Kun Feng

Impact of Shield Tunneling on Adjacent Pile Foundation in Sandy Cobble Strata

The assessment of the impact of urban area shield tunneling on adjacent pile foundations is essential to ensure the stability and integrity of the piled buildings. Sandy cobble strata has force transmission feature of strong dispersion; therefore the equilibrium state of original strata would be easily destroyed by shield tunneling. In this study, model tests referring to the Chengdu Metro Line 1 and using the Φ520 mm EPB model shield machine are carried out to investigate the impact of shield tunneling on the existing pile foundation deformation and internal forces. Meanwhile, particle distinct element method is applied to analyze the soil particle movement feature surrounding the pile foundation from the micro view. Results showed that soil disturbance surrounding the pile foundation caused by shield tunneling makes the ground surface subsidence and pile foundation tilt, leading to the occurrence of stress concentration at the pile foundation base and nearby regions. Cutter head positive resistance and friction effect between shield machine and surrounding strata lead to the pile foundation three-dimensional movement and deformation during the shield tunneling.

A Loading Test Method of Prototype Structure for Nanjing Changjiang Tunnel

Considering the features of underwater shield tunnel with large cross-section, a prototype test of segmental lining structure for Nanjing Changjiang Tunnel (Φ14.5m) is carried out by using a new loading test method. And with “Multi-function Shield Tunnel Structure Test System” developed according to this test method, the effect of high hydraulic pressure can be equivalently imposed upon the structure by hoop, and then the earth pressure can be equivalently applied to the structure by radial concentrated force. The structures were loaded by the device according to a certain hydraulic and earth pressure. Meanwhile, the mechanical characteristics can be further studied. In a word, it can provide reliable test means for research, design and construction of underwater shield tunnel project.

Experiment study on chloride corrosion deterioration of load-bearing concrete segment

In order to study the combined action of compression-bending load and surrounding ion erosive environment on underwater shield tunnel, a series of cofferdam-type electrochemical-accelerated corrosion tests of mini segments are carried out to investigate the segment reinforcement corrosion under different compression-bending loads and the change of internal force and rigidity of mini segments under different load-bearing and corroding conditions. Then, the failure pattern of mini segments under different loading and corroding states are recorded and analyzed. The results indicate that the following: (1) the larger the external load, the shorter the initial rust time of the steel bar; (2) the corrosion rate of steel bar increases linearly with time, and the ratio of corrosion of steel bar increases quadratically with time, the larger the load, the more obvious the increase will be; (3) after the corrosion of steel bar, the change rate of the strain for the steel bar increases as the external load augments, and as a matter of fact, the change rate of the strain increases as well, besides, the degree of strain change for compressive steel is obviously lower compared with that of tensile steel bar; (4) the effect of electric corrosion on the deflection of the segments is more obvious with the increase of external load, and a quadratic increase relationship between the deflection and the corrosion is observed in the process of corrosion; (5) It can be concluded that plastic failure is observed for the segments without loading and for those without cracks in the initial stage of loading, which can be indicated directly by the relatively smaller loss rate of steel section, while brittle failure is presented as the failure pattern for the segments with cracks after loading for certain period, which means the loss rate of steel section is relatively larger. The results can briefly provide useful reference for rational design and durability assessment of shield tunnel segmental linings.

Bending Behavior of Segmental Joint Structure of Under-River Shield Tunnel

The bending stiffness of segmental joints is the key factor which affects the mechanical characteristics of shield tunnel. In this paper, full-scale tests and numerical analysis were carried out to study the bending stiffness, joint opening variation and failure characteristics of segmental joint structure for under-river shield tunnel. The results showed the bending stiffness and joint opening behaving non-linear significantly. And the concrete cracking and bolt breaking were detected in the tests.

LIMITED VALUE OF LONGITUDINAL SEAM STRETCHING FOR UNDERWATER HIGH-SPEED RAILWAY SHIELD TUNNEL

The limited value of longitudinal seam stretching is important for the safety of underwater high-speed railway tunnels. This paper discusses the limited value by carrying out the full-scale joint test and whole ring prototype test, and the relationship between the amount of longitudinal seam stretching and a series of control values, such as maximum stress, maximum displacement, and maximum crack width, has been tested. Furthermore, the limited value of longitudinal seam stretching is recommended to be 3mm.

Model Test on Structural Behaviour of Underwater Shield Tunnel with Large Cross-Section Considering Assembling Modes

Taking Nanjing Yangtze River Shield Tunnel with large cross-section (Φ14.5m) as background, the mechanical characteristic of lining structure under high hydrostatic water pressure for different segmental assembling modes is studied by large-scale similar model test. The test system can control earth pressure, uniform and non-uniform water pressure acting on lining respectively and cooperatively. The study results show that the values and distribution of deformation and internal force vary with different assembling modes. The rigidity of the whole ring for straight joint assembling is less, inducing the deformation larger and internal force smaller, which is unfavorable for waterproofing requirements. The peak positions of bending moment change with the difference of staggered joint assembling modes. Due to the smaller rigidity of K segment, the value of bending moment on that position is less. The most favorable and unfavorable assembling modes are proposed for construction design for Nanjing Yangtze River Shield Tunnel; meanwhile it can also provide important reference to the correlative project.