Correlations between the mechanical properties and surface scratch resistance of polylactic acid (PLA) are investigated via tensile and scratch tests on samples after degradation in soil for various times. The results show that the tensile yield strength of PLA is inversely proportional to the natural logarithm of the degradation time, and the scratch resistance and fracture toughness of PLA and the temperature rise near the indenter all increase and then decrease. The surface crystallinity of PLA also increases and then decreases, indicating that it and the scratch resistance are closely related. These findings provide useful information about how PLA behaves under degradation conditions. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).

The service performance of frozen soil is one of the important factors that needs to be considered in designing and assessing the safety of artificial ground freezing projects. We conducted shear tests on ice-containing frozen soil and assessed soil performance and damage characteristics of the ice-frozen soil interface. On the basis of experimental results, we further investigated the damage of ice-containing frozen soil numerically using the finite-discrete element method. Experimental and numerical results show that temperature, the normal load, and moisture content are the primary factors influencing the mechanical properties of the ice-frozen soil interface. The effects of these parameters on shear strength, shear modulus, cohesion, and angle of internal friction were analyzed and discussed. There was a transition from ductile to brittle behavior at the ice-frozen soil interface with decreasing temperature. Transition occurred at higher temperatures in soils with higher moisture content. Because ice and sand differ in terms of stiffness, fractures appeared first at the ice-frozen sand interface. Under continued loading, the specific form of damage and maximum load-bearing capacity varied as a function of the location of the maximum shear stress zone and the ice in the soil. Our research findings provide valuable theoretical insights for the design and evaluation of the safety of artificial ground freezing engineering projects.

In cold regions' engineering applications, cement stabilized soils are susceptible to strength degradation under freeze-thaw (F-T) cycles, posing significant challenges to infrastructure durability. While metakaolin (MK) modification has shown potential in enhancing static mechanical properties, its dynamic response under simultaneous F-T cycling and impact loading remains poorly understood. This study investigates the dynamic mechanical behavior of cement-MK stabilized soil through split Hopkinson pressure bar (SHPB) tests under varying F-T cycles. The effects of strain rate and F-T cycles on the dynamic failure process and mechanical properties of cement-MK stabilized soil were investigated. Pore characteristics were analyzed using a nuclear magnetic resonance (NMR) system, providing an experimental basis for revealing the degradation mechanism of F-T cycles on the strength of cement-MK stabilized soil. Based on the Lemaitre's strain equivalence principle, a composite damage variable was derived to comprehensively characterize the coupled effects of F-T cycles and strain rate. A dynamic constitutive model is established based on damage mechanics theory and the Z-W-T model. The results indicate that under the effect of F-T cycles induce progressive porosity increase and aggravated specimen damage. At varying strain rates, the strength of cement-MK stabilized soil decreases with increasing F-T cycles, while the rate of strength reduction gradually diminishes. Under impact loading, both strain rate and the number of F-T cycles significantly reduce the average fragment size of fractured specimens. The modified Z-W-T model effectively predicts the stress-strain relationship of the cement-MK stabilized soil under impact loading.

PurposeShield tunnel is usually used as permanent underground facilities with a design service life of 100 years, and operational safety is very important. The objective of this paper is to investigate the failure mechanism and resilience evolution of double-layer lining structures of shield tunnels and to maintain the safety of structural operation.Design/methodology/approachA macro-micro model is established based on the refinement concept, considering the influences of hand-hole weakening, multi-contact interactions and reinforcement bars. The macro model describes the stress and deformation of the soil-reinforced structure using the stratum-structure method. The micro model introduces the total strain crack model, which accurately characterizes the tensile, compressive and shear behavior of concrete, calculating the millimeter-scale crack characteristics at the interface between the double-layer lining and the concrete. The mechanical response and resilience evolution of the reinforced structure are studied.FindingsThe results show that the segmental lining joint is the weakest part of the reinforced structure. The primary failure modes include the destruction of the arch vault and left-right spandrel joints, fractures in the tension zone and crack propagation and penetration at the interface. The segmental lining and secondary lining are not perfectly connected, resulting in different internal force distribution patterns, and the secondary lining exhibits a deformation mode different from the typical elliptical type. There is a significant difference between the normal and tangential displacement distributions at the interface of the double-layer lining structure, with interface failure mainly characterized by shear slip. Reinforcement of the secondary lining can significantly enhance the resilience of the segmental lining, and the resilience recovery of the structure is more pronounced with earlier reinforcement intervention.Originality/valueThis study demonstrates notable originality and value. It develops a refined model to simulate the failure and damage of a double-layer lining structure, with millimeter-scale simulations of crack propagation at the interface of the interlayer area. A framework for evaluating the structural resilience of shield tunnels reinforced with double-layer linings is established, and the evolution of performance and structural resilience throughout the loading process and subsequent lining reinforcement was thoroughly analyzed. The findings provide valuable recommendations for the reinforcement of double-layer linings in shield tunnel projects.

