We conducted a field test on Huitougou (HTG) Tunnel, which is a typical shallow-buried and unsymmetrically loaded tunnel. The on-site monitoring data indicated that the surrounding rock pressure and lining stress on both sides of the tunnel were indeed asymmetrical and that the pressure ratios (original unsymmetrical coefficient) of each corresponding monitoring point were different. According to the tunnel design principle, we proposed the unsymmetrical coefficient (UC) to characterize the asymmetrical degree of the tunnel, and verified and compared the UC of the field test and numerical simulation results. The effects of different factors on the UC such as the slope angle of the ground, the thickness of the overburden cover, the physical and mechanical properties of the surrounding rock, and the construction method were studied and analyzed. The research results reveal that the bias coefficient calculated by the numerical simulation was close to the monitoring results. The results of the factor analysis indicate that the slope angle, overburden thickness, and elastic modulus significantly affected the bias degree, while other factors had little effect. The concise and clear UC accurately described the unsymmetrical degree of any unsymmetrical-loaded tunnel and provided more accurate judgment regarding the safety of the tunnel design phase and construction phase.
Fatigue of steel bridges is a major concern for bridge engineers. Previous fatigue-based weight-limiting method of steel bridges is founded on the Palmgren–Miner’s rule and S-N curves, which overlook the effect of existing cracks on the fatigue life of in-service steel bridges. In the present study, based on the theory of linear elastic fracture mechanics, a framework combining the artificial neural networks and Monte Carlo simulations is proposed to analyze the fatigue reliability of steel bridges with the effects of cracks and truck weight limits considered. Using the framework, a new method of setting the gross vehicle weight limit for in-service steel bridges with cracks is proposed. The influences of four key parameters, including the average daily truck traffic, the gross vehicle weight limit, the violation rate, and the detected crack size, on the fatigue reliability of a steel bridge are analyzed quantitatively with the new framework. Results show that the suggested framework can enhance the fatigue reliability assessment process in terms of accuracy and efficiency. The method of setting gross vehicle weight limits can effectively control the fatigue failure probability to be within 2.3% according to the desired remaining service time and the detected crack size.
Soil reinforcement with natural or synthetic fibers enhances its mechanical behavior in various applications. Fiber-reinforced sands (FRS) can be relatively anisotropic because of the fiber self-weight and the compaction technique. However, the microscopic mechanisms underlying the anisotropy are still poorly understood. This study used a discrete element approach to analyze the microscopic mechanisms underlying the strength anisotropy of FRS due to fiber orientation. Analysis of contact networks revealed that the optimum fiber orientation angle is perpendicular to the main direction of strong contact force in direct shear testing. These fibers produced the largest increase in shear zone thickness, normal force around the fiber body, effective contact area, tensile force along fibers, and energy storage/dissipation. This study is valuable for further understanding of the mechanical behaviors of FRS.
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