The mechanism governing the transition from creep to rapid movement is a central challenge in understanding the instability of reservoir landslides. This study focuses on the Muyubao landslide, a giant bedding landslide in the Three Gorges Reservoir Area that exhibits persistent creep. This study focuses on the Muyubao landslide, a giant bedding landslide exhibiting persistent creep in the Three Gorges Reservoir Area. A series of ring-shear tests were conducted on the slip zone soil, revealing that its residual friction coefficient depends on both normal stress and displacement rate. Specifically, friction weakening, characterized by exponential decay, occurred at low displacement rates, whereas slight friction strengthening, characterized by logarithmic increase, emerged when the displacement rate exceeded a critical threshold (v = 3.33 u00D7 10u22124 m/s). The research indicate that friction weakening is the dominant mechanism driving the transition from slow creep to catastrophic failure by promoting accelerated creep through a positive feedback loop of u201Crate increaseu2013friction weakeningu2013further rate increase.u201D Based on the experimental results, a 3D slice-based dynamic calculation model was established that incorporates normal stress, rate-dependent frictional behavior, and variations in pore water pressure. This study reveals the potential deformation and instability mechanisms of the MYB landslide and provides essential theoretical support for predicting instability velocity and evaluating the movement tendency of creep-type landslides in reservoir areas.
Soil heavy metal (HM) contamination is a widespread and serious environmental challenge. Even after treatment, contaminated soil may still pose a risk of secondary metal release under complex environmental conditions. In this study, a novel solidifying agent, a diatomaceous earthu2013fly ash-based geopolymer (D-FA), was synthesized from phosphoric acid (H3PO4), fly ash, and diatomaceous earth for the solidification/stabilization of contaminated lead-zinc red clay. Under coupled acid exposure and wetu2013dry cycling conditions, short-term effectiveness was evaluated using the toxicity characterization leaching procedure (TCLP), whereas the accelerated TCLP (ATCLP) was applied to analyze leaching kinetics and predict long-term performance. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were employed to characterize microstructural evolution and degradation mechanisms across multiple scales. A durability assessment framework based on cumulative leaching fraction (CFL) and effective diffusion coefficient (De) was established to predict the environmental safety period. The results showed that D-FA increased the strength of red clay by 6.59-fold and achieved fixation efficiencies of 99.99% for Pb2+ and 73.95% for Zn2+ within 28 days. Under long-term acid exposure and wetu2013dry cycling conditions, D-FA exhibited greater stability and durability in immobilizing Zn2+ than Pb2+. According to predictions based on Ficku2019s diffusion model, the environmental safety period reaches several decades for farmland at pH=5, exceeds 200 a for grassland and forest land, and may extend to several centuries for construction sites.
Soft rock tunnels in red beds frequently encounter anchor failure issues. Improving the mechanical properties of the red-bed soft rock-grout interface is highly significant for ensuring the stability of anchor support. This study employs laboratory direct shear tests in combination with digital image correlation (DIC) technology to investigate the mechanical properties (peak shear strength zp, residual shear strength zr, and shear stiffness ks) of the grout-rock interface (GRI) among three typical soft rocks from red beds (red sandstone, mudstone, and grey sandstone) and two grout materials (ordinary Portland cement (OPC) and early high-strength cement (EHC)) under varying curing periods (6 h, 1 d, 2 d, and 7 d). The shear behavior and DIC-based failure mode are analyzed for red beds GRIs. The following key findings were observed: (1) As normal stress increases, both the shear strength (zp) and shear stiffness (ks) of the GRI also increase, following the trend: red sandstone > mudstone > grey sandstone. The cohesion values of the red sandstone, mudstone, and green sandstone with the EHC grout-rock interface at 2 days are 2.4, 0.9, and 1.2 MPa, respectively. The corresponding internal friction angles are 57.6 degrees, 38.0 degrees, and 27.0 degrees, respectively. (2) With an increase in curing age, both zp and ks at the GRI increase non-linearly. EHC exhibited superior bonding performance compared to OPC, with zp reaching 7.9 MPa at 6 hand 90% of the 7-day zp being achieved at 2 din red sandstone conditions. (3) The OPC-bonded specimens primarily exhibit grout failure near the GRI, whereas the EHC-bonded specimens show rock failure in red sandstone and mudstone conditions, and adhesive failure at the interface in grey sandstone. (4) An empirical model for the shear strength of the GRI in red bed soft rocks is proposed and validated, providing a framework for the rapid and reliable evaluation of anchorage strength in red bed soft rock tunnels.