A microstructural rock model based on the distinct element method employing the Subspring Network contact model with rigid, Breakable, Voronoi-shaped grains (SNBV model) is proposed. The model consists of a mesh (3D Voronoi tessellation) of rigid, breakable, Voronoi blocks. The SNBV model is a microstructural rock model because it is a discrete model that can mimic rock microstructure at the grain scale. SNBV material mimics the microstructure of angular, interlocked, breakable grains with interfaces that may have an initial gap and can sustain partial damage. The model embodies the microstructural features and damage mechanisms that occur at the grain scale: initial microcrack fabric; heterogeneity-induced local tension; and intergranular and transgranular damage. The heterogeneity-induced local tension can be introduced in a controlled fashion that is not tied directly to the shape and packing of the grains and the interface stiffnesses. The synthetic material exhibits behavior during direct-tension and triaxial compression tests that matches the behavior of compact rock. The material can be calibrated to match the standard material properties and characteristic stresses of pink Lac du Bonnet granite. The material properties consist of Young's modulus and Poisson's ratio corresponding with uniaxial compression and Young's modulus corresponding with direct tension, as well as tensile strength, crack-closure stress, crack-initiation stress, secondary crack-initiation stress to mark the onset of grain breakage, crack-damage stress, and compressive strengths up to 4 MPa confinement. The model is suitable for studying the grain-scale micromechanics of brittle rock fracture.

Fracture toughness and cohesive fracturing properties of two classes of sandy-clay soils, (A) with fine and (B) coarse grains and stabilized with low (2%) and high (10%) cement (as soil stabilizer), were investigated using a chevron-notched semicircular bend (CN-SCB) sample under static and cyclic loads. The samples with coarser grains and higher amounts of cement stabilizer showed higher KIc compared to the soils containing low cement and fine grains. A noticeable reduction in KIc was also observed under cyclic loading compared to the monotonic loading. Load-crack opening displacement (COD) graphs obtained during cyclic loading showed high plastic deformation accumulation before the final fracture. The cycles required for the fatigue crack growth of the Class A soil were noticeably (three to six times) higher than the Class B. The FRANC2D nonlinear simulations, cohesive fracture analyses, and maximum stress theory were utilized for estimating the critical crack length and the onset of cohesive unstable crack propagation.

The creep phenomenon of inelastic deformation of surrounding rock may occur under the action of deep geological stress for a long period of time, potentially resulting in large-scale deformations or even instability failure of the underground engineering. Accurate characterization of the creep behavior of the surrounding rock is essential for evaluating the long-term stability and safety of high-level radioactive waste (HLW) disposal repositories. Although the laboratory creep tests of brittle undamaged rocks, such as granite, have been extensively performed, the creep characteristics of fractured surrounding rock under the multi-field coupling environment still require attention. In this study, a series of creep experiments was conducted on Beishan granite, which was identified as the optimal candidate surrounding rock for the disposal repository in China. The effects of various factors, including inclination angle of fractures, stress conditions, temperatures, and water content, were investigated. The experimental results show that the axial total strain increases linearly with increasing stress level, while the lateral total strain, axial and lateral creep strain rates increase exponentially. The failure time of saturated specimens fractured at 45 degrees and 60 degrees is approximately 1.05 parts per thousand and 0.84 parts per thousand of that of dry specimens, respectively. The effect of temperature, ranging from room temperature to 120 degrees C, is minimal, compared to the substantial variations in strain and creep rates caused by stress and water content. The creep failure of specimens fractured at 30 degrees is dominated by rock material failure, whereas the creep failure of specimens fractured at 60 degrees is dominated by pre-existing fracture slip. At a 45 degrees fracture angle, a composite failure mechanism is observed that includes both rock material failure and pre-existing fracture slip. (c) 2025 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/).

