浅埋膨胀土隧道围岩抗剪强度与支护结构受力特征关系研究

Study on the Shear Strength of Surrounding Rocks and Mechanical Behaviors of Supporting Structure of the Shallow-buried Tunnel in Swelling Soil

膨胀土吸水后产生的膨胀问题,导致隧道支护结构承受复杂的膨压应力。为研究浅埋膨胀土强度衰减和膨胀效应对隧道支护结构的影响,文章以呈贡隧道工程为背景,首先利用室内直剪试验方法,探明膨胀土的抗剪强度与初始含水量的变化关系;然后基于室内试验结果,采用ABAQUS三维有限元分析模拟软件,研究膨胀土吸水膨胀对隧道支护结构的影响,揭示不同埋深下膨胀土膨胀效应对围岩变形和支护结构内力影响规律。研究结果表明:(1)摩擦角和粘聚力均随含水量的增大而下降,粘聚力受到的影响较大,膨胀土抗剪强度与含水量的关系可采用二次抛物线表征;(2)膨胀土围岩吸水后受到支护结构约束,产生较大的膨胀压力,导致围岩出现破坏,造成隧道仰拱隆起量和边墙水平收敛增大;(3)围岩膨胀后,初期支护结构轴力均匀增加,拱腰处弯矩增加较小,墙脚处弯矩增加较大,使支护结构处于不安全状态;(4)埋深对膨胀变形产生很大的影响,但达到某一极限埋深后将不发生膨胀变形。

Swelling induced by water absorption of swelling soil results in complex swelling stress on tunnel supporting structure.In order to investigate the impact of strength declining and swelling effect of shallow-buried swelling soil on supporting structure,taking the Chenggong tunnel as the background,the relationship of shear strength and initial moisture content is verified by indoor direct shear test;based on the result of laboratory test,ABAQUS 3D finite element software is used to study the effect of soil swelling on tunnel support structure,and the im⁃pact of swelling effect on deformation of surrounding rocks and internal force of supporting structure under different buried depths is revealed.The results show that:friction angel and cohe sion decrease with an increase of moisture con⁃tent,cohesion is significantly affected,the relationship between the shear strength and moisture content of swelling soil can be represented by quadratic parabola;large swelling pressure is produced due to restraint of supporting struc⁃ture after water absorption of swelling soil and it results in damage of surrounding rocks and increase of invert heaving and horizontal convergence of sidewall;after swelling of surrounding rocks,the axial force of primary supporting struc⁃ture increases evenly,the bending moment increases slightly at haunch but largely at the foot of sidewall,and the supporting structure is in an unsafe state;swelling is largely affected by buried depth and no further swelling occurs when it reaches certain ultimate buried depth.