The excavation of the foundation pit will cause changes in the soil stress field around the foundation pit, and that may have adverse effects on the adjacent subway tunnels. In this paper, a complex deep foundation pit excavated in different sections is taken as the research object, and the support structure of the complex foundation pit project is introduced, which accumulates experience in the selection of support structure for similar projects. The finite element models are established by MIDAS/GTS software to evaluate the influence of excavation in different sections of the foundation pit on the tunnel deformation, and the accuracy of the finite element calculation results is verified by comparing the monitoring data. The results show that: The horizontal deformation of the subway tunnel is generally smaller than the vertical deformation. Tunnel monitoring should focus more on the development of the vertical deformation of the tunnel. The maximum vertical deformation and horizontal deformation of the tunnel are both smaller than the local specification limits, and the excavation of the foundation pit in this project has little influence on the deformation of the subway tunnel.
The vertical rotation method is a special option for steel tower construction in fabricated bridge. The tall tower is prefabricated on the ground and then pulled to its designed position using steel wires. Traditional vertical rotation method always uses a taller temporary structure to provide an upward pull force to lift the rotation member; however, the temporary structure would spend much time, cost, and work high above the ground. For instance, the Jinwu Bridge tower’s weight was so heavy that the ordinary rotating method was not feasible. Therefore, a relay traction system with two auxiliary struts was employed to rotate the tower. The chief strut was first rotated to an inclined angle of 60° by an assistant strut to decrease the lateral component force of tension. Then, the tower was pulled from horizontal to vertical by the chief strut. Furthermore, a numerical model was established to analyze the mechanical behavior of the inner force, stress, and deformation of the chief strut, assistant strut, and tower. The study identified critical conditions such as the reverse of axial force for the assistant strut, intervention of back cables, and release of cable tension. The relay traction system effectively reduced initial pulling stress, spending less cost and time. Besides, the analysis method can be an innovate reference for other vertical rotating projects.
This paper investigates the effect of fiber volume fraction on fiber distribution in steel fiber reinforced self-compacting concrete (SFRSCC) through experiments and numerical simulations. Three types of SFRSCC beam specimens with different fiber volume fractions (0.3%, 0.6%, and 0.9%) were cut to expose the steel fibers. The number and the orientation angle of the steel fibers on the beam sections were determined by image analysis techniques. Fiber density, fiber segregation coefficient, fiber dispersion coefficient and fiber orientation coefficient were applied to evaluate fiber distribution on the beam sections. Based on the experimental data, numerical models simulating the pouring process of fresh SFRSCC were established to analyze the overall fiber distribution in the specimens. The results show that the distribution state of the fibers on the beam sections is not random and uniform, which is correlated to the fiber volume fraction. Due to the variable rheological properties, a greater fiber volume fraction causes better fiber uniformity, lower fiber segregation and worse fiber alignment on the beam sections. Meanwhile, the numerical results show that the distribution law of fibers along the length direction of the specimens is almost independent of the fiber volume fraction. In addition, increasing the fiber volume fraction results in the increase of the average angle of the fiber orientation in the specimens. The results can provide a reference for optimizing the fiber distribution in the concrete matrix.
A semi-analytical method is developed to study the visco-elastic interface effect on the dynamic stress of a non-circular symmetrical tunnel in a half-plane subjected to P waves, and the interaction between the visco-elastic interface around the tunnel and the traction free boundary at the half-plane is analyzed. The complex variable function method combined with the wave function expansion method is introduced to obtain the theoretical expressions of waves around the non-circular tunnel. To satisfy the traction-free boundary condition at the half-plane, the large circle assumption is applied. The expanded coefficients are determined by using appropriate boundary conditions with stiffness parameters and viscosity coefficients of the interface. Selected numerical results are presented, and the interface effect on the dynamic stress under different embedded depths is discussed. It is found that the interacting effect of the visco-elastic interface and the traction-free boundary is quite related with the wave frequency. Comparison with existing results is also given to validate the semi-analytical method.
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