For the simple bridge structure, the finite element model established by drawing and elastic mechanics method is accurate. However, when faced with large and complex long-span bridge structures, there are inevitable differences between the finite element model and the physical model, where the model has to be updated. It is problematic that the updating structural matrix cannot be fed back into the existing general finite element calculation software in the traditional structural matrix updating method. In this paper, a parameter-type updating method based on the “Kriging model + swarm intelligence” optimization is proposed. The Kriging model, based on Genetic Algorithm (GA), Bird Mating Optimizer (BMO), and Particle Swarm Optimization algorithm (PSO), is introduced into the finite element model, updating this to correct the design parameters of the finite element model. Firstly, a truss structure was used to verify the effectiveness of the proposed optimization method, and then a cable-stayed bridge was taken as an example. Three methods were used to update the finite element model of the bridge, and the results of the three optimization algorithms were compared and analyzed. The results show that, compared with the other two methods, the GA-based model updating method has the least time due to the small computation. The results of the BMO-based model were time consuming compared to the other two algorithms, and the parameter identification results were better than the GA algorithm. The PSO algorithm-based model updating method to solve the finite element model was repeated, which required a large amount of computation and was more time consuming; however, it had the highest parameter correction accuracy.
The study of the slurry reinforcement mechanism is mainly focused on the interaction between slurry and soil. The seepage effect of the slurry always exists no matter what way the slurry interacts with the soil around the pile. In the process of slurry diffusion, the porosity of the soil, the permeability of the slurry, and the slurry pressure vary due to some cement particles being blocked by the soil particle skeleton. Therefore, the study of the slurry filtration effect is of great significance for predicting the permeation and diffusion law of slurry. In this paper, a macroscopic linear filtration model was introduced and the changes of slurry properties in the permeation diffusion process were considered. Firstly, a spherical (cylindrical) permeation diffusion model, which takes the linear filtration effect and the variation of slurry viscosity into account, was derived based on the conservation of mass. Furthermore, in order to more accurately reflect the influence of the filtration effect on the slurry permeation diffusion model, a polynomial nonlinear filtration model was proposed, and the numerical solution for the permeation diffusion model was derived using finite difference and finite element methods. Finally, the numerically simulated values, the measured values, and the values from the spherical permeation diffusion model that does not consider slurry viscosity variations were compared. The results indicate that the grout pressure is inconsistent with the measured value without considering the effect of the filtration. The initial grouting pressure calculated by the model in this paper is slightly larger, and the required grouting pressure over time is greater than that without considering the filtration effect, regardless of whether the grout diffuses in a spherical or cylindrical manner. The results of this study can contribute to a better understanding of grouting engineering and provide some theoretical guidance for actual grouting.
In the study of the impact of rainfall on the unsaturated soil slope, the changes of pore water pressure and effective stress are frequently analyzed, while the loading effect caused by the change of pore water content in unsaturated soils is often neglected. In order to realize the coupling effect of the above two, a coupling model involving pore water pressure and pore water gravity was established based on the principle of seepage-stress coupling in unsaturated soils. Through a case verification, the coupling effect of pore water pressure and pore water gravity on the unsaturated soil slope was analyzed from the aspects of effective saturation, pore water pressure, effective stress, displacement, and stability. At the same time, the results were compared with those considering only the pore water pressure. The results show that the slope stability is relatively poor considering the coupling of unsaturated pore water pressure and pore water gravity. Therefore, the gravity effect of pore water in unsaturated soils cannot be neglected when calculating the stability of unsaturated soil slope under rainfall condition.
Abstract To reveal the deformation law and mechanism of bedding slopes under excavation unloading, an unloading rebound model of slope deformation is established on the basis of Mindlin’s strain solution, and a bedding-slip model of slope deformation is deduced on the basis of the Kalhaway constitutive model. Combining the two models, this study presents a computational model for the deformation response of bedding slope excavation. This model can reflect the mechanism of excavation unloading and the characteristics of rock mass structure. The reliability of the model is verified by comparing the calculated results of the analytical model with the experimental results in the laboratory. On this basis, the influences of excavation angle, excavation depth, and stratum thickness are analyzed by using several calculation examples. The calculation results show that the deformation induced by excavation increases with the increase in excavation angle or depth and decreases with the increase in stratum thickness. The excavation response of bedding slopes is mainly affected by the effect of unloading and the slip of the structural plane. Moreover, the unloading effect is controlled by the amount of excavation, and the rebound deformation of slopes is approximately linearly correlated with excavation volume. Bedding slip is affected by many factors because the increase in excavation angle or the amount of rock stratum leads to the increase in slip deformation. The proposed model can provide a basis for the deformation mechanism of bedding slopes under excavation.
