Research on the Construction Mechanical Behavior and Deformation Characteristics of Lining Structure

Different excavation methods lead to substantial changes in the relaxation zone of the surrounding rock. The stress characteristics of the support structure become more complex during the process of excavation method conversion. It is essential to design a well-considered construction plan to minimize the disruptions caused by excavation method conversion. This work takes a tunnel in Jiangsu Province, China, as the engineering background and establishes a numerical model for the conversion from the double-side-drift method to the three-bench method. Based on a numerical investigation, this study analyzed the deformation of surrounding rock and the stress state of the support structure during the excavation method conversion. The results showed that excavation method conversion can accelerate the deformation rate of the surrounding rock, causing the support structure to bear greater pressure. This leads to a significant increase in the circumferential stress at the junction of two excavation methods. Setting up a reinforced area during the process of excavation method conversion can improve the stress state of the support structure. Finally, an analysis of the parameters of the reinforced area was conducted, and a reasonable construction plan was proposed. This study can provide guidance for subsequent construction projects. Full article

To investigate the impact of various compartment partition plate connection methods within a shield utility tunnel on the mechanics behavior of the connecting nodes and the overall structural integrity, this study examines and simulates three distinct connection approaches in a laboratory. These approaches include a steel corbel and rear expansion anchor bolt connection, an embedded part and steel corbel welding connection, and a reinforced concrete corbel connection. The objective in selecting the above three connection methods was to gain insights into how they influence the mechanical properties of the connections and the tunnel structure itself. The failure criteria of the structure dictate that neither the steel bar nor the steel plate should exceed their respective yield strength. Furthermore, the concrete damage zone surrounding the anchor should not exhibit any connectivity. The findings of our study indicate that: (1) The weak link in the steel truss-rear expansion anchor bolt connection scheme is centered within the connection section. With six rear expansion anchor bolts, the load capacity reached 180 kN. Conversely, when employing nine rear expansion anchor bolts, the reduced spacing between the bolts led to premature concrete breakage, decreasing the bearing capacity to 170 kN. (2) Arranging the six anchor bolts into two rows and three columns enhanced the load-bearing capacity, yet one must be cautious to prevent damage from incorrect bolt spacing. According to the conditions outlined in this study, the ideal bolt spacing fell within the range from 66.7 mm to 100 mm. Additionally, it is worth noting that the bolt deformation was concentrated within 5 cm and 6 cm around the bolt. (3) The connection scheme of the embedded part and steel corbel demonstrated impressive load-bearing capabilities, showing the ability to withstand a load of 220 kN within the elastic stage. Notably, the deformation of the anchor bar was concentrated primarily within a 5 cm radius around the corbel. (4) In the reinforced concrete corbel connection scheme, the load-bearing capacity reached 240 kN. The key factor influencing this capacity was the presence of cracks. Initially, these cracks appeared symmetrically on both sides of the corbel, and gradually extended to the width and height of the corbel structure. Full article

Shield misalignment is a common problem in shield tunnels, which seriously affects the safety and durability of tunnels. However, at present, there is a lack of research on the influence of shield misalignment on the shear capacity of the circumferential joint structure, and the failure mechanism of the circumferential joint structure before and after reinforcement is not clear. Therefore, this paper simulates the influence of misalignment on the performance mechanism of segmented circumferential connection and the effect of channel reinforcement on the ABAQUS platform. The simulation results are compared with the full-scale test results, and the results show that the shear failure process of the circumferential joint can be divided into three stages under the condition of no reinforcement. In the first stage, the vertical load increases, but the misalignment between the shield tunneling sections is very small. In the second stage, the load almost does not increase, but the degree of misalignment increases. In the third stage, the load–displacement relationship is nonlinear, indicating that the bending bolt has been sheared. Under the condition of unreinforced, the bolt will form two plastic hinges when it fails. After reinforcing the channel, the removal of the bolt forms only one plastic hinge. After channel steel reinforcement, the boundary area between the channel steel web and the steel plate first reaches the ultimate tensile strength of the steel plate, and the failure mode becomes channel steel reinforcement failure. Under the same shear load, the misalignment of the circumferential joint reinforced with channel steel is reduced. In this paper, the misalignment relationship of shear load and the yield of the bending bolt obtained through numerical calculation is consistent with the conclusion of the full-scale test. However, the circumferential connection misalignment obtained via numerical calculation is relatively small. The yield position of the bending bolt is also in good agreement with the test results, and the bolt strain obtained through the test is relatively small. Full article

