Based On The Space Effect Of Small Clear Distance Tunnel Displacement Back Analysis

The development and proliferation of expressway network has witnessed a rapid growth in recent years. The vast territory and complex geographical pattern generate an increasing number of obstacles in the tunnel project of expressways, among which, twin tunnels with small clear spacing is a common form. Mechanical parameter of surrounding rocks serves as the basic element in analyzing the stability of tunnels. Owing to the series of problems during the test on-the-spot, back analysis of displacement turns out to be a crucial method in obtaining parameters, thus widely applied in calculating tunnel stability. Based on the Space Effect on twin tunnels with small clear spacing, this paper tries to put forward a method of back-analyzing displacement after revising the statistics from monitoring spot according to the outcome of numerical simulation. Afterwards, BP neural network is applied to conduct back analysis of twin tunnels with small clear spacing. The application reveals that the method proposed in this paper is an effective solution. Here are the principal findings and conclusions of this paper:1. Conclusions on the exclusivity of back analysis of displacement are delivered based on existing theories. On the premise of proper monitoring spot, back analysis of displacement lays bare the modulus E of deformation, lateral pressure coefficient and ratio v, and proves its exclusivity. Back analysis of twin tunnels with small clear spacing can prove the point as well.2. Monitor spots are installed on the basis of back analysis theory to calculate the displacement and on the BP neural network. The result confirms that the installment is appropriate for the displacement, deriving statistics such as the modulus E of deformation, lateral pressure coefficient and ratio v. Besides, the actual figure is smaller and revision are demanded to be employed in back-analyzing the displacement.3. Statistic modules are established according to the engineering cases, diggings are conducted in simulation of tunnels with small clear spacing and monitor spot is erected to calculate the displacement. In this way, the relations between deformation of surrounding rocks and the digging sequence as well as the digging schedule are proposed, offering solid foundations for analysis of twin tunnels with small clear spacing on the basis of Space Effect.4. Conclusions are made according to the statistics. The previous digging project is responsible for the space effect of subsequent work. The actual displacement is smaller in comparison with the overall stable displacement, which proves that the gap can be ascribed to the Space Effect. The adjacent horizontal tunnels are under strong impact from the previous digging, making the overlap of displacement. The figure observed can be used directly to illustrate that the back analysis is fallacious, contributing to parametric errors and inaccurate assessment of the stability of tunnels. Afterwards, the errors are corrected according to statistical simulation.5. Space Effect is categorized into pre-effect and post-effect, resulting in the conclusion that digging distance affects the calculation. The revising coefficient is put forward to resolve the conflict of having different set of parameters in the back analysis. Consequently, the displacement calculated after revision can be applied to back-analyze tunnel displacement. For projects of tunnels with small clear spacing, confined by horizontal digging, the revising method still works.