基于非线性Hvorslev面的超固结土层隧道掌子面稳定性分析

Stability of tunnel face in overconsolidated soil layer based on nonlinear Hvorslev surface

受沉积历史的影响,天然土层通常表现出一定程度的超固结特性,对土体强度具有显著的影响。然而,传统分析方法无法直接反映土体的超固结特性对隧道掌子面极限支护力的影响。引入非线性Hvorslev面描述地层土体的强度特性,通过切线技术得到土体的等效的摩尔-库仑强度参数,将其应用在修正后的三维坍塌机制分析,得到了超固结比随深度变化的黏土层中隧道掌子面的极限支护力。通过将模型退化形式与经典的模型计算结果进行对比,验证了所提方法的合理性。超固结土层中隧道掌子面极限支护力σ_(c)与土层超固结比、隧道直径D、回弹曲线斜率κ*与压缩曲线斜率λ*之比κ*/λ*、孔隙水压系数r_(u)、侧压力系数K_(0)、隧道深径比C/D和临界状态应力比M等因素相关。计算结果表明,随着超固结比增大,掌子面坍塌范围和相应的极限支护力σ_(c)减小。当土体超固结比OCR不变时,σ_(c)与D、κ*/λ*和r_(u)呈正相关,而与K_(0)、C/D和M呈负相关。当土体超固结比较高时,σ_(c)受κ*/λ*的影响较为显著;当超固结比较低时,σ_(c)对C/D和K_(0)的敏感度较高。在超固结土层中设计隧道掌子面支护力时,应根据实际工况综合考虑土体的应力历史、超固结比、隧道尺寸和埋深等因素。

Natural soil layers often exhibit overconsolidation due to their deposition history,which significantly affects soil mechanical properties.However,traditional analytical methods for determining critical tunnel face pressure are ineffective in considering the overconsolidation effect.This study introduces a nonlinear Hvorslev surface as the strength criterion for overconsolidated soil.The equivalent Mohr-Coulomb strength parameters are derived using the tangent technique and then incorporated into the modified three-dimensional collapse analysis.A new model is established to predict the critical face pressure of tunnel faces in clay layers with varying overconsolidation ratios(OCR).The model’s validity is confirmed by comparing it with the existing model in its simplified form.The critical tunnel face pressure(σ_(c))in overconsolidated soil is influenced by the overconsolidation ratio(OCR),tunnel diameter(D),the ratio of the swelling line slope to the compression line slope(κ*/λ*),pore water pressure coefficient(r_(u)),soil lateral pressure coefficient(K0),tunnel depth-to-diameter ratio(C/D),and the stress ratio at critical state(M).The findings show that with increasing OCR,the collapse zone at the tunnel face shrinks,leading to a decrease in the critical tunnel face pressure(σ_(c)).When OCR is constant,sc positively correlates with D,κ*/λ*,and r_(u),while negatively correlating with K_(0),C/D,and M.The impact of κ*/λ* onsc is significant at high OCR values,and C/D and K_(0) have a high sensitivity at low OCR values.Therefore,to enhance the design of tunnel face pressure in overconsolidated soil,engineers should consider factors like stress history,OCR,tunnel dimensions,and depth.