This study presents adaptive stable node-based smoothed upper bound finite element limit analysis (adaptive SNS-UBFELA) for soil-structure interaction problems under water table. A second-order cone programming (SOCP) formulation is first established by incorporating discontinuous velocity fields and pore water pressure within the framework of the Mohr-Coulomb yield criterion and the associated flow rule. An adaptive mesh refinement scheme is then introduced to enhance both computational accuracy and efficiency. The proposed method is implemented in MATLAB using the MOSEK Optimization Toolbox and validated through three numerical examples, including a tunnel, a cantilever retaining wall, and a pipeline. Comparative results show that adaptive SNS-UBFELA substantially mitigates numerical diffusion and oscillation observed in other adaptive UBFELA variants in investigated cases, while achieving higher efficiency than UBFELA discretized with six-node quadratic triangular elements (T6-UBFELA). The limit loads predicted by the proposed method show negligible deviation from those obtained using other methods in investigated cases, further demonstrating its favorable accuracy. Retaining wall and pipeline examples further demonstrate that increasing interface roughness and lowering water table significantly increase limit loads and alter failure modes. Overall, the proposed method provides a promising numerical framework for analyzing soil-structure interaction problems under water in geotechnical engineering.
Contamination by potentially toxic elements (PTEs) in coastal sediments poses increasing threats to marine ecosystems and human health. This study quantified eight potentially toxic elements (PTEs), including As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, in nearshore and beach surface sediments collected from 18 and 24 sites in the northern waters of the Beibu Gulf, respectively. Principal component analysis, positive matrix factorization, and Monte Carlo simulation were integrated to resolve sources and probabilistic risks. In nearshore sediments, Cd and As concentrations exceeded regional background values by 29.91-fold and 2.18-fold, respectively. Bay-specific comparisons showed significantly higher Cd concentrations in beach sediments than in corresponding nearshore sediments in EB and BE, whereas the mean contamination factors of Hg and As were higher in beach sediments overall. Source apportionment indicated contributions from maritime transport and tourism, aquaculture and agriculture, and industrial activities. Cd dominated the ecological risk assessment, with a sensitivity exceeding 96%, resulting in a high overall ecological risk across the coastal zone. Under the adopted recreational exposure assumptions, non-carcinogenic health-risk estimates for beach-sediment exposure remained below the screening benchmark. These findings identify Cd and As as priority contaminants for source control, targeted beach monitoring, and risk management for sensitive populations.
Abstract Accurate characterization of the accelerated creep stage in rock is essential for the long-term stability evaluation of deep geotechnical infrastructures, including deep-buried tunnels, high-dam foundations, and nuclear waste repositories. Traditional creep constitutive models, exemplified by the classical Nishihara model, are mostly established through a phenomenological combination of mechanical elements. These models fail to establish an intrinsic coupling relationship between energy dissipation and damage evolution within a unified thermodynamic framework, resulting in pronounced fitting deviations during the accelerated creep stage. In addition, the physical implication of some empirical parameters in these models remains ambiguous. To address the aforementioned limitations, this paper proposes an accelerated creep damage model for rock based on irreversible thermodynamics and free-energy function. Taking free-energy density as the core state variable, the model establishes a quantitative link between elastic strain energy release and internal microcrack propagation via the damage energy release rate and constructs an energy-driven, damage evolution–coupled constitutive relation. The damage-modified viscoelastic and viscoplastic rheological equations are derived, and a damage-weakening coefficient is introduced to describe the attenuation law of the equivalent viscosity coefficient during the accelerated creep stage. All parameters in the proposed model have explicit physical connotations: energy-damage coupling parameters reflect the rate of development of internal microcrack damage, rheological constitutive parameters characterize the rock’s resistance to viscous deformation, and accelerated creep characteristic parameters quantify the evolution intensity of accelerated deformation induced by damage accumulation. The proposed model is validated against triaxial step-loading creep test data of sandstone and quantitatively compared with the classical Nishihara model using multiple evaluation indicators. The results indicate that the model can fully reproduce the three-stage creep deformation law of rock, i.e., decelerating creep, steady-state creep, and accelerated creep. Under different stress levels, the correlation coefficients ( R 2 ) between fitted curves and experimental data are all above 0.90, and the root mean square error (RMSE) of full-stage creep strain is controlled within 2.1 × 10 − 5. Specifically, for the critical accelerated creep stage, the RMSE of the proposed model is 68%–75% lower than that of the Nishihara model, and the relative fitting error is controlled within 7%. The model can also accurately capture the inflection point where the deformation rate shifts from steady growth to rapid increase. This work reveals the internal mechanism of rock creep damage evolution from the perspective of the essence of energy, and provides a more reliable theoretical tool for long-term stability prediction in deep geotechnical engineering.
Calcium bismuth niobate (CBNO), known for its high Curie temperature (T-C), has been investigated as a potential material for vibration sensor due to its ability to operate at elevated temperatures. However, the inherent weakness in piezoelectric response of CBNO has limited its sensing performance. This study successfully induced pseudo-tetragonal distortion in CBNO through the co-doping effects of K/Ce at A site and In/W at B site. This modification altered the interaction between the perovskite layer and the bismuth layer, thereby enhancing both piezoelectric and ferroelectric properties. The co-doped Ca-0.94(K0.5Ce0.5)(0.06)Bi2Nb1.96(In1/3W2/3)(0.04)O-9 exhibits a significantly enhanced piezoelectric coefficient (d(33)) of 22.3 pC/N, compared to the 5 similar to 7 pC/N for pure CBNO ceramics, and the remanent polarization (P-r) increased to 11.91 mu C/cm(2), compared to 3.83 mu C/cm(2) for CBNO. Furthermore, the sample maintains a suitable resistivity (rho = 2.46 & times; 10(5) Omega & centerdot;cm) even at 600 degrees C. This work not only deepens the understanding of bismuth layer structure ferroelectrics (BLSFs) but also proposes a viable co-doping strategy, providing an effective approach for developing high-performance, high-temperature-resistant piezoelectric sensors.
Sustainable rice production in trace element-contaminated farmlands requires management strategies that simultaneously reduce grain metal accumulation and greenhouse gas emissions while maintaining yield. This study aims to evaluate how different fertilizer types-nitrogen, phosphorus, and potassium-affect these sustainability indicators in a rice-caixin rotation system. A pot experiment was conducted with trace element contaminated soil cultivated with two rice varieties, conventional Xiangzaoxian 45 (Oryza sativa L. subsp. Indica, Rice A) and hybrid Pengyou 1269 (Oryza sativa L. subsp. Indica, Rice B). Two rice–caixin rotation systems (A-G and B-G) were established by alternating Rice A and B with caixin (Brassica rapa var. parachinensis ‘Zengcheng Chicaixin’). The treatments were urea, calcium-magnesium phosphate, potassium chloride and unfertilized control. The total zinc concentration in the soil of Rice A was decreased by 41.28
