Microbially induced calcium carbonate (CaCO₃) precipitation (MICP) is an emerging soil-treatment method. To explore the effect of this technology on granite residual soil, this study investigated the effects of the mechanical properties and disintegration resistance of microbially cured granite residual soil under different moisture contents by conducting direct shear and disintegration tests. The curing mechanism was also discussed and analyzed. Results showed that MICP can be used as reinforcement for granite residual soil. Compared with those of untreated granite residual soil, the internal friction angle of MICP-treated granite residual soil increased by 10% under a moisture content of 30%, while its cohesion increased by 218%. The disintegration rate of the MICP-treated granite residual soil stabilized after a maintenance time of 5 days under different water contents. Therefore, we provide the explanation that the improvement of the shear strength and disintegration resistance of granite residual soil is due to CaCO₃ precipitation and the surface coating.

To study the influence of sand particles on the strength and dry–wet cycle characteristics of cement-solidified South China coastal soft clay, a series of cement-solidified South China coastal soft clay samples with different contents and sizes of sand particles were prepared, and unconfined compression strength (UCS) tests, dry–wet cycle tests under seawater and freshwater conditions, scanning electron microscopy tests, and X-ray diffraction tests were carried out. The test results show that the UCS of cement–sand-solidified soil (CS-SS) samples at 7, 14 and 28 d increase as sand particle content increases, and their 28 d strength increase as sand particle size decreases; the average mass loss rate of sand–cement samples ranges from 14% to 61%. The properties of strength and dry–wet cycle durability improve as the sand particle content increases and the sand particle size decreases. Moreover, the anti-dry–wet cycle ability of samples under freshwater conditions is better than those under seawater conditions. The scanning electron microscopy (SEM), X-ray diffraction (XRD), and ion chromatography test results show that the stiffness replacement effect (the high stiffness of sand particles replaces the low stiffness of soft clay), the interface cementation effect between the sand particles and cemented soil, and the microcrack expansion-obstructing effects of sand particles contribute to the improvement of the strength and dry–wet cycle durability of cement–sand solidified South China coastal soft clay.

Fiber-reinforced cemented soil (F-RCS) is an artificial multiscale geo-material, the strength of which is determined by the physical and mechanical properties of various substances of the F-RCS. To study the effect of fiber content and fiber length on the shear strength of the F-RCS, the substance phases of the F-RCS are divided into reinforcement fiber and cemented soil matrix to establish a meso cell structure of the F-RCS, which can reflect the internal substance properties of the F‑RCS. Moreover, according to microscopic kinetic characteristics of reinforcement fiber and cemented soil matrix and the mesoscopic strain gradient theory, a multiscale Mohr-Coulomb strength criterion (MCSC) of the F-RCS is deduced, and its yield locus is drawn on the π plane. Furthermore, consolidated and undrained triaxial compression tests are conducted on the F-RCS samples with various fibre content and fibre length to obtain the model parameters, and verify the proposed multiscale MCSC of the F-RCS. Results show that the multiscale MCSC the F-RCS is capabel of effectively predicting the shear strength of the F-RCS. The shape of the yield locus of the MCSC of the F-RCS is hexagonal and expands with increasing fiber content and fiber length. The shear stress of the F-RCS predicted by the multiscale MCSC of the F-RCS showcases good agreement with the test results.

Soil–rock mixture (S-RM) is a natural geomaterial characterized by multiple grain size grades and pronounced trans-scale hierarchical features. To investigate the multiscale coupling shear strength of S-RM, the material is decomposed into a soil matrix and rock blocks based on the deformation characteristics of mineral particles at different scales. A multiscale soil–rock cell element model is proposed. Moreover, three groups of in situ large-scale direct shear tests were conducted on S-RM samples with varying rock block contents to calibrate the microscale parameters of the model. The results show that rock blocks significantly affect the mechanical behavior of S-RM. The trans-scale, coordinated deformation between the soil matrix and rock blocks induces strain gradients at the mesoscale and microcrack coordination at the microscale, particularly at the matrix–block interfaces. This interaction leads to increased energy release at the macroscale compared with that of the pure soil matrix. This phenomenon constitutes the multiscale physical mechanism underlying the shear strength enhancement due to rock blocks. The proposed model accurately predicts the shear strength of S-RM, consistent with experimental observations.