水平-竖向组合加筋地基力学行为的试验研究及细观模拟分析

Geosynthetics have been successfully applied in foundations for three decades. Recently, considerable attention has been given to the development of advanced three-dimensional reinforcement. Some model tests have shown that the H-V reinforcement was superior to the traditional strip reinforcement. Comparisons between sand beds reinforced with H-V reinforcement and strip-reinforcement revealed that the H-V reinforcement system behaves more uniformly, carries greater surcharge, and settles less than the equivalent strip reinforcement. The test results also demonstrate that the vertical elements of H-V reinforcement kept the sand from being displaced under the applied load and redistributed the footing load over a wider area, thereby increasing the shear strength of the composite system, which in turn substantially improves the bearing capacity of the H-V reinforced sand bed. However, the failure mode and mechanism of the H-V reinforced soil foundation is not well understood. Meanwhile, there is still a lack of analytical models for estimating the ultimate bearing capacity of H-V reinforced strip footing. Particle Flow Code (PFC), based on the discrete element method (DEM), is a useful method to investigate the soil properties from the micro point of view. By investigating the stress distribution and displacement in H-V reinforced soil foundation using PFC2D (Itasca 2008), the H-V reinforced soil foundation can be simulated with meso-mechanics by PFC, and the macro-response of soil can be analyzed by investigating its meso-parameters. The purpose of this grant is to: 1) investigate the effect of the distance between consecutive layers of reinforcement, the depth of reinforcement zone and the number of reinforcements on the load-settlement curve and the deformation of the sand surface, 2) compare the difference between the failure mode and mechanism of the H-V reinforced sand beds and with strip reinforcement from micro point of view, 3) study the behavior of progressive failure and the possible mechanism of the H-V reinforced sand bed, 4) present the analytical models for estimating the ultimate bearing capacity of H-V reinforced strip footing. This research is very important and contributes to the geosynthetics industry.

土工材料已经成为继钢材、水泥、木材之后的第四大建筑材料，其在地基中应用的主要目标是高效率、低成本地改善软弱地基的工作性能。水平-竖向三维立体加筋地基的工作性能优于传统水平加筋地基，申请者通过模型试验验证了这一构想。但是，其中的一些力学行为只局限于推测分析，对其认识还不够深入系统；筋-土作用机理和地基破坏模式只局限于宏观观测，还缺乏微观的模拟和佐证；同时缺少预测水平-竖向加筋地基承载力的力学计算模型，使得地基性能与筋材几何参数之间的关系不太明确。本项目拟采用试验测试、离散元数值模拟和理论分析相结合的技术路线，着力解决这些关键问题。一方面为水平-竖向三维立体加筋地基的推广应用提供科学支撑，另一方面探讨加筋地基研究中的新思路和新方法。项目的特色是从具有重要应用前景的工程需求中提炼科学问题，主要的创新点在于将水平-竖向三维立体筋用于开发新概念地基，微观分析其中的关键力学问题并建立相关理论计算模型。

项目采用模型试验、离散元数值模拟结合理论分析研究了水平-竖向（H-V）组合加筋地基的加固机理和破坏模式，并建立相应的极限承载力计算公式。主要成果包括：1) 对比了静载条件下不同类型加筋地基的强度与变形特性。分析了筋材的构造形式、材料性质及布置参数如首层加筋深度、加筋层数、层间间距等对地基强度与变形特性的影响。通过PIV数字图像变形量测技术，真实摄录和分析了不同加筋地基类型中破裂面的出现、扩展规律以及地基破坏模式等。2) 细观仿真模拟并分析了不同加筋地基的力学行为。通过对不同加筋地基建立细观仿真模型，分析了地基中砂土颗粒的运行规律及相互间力的传递路径等，重点研究了竖筋对砂土颗粒的阻隔、约束和锚固作用，进而深入分析了竖筋对H-V加筋地基宏观力学性能的影响。3) 建立了条形基础下H-V加筋地基的附加应力计算公式及极限承载力计算公式。在经典太沙基未加筋地基承载力计算理论的基础上，主要考虑了竖向筋的锚固和约束作用，分别提出了包含H-V 筋集合特征参数的附加应力计算公式及地基极限承载力计算公式。除此之外，增加了对土工格栅、土工格室及土工膜等不同材料制H-V筋材的对比研究。增加了对不同加筋地基类型的二维有限元模拟，探明了竖筋及地基中应力的分布。增加了三维筋材加筋地基的三维有限元模拟分析，发现三维筋材能更有效地均化地基中的应力、限制地基中砂土颗粒的侧向位移。项目成果可望为H-V这种新型筋材的研发和推广应用提供坚实的科学支撑。