To address the engineering problems of road subsidence and subgrade instability in aeolian soil under traffic loads, the aeolian soil was improved with rubber particles and cement. Uniaxial compression tests and Digital speckle correlation method (DSCM) were conducted on rubber particles-cement improved soil (RP-CIS) with different mixing ratios using the WDW-100 universal testing machine. The microcrack and force chain evolution in samples were analysed using PFC2D. The results showed that: (1) The incorporation of rubber particles and cement enhanced the strength of the samples. When the rubber particles content was 1% and the cement content was 5%, the uniaxial compressive strength of the RP-CIS reached its maximum. Based on the experimental results, a power function model was established to predict the uniaxial compressive strength of RP-CIS; (2) The deformation of the samples remains stable during the compaction stage, with cracks gradually developing and penetrating, eventually entering the shear failure stage; (3) The crack and failure modes simulated by PFC2D are consistent with the DSCM test. The development of microcracks and the contact force between particles during the loading are described from a microscopic perspective. The research findings provide scientific support for subgrade soil improvement and disaster prevention in subgrade engineering.

In the construction of cold region engineering and artificial freezing engineering, soil-rock mixture (SRM) is a frequently encountered geomaterial. Understanding the mechanical properties of frozen SRM is crucial for ensuring construction safety. In this paper, frozen SRM is considered as a multiphase material consisting of a soil matrix and rock. By employing a single-variable approach, the relationship between UCS and rock content was revealed, and the effects of rock content on the stress-strain curve shape and failure mode were analyzed. The test results indicate that rock content significantly influences the stress-strain curve and failure mode of SRM. The specimen preparation with different rock content is unified using a given relative compactness. The uniaxial compressive strength (UCS) of the frozen specimens increases firstly and then decreases as rock content increases, which is unaffected by temperature or rock size. The classic quadratic polynomial is suggested to describe the variation rule. The failure modes of specimens with low, medium and high rock content correspond to shear failure, bulge failure and splitting failures, respectively, which transmits from shear failure to splitting failure as the rock content increases.

The mechanical properties and failure characteristics of soil-rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite-discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil-rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young's modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil-rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper.

Fiber-reinforced polymer (FRP) wrapping is a potential technique for coal pillar reinforcement. In this study, an acoustic emission (AE) technique was employed to monitor coal specimens with carbon FRP (CFRP) jackets during uniaxial compression, which addressed the inability to observe the cracks inside the FRP-reinforced coal pillars by conventional field inspection techniques. The spatiotemporal fractal evolution of the cumulated AE events during loading was investigated based on fractal theory. The results indicated that the AE response and fractal features of the coal specimens were closely related to their damage evolution, with CFRP exerting a significant influence. In particular, during the unstable crack development stage, the evolutionary patterns of the AE count and energy curves of the CFRPconfined specimens underwent a transformation from the slight shock-major shock type to the slight shock-sub-major shock-slight shock-major shock type, in contrast to the unconfined coal specimens. The AE b-values decreased to a minimum and then increased marginally. The AE spatial fractal dimension increased rapidly, whereas the AE temporal fractal dimension fluctuated significantly during the accumulation and release of strain energy. Ultimately, based on the AE count and AE energy evolution, a damage factor was proposed for the coal samples with CFRP jackets. Furthermore, a damage constitutive model was established, considering the CFRP jacket and the compaction characteristics of the coal. This model provides an effective description of the stress-strain relationship of coal specimens with CFRP jackets. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The formation of multi-layer horizontal ice lenses in frozen soil significantly alters its internal structure, leading to changes in its mechanical properties. To quantitatively analyze the effects of multi-layer ice lenses on mechanical properties, a series of freezing tests were conducted with frost-susceptible clay materials at varied freezing ratios. Then, the uniaxial compression tests were conducted to investigate the deformation and strength properties of frozen soil at different freezing ratios and temperatures. The experimental results indicate that the unique ice skeleton structure formed by horizontal ice lenses and inclined ice wedges can significantly improve the strength of the samples, leading to the peak stress and secant modulus E-50 increase with the freezing ratio, and the presence of an ice skeleton makes the strength more sensitive to temperature changes. The frozen soil samples exhibit two failure modes (bulging failure and shearing failure), which significantly affect the mechanical parameters of the soil. Based on the test results, a frost heave-induced damage coefficient is introduced into the strain softening model to account for the initial stiffness reduction caused by microcracks generated during the ice skeleton growth. This modified model effectively predicts the stress-strain relationship of soils with varying ice skeleton structures. These findings have practical implications for predicting the properties of frozen soil constructed using artificial freezing methods.

