Study of the strength properties and micromechanisms of nano-Al 2 O 3 -modified predisintegrated carbonaceous mudstone based on orthogonal design

This study aimed to improve the mechanical properties of predisintegrated carbonaceous mudstone (PCM) used as an embankment fill. The four factors used in the orthogonal design test were nano-Al 2 O 3 content, cement content, water content and compaction. After the tests were completed the strength characteristics and micromechanisms of PCM modified by nano-Al 2 O 3 and cement were studied using triaxial compression tests, X-ray diffraction analysis and SEM observations. The results show that the failure mode of PCM changes from bulging failure to shear failure when the nano-Al 2 O 3 and cement contents are increased. The order in which the factors affected the cohesion of PCM is cement content, nano-Al 2 O 3 content, water content and compaction. At a given cement content, the cohesion of PCM with an optimal compaction of 96% and a water content of 8% increases and then decreases with increasing nano-Al 2 O 3 content. The increase in the internal friction angle is proportional to the nano-Al 2 O 3 content when the cement content is between 0 and 4%. Controlling the nano-Al 2 O 3 and cement contents to 0.3 and 8%, respectively, results in a synergistic effect of both materials on the shear strength. Nano-Al 2 O 3 improves the cohesion and friction strength of PCM by accelerating the hydration of cement and optimizing the structure of the hydration products.