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In order to study the influence of different forms of defects on the stress of lining structure, through the model test, different forms of defects were simulated, and the changes of bending moment, axial force and safety factor at different parts of lining structure were analyzed. The results showed that the defects at the connection between the side wall and the inverted arch increased the bending moment and axial force at the middle of the lining arch waist and the inverted arch, and decreased the bending moment and axial force at the vault. According to the different forms of defects, the effects on different parts of the lining were different. When there were only concrete shrinkage defects or unconnected steel defects, the main influence parts of lining structure were haunch and side wall. When the two defects coexisted, the middle part of vault and inverted arch would also be greatly affected. The influence of concrete loose defects on the safety factor of lining structure was generally greater than that of unconnected defects of steel bars. The main influence areas were arch waist and side wall. When the two defects coexisted? the safety lector at the middle of arch waist and invert decreased obviously 3 which was 52.03% and 32.40% respectively. The effect of defects on the safety factor at the middle of the hance and inverted arch was greater than that at the vault and side wall. During construction? the quality of concrete pouring here should be strictly controlled to ensure the strength after forming, and the pouring thickness can be appropriately increased to make it have a higher safety reserve. [ABSTRACT FROM AUTHOR]

In order to study the damage mechanism of shield segment structure of shield tunnel with small curvature radius, based on practical engineering cases, a fine lining segment model considering segment joints and inter-ring joints was established to reveal the segment damage mechanism in the construction stage of shield tunnels with small curvature radius. The results showed that the axial force, shear force, positive bending moment and Mises stress of the segment all peaked at the inner and outer arch waists when the shield tunnel with small curvature radius was constructed in the turning section. The arch waist position of segments were more likely to be damaged during the excavation process. When the rectification angle of the jack thrust increased, the overall tunnel deviated to the outside. The outer side of the shield tunnel waist was more obviously affected, since the offset of outer arch waist was significantly larger than that of inner arch waist. The numerical simulation was consistent with the field observation of segment damage, which could provide reference for practical engineering. [ABSTRACT FROM AUTHOR]

Relying on the open excavation subway foundation pit project of Aixihu in Nanchang, the excavation of the foundation pit was numerically simulated by ABAQUS software. The reliability and applicability of the numerical model were verified by comparing the numerical calculation and field monitoring results of the horizontal displacement of the diaphragm wall, supported axial force, surface settlement. The bending moment variation law of diaphragm wall during excavation was analyzed. The research showed that there was a significant difference in the bending moment between the earth facing side and the excavation side of the diaphragm wall, the excavation side was tensioned as a whole and the earth facing side was compressed as a whole. The maximum bending moment of the excavation side was 2.3 times than that of the earth facing side. In the original design scheme, the main reinforcement on both sides of the diaphragm wall was symmetrically reinforced, and there was a large optimization space in the design scheme; the effect of crack control was not good only by increasing the amount of reinforcement. Under the condition of constant excavation depth and internal support spacing, after the asymmetric reinforcement optimization of the existing design, the reinforcement amount on the earth facing side and excavation side was reduced by 38.3% and 11.4% respectively, and the load sharing characteristics of the structure were more reasonable, which could greatly reduce the use of reinforcement, so as to reduce the project investment and construction scale. [ABSTRACT FROM AUTHOR]

A lateral loading model box was used to carry out model tests under two cases: the tunnel was located in loess (case 1) and penetrated by potential sliding surface in loess (case 2). The stress characteristics of tunnel lining in the process of slope deformation were studied, and the laws of slope deformation, pressure change of tunnel surrounding rock and lining moment change were analyzed. Results showed that the surrounding rock near the slope side of the tunnel lining was easy to form a void zone under the two cases. The maximum width of the void zone was about 1 cm in case 1 and close to 2 cm in case 2. The void zone in case 2 was much larger than that in case 1, with a relative increase of 100%; Compared with case 1, the peak value of lining bending moment in case 2 increased significantly, with a relative increase of 159.33%, and the maximum increase was located in the area near the side arch foot of the slope. The slide of the potential sliding surface in the slope significantly increased the possibility of tunnel lining damage. [ABSTRACT FROM AUTHOR]