Soil-rock mixture is a common geo-material found in natural deposit slopes and various constructions, such as tunnels, hydropower stations, and subgrades. The complex mechanical characteristics of soil-rock mixture arise from its multi-phase compositions and cooperative interactions. This paper investigated the mechanical properties of soil-rock mixture, focusing on the influence of rock content, and soil-rock interface strength was discussed. Specimens with varying rock contents were subjected to uniaxial compression tests. The results indicated that rock content, as a key structural parameter, significantly controls the crack propagation trends. As rock content increases, the initial structure of the soil matrix is damaged, leading to the formation of a weak-strength soil-rock interface. The failure mode transitions from longitudinal cracking to multiple shear fractures. To analyze the strength of the soil-rock interface from a mesoscopic perspective, simulations of soil-rock mixture specimens with irregular rock blocks were conducted using the particle discrete element method (PDEM). At the meso-scale, the specimen with 30% rock content exhibited a complex particle displacement distribution, with differences in the direction and magnitude of displacement between soil and rock particles being critical to the failure modes of the specimen. As the soil-rock interface strength increased from 0.1 to 0.9, the distribution of force chains within the specimen shifted from a centralized to a more uniform distribution, and the thickness of force chains became increasingly uniform. The strength responses of the soil-rock mixture under uniaxial compression condition were discussed, revealing that the uniaxial compression strength (UCS) of soil-rock mixture decreases exponentially with increasing rock content. An estimation formula was developed to characterize the UCS of soil-rock mixture in relation to rock content and interface strength. The findings from both the experiments and simulations can provide valuable insights for evaluating the stability of deposit slopes and other constructions involving soil-rock mixture.

Loose and uncemented calcareous sand slopes are prone to collapse under rainstorm erosion. In order to improve the erosion resistance stability of slopes, it is crucial to enhance the erosion resistance of calcareous sand. In this study, a new method of cementing calcareous sand with zinc sulfate solution (ZSS) is proposed. The ZSS reinforcement technique can effectively cement calcareous sand, enhance the mechanical properties and help reduce erosion on calcareous sand slopes. A series of laboratory experiments were conducted, including uniaxial compression tests, Brazilian splitting tests, surface penetration tests, microscopic tests, and rainfall scouring tests. The test results show that the uniaxial compressive strength of calcareous sand achieved 8.3 MPa reinforced with ZSS. Microscopic analyses revealed the mechanism of reinforcement, discovering the formation of environmentally friendly compounds such as ZnCO3 and CaSO4 & sdot;2 H2O between calcareous sand particles, which enhanced the soil mechanical properties. The calcareous sand slope reinforced with ZSS forms a hard shell on the slope surface, which effectively improves the erosion resistance of the slope. After being reinforced with a ZSS concentration of 1.0 mol/L, the slope remained stable after 20 min of scouring at a rainfall intensity of 80 mm/h. This method provides a quick solution for reinforcing calcareous sand slopes and holds promising potential for practical engineering applications.

