To study the disintegration behavior and characterization indexes of Modified Graded Carbonaceous Mudstone (MGCM), soaking disintegration tests of MGCM under vertical loading and cyclic drying-wetting were carried out with a disintegration test instrument which self-designed by our team. The grain size distribution of MGCM during drying-wetting cycles was analysed. Standard basal entropy, as an important parameter of grading entropy that quantitatively characterizes distribution curves, was introduced to characterize the disintegration behavior of MGCM and correlated with the comprehensive evaluation index, namely, disintegration ratio. The results show that as the number of drying-wetting cycles increases, the Graded Carbonaceous Mudstone (GCM) blocks disintegrate rapidly and the fine-grain content increases. With an increase in vertical load, the particles disintegrate more completely. The contents of each particle group in the GCM test groups stabilize after 9, 7, and 4 drying-wetting cycles under vertical loads of 0, 100, and 200 kPa, respectively. Under the same vertical load of 200 kPa, the contents of each particle group in MGCM test groups with Polyurea (PU) content 0, 5, and 10 wt% stabilize after 4, 6, and 8 drying-wetting cycles, respectively. The inclusion of PU can effectively retard the disintegration of GCM, and the effect is more pronounced with 5 wt% PU content compared to 10 wt%. However, it is also susceptible to the deterioration of PU layer caused by mechanical screen. The grading entropy model of MGCM under loading and cyclic drying-wetting is established. There is a significant positive, linear correlation between the standard basal entropy and the disintegration ratio. A smaller standard basal entropy to a smaller disintegration ratio, indicating a greater degree of particle disintegration and fragmentation. The standard basal entropy can characterize the disintegrated particles of MGCM with different PU content under vertical loading and drying-wetting cycles. The standard basal entropy of GCM decreases rapidly initially and then stabilizes as the number of drying-wetting cycles increases. The standard basal entropy decreases exponentially as the vertical load increases. The results provide a new quantitative index for analyzing the grading characteristics of MGCM following disintegration, which are valuable for engineering construction and disaster prevention in carbonaceous mudstone areas.
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