Mechanical behavior and microstructural mechanism of improved disintegrated carbonaceous mudstone

Abstract

This study aims to improve the mechanical behavior of disintegrated carbonaceous mudstone, which is used as road embankment filler in southwestern China. Triaxial tests were performed on disintegrated carbonaceous mudstone modified by fly ash, cement, and red clay. Then the stress-strain relationships and shear strength parameters were analyzed. The microstructure and mineral composition of the materials were identified via scanning electron microscopy and X-ray diffraction. The results show that the stress-strain relationships changed from strain-hardening to strain-softening when disintegrated carbonaceous mudstone was modified with cement. By contrast, the addition of fly ash and red clay did not change the type of stress-strain relationships. The order of these three additives is cement, red clay and fly ash according to their influences on the cohesion. Disintegrated carbonaceous mudstone without cement all showed bulging failures, and that modified with cement exhibited shear failures or bulging-shear failures. The soil particles of the improved soil were well bonded by cementitious substances, so the microstructure was denser and more stable, which highly enhanced the mechanical behavior of disintegrated carbonaceous mudstone. The findings could offer references for the use of carbonaceous mudstone in embankment engineering.

摘要

预崩解炭质泥岩在中国西南地区常用作路堤填料。为改善预崩解炭质泥岩力学特性,采用粉煤 灰、水泥和红黏土对预崩解炭质泥岩进行处理,通过三轴试验分析改良土的应力−应变关系和抗剪强 度指标,并利用扫描电镜和X 射线衍射表征其微观结构和矿物成分。结果表明,经水泥改良后预崩解 炭质泥岩的应力−应变关系曲线由应变硬化型转变为应变软化型,但粉煤灰和红黏土不改变其应力− 应变关系类型。三种添加剂对预崩解炭质泥岩黏聚力影响的大小顺序为:水泥>红黏土>粉煤灰。未加 水泥的预崩解炭质泥岩均表现为鼓胀破坏,而经水泥改良的预崩解炭质泥岩均表现为剪切破坏或鼓 胀−剪切破坏。由于胶结物能将土颗粒紧密胶结成团,使微观结构更加致密、稳定,因此,改良后预 崩解炭质泥岩的力学特性得到显著增强。研究结果可为炭质泥岩在路基工程中的应用提供参考。