Predisintegrated carbonaceous mudstone (PCM) that exhibits low strength and continuous disintegration is prone to wetting deformation after repeated seasonal rainfall. A reasonable assessment of wetting deformation is required to facilitate the settlement control of the PCM embankment when exposed to repeated rainfall. Herein, to reveal the wetting deformation mechanism of the PCM subjected to drying-wetting cycles, the effects of drying-wetting cycles on the wetting deformation characteristics of the PCM are investigated using the double-line method. Microscopic pore characteristics of the PCM under different drying-wetting cycles were analyzed through scanning electron microscope (SEM) micrographs. Comparative analysis of the wetting deformation data between the tests and the constitutive model considering the damage of drying-wetting cycles was carried out. The results showed that the deviator stress-strain relationship curves of the PCM exhibit the strain hardening without obvious peak and no strain softening phenomena. The critical wetting strain of the PCM was positively correlated with the number of drying-wetting cycles, while the critical deviator stress decreased with an increase in the number of drying-wetting cycles. As the number of cycles increased, the gelling material between the particles dissolved, the volume of pores inside the PCM increased, and the number of pores inside the PCM decreased. The porosity of PCM had a significant quadratic function with the number of drying-wetting cycles. A wetting deformation damage model was developed to calculate the wetting deformation of the PCM by considering the effects of drying-wetting cycles, which can be useful for evaluating rainfall-induced settlements of relevant engineering structures made from PCM.

Traditional slope protection methods face many challenges when applied to carbonaceous mudstone slopes. The objective of this study was to develop a novel protection method based on vegetation concrete with carbonaceous mudstone aggregates (VCCMA) and then examine its performance and underlying protective mechanism. Hence, physical model tests were performed on highly-weathered carbonaceous mudstone slopes under wet-dry cycles considering three different protection cases, i.e., no protection, protection using porous concrete with carbonaceous mudstone aggregates (PCCMA) and protection using VCCMA. The erosion characteristics, volumetric moisture contents, and slope deformations of the slopes were measured. Finally, the performances and underlying mechanisms of the protection methods for slopes were compared. The results demonstrate that the unprotected slope, the PCCMA-protected slope, and the VCCMA-protected slope were descending according to the erosion damage, the particle loss amount, and the deformation during five wet-dry cycles. Among the two protected cases, the VCCMA exhibits better erosion coefficient, water retention capacity and disintegration resistance of the slope. The runoff volume depends on the protection method and shows a weaker correlation with wet-dry cycles. In the case of PCCMA protection, the protection effects come from self-weight consolidation, water interception, and integral protection structure. The VCCMA protection case incorporates additional protective mechanisms, including soil moisture regulation by leaf transpiration, resistance to rainfall splashing and scouring by stems and leaves, and soil reinforcement and anchoring by roots. Therefore, the VCCMA holds significant potential for effectively protecting problematic slopes. These findings provide valuable guidance for the protection of highly-weathered carbonaceous mudstone slopes.

The abandoned carbonaceous mudstone has caused severe environmental problems such as land occupation and landslides. For the consideration of economic and ecological factors, carbonaceous mudstone soil-rock mixture (CMSRM) is used as an embankment material assessed by California bearing ratio (CBR) and unconfined compression strength (UCS). A series of experiments were conducted to measure the CBR and UCS of the CMSRM with different wet-dry cycles (0, 2, 4, 6 and 8) and different rock contents (0, 20, 40, 60 and 80%). The experimental results were predicted and analysed by a convolutional neural network (CNN). The experiment results show that the CBR and UCS of CMSRM increased at first and then decreased with the increase of rock content and were negatively correlated with wet-dry cycles. The CNN predicted values were highly correlated with the measured values. The CNN model enables variable parameter analysis of the experiment results via deep learning, which provides a new method to the CMSRM embankment road performance prediction.

