Cemented granular materials play an important role in both natural and engineered structures, as they are able to resist traction forces. However, modeling the mechanical behavior of such materials is still challenging, and most of existing constitutive models follow phenomenological approaches that unavoidably disregard the microstructural mechanisms taking place on the bonded grains scale. This paper presents a multiscale approach applicable to any kind of granular materials with solid bonds between particles. Inspired from the H-model, this approach allows simulating the behavior of cemented materials along various loading paths, by describing the elementary mechanisms taking place between bonded grains. In particular, the effect of local bond failure process on the macroscopic response of the whole specimen is investigated according to the bond strength characteristics.

To essentially explore and quantitatively clarify the mesoscopic failure mechanism of deep weak interlayer zone (WIZ) induced by complex stress levels and stress paths (i.e., particle breakage and orientation, pore morphology, etc.), a semi-quantitative mesoscopic structural damage analysis methodology has been proposed, by involving SEM-MATLAB image processing technique with representative meso-structural parameters after sufficient analysis of basic geotechnical properties of WIZ. Results show that the natural WIZ exhibiting a flocculated structure could be characterized as a well-graded geotechnical material forming main clay minerals, in which most pores are intergranular, with the pore size distribution concentrated in 0.007-200 mu m. Higher initial confining pressure and axial loading tend to intensify the particle breakage degree and particle size distribution characteristics of WIZ more than that of axial and circumferential unloading, in which the stress path II of axial pressure loading and confining pressure unloading under the initial confining pressure of 25 MPa is the most severe with average particle area reduced by 56% and particle Korcak fractal dimension increased by 36%. The broken particles undergoing a series of irreversible dislocation, tumbling and rotation under the action of shear and tensile stress, tend to orient in the direction of 0 degrees-15 degrees, in which particles in stress path IV aggregate in two directions of 0-15 degrees and 60-90 degrees due to the bidirectional unloading. The unloading stress path IV shows the most distinct directional orientation and orderliness, with particle anisotropy increased by 267% and directional probability entropy reduced by 13%. Particle breakage and orientation in WIZ are accompanied by obvious filling, expansion and propagation of the meso-pores and meso-cracks, in which stress path IV under lower confining pressure most affects the morphological complexity of pore and crack boundaries with the pore morphology fraction dimension increased by 13.5%. The quantitative theoretical correlation of macro-meso parameters has been established by the stepwise regression analysis of two most relevant and representative correlation indexes (i.e., Korcak fractal dimension and pore morphology fractal dimension) with the ultimate bearing strength of WIZ, which has been proved to have high fitting accuracy by comparing the regression results with the test measured values. The meso-structural damage mechanism of WIZ under stress paths II and IV could, respectively, match the failure law of structural stress-induced collapse in the spandrel and the plastic squeezing-out failure of WIZ on the high sidewall of underground excavations. Research could provide feasible ideas for the relationship between macroscopic failure and mesoscopic damage of WIZ, as well as the effective basis for the further discussion of macro-meso constitutive model establishment. A semi-quantitative method by SEM-MATLAB image processing technique was proposed to explore the mesoscopic failure mechanism of weak interlayer zone.The particle breakage, particle orientation, pore morphology and crack evolution induced by complex stress paths were quantitatively explored.The quantitative theoretical correlation of macro-meso parameters was established by stepwise regression analysis.The correlation between meso-structural variation and engineering failure mechanism of weak interlayer zone was discussed.

The cumulative deformation properties of subgrade soil under cyclic traffic loads are critical for optimizing pavement structure design and ensuring long-term highway structural performance. This study aims to investigate the coupling effect of freeze-thaw cycles and cyclic loads on the cumulative deformation behaviors and meso-structure of coarse-grained saline soil (CGSS) subgrade filling in high-cold areas. Dynamic triaxial tests and computed tomography (CT) scanning were conducted to analyze the CGSS under different working conditions. The research focused on the dynamic deformation development and damage evolution under varying freeze-thaw cycles and load amplitudes. The research results show that the cumulative deformation behavior of CGSS under cyclic loading is relatively sensitive to the freeze-thaw process. The cumulative dynamic strain increases as the freeze-thaw cycles, with a critical freeze-thaw cycle number of five. The stable cumulative dynamic strain curve exhibits clear three-stage characteristics when plotted in semi-log coordination, with critical loading cycles at 20 and 1,000. After 10-100 loading cycles, the cumulative strain curve quickly shows failure. The CGSS's low density and pore regions greatly increase after a freeze-thaw cycle. The rise in dynamic stress amplitude notably affects the bonding between soil particles and crystalline salts. The coupling effect of the freeze-thaw cycle and dynamic activity exacerbates the deterioration of soil structure, resulting in variations in CT values within the scanning layer in the final state.