In this paper, a single-tier beam-spring-damping system and a two-tier beam-spring-damping system are adopted to simulate the FT (fixed track) and FST (floating slab track) system, respectively. The tunnel is modeled as an infinitely long Euler—Bernoulli beam embedded in the layered saturated soil. By solving the governing equations of the saturated soil and employing the TRM (transmission and reflection matrices) method, the frequency response function of the tunnel-layered saturated soil model is obtained. Making use of the interaction between the tunnel and track systems, the track system is coupled with the tunnel-layered saturated ground model. The solutions for the dynamic response of the track system–tunnel-layered saturated ground model under moving loads in the time–space domain are obtained using the inverse Fourier integral transform. To evaluate the damping effect of the FST system on the vibration of tunnel and soil, four damping coefficients are defined and the vibration results of the FT system–tunnel-layered saturated soil model are compared with those of the FST system–tunnel-layered saturated soil under different moving loads and soil conditions. The numerical results show that both the vibration displacement and acceleration amplitude are attenuated after using the FST system, and the damping coefficient of acceleration is about 30% greater than that of the displacement. In addition, the damping effect of the FST system on the ground surface vibration is associated with the embedded depth of the tunnel and the soil stiffness.
Foamed cement-based materials have attracted much attention as a new type of thermal insulation materials (TIMs) that may offer a sustainable solution to the built environments. This laboratory study explores the combined use of nano-montmorillonite and polyethylene microfiber in foamed paste with high volume fly ash (HVFA) binder. A total of 16 foamed HVFA paste mixtures were fabricated which consisted of 70% Class F fly ash, 30% Portland cement, 2% sodium alpha-olefin sulfonate, 0.38% Na₃PO₄, and 2% nano-montmorillonite. The dosage and type of polyethylene microfibers (90 μm in diameter) were explored in the present study, with six dosages (0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% by volume) and three lengths (3 mm, 6 mm, and 9 mm) tested. Based on the experimental results, the highest 28-day rupture strength (1.51 MPa) was achieved with the use of 3-mm long PE microfibers at 0.4 vol.%. Synergistic utilization of nMMT and microfibers exhibited a great influence on the dry density and water absorption of the foamed paste. The SEM micrographs illustrated the multiple mechanisms by which the microfibers serve to reduce shrinkage-induced cracking of the foamed paste. Energy-dispersive X-ray spectroscopy was employed to obtain the contents of Ca, Si, Al, S and mole ratios of Ca/Si, Ca/(Si + Al), S/Ca, and Al/Si in the hardened pastes, which reveal the difference in hydration products near or away from the nMMT-pretreated polyethylene microfibers. The results of microhardness test were also used to elucidate such nano-/micro-synergistic effects, which improved the bonding between microfibers and foamed paste matrix. A mechanism was proposed to explain the role of various admixtures and the balanced performance of such inorganic TIMs.
In this study, paraffin (PA)/expanded perlite (EP) form-stable phase change material (PCM) was first fabricated using the direct impregnation method without vacuum treatment. Absorptive capacity results showed that the PA/EP composite can obtain good absorptive capacity with the temperature 80 °C and the time 2 h. Compared with the water absorption of EP, the decrease in the water absorption of PA/EP form-stable proved that the absorption of PA into porous EP has been carried out successfully. Scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) results show that paraffin can be well impregnated into EP pores and has good compatibility with it. Differential scanning calorimetry (DSC) results reveal that paraffin/EP composite PCM has melting temperature and latent heat of 53.6 °C and 91.3 J/g, respectively. The durability cycles results suggest that form-stable PA/EP PCM shows good durability.
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