Shallow Overburden Tunnel Shed Forepolling Mechanism And Its Utility

Barrel vault advanced support technology, as an auxiliary technique in tunnel excavation, is applied popularly. Its reliability has been approved by lots of underground projects in soft soil. It can solve the tunnel excavating problem effectively when the tunnel is constructed in soft or weak strata, such as shallow buried, crashed soft surrounding rock and abundant underground water. Thus, it is important to study the mechanism of the pipe unbrella advanced support method. Taking the mechanism application between the pipe unbrella pre-brace structure and the surrounding rock as the object to be investigated, the work was carried out aiming at the four aspects: (Dthe design and construction of the pipe umbrella advanced support structure; ?the interaction between the support structure and the surrounding rock; (3)in-site survey; (D finite-element analyses about the support effect of the pipe umbrella. The main content of the work were shown as followings:(1) The advantage and shortage of the diversified pre-brace method were systematically analyzed. Aiming at the characteristic of the pipe umbrella pre-brace, the strata adaptability, design parameters and the constructing technology of the the pipe unbrella pre-brace structure were systematically summarized. Further, the method to slove the related engineering problem during the constructing was put forward.(2) Based on the principle of the interaction between the soil and the foundation, the interaction mode, which is founded on the double -parameter model between the pipe umbrella pre-brace structure and the surrounding rock, was established. The deformation equation, rotating angle equation and bending equation were deduced. Next, the evaluating model of slope stability accounting for the contact pressure equation of the foundation was put forward. Further, using the above mode, the key parameters, such as the deformation curve, the contact pressure of the foundation and the safety factor of the tunnel excavating face under the contact pressure, were obtained. Finally, some useful conclusions werededuced by comparing the parameters obtained from the calculation of the above mentioned model with the monitoring results.(3) The function of the the pipe umbrella pre-brace in controlling surface settlements and maintaining face stability was proved by the in-site necessary monitoring parameters, such as the settlement of the ground and vault, and the strain of pipe in a shallow buried tunnel.(4) Using the 3-D FEM and 2-D FEM, the compare between the numerical results and the in-site monitoring results proved that the pre-brace mechanism of pipe umbrella advanced support technology method was right in controlling the settlement of the ground and vault further.