Safety assessment of upper buried gas pipeline under blasting vibration of subway tunnel: a case study in Beijing subway line

As the buried gas pipelines are not easily field monitored, its status under the influence of tunnel blasting vibration is often difficult to obtain. In order to assess the safety of an upper buried gas pipeline under blasting vibration in the Beijing subway line 16, we established the 3D numerical model of the real field engineering to calculate and analyze the distribution of peak particle velocity (PPV) on the surface soil, proved its reliability by using the field monitoring data and discussed the dynamic response of the pipeline. Based on the analysis, we further assessed the safety of pipeline subjected to tunnel blasting vibration and concluded that the pipeline is only subjected to limited effect of tunnel blasting vibration and thus is safe

Damage Effect of Terrorist Attack Explosion-induced Shock Wave in a Double-deck Island Platform Metro Station

The objective of this research was to reasonably assess the damage to people and station structures caused by terrorist attack explosion at metro stations, taking the Liyuan station of Wuhan metro which adopts double-deck island platform as an typical example. The TNT explosion process inside the metro station was calculated and analyzed using the dynamic finite element numerical simulation software LS-DYNA. First, the peak overpressure curve and the positive pressure time curve of the shock wave of explosive under the condition of confined space in the metro station were obtained. Then, through the comparison and analysis of the theoretical formulas of explosive shock wave propagation characteristics, the accuracy and reliability of numerical calculation methods and model parameters were verified. At last, combining with the overpressure criterion of shock wave in explosive air, the distribution characteristics of the casualties in the metro station under the explosion shock wave are analyzed, and the dynamic response and damage effect of the pillar structure of the metro station under the explosion shock wave are studied

Uniaxial Compression Fractal Damage Constitutive Model of Rock Subjected to Freezing and Thawing

Mechanical properties of the rock in the cold regions are often affected by freeze-thaw cycles and loads. It is of great theoretical significance and engineering value to establish a uniaxial compression damage constitutive model of the rock under freeze-thaw cycles that can reflect the relationship between macroscopic and mesoscopic structural damage. In this paper, macroscopic and mesoscopic methods are combined with statistical methods to quantitatively analyze the damage degree of rock under freeze-thaw cycles and loads. Combined with the fractal features of the macroscopic image of the section, a fractal damage constitutive model considering the residual strength of rock is established. In addition, the model is subsequently verified by the experiment. The experiment shows that the mechanical properties of rocks subjected to freeze-thaw cycles and loads are determined by freeze-thaw damage variables, load damage variables, and their coupling effects. As the number of freeze-thaw cycles increases, the uniaxial compressive strength and elastic modulus of rocks decrease, and peak strain increases. By using the fractal dimension of the compression fracture surface as a bridge considering the residual strength of the rock, the constitutive model can better reflect the compaction stage, elastic deformation stage and plastic deformation stage of the uniaxial compression process of the freeze-thaw rocks

Stability Analysis of Train Movement with Uncertain Factors

We propose a new traffic model which is based on the traditional OV (optimal velocity) car-following model. Here, some realistic factors are regarded as uncertain quantity, such as the headway distance. Our aim is to analyze and discuss the stability of car-following model under the constraint of uncertain factors. Then, according to the principle of expected value in fuzzy theory, an improved OV traffic model is constructed. Simulation results show that our proposed model can avoid collisions effectively under uncertain environment, and its stability can also be improved. Moreover, we discuss its stability as some parameters change, such as the relaxation time

Anisotropic elastic constants calculation of stainless steel cladded layers of pressure vessel steel plate

Cladding stainless steel layer on the inner surface of ferrite pressure vessel is a common method to improve the corrosion resistance and save the economic cost. However, the movement of heat source and temperature gradient in the process of cladded welding will lead to the anisotropy of cladded layer material. When measuring the residual stress of pressure vessel steel plate with stainless steel cladded layers (SSCL) by contour method, it is necessary to know the elastic mechanical properties of stainless steel cladded layers accurately. The assumption of transversely isotropy (TI) was employed, and the relationship between the material compliance matrix and the elastic modulus of transversely isotropic material was utilized. Based on the elastic modulus of each cladded layer and the whole steel plate from the longitudinal direction (0°) until the transverse direction (90°) measured by the experiment, the independent constants S11, S13, S33 and S44 in the compliance matrix of each cladded layer and the whole steel plate were obtained by regression analysis method. Furthermore, by using the relationship between the independent constants of the stiffness matrix of the transversely isotropic material and the single crystal material, the independent constant S12 in the compliance matrix of each stainless steel cladded layer and the whole steel plate were obtained. And then the independent constants of the stiffness matrix of each cladded layer and the whole steel plate were acquired. Hence, a method for calculating the anisotropic elastic constants of the stainless steel cladded layer and the whole steel plate was proposed. The results will provide material data support for measuring residual stress of pressure vessel steel plate with stainless steel cladded layers by contour method

A Comparative Study on Root Canal Repair Materials: A Cytocompatibility Assessment in L929 and MG63 Cells

Cytocompatibility of repair materials plays a significant role in the success of root canal repair. We conducted a comparative study on the cytocompatibility among iRoot BP Plus, iRoot FS, ProRoot MTA, and Super-EBA in L929 cells and MG63 cells. The results revealed that iRoot FS was able to completely solidify within 1 hour. iRoot BP Plus required 7-day incubation, which was much longer than expected (2 hours), to completely set. ProRoot MTA and Super-EBA exhibited a similar setting duration of 12 hours. All the materials except Super-EBA possessed negligible in vitro cytotoxicity. iRoot FS had the best cell adhesion capacity in both L929 and MG63 cells. With rapid setting, negligible cytotoxicity, and enhanced cell adhesion capacity, iRoot FS demonstrated great potential in clinical applications. Future work should focus on longer-term in vitro cytocompatibility and an in vivo assessment