J. Cent. South Univ. (2020) 27: 1992−2002 DOI: https://doi.org/10.1007/s11771-020-4425-8 Mechanical behavior and microstructural mechanism of improved disintegrated carbonaceous mudstone ZENG Ling(曾铃) 1 , YU Hui-cong(余慧聪) 1 , GAO Qian-feng(高乾丰) 2 , BIAN Han-bing(卞汉兵) 3 1. School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, China; 2. Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province, Changsha University of Science & Technology, Changsha 410114, China; 3. Laboratoire de Génie Civil et Géo-environnement, Université de Lille, Lille 5900, France © Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 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. Key words: embankment engineering; carbonaceous mudstone; additive; mechanical properties; microstructure Cite this article as: ZENG Ling, YU Hui-cong, GAO Qian-feng, BIAN Han-bing. Mechanical behavior and microstructural mechanism of improved disintegrated carbonaceous mudstone [J]. Journal of Central South University, 2020, 27(7): 1992−2002. DOI: https://doi.org/10.1007/s11771-020-4425-8. 1 Introduction Carbonaceous mudstone is a typical soft rock that is extensively distributed in the southwest of China [1, 2]. In this region, carbonaceous mudstone sometimes has to be used to fill road embankment to reduce construction costs. However, this material rapidly softens and disintegrates when meeting water, showing low strength and large deformability [3]. As a result, the road embankment filled with carbonaceous mudstone may show insufficient bearing capacity and resilient modulus [4]. Therefore, the mechanical behavior of Foundation item: Projects(51908069, 51908073, 51838001, 51878070) supported by the National Natural Science Foundation of China; Project(2019SK2171) supported by the Key Research and Development Program of Hunan Province, China; Project(2019IC04) supported by the Double First-Class Scientific Research International Cooperation Expansion Project of Changsha University of Science & Technology, China; Project(kfj190605) supported by the Open Fund of Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province (Changsha University of Science & Technology), China; Project(kq1905043) supported by the Training Program for Excellent Young Innovators of Changsha, China; Project(SJCX202017) supported by the Practical Innovation Program for Graduates of Changsha University of Science & Technology, China Received date: 2020-03-30; Accepted date: 2020-04-26 Corresponding author: GAO Qian-feng, PhD, Lecturer; Tel: +86-15173240865; E-mail: qianfeng.gao@csust.edu.cn; ORCID: 0000- 0003-4844-2345