Granitic veins (GVs) have a significant influence on the mechanical responses of tunnels excavated in granitic strata. Distinguishing the mechanical properties of host granites (HGs), GVs and vein-granite interfaces (VGIs) is critical. For this, this paper analyzed the mechanical behaviors and rupture processes of typical HG, GV, and VGI samples under uniaxial compression condition. For the rocks studied, although the linear axial stress-strain relation can be identified and the deformation modulus can be determined, the transverse deformation developed nonlinearly with axial stress. As a result, the instantaneous Poisson's ratio increases continuously and may even exceed 0.5, making it extremely difficult to accurately determine the Poisson's ratio. In addition, the studied GV samples were found to be significantly brittle, indicating that large-scale GVs cannot be ignored when assessing rockburst hazards in granitic strata with brittle GVs. In terms of the rupture process, the HG and GV samples were gradually damaged by the formation of small-scale cracks and then ruptured by large cracks formed from smallscale cracks, whereas the VGI samples ruptured along large cracks with significant energy release. By examining the characteristic stress thresholds of these three granites, it is noted that the crack closure stress scc exceeds both the crack initiation stress sci and the crack damage stress scd for the HG and VGI samples. The transverse damage to a tested sample appears to be significantly greater than the axial damage, which is essentially related to the rock grain size and grain size distribution. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.

To investigate the macroscopic mechanical properties and failure evolution mechanism of desulfurization gypsum-fly ash fluid lightweight soil, a microscale numerical model using PFC2D (Particle Flow Code) was constructed. Uniaxial compression tests were conducted to determine the microscopic parameters of the model, extracting information on the discrete fracture network type, quantity, age, and particle displacement trend. The crack morphology and propagation evolution of desulfurization gypsum-fly ash fluid lightweight soil were explored, and the destructive properties of desulfurization gypsum-fly ash fluid lightweight soil material were evaluated through energy indicators. The research findings suggest that the discrete element numerical model effectively simulates the stress-strain curve and failure characteristics of materials. Under uniaxial compression conditions, microcracks dominated by shear failure occur in the initial loading stage of desulfurization gypsum-fly ash fluid lightweight soil, with a through crack dominated by tensile failure appearing once the load exceeds the peak stress. The dissipated energy evolution in the flow state of desulfurization gypsum-fly ash fluid lightweight soil is relatively gentle, leading to delayed cracking after surpassing the peak stress point.

Geological exploration cores obtained from shale gas wells several kilometers deep often show different height-diameter ratios (H/D) because of complex geological conditions (core disking or developed fractures), which makes further standard specimen preparation for mechanical evaluation of reservoirs difficult. In multi-cluster hydraulic fracturing, shale reservoirs between planes of hydraulic fractures with different lengths could be simplified to have different H/D ratios. Discovering the effect of H/D on the mechanical characteristics of shale specimens with different bedding orientations will support mechanical evaluation tests of reservoirs based on disked geological cores and help to optimize multicluster fracturing programs. In this study, we performed uniaxial compression tests and acoustic emission (AE) monitoring on cylindrical Longmaxi shale specimens under five bedding orientations and four H/D ratios. The experimental results showed that both the H/D-dependent mechanical properties and AE parameters demonstrated significant anisotropy. Increasing H/D did not change the uniaxial compressive strength (UCS) evolution versus bedding orientation, demonstrating a V-shaped relationship, but enhanced the curve shape. The stress level of crack damage for the specimens significantly increased with increasing H/D, excluding the specimens with a bedding orientation of 0 degrees. With increasing H/D, the cumulative AE counts of the specimens with each bedding orientation tended to exhibit a stepped jump against the loading time. The proportion of low-average-frequency AE signals (below 100 kHz) in specimens with bedding orientations of 45 degrees and 60 degrees increased to over 70% by increasing H/D, but it only increased to 40% in specimens with bedding orientations of 0 degrees, 30 degrees, and 90 degrees. Finally, an empirical model that can reveal the effect of H/D on anisotropic UCS of shale reservoir was proposed, the anisotropic proportion of tensile and shear failure cracks in specimens under four H/D ratios was classified based on the AE data, and the effect of H/D on the anisotropic crack growth of specimens was discussed. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).