Advances in Civil Engineering

The tunnel lining segments are assumed to be rigid, and the tensile, compression, shear, and bending properties of the joints are considered. A simplified calculation method for the dynamic response of the structure under the ground shock is proposed, and its correctness is verified by comparing it with results from the finite element method. Using this method, the dynamic response of a subway tunnel lining is calculated, the change in joint force is studied, and the influence of the angle between the load and the center of the minimum segment and the wavelength–diameter ratio on the peak joint force is examined. The results indicate that under the ground shock, shallow tunnel lining is in the impulsive regime, and the force of segment joints is mainly compressed. As the wavelength–diameter ratio increases, the peak values of the lining top displacement and vertical deformation increase significantly, and the proportion of displacement and deformation caused by the inertial force gradually decreases. Sine and cosine functions can be used to preliminarily judge if the bending moment and radial force of the joint are too large or too small, so that the resistance of the lining to ground shock can be improved to a certain extent by setting the positions of lining joints reasonably.

As a new type of green soil-curing agent, geopolymers have the advantages of high strength, good durability, and low carbon emissions, and slag is widely used as a common geopolymer precursor in geopolymer production. Therefore, it is important to investigate the strength and durability of slag-based polymer-solidified sludge under the action of dry–wet cycling with chloride salt solutions. After curing the slag-based polymer-solidified sludge with NaOH (NO), Na₂SiO₃ (NS), and calcium carbide slag (CS) as alkali excitants to different curing ages (7, 14, 28 days), experiments involving different numbers of dry–wet cycles (0, 5, 10, 20, 30) with NaCl solutions of different concentrations (0%, 5%, 10%) were performed to investigate the unconfined compressive strength and micromorphology of the solidified sludge after undergoing dry–wet cycling. The test results showed that the strength of sludge cured with NO for 7 and 14 days showed a trend of increasing and then decreasing with an increasing number of dry–wet cycles, and the strength of sludge cured with NO for 28 days showed a trend of gradually decreasing with an increasing number of dry–wet cycles. The order of the resistance of sludge cured with the three excitants to the effect of the dry–wet cycles of chlorine salt was CS > NO > NS. After the dry–wet cycling, small cracks appeared on the surface of the NS-cured soil, the surface of the NO-cured soil was intact, and a small amount of surface peeling was observed for the CS-cured soil. Scanning electron microscopy test results showed that the chloride salt dry–wet cycles caused the formation of pores and cracks in the soil, and NaCl crystallization and Friedel’s salt production were observed in the soil, thus reducing the strength of the solidified sludge.

The demand for urban transport is increasing globally, and urban rail transit is an important infrastructure for meeting this demand. The objectives of this study were to effectively control and prevent all types of risks in the construction of metro projects and improve the quality and safety control of urban metro project construction. First, 20 index factors were selected from the five dimensions of “man–machinery–materials–methods–environment” and constructed an index system for assessing urban metro construction quality risks. Second, the analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE) methods were used to comprehensively evaluate the construction quality risks of subway projects, and the weights of the secondary indices were determined. Finally, the importance of secondary indicators was evaluated using the integrated AHP–FCE method, and the model was applied to engineering practice for validation. The results indicated that the comprehensive AHP–FCE method has good adaptability and rationality and has practical application value for metro project construction quality and safety risk assessment. It can help prevent urban metro construction quality accidents and provides a novel idea for metro project construction quality risk assessment.

Three groups of filling materials with different mix proportions were prepared. PO42.5 grade cement was selected as the binding material, mechanized granular coal gangue and fine sand were used as the filling aggregate, and then the specimens were curing at room temperature and 95% moisture. Through the uniaxial compression test, the influence of gangue–sand ratio, the mass fraction, and curing age on the mechanical properties of filling materials was analyzed. The microstructure analysis of SEM was conducted to explore the internal mechanism of the strength difference of filling materials. The results show that the gangue–sand ratio dramatically influences the uniaxial compressive strength. The strength increases first and then decreases with the gangue–sand ratio increase. The mass fraction of filling paste is positively correlated with specimen strength. When the sand–cement ratio, gangue–sand ratio, and the mass fraction remain unchanged, the longer the curing age, the greater the uniaxial compressive strength of specimens. The specimens with a sand–cement ratio of 3.5 : 1, a gangue–sand ratio of 5 : 5, and a mass fraction of 86% reach the maximum value of 11.03 MPa at a curing age of 10 days. It can be seen that when the gangue–sand ratio is 5 : 5, the filling material has the best mechanical properties, so it can be recommended as the optimal mix proportion for goaf filling. Thus, it provides a solid technical guarantee for the treatment of mine surface collapse disasters and the utilization of bulk coal gangue resources.

As the groundwater in karst areas is rich in calcium ions, when the groundwater flows out of the tunnel drainage pipe, calcium carbonate crystals will be precipitated and then adhere to the pipe wall, which will easily cause chemical blockage in the drainage pipe wall, thus affecting the drainage efficiency and leading to the increase of water pressure outside the tunnel lining, affecting the safety and stability of the structure. Therefore, the blockage of calcium carbonate crystals in tunnel drains is one of the most important problems for the safe and normal operation of tunnels. In order to quantify and qualify the process of crystalline blockage in the drainage system of tunnels in karst areas, this paper constructs a numerical model with coupled multiphysical fields of the flow field and particle concentration field and also combines data from indoor tests to compare and verify the simulation results and analyze the time-varying law of crystalline solids deposited on the pipe wall. In this paper, we consider the force situation of crystalline solids in the pipe by water flow, analyze the related theories, comprehensively study the migration and deposition law of crystalline particles in the drainage pipe, and establish a numerical simulation model of the pipe crystallization rate considering temperature, flow velocity and concentration of sediment particles based on ANSYS FLUENT software, and refine and analyze several parameters in the model, so that it can provide a theoretical analysis framework for the tunnel drainage pipe blockage in karst areas by providing a theoretical analysis framework.

A self-aware posttensioned prestressing intelligent reinforcement system with force and sensors is proposed by combining the advantages of posttensioned prestressing reinforcement technology and intelligent structure. A static test study is then conducted with brick masonry members (wall pieces) as reinforcement objects. The experimental results demonstrate that the intelligent strand can be deployed using the same process, tensioning apparatus, and anchoring equipment as ordinary strand. Furthermore, the mechanical performance indexes with and without intelligent strands are very close, and the differences in percentages of cracking load, cracking displacement, yielding load, yielding displacement, ultimate load, and ultimate displacement are 20%, 9%, 9%, 10%, 2%, and 26%.