| In the construction of shallow tunnel excavation, weak rock usually needs to be pre-reinforced before the excavation of tunnel face, because of its low strength and poor ability to resist surrounding rock settlement. Advanced small pipe grouting methed has a wide applicability because of its simple operation, low cost and the good effect of the waterproof reinforcement, But there are some problems about the advanced small pipe grouting does ont be resolved in the current study, for example, the parameters design of small pipe grouting is mainly based on engineering experience, the mechanism of forepale action and the equivalent simulation calculation of and so on research the parameters are not clear now.According to the above description, the numerical analysis about the mechanism stress of the advanced small pipe grouting and the relationship between its parameters and the settlement of surrounding rock using FLAC3D(fast Lagrangian analysis of continua), the conclusion as follows:(1) Tt is suggested that adopting the Beam element to simulate the small pipe when the extrapolation angle small to 15 o, esle suggested that the Cable elements are adopted. The value of Beam group in Fx is the biggest among the three directions, and the value of bending Mx is so small that we can ignore it. In addition, the maximum value of Fy, Fz, My and Mz appeared near the hance of tunnel; The distribution of axial stress and slurry stress of Cable unit is symmetrical, and the value of stress is uniform relatively.(2) In addition to the length of the Beam element, the rest parameters of the Beam tube are proportional to the value of rock differential settlement, the order of these parameters affect from large to small is: extrapolation Angle, tube spacing, tube diameter; When adopting Cable unit simulate small pipes, the order of its parameters affect from large to small is: scope of catheter placement, extrapolation angles, pipe diameter, pipe length, distance.(3) The values of E, c, φ of Equivalent reinforcement ring are proportional to the value of rock differential settlement, and the growth of E can control the settlement obviously on the premise of the value increase of c and φ. In addition, the improvement of c and φ has their limits value are 0.2 MPa and 45 o respectively; The change of Poisson’s ratio on the influence of the settlement is not big and can be ignored.(4) The relationship formula of the surrounding rock settlement with small ducts and reinforcded ring is concluded, and the formula was corrected by the tunnel span and depth. The relation formula was programmed through the C++ language, through inputing the value of differential settlement, the program will output the design parameters of small pipe and the reinforced ring. The application of this program is convenient and quick.The research achievements was applied to the practical engineering, proved its reliability of the application. The program can provide certain guidances for the forepole design of tunnel. |
