Study On The Convergence-Confinement Method And Its Application In Tunnel Construction

The pressure acting on the support in the tunnel is always uncertainty for a long time. This is actually a four-dimentional problem composed of the three-dimentional space and the time. For this complex problem, it still has some difficultes to analyze even though using the three-dimentional numerical methods. However, the convergence- confinement method, which is a new tool developed in the recent thirty years for tunnel support design, can provide an effective approach for analyzing the above problem. Different from other conventional support design methods, the convergence-confinement method is mainly focused on the ground behavior responded to the support service quality. The basic principle of this method can be described as: a tunnel support is used to stabilize the ground movements rather than to support the ground pressures.The three basic components of the convergence-confinement methods are the Ground Response Curve (GRC), the Support Characteristic Curve (SCC) and the Longitudinal Deformation Profile (LDP). Here GRC represents the support requirements of the ground convergence, SCC represents the ground behaviours under support confinement, and LDP represents the confinement characteristics of the tunnel face. In the present study the relative theories and the constuctions of the three curves are carried out. For examining their application effects, the basic theory of the convergence-confinement method is implemented in Erdaoya Tunnel of Shiman highway, where the the measuring data of the support pressures and boundary convergences are analyzed. The dissertation includes the following contents:(1) The priciples of the convergence-confinement method are illustrated by the graphical representions. Based on the continuum medium theory, the stress characteristics fore and after the ground excavated are analyzed. The fundamental functions and design gists of the support are studied. The expressions for the support design loads are determined by the equilibrium of GRC and SCC.(2) The post failure behaviours of the perfect plastic, strain softening and elastic-brittle-plastic rock masses are discussed. The boundary conditions at the elasto-plastic interface are studied. The results show that, for the perfect plastic and strain softening rock masses, both the stresses and the displacements at the interface are continuous. While for the elastic-brittle-plastic rock mass, the radial stress and radial displacement are continuous and the tangential stress is discontinous which shows a sudden drop along the interface.(3) The elasto-plastic analysis for the axisymmetric excavation model is obtained. Based on the self-similarity theory, the differential equations for calculating the stresses and displacements around a circular tunnel driven in a hydrostatic stresses are obtained. The constants for the solutions of the liner Mohr-Coulomb and the non-linear Hoek-Brown failure critera are presented. Based on the above, the corresponding programs for solving the differential equations are establisehed, and the typical ground response curves of different rock mass model are determined by using the results of the elastic-plastic analysis.(4) Based on the elasto-plastic analysis, a new equivalent method for determining the Mohr-Coulomb strength parameters of the elasto-perfectly plastic and the elasto-brittle-plastic rock masses is provided. In order to check the applicability of this mechod, another two equivalent methods are compared and showed that, the new equivalent method can be conveniently used to analyze the axisymmetry problem and construct the ground response curves.(5) Based on the elastic theory of thick cylinder, the stiffnesses and the maximum pressures for the circular monolayer and compound liners are derived. The ground/support interactions are illustrated by using the convergence-confinement principle. The results show that, when the preliminary support presence is neglected, the final equilibrium pressure of the compound support is obviously lower than that when the preliminary support presence is considered. On the other side, the design pressure for the second liner is higher and seems to be more conservative.(6) Based on the numerical simulation, the parameter affects of rock mass to the confinement loss are studied. The regulities of the radial displacements release factor varied with the dilation angel, friction angel and cohesion are obtained. The results show that, the dilation has significantly influence on the radial displacement release factors, the support pressure transmitted by a dilation ground is much higher than that by a non-dilation ground when the convergence-confinement analysis is used. The friction angel has also significantly influence on the radial displacement release factors of the cross-section behind the tunnel face. At the same time, it has little influence on that ahead of the runnel face. The affects of the cohesion seems to be unconspicuous.(7) According to the support characteristics of different rock mass type in Erdaoya Tunnel, the curves of convergence and confinement are proposed by the above theory. The measured data of the support pressures and boundary convergences are analyzed by these curves. The results show that, the support pressues calculated by the convergence-confinement method are relatively approximated to the measured data, and the deformation exception of the tunnel has been reasonably interpreted by the application of this method. The results ont only provide advice for the present tunnel construction, but also give an effective reference for the similar underground engineering.