During the excavation of large-scale rock slopes and deep hard rock engineering, the induced rapid unloading serves as the primary cause of rock mass deformation and failure. The essence of this phenomenon lies in the opening-shear failure process triggered by the normal stress unloading of fractured rock mass. In this study, we focus on local-scale rock fracture and conduct direct shear tests under different normal stress unloading rates on five types of non-persistent fractured hard rocks. The aim is to analyze the influence of normal stress unloading rates on the failure modes and shear mechanical characteristics of non-persistent fractured rocks. The results indicate that the normal unloading displacement decreases gradually with increasing normal stress unloading rate, while the influence of normal stress unloading rate on shear displacement is not significant. As the normal stress unloading rate increases, the rocks brittle failure process accelerates, and the degree of rocks damage decreases. Analysis of the stress state on rock fracture surfaces reveals that increasing the normal stress unloading rate enhances the compressive stress on rocks, leading to a transition in the failure mode from shear failure to tensile failure. A negative exponential strength formula was proposed, which effectively fits the relationship between failure normal stress and normal stress unloading rate. The findings enrich the theoretical foundation of unloading rock mechanics and provide theoretical support for disasters prevention and control in rock engineering excavations. (c) 2025 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/).

Improving the fracture toughness of agricultural soil-engaging components can mitigate the detrimental effects of hard particles in the soil while maintaining the wear resistance of the components, thereby improving the service performance. The wear resistance of the parts can be improved by surface treatment, but the surface toughness after treatment still needs to be further improved. In this study, WC10Co4Cr@YSZ (Yttria Stabilized Zirconia) core-shell structured composite powder was synthesized by modifying commercial WC10Co4Cr powder using the sol-gel method, and WC10Co4Cr coatings were prepared using the powders before and after modification. The microstructure of the powder and coatings were characterized. The mechanical properties and wear resistance of the coatings were evaluated through microhardness, nanoindentation, and friction testing. The hardness of the YSZ-modified composite coating was comparable to that of the unmodified coating, yet it exhibited lower porosity and twice the fracture toughness. Wear test results indicated that the coating's wear loss was greatly reduced compared with the substrate. In addition, the wear rate of the YSZ-modified coating was 71.11 % lower than the unmodified coating, demonstrating its exceptional wear resistance. The findings show that incorporation of YSZ into the coating system further enhanced wear resistance. The strengthening mechanisms resulting from the YSZ inclusion include the pinning effect, which controls the size and distribution of the WC grains, the shell structure that prevents overheating, and the improved fracture toughness of the coating. This work provides a new way to extend the service time of agricultural soil-engaging components.

The deterioration of rock mass in the Three Gorges reservoir area results from the coupled damage effects of macro-micro cracks and dry-wet cycles, and the coupled damage progression can be characterized by energy release rate. In this study, a series of dry-wet cycle uniaxial compression tests was conducted on fractured sandstone, and a method was developed for calculating macro-micro damage (DR) and energy release rates (YR) of fractured sandstone subjected to dry-wet cycles by considering energy release rate, dry-wet damage and macro-micro damage. Therewith, the damage mechanisms and complex microcrack propagation patterns of rocks were investigated. Research indicates that sandstone degradation after a limited cycle count primarily exhibits exsolution of internal fillers, progressing to grain skeleton alteration and erosion with increased cycles. Compared with conventional methods, the DR and YR methodologies exhibit heightened sensitivity to microcrack closure during compaction and abrupt energy release at the point of failure. Based on DR and YR, the failure process of fractured sandstone can be classified into six stages: stress adjustment (I), microcracks equal closure (II), nonlinear slow closure (III), low-speed extension (IV), rapid extension (V), and macroscopic main fracture emergence (VI). The abrupt change in damage energy release rate during stage V may serve as a reliable precursor for inducing failure. The stage-based classification may enhance traditional methods by tracking damage progression and accurately identifying rock failure precursors. The findings are expected to provide a scientific basis for understanding damage mechanisms and enabling early warning of reservoir-bank slope failure. (c) 2025 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/).