高聚物固化钙质砂应力变形特性与动力循环边界面本构模型研究

Due to the national strategic importance, infrastructures have been massively constructed at the islands of the South China Sea over the past few years. Calcareous soils that are widely encountered in the engineering practice could be easily crushable even under low stress conditions, thereby often leading to excessive differential settlement of foundations and cracks of pavements. This would pose serious risks of instability in surface infrastructures such as the airport runway, and cause more engineering accidents. The issue with relation to calcareous soil foundation has already become a key scientific problem with significant urgency to be solved. In such context, a new environmental-friendly stabilizer polyurethane foam adhesive (PFA) is proposed to stabilize the calcareous soil foundation by improving its mechanical characteristics. The stress-strain responses of improved soils under static and dynamic loading as well as the evolution of micro-structure of improved soils for assessing its cyclic degradation will be investigated using triaxial testing and microstructural studies. On the basis of micro-macro testing results together with bounding surface plasticity theory within a critical state framework, an analytically sound and experimentally validated cyclic constitutive model capable of capturing the main features of mechanical behaviour of PFA improved calcareous soils will be developed through incorporating the novel stress-dilatancy equation, flow rule, plastic modulus functions, as well as degradation law for PFA-improved soils. The main anticipated outcome of this project is not only to provide an alternative sustainable design method for the ground improvement of calcareous soil foundation in the South China Sea, but also to deliver the theoretical and experimental basis for the application of an innovative ground improvement technique using polyurethane foam adhesive. Therefore, this research is of great significance for both academics and engineering practice, and it would be also beneficial for the design and construction of the infrastructure on the calcareous soil foundation encountered at the islands of South China Sea.

近年来，围绕“海洋强国”战略，我国正大规模进行南海开发与建设。钙质砂地基问题在岛礁工程建设中频繁遇到, 其颗粒极易破碎的天然特性可导致机场跑道等出现地基沉降和道面断裂，引发工程事故，已成为当前亟待解决的关键科学问题。本课题拟采用新型固化剂高聚物改良钙质砂地基工程特性, 展开三轴剪切试验研究高聚物固化钙质砂的静动力特性，并结合微观试验手段，建立微观结构变化和宏观力学特性关系，揭示高聚物改良钙质砂的固化机理及其在循环荷载作用下的动力损伤机制，同时在边界面弹塑性理论框架下，修正剪胀方程、流动法则和塑性模量，建立动力边界面本构模型，用于分析高聚物固化钙质砂地基在循环交通荷载作用下的变形和动力损伤响应特性。研究成果不仅可以为南海钙质砂地基处理提供方案设计和施工技术参考，同时可以为新型固化剂高聚物在加固钙质砂工程中的应用提供理论和试验依据，因而具有显著的学术和工程实践价值，更具有广阔的应用前景。

钙质砂地基问题在岛礁工程建设中频繁遇到, 其颗粒极易破碎的天然特性可导致机场跑道等出现地基沉降和道面断裂，引发工程事故，已成为当前亟待解决的关键科学问题。针对该科学问题，本课题提出采用新型固化剂高聚物改良钙质砂地基工程特性。 .首先提出了一种既能保证高聚物与钙质砂颗粒均匀混合，又能防止钙质砂在制样过程中破碎的高聚物钙质砂试样制作方法。.然后，通过开展直接剪切试验、无侧限抗压强度试验、固结压缩试验和大型三轴剪切试验，研究了不同级配、不同高聚物掺量固化钙质砂试样的抗剪强度和变形特性，提出了钙质砂级配、高聚物掺量与高聚物固化钙质砂试样黏聚力、内摩擦角以及压缩变形指标的关系模型。结果表明：高聚物掺量越大，各颗粒级配条件下的高聚物固化钙质砂抗剪强度包络线均向上平行移动，高聚物固化钙质砂的抗剪强度大幅提升；钙质砂中粗颗粒含量越多，其孔隙越大，高聚物反应越明显，其强度变化也越明显；此外，高聚物可以明显地改善钙质砂土样的黏聚力，但对其摩擦角的影响较小。.通过开展GDS动三轴试验,研究了高聚物固化钙质砂在不同围压、高聚物掺量下，土体动弹性模量与等效阻尼比等动力特性参数的变化规律, 并建立了关系模型。试验结果表明:高聚物固化钙质砂的应力-应变曲线整体呈双曲线关系；随着动应变增加，高聚物固化钙质砂的动弹性模量减小，阻尼比增大；随着围压和高聚物掺量的增大，高聚物固化钙质砂的动弹性模量增大，阻尼比减小；动应变较大时，高聚物掺量对阻尼比的影响比较明显。.通过开展不同颗粒级配条件下的高聚物固化钙质砂试样进行加州承载比试验，获得了不同含量高聚物固化不同颗粒级配钙质砂的单位压力-贯入量曲线及各试样的承载比值。试验结果表明，对于相同高聚物含量的试样，钙质中砂的承载比值最大，但高聚物对于天然级配钙质砂承载能力的提升效果最好。.通过开展SEM微观结构试验，揭示了不同级配、不同高聚物掺量固化钙质砂的细观形态。结果表明：钙质砂中粗细颗粒含量对高聚物的粘结方式有明显的影响；高聚物固化钙质砂剪切强度的方式，主要是通过高聚物包裹钙质砂颗粒表面，逐渐改变钙质砂颗粒间的接触形式（由点接触逐渐变为面接触），进而加强颗粒间的胶结作用。.研究成果可以为南海钙质砂地基处理提供方案设计和施工技术参考，同时可以为新型固化剂高聚物在加固钙质砂工程中的应用提供理论和试验依据。