To elucidate the unclear mechanism by which the geo-stress field influences the cracking of layered soft rock tunnel linings,this study examines a typical layered soft rock tunnel along the Wen-Ma expressway as a case study.By integrating model tests with numerical simulations,we investigate the deformation,stress,and failure behavior of layered soft rock tunnel linings under the impact of the geo-stress field.The damage characteristics and cracking patterns of the tunnel lining structure under varying lateral pressure coefficients are analyzed,thereby revealing the mechanism through which the geo-stress field affects tunnel lining cracking.The results indicate that,with a bedding angle of 45° and a strike of 90°,as the lateral pressure coefficient increases from 0.5 to 1.5,the morphology of the lining cracks transitions from vertical compression failure to bedding-plane dominated failure,and subsequently to horizontal compression failure.The cracking pattern evolves from tensile-shear composite failure to shear failure,and then back to tensile-shear composite failure.Correspondingly,the location of cracking shifts from the vault to the right spandrel,and from the left arch foot to the left haunch.When the lateral pressure coefficient is 1.00,the stress distribution of the surrounding rock is the most uniform,leading to minimal deformation and contact pressure of the lining,maximal bearing capacity of the lining,and optimal overall stability of the tunnel.Further analysis reveals that the location of surrounding rock damage exhibits spatial consistency with the area of lining fractures.The surrounding rock damage manifests as compression failure along the normal bedding plane surrounding the tunnel,along with shear sliding along the bedding plane away from the tunnel area.
The closure behavior of rock joints significantly influences their shear mechanics.This study employs pressure-sensitive films to measure three groups of sandstone joints,discussing the relationship between effective contact characteristics and shear strength.The results indicate that:(1)Under identical normal stress,the effective contact area ratio varies with different shear directions.As normal stress increases,the effective contact area ratio exhibits a linear growth trend,ultimately reaching approximately 50％of the actual contact area ratio.(2)Variations in effective average contact stress also show significant differences across shear directions.Additionally,the rougher the joint surface,the more pronounced the fluctuations in effective average contact stress.Furthermore,the average effective dip angle decreases following a negative exponential trend as normal stress increases,gradually approaching a stable value indicative of a fully contacted state.(3)An effective roughness indicator,which accounts for the influence of normal stress,is modified based on the effective contact area ratio.Building on this,a new peak shear strength model for rock joints is developed using the Barton criterion.This model satisfies boundary condition constraints,and its accuracy in predicting the peak shear strength of rock joints has been validated through direct shear tests and comparisons with several published datasets.These findings provide a theoretical foundation for understanding the shear mechanisms of sandstone joints.
Elastic beam-spring models are widely used in performance-based design for confined excavations;however,existing methodologies are often insufficient in accurately capturing the evolution of earth pressures under confined spatial constraints and the nonlinear stiffness behavior of soil.To address these limitations,this study develops a hardening soil-spring model with small-strain stiffness within a nonlinear elastic beam-spring framework to predict deformations in confined excavations.The proposed model features a displacement-dependent earth pressure formulation with a modified factor applied to the active side of the retaining structure,effectively accounting for soil arching effects and horizontal shear stresses within the confined soil.On the passive side,nonlinear soil springs simulate both the hardening behavior and small-strain characteristics of soil based on the hardening soil model with small-strain stiffness(HSS).The proposed model is validated against centrifuge test results and numerical simulations,followed by a parametric analysis that examines the effects of excavation depth,confined soil width,wall bending stiffness,and soil stiffness parameters—including Young's modulus and small-strain stiffness—on wall deflections.Additionally,the model is applied to a real-world case involving deep excavations adjacent to bridge piers in a coastal composite stratum,with soil parameters derived from in-situ standard penetration tests(SPT)and cross-hole seismic tests.The close agreement between predictions and field monitoring results highlights the practical applicability of the proposed model.
To enhance the long-term service performance of solidified soft soil in plateau regions,this study employed ordinary Portland cement for stabilization.A series of unconfined compression tests,direct shear tests,and microstructural characterization techniques(XRD,SEM,NMR)were utilized to systematically investigate the strength deterioration patterns of cement-stabilized soil under freeze-thaw cycles and elucidate the intrinsic relationship between macroscopic mechanical behavior and microscopic mechanisms.The results show that the strength deterioration of cement-stabilized soil exhibits distinct stage characteristics.The first five freeze-thaw cycles result in the most significant strength reduction,with markedly diminished effects observed thereafter,identifying this initial phase as the critical period for strength degradation.A predictive model based on a 30-year service life established strength deterioration thresholds.The stress-strain curves reveal a three-stage evolution,with specimens demonstrating similar strength development trends in the linear elastic stage across all cement contents,followed by a sharp stress drop post-peak,indicating a notable transition from plastic to brittle failure.The incorporation of cement significantly enhances soil strength,with the unconfined compressive and shear strengths of specimens containing 4％-10％cement after 10 freeze-thaw cycles substantially exceeding those of untreated soil.The increase in cohesion was significantly more pronounced than that of the internal friction angle.Microstructural analysis indicates that repeated freeze-thaw cycles weaken interparticle bonding,reduce particle contacts,and promote pore evolution and development,thereby providing a microscopic interpretation of the macroscopic strength deterioration mechanisms.These findings offer theoretical and technical support for the application of soil stabilization technologies in cold plateau regions.
Time-dependent deformation of rock and soil masses plays a fundamental role in their long-term evolution and instability.However,conventional theories are often insufficient to characterize the differential features of deformation evolution in both temporal and spatial dimensions.To address this limitation,the concept of differential time-dependent deformation is proposed,which states that different parts of a geotechnical system undergo creep deformation at different displacement rates.Based on this concept,a systematic theoretical framework is established,ranging from the analysis of time-dependent response mechanisms to the formulation of constitutive models.First,homogeneous landslide basal-friction experiments and slope model tests containing weak interlayers were conducted.Combined with particle image velocimetry(PIV),digital image correlation(DIC),and environmental scanning electron microscopy(ESEM),the spatial distribution characteristics of deformation in geomaterials were systematically revealed.The results indicate that deformation progressively intensifies from the rear edge to the toe of the slope and from shallow layers to deeper regions,accompanied by distinct time-dependent response mechanisms in different zones.Based on these observations,a visco-elastic-plastic constitutive model is developed by connecting a Burgers model in series with a plastic element incorporating strain-softening behavior.The model quantitatively describes the gradual degradation of cohesion and internal friction angle during the differential time-dependent deformation process of geomaterials.The proposed model is implemented into the FLAC and 3DEC numerical platforms.Numerical analyses demonstrate that the model successfully reproduces the complete deformation process of the Danba landslide,including initial deformation,steady-state creep,and accelerated failure.In addition,it effectively captures the interface effect occurring at the boundary between soft and hard rocks in the Jinping Hydropower Station slope and reveals the formation mechanism of deep unloading fractures.The proposed theoretical framework clarifies the universality and controlling role of spatiotemporal differential deformation during the time-dependent evolution of geomaterials,providing a new theoretical basis for deformation-failure warning and dynamic stability assessment in geotechnical engineering.
