盾构壁后浆体-扰动土体的广义复合土层大应变固结研究

The key soil mechanics problem of increasingly severe soft-ground settlement for post-construction of shield tunneling in metrolines, contributes to the theory of consolidation of backfill-grout and disturbed subsoil. Samll-strain Terzaghi or Biot theory was used traditionally whereas in contraction with the fact of over 10% large-strain of grouts. Within the framework of general porous media, a novel large-strain consolidation theory for general composite stratum consisting of grouts and disturbed subsoils will be studied, viewing backfill-grout as general soil with consolidation-cementation behavior. Firstly based on finite deformation theory and large-strain consolidation theory development, the govening equations of general composite strata consolidation model will be proposed with introduction of both general effective stress principle and objective constitutive model considering the cementation characteristics. Then large-strain quasi-variational priciple and virtual work theorem will be studied followed by formulations of Lagrangian and ALE FEMs with their programs. The practical multi-dimentional large-strain constitutive model is put forward according to laboratory lare-strain test for backfill grouts, disturbed subsoil and composite stratum. Through test results comparison, case studies and parametric analysis, the validation and reliability of the proposed new theory with its FEM programs is conducted with conclusions of application scope of conventional small-strain theory models and so on.

软土地区盾构隧道工后沉降病害日益困扰着不少城铁的正常运营,其在土力学方面的关键问题可归于壁后浆体及周围扰动土体的固结理论。以往研究通常基于小应变太沙基或比奥固结理论，与实际浆体应变一般高于10%的大应变事实不符。项目拟在广义多孔介质范畴内，将壁后浆体作为具有固结-胶结特性的广义土体，与周围扰动土体形成广义复合土层，开展其大应变固结理论研究。首先基于有限变形理论及大应变固结理论既有成果，新引入反映胶结特性的广义有效应力原理及客观性本构模型，提出广义复合土层多维大应变固结模型控制方程；然后研究其大应变拟变分原理及虚功原理，据此导出拉格朗日和ALE描述的有限元法，并编制程序。通过浆体、扰动土体和复合土层的固结-胶结与固结大应变室内试验成果，提出实用的多维大应变客观本构模型等。结合试验结果对比、工程实例应用以及参数研究，验证理论模型及其有限元法和程序的合理性与可靠性，给出传统小应变方法的适用范围。

城市地铁建设尤其是软土地区以盾构工法为代表修建区间隧道的工程实践中，由于软土具有高压缩性等特性并且容易受到施工扰动而发生地层过大变形，继而会在不同程度上影响到盾构隧道和邻近建（构）筑物的正常运营或使用。盾构隧道工后沉降预测和控制的关键在于弄清壁后浆体及其周围扰动土体随时间发展的变形特性。把盾构壁后浆体和周围扰动土体作为一个整体的广义复合土层，深入开展相应的理论和试验研究，将具有较好的学术和工程意义。项目重点研究了壁后浆体扰动土体物理力学性质室内试验性状，以及采用透明土试验技术和相似模型试验方法研究了壁后浆体的填充和扩散范围、固结变形、注浆压力分布模型等及其在控制广义复合地层沉降方面的机理。主要结果有：（1）透明土透明效果随熔融石英砂粒径的减小和骨料中细粒粒径颗粒含量的增加而逐渐减弱。（2）各级配透明土与标准砂土摩擦角、压缩性具有相同的变化趋势，但黏聚力有差异，黏聚力三轴试验值较直剪试验结果偏大，各级配透明土的压缩性较相应级配标准砂土要小。（3）提高注浆压力会减小地层沉降，但过大的注浆压力会导致地层隆起；注浆压力越大浆液的填充性越好、扩散范围也越大；但在同种注浆压力下浆液的扩散范围基本不随隧道埋深的变化而改变。(4)影响浆体固结变形最本质的因素还是浆液自身性质，只有合理地根据施工环境确定合理的注浆浆液才能保证浆液的固结压缩控制在一定范围内。（5）粘土和砂土地层相同注浆压力下体积压缩曲线实测结果表明，复合土层体积应变可能达到10%或以上的大应变标准，意味着在盾构隧道壁后注浆问题中深入开展大变形理论研究很有必要。所得结论的支持依据主要来自室内剪切和三轴剪切试验以及相似模型试验实测数据。项目初步成果表明了盾构壁后浆液物理力学性质在控制地层固结沉降方面的重要意义。