The bearing stratum of high-rise and ultra-high-rise buildings in southwest China has inevitably faced moderately weathered red mudstone. It was a waste of the potential bearing stratum calculated according to the specification, as the bearing stratum obtained from laboratory and in situ tests was much higher than the values suggested by the specification. Rock mass surface deformation detection is of great significance in the safety management of a foundation project. Some correlation between surface deformation and failure characteristics may exist that could help to understand the bearing stratum of the moderately weathered red mudstone. This research was conducted to study the progressive failure characteristics of the moderately weathered red mudstone through surface deformation. In situ load, triaxial, and binocular visual technology were employed for data acquisition. The proposed conjecture was illustrated and verified by a group of experiments from three construction sites. Five stages could be described as the progressive failure of the moderately weathered red mudstone: compaction, elasticity, elastoplasticity, plasticity, and failure. Furthermore, the surface displacement increment fluctuates with the loading time and fades into the distance. Therefore, this research could provide a robust, practical application for analyzing the progressive failure of moderately weathered red mudstone.

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Microwave heating potentially reinforces the muddy intercalation to eliminate slope failure. Montmorillonite has the worst water resistance among the muddy intercalation components, which is a primary facet of inducing muddy intercalation failure. This study investigates the mechanism of shear strength and water stability enhancement of montmorillonite heated by the microwave oven and muffle furnace from room temperature to 800 °C. Results show that montmorillonite mineralogical evolution can be divided into three stages: room temperature-300 °C, 300-600 °C, and 600-800 °C. Microwave heating is more efficient in montmorillonite heat treatment than muffle furnace heating and makes the montmorillonite dehydroxylated earlier. It is worth noting that hot spots formed inside the montmorillonite specimens during the microwave heat treatment. Microwave significantly promotes the shear resistance of montmorillonite, where the maximum increases are 39.94% of cohesion at 600 °C and 20.54% of internal friction angle at 700 °C. This enhancement is due to the rough surfaces and large particles produced by dehydroxylation and Mg-Al spinel synthesis, and the significant degree of disorder state of MMT after dehydroxylation also plays a vital role. The microwave-heated montmorillonite over 500 °C presents good integrity in the water immersion test over 24 h. Considering the shear behavior and water stability, we believe the most reasonable heating interval for microwaves is 500-600°C.

The mechanical behavior of mudstones is significantly affected by their mesostructure. This study investigates the damage evolution of red mudstone mesostructures under uniaxial compression through U-Net image segmentation, mesoscopic representative elementary area (mREA), meso-element equivalent method, and linearly superimposed model. Results show that the mREAs can be simplified as a binary structure comprising nonclayey minerals and a porous matrix. The inclusion-matrix interfaces constituted by the dominant inclusions, such as large inclusions and a series of inclusions with specific arrangements, are the weakest regions at the postpeak stage. The shear failure of these interfaces leads to general shear failure with a penetrating principal fracture or local shear with several nonpenetrating local fractures in the mREAs. The damage evolution and failure mode are sensitive to the inclusion geometric features, e.g., inclination, grain size, and spacing. However, the uniaxial compressive strength (UCS) is mainly determined by the included angle between the dominant inclusion inclination and the loading direction. With consistent composition, an increase in the included angle from 0 to 90° results in an increase in the UCS of the muddy facies and a decrease in the sandy facies, with the UCS of the sandy facies being more sensitive to changes in the included angle. Our findings indicate that the structural failure of red mudstones from mesoscopic to macroscopic is driven by the accumulation and expansion of shear failure at multiple scales due to the presence of hard–soft interfaces. This study enhances our understanding of the structural failure mechanism of mudstones and serves as a practical reference for the mesomechanical testing of clay rocks.