Mechanical Characteristics and Failure Mode of Wasted Polyester Fiber-reinforced and Cement-stabilized Sand
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摘要: 水泥固化砂土的低成本、无害化改良是岩土工程领域的热点问题。利用废弃服装制备的涤纶纤维对水泥固化砂土进行改良，研究纤维含量和纤维长度对水泥固化砂土无侧限抗压强度特性的影响。基于试样的宏观破坏形貌，定性分析改良前后水泥固化砂土的破坏模式及破坏模式的转变方式，利用脆性指数，研究纤维含量、纤维长度影响下水泥固化砂土破坏模式的转变规律，定量评价脆性破坏向延性破坏的转变程度。研究结果表明：在最优纤维含量1.0%、最优纤维长度9 mm条件下，废弃涤纶纤维的改良效果最佳，水泥固化砂土的无侧限抗压强度、峰值应变、残余强度、残余应变的增长幅度分别为43.3%、18.2%、276.9%、190.9%。水泥固化砂土改良后，由最初的脆性破坏向半延性、延性破坏转变，宏观破坏形貌由脆性破坏时纵向贯通相互独立的裂隙向半延性破坏时单斜或稀疏的共轭破裂裂纹、延性破坏时稠密的网状共轭裂纹转变。在最优纤维含量、最优纤维长度条件下，试样破坏后表面共轭裂纹数量最多，脆性指数最小，试样由脆性破坏向延性破坏转变程度最高。研究结果为水泥土的无害化改良和纤维土的破坏模式分析提供科学依据。Abstract: Using a low-cost and environmentally benign method to reinforce cement-stabilized sand is a key issue in geotechnical engineering. Polyester fiber from waste clothes was used to reinforce cement-stabilized sand in this study. The effects of the fiber content and fiber length on the unconfined compressive strength of cement-stabilized sand were examined. The failure modes of the cement-stabilized sand before and after reinforcement were qualitatively analyzed according to the macroscopic damage morphology of a test sample. The impacts of the fiber content and fiber length on changes in the failure mode of the cement-stabilized sand were analyzed according to the brittleness index. The degree of transformation from brittle failure to ductile failure of the cement-stabilized sand was evaluated. The results showed that the optimum reinforcement performance with waste polyester was obtained at a fiber content of 1.0% and fiber length of 9 mm. These conditions realized improvements in the unconfined compressive strength, peak strain, residual strength, and residual strain of the cement-stabilized sand of 43.3%, 18.2%, 276.9%, and 190.9%, respectively. After polyester reinforcement, the failure mode of the cement-stabilized sand gradually transformed from brittle failure to semi-ductile and ductile failure, as reflected by changes in the macroscopic damage morphology. Before reinforcement, the damage morphology consisted of individual cracks extending through the sample in the longitudinal direction, which is typical of brittle failure. After reinforcement, the damage morphology of the sample transformed into unilateral or sparse conjugate cracks representative of semi-ductile failure and dense network-type conjugate cracks representative of ductile failure. Using the optimum fiber content and fiber length yielded the most conjugated cracks on the sample surface, lowest brittleness index, and highest degree of transition from brittle failure to ductile failure. These research results provide a scientific basis for enhancing cement soil with an environmentally benign approach and for analyzing the failure mode of fiber soil.
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表 3 试验变量和试样参数
试验
编号水泥
含量/%压实度
/%含水率
/%纤维含量
/%纤维尺寸
(L×W) /mm养护时间
/d未掺加 3.0 70 15.2 0.0 7 6～0.5 3.0 70 15.2 0.5 6×3 7 6～1.0 3.0 70 15.2 1.0 6×3 7 6～1.5 3.0 70 15.2 1.5 6×3 7 9～0.5 3.0 70 15.2 0.5 9×3 7 9～1.0 3.0 70 15.2 1.0 9×3 7 9～1.5 3.0 70 15.2 1.5 9×3 7 12～0.5 3.0 70 15.2 0.5 12×3 7 12～1.0 3.0 70 15.2 1.0 12×3 7 12～1.5 3.0 70 15.2 1.5 12×3 7 
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