Foamed lightweight soil is widely used in subgrade engineering as a lightweight, high fluidity material. However, due to the use of cement as the main raw material, its cost is relatively high. Therefore, the preparation of foamed lightweight soil by mixing muck excavated at the project site with iron ore tailings (IOT) is not only helpful to reduce costs, but also can promote the efficient and comprehensive utilization of inactive solid waste. In this paper, the fluidity, wet density, compressive strength and specific strength of muck-IOT foamed lightweight soil with different content were tested, and the optimal mixing ratio was selected according to the engineering specifications. Then, through uniaxial and triaxial compression tests, the strength and deformation characteristics of muck-IOT foamed lightweight soil under different dosage, wet density and confining pressure conditions were studied. Finally, the influence mechanism of muck and IOT on the strength and structure of foamed lightweight soil was revealed through Scanning Electron Microscope (SEM) analysis. The research results show that the wet density of foamed lightweight soil prepared by the optimal mixing amount (20% muck and 10% IOT) is 894 kg/m3, and the uniaxial compressive strength is 4.6 MPa. While meeting the requirements of fluidity, the mixing amount of solid waste is higher, with the specific strength increased by 28.12%. In the triaxial compression test, for every 100 kg/m3 increase in wet density, the peak strength and residual strength increase by 1.30 MPa and 1.00 MPa, respectively; For every 200 kPa increase in confining pressure, the peak strength and residual strength increase by 0.27 MPa and 0.32 MPa, respectively. In addition, the shear strength levels of muck-IOT foamed lightweight soil under different normal stress conditions under different wet densities were determined by establishing the linear equations of c and phi related to the wet density. From the microstructure, it can be seen that the pores in the muck-IOT foamed lightweight soil are evenly distributed, resulting in a denser structure and reduced stress concentration, which significantly enhances the material's compressive strength.

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.