基于负泊松比土工格栅拉胀效应的筋土界面协同作用与强化机理研究

At present, the theories of tall reinforced earth structure design are inadequate, which mainly follows the ordinary reinforced earth structure theories and methods and results in many collapse disasters. Previous researches have shown that it is the shear contraction of the soil and the tensive thining of the reinforcement which reduce the occlusion effect of the soil-geosynthetic interface in the deeper layer of the reinforced earth stucture and make the friction coefficient of the interface much lower than shallower layer. In this project, a kind of polyethylene/polypropylene geogrid with negative Poison's ratio will be developed through the hybrid technology. The process parameters of the geogrid will be optimized with the tests on the auxetic effect and vibration-absorbing property. Poison's ration-tensile deformation model and creep model will be established by tests. Furthermore, this project will also study on the static and dynamic characteristics of the fill-geogrid interface and reveal the macro-micro synergy interaction mechanism of the fill and the geogrid with negative Poison's ratio. The deformation and failure mode of the earth structure reinforced with negative Poison's ratio geogrid under both static and dynamic loads will be studied. Considering the auxetic effect of geogrid, the deformation calculation method and the stability analysis method of the reinforced earth structure will be put forward. These studies will play an important role in the reinforcement of soil-geosynthetic interface and the enhancement of the stability of tall reinforced earth structural.

目前高大加筋土结构设计理论尚不完善，主要沿用一般加筋结构的理论与方法，导致垮塌事故时有发生。已有研究表明，高大加筋土结构中深层筋-土界面附近土的剪缩和筋材的拉缩特性降低了筋土的咬合作用，使得深层界面似摩擦系数明显低于浅层。鉴于此，本项目拟通过多学科交叉，基于负泊松比聚合物的拉胀效应，通过聚合物（聚乙烯/聚丙烯）的共混技术，研制一种负泊松比土工格栅。项目将对负泊松比土工格栅的制备工艺参数进行优化，研究其拉胀效应和吸振特性，建立泊松比-拉伸变形模型和蠕变模型；研究负泊松比土工格栅与填料界面的静、动态特性，并揭示负泊松比土工格栅与填料的宏细观协同作用机理；研究静、动荷载作用下负泊松比土工格栅加筋土结构的变形规律，揭示土工格栅拉胀效应对加筋土破坏模式的影响；提出考虑格栅拉胀效应的加筋土结构变形计算与稳定性分析方法。本项目研究将对强化筋土界面作用和增强高大加筋土结构的稳定性起到重要作用。

本项目旨在通过对传统土工材料进行改造，提高其在土中的拉拔阻力。采用了三种手段：<1>以高密度聚乙烯（HDPE）做连续相，聚丙烯（PP）做分散相，采用共混法制备负泊松比材料；<2>通过对普通土工格栅进行结构改造，研制肋条加固式负泊松比土工格栅（RNPR土工格栅）；<3>研发排扣式嵌固土工格栅，通过改变肋条表面构型提升筋土界面作用。研究发现，第一种土工合成材料只能在较小的拉伸应变范围内表现为小泊松比，但未能出现负泊松比现象。后两种土工合成材料能够显著提升筋土界面作用。通过拉伸试验和有限元模拟，研究了RNPR格栅的拉胀效应，建立了拉伸变形-厚度变化关系曲线；对排扣式嵌固土工格栅进行力学性能试验，确定了其性能参数。通过室内试验，从宏观和细观角度研究了两种格栅在土中的变形规律，揭示了界面作用力在筋土间的传递方式。利用离散元模拟从细观尺度研究了RNPR格栅与填料的细观协同作用机理。通过排扣式嵌固土工格栅加筋挡墙足尺模型试验，发现排扣式嵌固土工格栅能够有效地控制土体变形，提高结构整体稳定性。RNPR土工格栅和排扣式嵌固土工格栅强度高、成本低，能有效增强筋-土作用强度，对增强高大加筋土结构的稳定性起到重要作用，应用前景广阔。