The service performance of tunnel lining is affected by crack properties and development states. In this paper, numerical simulation models were established to investigate the mechanics characteristics and safety performance for lining structures under different cracks based on the extended finite element method (XFEM). Analyze multiple quantitative factors in simulation, including changes in crack location, crack length, and crack distribution range in the lining structure. The axial force and bending moment of the preset cracks in the lining structures were first studied. The maximum safety factor attenuation rate ($D_{kmax}$) was proposed to analyze the impact of longitudinal and annular cracks on the safety performance. The axial force at the vault of the lining arch is the most significantly affected by the combined longitudinal cracks at multiple locations. When the length of a longitudinal crack increases from 1 m to 6 m, the axial force value at the crack point decreases by 33.77%, 36.15%, and 11.32%. However, the bending moment value increases by 4.47 times, 2.50 times, and 1.69 times. Under the influence of longitudinal cracks in an “arch crown + arch shoulder”, “arch crown + arch waist”, and “arch crown + arch shoulder + arch waist”, the axial force in the arch vault increased by 21.55%, decreased by 17.52%, and decreased by 13.45%. The distribution pattern of the bending moment under the influence of circumferential cracks shows convexity at the arch shoulder and arch foot, and concavity at the arch waist and side walls. The safety factor scatter curve with longitudinal cracks shows a gradual transition from a “W” shape to a “U” shape. The safety factor curve with circumferential cracks presents an approximately symmetrical wave-shaped distribution. Full article

There are many problems in the development of urban space in China. Among them, urban tunnels generally pass through many sections with very complicated geological conditions, and the construction will encounter great difficulties, so the mechanical behavior of shield segments in different complex strata is worth discussing. In this paper, the axial force, bending moment and pore water pressure of shield tunnel segments in the soft and hard uneven stratum, clay stratum and fully weathered granite stratum of overlying buildings are studied by establishing a rectangular element mechanical model based on the field test method. The analysis shows that the mechanical properties of shield tunnels in different strata are quite different, but their mechanical properties change stages are the same. The earth pressure on the left and right sides of the test ring is asymmetric in the soft and hard uneven stratum, and the vault pressure is much greater than the vault bottom pressure. The distribution of earth pressure in each position of the segment ring in clay stratum is relatively balanced, and the earth pressure on both sides is relatively small; in the fully weathered granite layer of the overlying building, the segment ring of the test ring is subjected to greater additional stress, and the internal force of the segment is much greater than that without the overlying building. Exploring the similarities and differences of segment stress in these three complex strata can provide an important basis for the design and construction of shield segments in complex strata. Full article

The surrounding rock and high water pressure in weak watery strata have adverse effects on the mechanical properties of tunnel support structures. In order to optimize the anti-drainage design of tunnels in weak watery strata and evaluate their structural safety, this paper relies on the Taidacun Tunnel of the China–Laos Railway to carry out field monitoring research. A dual-field fluid–solid coupling calculation model is established to optimize the tunnel’s waterproof and drainage design, combined with a bending moment curvature model to evaluate structural safety. The main conclusions are as follows: Under the action of high water and soil pressure, the structural safety margin of the water-rich fine sand section of the Taidacun Tunnel is small, and waterproof and drainage design optimization is required. Combined with the proposed average pressure reduction coefficient, the influence of the water level and annular blind pipe spacing on the water pressure of the lining is proved, and then the optimal annular blind pipe spacing in the water-rich area of the tunnel is determined. A structural safety evaluation method based on the bending moment curvature model is proposed. Two models of elastic beam and moment–curvature beam are used to analyze the mechanical characteristics and optimization effects of the structure under optimal annular blind pipe spacing. Full article