缓倾软岩隧道底部结构劣化因素及影响机制分析

Analysis of structural degradation factors and influencing mechanism of gently inclined soft rock tunnel bottom

【目的】探明缓倾软岩隧道底部结构劣化的影响因素及影响机制,研究在不同围岩强度、岩层产状、地应力作用下的缓倾软岩隧道底部变形及塑性区发展趋势。【方法】基于Hoek-Brown强度准则和遍布节理本构模型确定数值模拟的力学参数并构建开挖模型,通过改变Hoek-Brown参数、岩层产状、地应力状态分析隧道的变形规律。【结果】深埋缓倾软岩隧道拱底两侧具有明显非对称变形,随着Hoek-Brown参数和围岩强度的提高,隧道拱底隆起量不断降低,且拱底两侧的非对称变形有所减弱并趋向于对称变形。当围岩强度较低时,围岩混合剪切型塑性区主要分布在拱底,基体剪切破坏主要分布在边墙,且剪切破坏范围随围岩强度的提高呈不断减小趋势。在倾角为0°~30°条件下,随着岩层倾角的增大,隧道底部隆起呈不断减小趋势,且拱底塑性区分布深度逐渐减小。随着岩层倾向角增大,隧道底部非对称变形和变形量增加,且拱底混合剪切塑性破坏区不断向深处延伸。随着侧压力系数和隧道埋深的增大,隧道仰拱处的变形量和变形速率比其他位置的大,且埋深的改变主要影响围岩塑性区体积和分布深度,而侧压力系数的改变还影响塑性区的分布形态。【结论】缓倾软岩隧道的变形发展趋势和塑性区破坏模式均与岩层产状有关,缓倾角条件下的拱底变形较大,且围岩节理剪切破坏主要发生在岩层倾斜方向上。该研究结果可为类似工程在施工过程中确定不利变形位置及优化支护方案提供参考。

[Purposes]The study aims to investigate the structural degradation factors and influencing mechanism of gently inclined soft rock tunnel bottom and explore the deformation and plastic zone development trends of gently inclined soft rock tunnel bottom under varying surrounding rock strength,attitude of rock formation,and ground stress conditions.[Methods]The mechanical parameters for numerical simulation were determined using the Hoek-Brown strength criterion and pervasive joint constitutive model.An excavation model was created.The deformation law of the tunnel was analyzed by changing the Hoek-Brown parameter,attitude of rock formation,and ground stress state.[Findings]The deep-buried gently inclined soft rock tunnel exhibits noticeable asymmetric deformation on both sides of the arch bottom.As the Hoek-Brown parameter and surrounding rock strength increase,the uplift of the arch bottom reduces,and the asymmetric deformation on both sides of the arch bottom is weakened and tends to be symmetrical.When surrounding rock strength is low,the mixed shear plastic zone mainly concentrates at the arch bottom,while matrix shear failure primarily occurs at the side walls.This shear failure range decreases as surrounding rock strength increases.For dip angles of 0°~30°,the uplift at the tunnel bottom decreases as the rock dip angle increases.Additionally,the depth of the plastic zone at the arch bottom progressively decreases.As the rock inclination angle increases,both the asymmetric deformation and deformation magnitude at the tunnel bottom increase.The mixed shear plastic failure zone at the arch bottom extends to greater depths.Increasing lateral pressure coefficient and burial depth results in larger deformation magnitudes and rates at the tunnel invert compared to other locations.Changes in burial depth primarily affect the volume and depth distribution of the surrounding rock’s plastic zone,whereas changes in the lateral pressure coefficient mainly impact the form of plastic zone distribution.[Conclusions]The deformation and failure mode of the plastic zone in a gently inclined surrounding rock tunnel are influenced by the attitude of rock formation.At low gently inclined angles,the arch bottom experiences significant deformation,while the shear failure of the surrounding rock joint occurs mainly in the direction of rock formation inclination.The research results can provide a reference for determining the unfavorable deformation position and optimizing support schemes in the construction process of similar projects.