Yhe Compression Meso-Mechanics Theoretical Model and Experimental Verification of Polyurethane-Based Warp-Knit Spacer Fabric Composites

In this research, a new type of binary material, a polyurethane-based warp-knitted spacer fabric composite (PWSF), having a unique three-dimensional structure, high strength, and a variety of surface structures was prepared. The compression meso-mechanics theoretical model based on the Winkler elastic foundation beam theory and structural parameters of PWSF were used to predict the compression performance of PWSF. To verify the validity of compression model, the compression stress-strain curves of theoretical simulation were compared with the quasi-static compression test results. The deviation between these two compression moduli was less than 7%. The compression meso-mechanics model established in this study can effectively simulate the actual compression behaviors for different PWSF specimens. A regular pattern of compression properties of this novel composite from the theoretical research on meso-mechanics perspectives can be proposed.

The Environmental Effects Induced by a Metro Shield Tunnel Side-Crossing on Adjacent Pile Foundations and Its Impact Partition

With the advantages of fast construction speed and small disturbance to stratum, shield tunneling is becoming the preferred construction scheme for metro construction. However, if the disturbance of stratum cannot be clearly understood, it will affect the safety of adjacent underground structures and aboveground buildings. Based on the construction of the interval tunnel between Shizishan station and Chuanshi station of Chengdu metro line 7 project, this paper proposed a simplified calculation method to analyze the impact of shield excavation on adjacent pile foundation. A two-stage method of modified Peck formula and Winkler elastic foundation model was used to investigate the additional displacement and internal force of pile. A three-dimensional numerical model validated with the field test data was performed to compare with the theoretical results. The impact factors and their impact degree were discussed. The results show that the additional displacement and internal force are at a reasonable and acceptable level. The permanent pile foundation should adopt the small diameter pile as far as possible. When the small diameter pile foundation cannot meet the stress requirements, the design scheme of the pile group should be adopted. The area around shield tunnel is divided into strong impact area of pile foundation (S ≤ 0.75 D), slight impact area (0.75 D ≤ S ≤ 1.5 D), and no impact area (S > 1.5 D). The pile researched in this paper (S = 0.83 D) is in the slight impact area.

Study on Gas Enrichment Mechanism of Coal Seam Influenced by Vertical Stress on Mountainous Region Condition

The controlling effect of vertical stress of mountainous region on gas occurrence of the coal seam below it has always been ignored. In order to clearly express its influence mechanism, the change laws of depth, stress, and permeability of coal seam pressurised by the overlying mountain were studied based on the Winkler elastic foundation beam theory and seepage theory in the paper. At the same time, the enrichment mechanism of the coal seam pressurised by the overlying mountain was analyzed. The results showed the following: (1) There was a significantly strong correlation between the stress, permeability change rule of the coal seam, burial depth, and surface elevation under such condition. (2) Under the action of the vertical pressure of the mountain, the stress and permeability distribution of the coal seam showed significant nonlinear characteristics. The stress was the greatest under the peak, and the permeability was the smallest. (3) The initial gas content value was controlled by the permeability and the stress of the coal seam in the situation. Moreover, the field practice showed that under the action of vertical pressure of the mountain, the evaluation law of gas content was coupling with the surface elevation of the overlying mountain. In addition, the gas emission change law during the excavation of the driving face also showed the same characteristics. The results might be of great significance for the development and utilization of coal-bed gas and the safe exploitation of coal resources.

Nonlinear Dynamic Behavior of Porous and Imperfect Bernoulli-Euler Functionally Graded Nanobeams Resting on Winkler Elastic Foundation

Nonlinear free vibrations of functionally graded porous Bernoulli–Euler nano-beams resting on an elastic foundation through a stress-driven nonlocal elasticity model are studied taking into account von Kármán type nonlinearity and initial geometric imperfection. By using the Galerkin method, the governing equations are reduced to a nonlinear ordinary differential equation. The closed form analytical solution of the nonlinear natural flexural frequency is then established using the Hamiltonian approach to nonlinear oscillators. Several comparisons with existing models in the literature are performed to validate the accuracy and reliability of the proposed approach. Finally, a numerical investigation is developed in order to analyze the effects of the gradient index coefficient, porosity volume fraction, initial geometric imperfection, and the Winkler elastic foundation coefficient, on the nonlinear flexural vibrations of metal–ceramic FG porous Bernoulli–Euler nano-beams.