基于核磁共振与无侧限抗压试验对纤维加固红黏土的宏微观特性研究

Study on macro-and micro-scale properties of fiber reinforced red clay based on NMR and unconfined compressive strength tests

红黏土因其具有孔隙比大、易压缩等不良工程特性,常在工程建设中引起一列工程问题。为此,采用聚丙烯纤维对红黏土进行加固,并采用核磁共振(NMR)技术和无侧限抗压强度试验对不同含量纤维加固后土体的宏微观特性进行测试,得到以下结论:1)不同含量纤维加固后红黏土的T2谱形态基本保持一致,均在弛豫时间为1 ms附近出现峰值,且纤维含量为0.2%时,试样内部信号最强;不同含量纤维加筋土内部的孔径主要分布在0.01μm到0.05μm之间,且0.02μm孔径所占比例最大;试样的孔隙度和T2谱峰值面积随纤维含量的增加表现出先增加后减小的趋势,且均在纤维含量为0.2%时到达最大值;2)纤维能够明显增加红黏土的抗压强度,加筋土的抗压强度与纤维含量保持良好的线性增加关系;且随着纤维含量的增加,试样由脆性破坏逐渐表现为韧性破坏特征。3)纤维在土体中起到加筋作用,显著增加了土体间的连接力,且纤维相互交叉连接形成了空间网状结构,限制了土体的变形,使得加筋土抗压强度增加并表现出韧性破坏特征。

Red clay often causes a series of engineering problems in engineering construction because of its large void ratio and high compressibility.Thus,this study used polypropylene fiber to reinforce red clay,and nuclear magnetic resonance(NMR)technology and unconfined compressive strength tests were used to investigate the macro-and micro-scale characteristics of red clay soil reinforced with different contents of fiber.The results are as followed:(1)the T2 spectrum of red clay soil reinforced with different contentsof fiber is basically consistent,and the peak relaxation time is 1 ms;when the fiber content is 0.2%,the internal signal of the specimen is the strongest;the pore size of different fiber reinforced soilsis mainly distributed between 0.01μm and 0.05μm,and the proportion of 0.02μm pore diameter is the largest;the porosity and peak area of T2 spectrum of the specimen increase first and then decrease with increasingfiber content,and reach the maximum value when the fiber content is 0.2%;(2)the results show that fiber can significantly increase the compressive strength of red clay,and the compressive strength of reinforced soil exhibits a good linear relationship with fiber content;and with fiber contentincreasing,the specimens gradually show the characteristics of ductile failure;(3)the fiber plays a reinforcing role in the soil,which significantly increases internal connection forcesof soil;the inter-connection of the fibersforms a spatial network structure,which limits the deformation of the soil and leads to increasing compressive strength of the reinforced soil that behaves with the characteristics of ductile failure.