盾构隧道接缝漏损诱发水土流失模型试验及离散元分析

Model Test and Discrete Element Analysis of Soil and Water Loss Induced by Joint Leakage of Shield Tunnel

盾构隧道接缝漏损是诱发地面塌陷的主要因素,掌控水土流失发展规律是规避地面塌陷风险的基础和前提。基于临界漏缝宽度,针对不同漏缝位置、不同覆土深度、不同上覆水位高度进行砂土沉降规律及孔隙水压力变化规律影响因素的模型试验分析,并设计一套渗流示踪装置探究渗流场的分布情况及其流线轨迹变化规律。试验结果表明:距离漏缝竖向距离越近的砂层沉降越明显,坍塌范围由隧道漏缝周围逐渐向上扩散至地表,砂层位置越高,沉降槽越宽,由深“V”形态、浅“V”形态向“高斯曲线形态”发展。漏缝越靠近拱底,砂土表面沉降越小,孔隙水压力消散值越小;覆土深度越高,砂土沉降越小,扰动范围越窄,孔隙水压力消散值越大;上覆水位高度越高,砂土沉降越大,扰动范围越宽,孔隙水压力消散值越大。示踪流线为一系列圆弧线,5条流线均向漏缝位置流动,距离漏缝较远处水的流动速度慢,导致流线变长,示踪流线向下发展将加速贯通至漏缝流线形成。此外,通过构建隧道-砂土离散元数值模型,对渗流侵蚀过程中的砂土成拱效应及位移演变规律进行分析,揭示了盾构隧道周围砂土颗粒迁移及损失对周围环境的细观尺度影响。离散元分析表明:在接缝未发生漏损时,没有产生渗流侵蚀通道,接缝周围土拱稳定,一旦发生漏损,土拱立刻发生破坏,在模型试验中表现为水土流失的开始,在随后的整个水土流失过程中,始终伴随着“砂土颗粒成拱→土拱发生破坏→土拱再生成→土拱继续破坏”的过程,最终,漏缝周围形成稳定土拱,合理解释了模型试验中漏砂终止、砂层位移收敛的现象。

The leakage of shield tunnel joints is the main factor in ground subsidence,and controlling the law for the soil and water loss development is the basis of methods to prevent the risk of ground subsidence.Based on the critical crack width,the settlement law of a sand layer and the influencing factors of the pore water pressure change law were analyzed using model tests for different crack positions,different overburden depths,and different overlying water levels.A set of seepage tracing devices was designed to investigate the distribution of a seepage field and change law of a streamline trajectory.The test results showed that the settlement of a sand layer was more obvious at a shorter vertical distance from the leakage,and the collapse area gradually diffused to the surface from the area around the leak,developing from a deep“V”type to shallow“V”type and“gauss curve type.”When the leakage joint was closer to the bottom of the arch,the settlement of the sand surface and dissipation of the pore water pressure were smaller.When the depth of the overlying soil was higher,the sand settlement was smaller,disturbance range was narrower,and dissipation of the pore water pressure was greater.When the overlying water level was higher,the sand settlement was greater,disturbance range was wider,and dissipation of the pore water pressure was greater.The tracer streamline was a series of circular arcs,and five streamlines flowed to the leak slot.The flow velocity of the water far from the leak slot was slow,which produced a longer streamline,and the downward development of the tracer streamline accelerated the penetration to the leak slot streamline.In addition,the arching effect of sandy soil and displacement evolution law during the process of seepage erosion were analyzed by constructing a numerical model of the sandy soil of the tunnel as a discrete element.This study revealed the influence of sand particle migration and loss around a shield tunnel on the mesoscale of the surrounding environment.The discrete element analysis showed that there was no leakage in the joint,and no seepage erosion passage.The soil arch around the joint was stable,and once leakage occurred,the soil arch was immediately destroyed,which was the beginning of the soil and water loss in the model test.The entire soil and water loss process was always accompanied by the following process:“sand particles arching→soil arching failure→soil arching regeneration→soil arching continued failure.”Finally,a stable soil arch was formed around the leakage joint,and the phenomena of the sand leakage stopping and sand layer displacement convergence in the model test were reasonably explained.