Understanding the dynamic resilient modulus (MR) of a recycled carbonaceous mudstone soil-rock mixture (CMSRM) embankment under wet-dry cycles can provide a basis for CMSRM embankment design and evaluation. The effects of the stress states, rock contents, and wet-dry cycles on MR were analyzed by dynamic triaxial tests, and the prediction model for MR of CMSRM was studied also. The results show that the MR of CMSRM is negatively correlated with the deviation stress and positively correlated with the minimum bulk stress, with significant stress-dependent characteristics. With the increase in rock content, the MR of CMSRM increases at first and decreases later. Grey correlation analysis showed that the MR of the CMSRM is affected by the rock content, minimum bulk stress, wet-dry cycles, and deviator stress in order of priority. Considering the comprehensive effects of stress states, wet-dry cycles and particle gradation, a model predicting the MR was proposed. The research can provide useful information for the application of carbonaceous mudstone embankment in humid-heat regions.

In order to eliminate the undesirable characteristics of carbonaceous mudstone roadbed fillers, cement and fly ash are used to modify the pre-disintegrated carbonaceous mudstone, and the stress-strain relationship of pre-disintegrated carbonaceous mudstone before and after modification are analyzed by a series of conventional unconsolidated undrained triaxial compression tests at different confining pressures and different ages. Based on the microscopic modification mechanism of carbonaceous mudstone and the concept of binary medium model, the products from hydration reaction of pre-disintegrated carbonaceous mudstone, cement, and fly ash are regarded as bonded elements, and the pre-disintegrated carbonaceous mudstones without hydration reaction are regarded as frictional elements, and the binary medium model of modified pre-disintegrated carbonaceous mudstone is established. The results show that the stress-strain curve of pre-disintegrated carbonaceous mudstone is strain-hardening type, and the stress-strain of pre-disintegrated carbonaceous mudstone modified by fly ash and cement is strain-softening type, and the mechanical properties of modified pre-disintegrated carbonaceous mudstone are significantly improved. The deformation and damage mechanism of modified carbonaceous mudstone is investigated by applying the concept of binary medium model from a mesoscopic perspective, and the stress-bearing mechanism of bonded elements and frictional elements in external loading and stressing processes are analyzed. Finally, the measured data reveals that the binary medium model can simulate both the stress-strain softening characteristics of modified pre-disintegrated carbonaceous mudstone and the stress-strain hardening characteristics of organic material-modified expansive soils reasonably well.

To investigate the effects of compaction (K), rock content (RC), and wet-dry cycle (WD) on the road performance of carbonaceous mudstone soil-rock mixtures (CMSRM), orthogonal tests were designed to measure the unconfined compressive strength (UCS) and California bearing ratio (CBR). The correlation degree of K, RC, and WD with the UCS and CBR of CMSRM was investigated using orthogonal theory and grey correlation theory. Based on multivariate nonlinear regression analysis, mathematical models of the road performance of CMSRM were built. The results show that the UCS and CBR of CMSRM were positively correlated with K and negatively correlated with the WD. With increasing RC, UCS increased at first and then decreased, while CBR increased continuously. The failure modes of CMSRM change from tensile failure to shear failure as the K increases under uniaxial compression. The RC and WD affect the structural integrity of the failed samples. Combining the results of range analysis, variance analysis, and grey relational analysis, the most significant influence on the UCS is K, and the most significant influence on the CBR is RC. It is recommended to select 94%-96% for K and 40%-60% for RC in engineering.

Fundamental research on single-particle breaking and the uniaxial compressive strength (UCS) of carbonaceous mudstone aggregates at different water contents was carried out to investigate the relationship between the single-particle crushing strength and UCS. Based on elasticity theory and the superposition principle, a shape factor alpha was introduced to propose a mechanical model of crushing strength that considers the effect of particle shape, and a model was developed to predict the UCS of soil-rock aggregates (SRAs) from the single-particle crushing strength. The test conditions were set to a dry state and a water content of 6-10% according to the water content test results for carbonaceous mudstones with different dimensions. The experimental results reveal that the shape factor alpha of particles ranges from 0.44 to 1.0 when the crushing strength model is applied considering shape effects. As the water content increases, the crushing strength of the carbonaceous mudstone decreases linearly, the effect of the dimension is significant, and the crushing strength decreases by 7.4% in the dry state and by 41.02% at a water content of 10%. The UCS model considering the single-particle crushing strength accurately reflects the variation of the UCS with the volume block proportion (VBP) and provides a new approach for predicting the UCS.