试验，研究其软化规律；通过试验获得石膏岩吸水率、弹性模量和泊松比分别与浸水时间之间的定量关系；在弹性模量与浸水时间及泊松比与浸水时间的定量关系中，引入完整性系数和富水系数，建立岩体力学参数软化方程。然后，基于经典的圆形轴对称隧道弹性解，考虑掌子面对隧道轴向位移的影响，推导出隧道临空面处无支护状态下的位移公式；把岩体力学参数软化方程嵌入此位移公式中，获得考虑软化效应的临空面位移解。最后，在此位移解中引入活跃跨度和围岩的临界位移值，建立考虑软化效应的隧道围岩自稳时间解析模型。该模型考虑了围岩体工程特性、岩石力学特性及岩石软化特性，能输出自稳时间与活跃跨度之间的关系曲线。经自洽分析法检验，该模型中自稳时间随各参数的变化规律与实际情况相符，模型具有自洽性。模型被应用于评价礼让隧道石膏围岩的自稳时间，现场反馈结果表明该模型更适合于现场应用。

Analytical Model for Stand-up Time of Rock Mass Surrounding Tunnel with Consideration of Softening Effect

The existing analytical solution of stand-up time neglected the softening effect of underground water,which resulted in overestimating the surrounding rock quality.This paper focused on the softening effect of water on stand-up time for the gypsum rocks with typical softening characteristics.The research method combined the softening test results of gypsum with the axisymmetric circular tunnel elastic theory.Firstly,the softening test of gypsum with different soaking time was carried out;thus,the absorption,elasticity modulus and Poisson''s ratio changing over soaking time were obtained,respectively.The integrality index and water content coefficient were introduced into the quantitative relationship between the elasticity modulus and the soaking time and that between the Poisson''s ratio and the soaking time; thus,the softening equation of mechanical parameter of rock mass was obtained.Then,based on the elastic solution of axisymmetric circular tunnel and the influence of tunnel face,the displacement formula of tunnel free face without supporting effects was developed.Then,the softening equation of mechanical parameter of rock mass was embedded into this displacement formula;thus,the displacement solution of free face considering softening effects was obtained.At last,the analytical model for stand-up time of rock mass surrounding tunnel with consideration of softening effect was established by introducing the active span and the critical displacement value into this displacement solution.This model takes into consideration the engineering features of rock mass,the mechanical performance of rock,and the softening behavior of rock.Moreover,it is able to show the relationship between the stand-up time and the active span.This model was further investigated by self-consistent analysis,which showed that the variation rule of each parameter accorded with actual situation and the self-consistency was met.This model was employed for the Lirang tunnel,which indicated that it is practical for in-site application.