Peaty soil,a distinct category of soft foundation soil,exhibits unique physical and mechanical properties that are strongly influenced by its microstructure.Its high water content,organic matter content,low strength and permeability often result in significant engineering challenges.Enhancing the mechanical strength of peaty soil has thus become a central focus in geotechnical engineering.Using slag-based geopolymer to synergize with cement for solidification,the mechanical properties of peaty soil before and after stabilization were examined through unconfined compressive strength and direct shear tests.The mechanisms of improvement were further analyzed through microscopic techniques,including scanning electron microscope(SEM),X-ray diffraction(XRD),mercury intrusion porosimetry(MIP),and Fourier transform infrared spectroscopy(FTIR).The results demonstrate that all three alkali activators contribute to the enhancement of the mechanical strength of the peaty soil,with NaOH showing the highest activation efficiency.Cement stabilization of peaty soil improves shear strength by reducing pore space and strengthening interparticle bonding via ion exchange,hydration product crystallization,and the formation of CaCO3 and calcium silicate hydrate(C-S-H).Four stages i.e.,dissolution activation,ion exchange,gel formation,and structural reorganization are identified in the reaction process of activated slag improving peat soil.The alkali activator facilitates the dissolution of the slag's vitreous phase,promoting ionic polymerization that leads to the formation of calcium-alumino-silicate-hydrate(C-A-S-H)gel.Simultaneously,organic functional groups in the peaty soil engage in ion exchange,forming CaSiO3 precipitates and establishing a"calcium bridge"structure.These reactions collectively contribute to the formation of a dense composite matrix,thus enhancing compressive strength.Grey relational analysis reveals that compressive strength is most strongly correlated with pore area,while shear strength shows the highest correlation with the shape factor.Modified soil specimens undergo five dry-wet cycles,with a minimum strength loss rate of 27%.These findings provide a theoretical foundation for the partial replacement of cement with alkali-activated slag in peaty soil stabilization,contributing both to soft soil improvement and the valorization of industrial byproducts.Furthermore,these results offer valuable insights for ground improvement in peat-rich regions,such as Yunnan,China.
3D printing has emerged as a valuable tool for studying the mechanical behavior of rock replicas under various stress-strain states.This technique enables the creation of an unlimited number of replicas with predetermined properties and a homogeneous structure.Among various 3D printing methods,liquid crystal display(LCD)-based printing offers a cost-effective and high-quality approach for rapid prototyping of rock samples.This study investigates the feasibility of using 3D LCD printing to create rock analogs for geomechanical investigations.We evaluate the microstructure of LCD-printed samples and its influence on their elastic and mechanical properties.To assess these properties,we subjected cylindrical samples to elastic wave propagation and uniaxial compression tests.Our results demonstrate that LCD-printed samples exhibit high homogeneity of elastic properties.The velocities of elastic wave propagation across and along the layers are essentially identical,differing only by the error value.Moreover,Young's moduli obtained under uniaxial loading are in good agreement with non-destructive test results,indicating a high degree of homogeneity in elastic properties up to 20 MPa.These findings suggest that 3D LCD-printed rock analogs are well-suited for investigating processes in rocks under purely elastic loading.Additionally,the technology's versatility allows for the creation of rock replicas with various features,providing researchers with the ability to study the mechanical behavior of rocks with specific characteristics.We demonstrate the potential of 3D LCD-printed rock analogs through a case study investigating the impact of cyclic deformations on the conductivity of thin capillaries in a porous medium.Our results provide a strong foundation for utilizing 3D LCD printing to advance our understanding of geomechanical processes in rocks.
